Context Menu commands to dynamically create UI controls using MVVM - c#

Hopefully this question isn't too general, but I have just started using WPF and I'm banging my head against this.
I am developing an application that uses dynamically created controls. However currently I can not figure out how to make the commands create and add more controls to the current window because the commands only work when created in the ViewModel which can not see the View. However I can't keep everything in the XAML because all controls except for a few initially empty stack panels are dynamic. I feel like I'm missing something easy here though.
So here I have the binding
<MenuItem Header="LabelMenuItem" Command="{Binding Path=SpawnLabel}"/>
And here I have the command
public ICommand SpawnLabel { get { return new DelegateCommand(OnSpawnLabel); } }
Delegate command works like a relay command as defined here.
public class DelegateCommand : ICommand
{
private readonly Action _command;
private readonly Func<bool> _canExecute;
public event EventHandler CanExecuteChanged
{
add { CommandManager.RequerySuggested += value; }
remove { CommandManager.RequerySuggested -= value; }
}
public DelegateCommand(Action command, Func<bool> canExecute = null)
{
if (command == null)
throw new ArgumentNullException();
_canExecute = canExecute;
_command = command;
}
public void Execute(object parameter)
{
_command();
}
public bool CanExecute(object parameter)
{
return _canExecute == null || _canExecute();
}
}
This works in the view Model but I can't figure out how on earth to make it work in the View (or talk to the view without breaking MVVM principles) so that I can actually change the UI using the current controls created in c#.
Currently when I do it I get a BindingExpression path error which makes sense but I can not figure out how to bind it to look for the command in the view.

You indirectly communicate with the UI via events, if you change a property you fire PropertyChanged, the UI will update a binding, if you change a collection you fire CollectionChanged and a new control is added or an old one removed.
The important interfaces are INotifyPropertyChanged and INotifyCollectionChanged, just bind an ItemsControl (via ItemsSource) to an ObservableCollection<T> in your view-model and add to that collection in your command (you may need to use the ItemsControl.ItemTemplate to specify the view for your view-models, depending on what MVVM framework you use).

Related

INotifyCollectionChanged UI not updated

I have problem with updating UI. I have class which, is used to binding my UI elements:
public class engine : INotifyCollectionChanged
{
RWProject project = new RWProject();
public ObservableCollection<string> ProjectListBinding
{
get { return project.list(); }
}
public event NotifyCollectionChangedEventHandler CollectionChanged;
private void OnCollectionChanged(NotifyCollectionChangedEventArgs eventArgs)
{
if (this.CollectionChanged != null)
{
this.CollectionChanged(this, eventArgs);
}
}
private ICommand _usunProjekt;
public ICommand UsunProjekt
{
get
{
_usunProjekt = new UsunProjektCommand();
return _usunProjekt;
}
}
private ICommand _dodajProjekt;
public ICommand DodajProjekt
{
get
{
_dodajProjekt = new DodajNowyProjektCommand();
return _dodajProjekt;
}
}
}
ProjectListBinding is a list of files names inside folder, and this names are displayed on listview control.
Commands DodajProjekt creating in same folder, new file (UsunProjekt - removing)
Commands are binded to buttons.
I need to rise event
OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset))
to update UI after command is executed, but I don't knew where to attach this part of code. Or maybe I should do it in different way ?
With code I already have, bindings and commands are working fine, only updating not working at all.
Can You help me solve this ?
Piotr
You should not be implementing INotifyCollectionChanged. From your view you need to bind to ProjectListBinding which will automatically raise INotifyCollectionChanged for you and update the UI. Of course, assuming that the class that you have (i.e. engine) is your view model.
When running your command, you should update ProjectListBinding for INotifyCollectionChanged events to be risen. That is, both your commands DodajNowyProjektCommand and UsunProjekt should be operating on ProjectListBinding.

Multiple views in a single window using MVVM - Need more information

Ok, so I found WPF MVVM navigate views in which Sheridan does a (mostly) great explanation on how to navigate multiple views in a single window. Following the code and explanation I was able to get the views switching using the code behind, however I can't manage to get his XAML Command="" version of the view switch working.
I had to search around to find a version of ActionCommand() that matches his inputs, but I'm not even sure it's the correct one, and I can't find anything on the IsViewModelOfType<T>() method at all. Which means the final solution given is partially broken.
How do I get that last part working without 3rd party libraries?
Unfortunately because StackOverflow hates new users participating in anything I couldn't just ask in the same thread.
From the above post, this is the part that doesn't work, because the two parts -- ActionCommand and IsViewModelOfType -- don't seem to exist anywhere and there's no information for them searching online
Finally, how do we change the views from other views? Well there are
several possible ways to do this, but the easiest way is to add a
Binding from the child view directly to an ICommand in the
MainViewModel. I use a custom version of the RelayComand, but you can
use any type you like and I'm guessing that you'll get the picture:
public ICommand DisplayPersonView
{
get { return new ActionCommand(action => ViewModel = new PersonViewModel(),
canExecute => !IsViewModelOfType<Person>()); }
}
In the child view XAML:
<Button Command="{Binding DataContext.DisplayPersonView, RelativeSource=
{RelativeSource AncestorType={x:Type MainViewModel}}, Mode=OneWay}" />
Update:
I tried returning both True and False from my own IsViewModelOfType<T>() (as well as actually testing) but to no avail. The key to the problem appears to be either the ActionCommand() method, for which I have no basis to go on, or that the XAML itself is incorrect.
The closest match I can find for ActionCommand() is from Microsoft.Expression.Interactivity.Core but it only accepts a single parameter and doesn't appear to behave correctly for this usage.
I also tried this code snippet I found online, but it doesn't do anything when using Sheridan's code either
class ActionCommand : ICommand
{
private readonly Action<object> _executeHandler;
private readonly Func<object, bool> _canExecuteHandler;
public ActionCommand(Action<object> execute, Func<object, bool> canExecute)
{
if (execute == null)
throw new ArgumentNullException("Execute cannot be null");
_executeHandler = execute;
_canExecuteHandler = canExecute;
}
public event EventHandler CanExecuteChanged
{
add { CommandManager.RequerySuggested += value; }
remove { CommandManager.RequerySuggested -= value; }
}
public void Execute(object parameter)
{
_executeHandler(parameter);
}
public bool CanExecute(object parameter)
{
if (_canExecuteHandler == null)
return true;
return _canExecuteHandler(parameter);
}
}
I would say from the code that I have seen in the answer you reference that IsViewModelOfType<Person>() method is using some type of mapping to get the view model type from a given object type. So the code
public ICommand DisplayPersonView
{
get { return new ActionCommand(action => ViewModel = new PersonViewModel(),
canExecute => !IsViewModelOfType<Person>()); }
}
would be referencing the generic method that might look like
public bool IsViewModelOfType<T>()
{
Type type = typeof(T);
if (!viewModelMapping.ContainsKey(type))
return false;
return viewModelMapping[type] == typeof(this);
}
where this in the above refers to the current View Model and where you might have view model type to object type mapping dictionary like
public Dictionary<Type, Type> viewModelMapping =
new Dictionary<Type, Type>()
{
{ typeof(Person), typeof(PersonViewModel) },
...
};
All that Sheriden is saying above, in the command is that if the type is not a Person then do not allow the display of the PersonViewModel. You can impose this logic anyway you like and it does not have to follow Sheriden's methodology.
I hope this helps.
Having read your edit, I would first try to remove the RelativeSource code, I don't think this is needed. Okay, now for the command class. Here is the one I used before I started using MVVM frameworks:
using System;
using System.Diagnostics;
using System.Windows.Input;
namespace ResourceStudio.Commands
{
/// <summary>
/// A command whose sole purpose is to relay its functionality to other
/// objects by invoking delegates. The default return value for the CanExecute
/// method is 'true'.
/// </summary>
public class RelayCommand : ICommand
{
readonly Action<object> execute;
readonly Predicate<object> canExecute;
#region Constructors
/// <summary>
/// Creates a new command that can always execute.
/// </summary>
/// <param name="execute">The execution logic.</param>
public RelayCommand(Action<object> execute)
: this(execute, null)
{
}
/// <summary>
/// Creates a new command.
/// </summary>
/// <param name="execute">The execution logic.</param>
/// <param name="canExecute">The execution status logic.</param>
public RelayCommand(Action<object> execute, Predicate<object> canExecute)
{
if (execute == null)
throw new ArgumentNullException("execute");
this.execute = execute;
this.canExecute = canExecute;
}
#endregion // Constructors
#region ICommand Members
[DebuggerStepThrough]
public bool CanExecute(object parameter)
{
return this.canExecute == null ? true : this.canExecute(parameter);
}
/// <summary>
/// Can execute changed event handler.
/// </summary>
public event EventHandler CanExecuteChanged
{
add { CommandManager.RequerySuggested += value; }
remove { CommandManager.RequerySuggested -= value; }
}
public void Execute(object parameter)
{
this.execute(parameter);
}
#endregion // ICommand Members
}
}
How this is used for a MenuItem click is:
<MenuItem Header="E_xit"
Command="{Binding CloseApplicationCommand}"/>
Where CloseApplicationCommand is
private RelayCommand closeApplicationCommand;
public RelayCommand CloseApplicationCommand
{
get
{
return closeApplicationCommand ?? (closeApplicationCommand =
new RelayCommand(o => this.CloseApplication(), o => CanCloseApplication));
}
}
where CanCloseApplication is some boolean property.
Okay, now, if you want to set the command to fire on a particular event, say a button MouseOver event, then you will have to write something like
<Button Content="SomeButton">
<Interactivity:Interaction.Triggers>
<Interactivity:EventTrigger EventName="MouseOver">
<Interactivity:InvokeCommandAction Command="{Binding SomeButtonMouseOverCommand}" />
</Interactivity:EventTrigger>
</Interactivity:Interaction.Triggers>
</Button>
using xmlns:Interactivity="http://schemas.microsoft.com/expression/2010/interactivity" namespace. A much better way however, is to use AttachedCommandBehaviours (if you're adverse to switching to an MVVM framework (e.g. Claiburn.Micro et al.)). You can down load the AttachedCommandBehavious here. Then you can write
<Button Content="Select"
AttachedCommand:CommandBehavior.Event="Click" // Or what ever event you want!
AttachedCommand:CommandBehavior.Command="{Binding DoSomethingCommand}" />
I would think seriously about using a MVVM framework. However, it is good to understnad this stuff before moving to one.
Ok, so turns out the problem was here
In the child view XAML:
<Button Command="{Binding DataContext.DisplayPersonView, RelativeSource=
{RelativeSource AncestorType={x:Type MainViewModel}}, Mode=OneWay}" />
This wasn't firing anything at all. Using this instead based on Killercam's feedback
<Button Command="{Binding DisplayPersonView}" />
where DisplayPersonView() also fires an event OnViewModelChanged contained within the BaseViewModel that all the view models inherit.
Unfortunately I had to break MVVM practice slightly, by adding a handler in the window's code behind
private void UpdateView(object sender, EventArgs e)
{
DataContext = (BaseViewModel)sender;
((BaseViewModel)DataContext).OnViewModelChange += UpdateView;
}
And in the window's constructor I call UpdateView() to set the initial ViewModel
This works with either the above described ActionCommand() or RelayCommand() just fine, and with or without the canExecute() just fine.

Correct approach to UserControl creation when using MVVM

This is more of a conceptual question rather than a practical one. I'm just starting to learn the MVVM concept for developing UI , and I've come across a dillema I'm not sure the answer to:
Say I have a main window and a little pop-up window (meaning it's a small window with some UI elements in it). The structure of the program will look something like this:
MainWindow
model <-- MainWindowViewModel.cs <-- MainWindowView.xaml (containing no code-behind)
PopUpWindow (A UserControl)
model <-- PopUpWindowViewModel.cs <-- PopUpWindowView.xaml (containing no code-behind)
*the model is just a bunch of BL classes that are irrelevant for this question.
Now , lets say I want to create a new PopUp window from inside the MainWindowViewModel (or even save an instance of it in a private data-member). What is the correct way of doing so?
The way I see it I can't do something like this :
PopUpWindow pop = new PopUpWindow()
Because it kind of defeats the purpose of abstracting the view from the view model(What if a year from now i'll want to create a better version of the PopUpWindow using the same PopUpWindowViewModel?).
On the other hand , I can't initialize a new instnace of the PopUpWindow using just it's view model (The viewModel as I understand is not supposed to know anything about the view that will use it).
Hope it all makes sense... so what would you do in that situation?
*Just to clarify it further , let's say for argument's sake that the situation I'm describing is a button on the MainWindowView that upon clicking will open a PopUpWindowView.
Thanks in advnace.
I had somewhat a similar dilemma and I'll explain how I solved it.
Let's say you have MainWindow and a SettingsWindow, which you want to display when the SettingsButton is clicked.
You have two respective view models, MainWindowViewModel and SettingsViewModel, which you will be passing as their Window.DataContext properties.
Your MainWindowViewModel should expose an ICommand property named SettingsButtonCommand (or similar). Bind this command to the SettingsButton.Command.
Now your command should invoke something like this:
void OnSettingsButtonClicked()
{
var viewModel = new SettingsViewModel();
var window = new SettingsWindow();
window.DataContext = viewModel;
window.Show();
}
There is a slight issue when you want to use Window.ShowDialog(), because you need to resume execution.
For these cases I have an asynchronous variant of the DelegateCommand:
public sealed class AsyncDelegateCommand : ICommand
{
readonly Func<object, Task> onExecute;
readonly Predicate<object> onCanExecute;
public event EventHandler CanExecuteChanged
{
add { CommandManager.RequerySuggested += value; }
remove { CommandManager.RequerySuggested -= value; }
}
public AsyncDelegateCommand(Func<object, Task> onExecute)
: this(onExecute, null) { }
public AsyncDelegateCommand(Func<object, Task> onExecute, Predicate<object> onCanExecute)
{
if (onExecute == null)
throw new ArgumentNullException("onExecute");
this.onExecute = onExecute;
this.onCanExecute = onCanExecute;
}
#region ICommand Methods
public async void Execute(object parameter)
{
await onExecute(parameter);
}
public bool CanExecute(object parameter)
{
return onCanExecute != null ? onCanExecute(parameter) : true;
}
#endregion
}
You've specifically said that the popup is a UserControl so you can use basic data templating. First create view models for your main window and popup control:
public class MainViewModel : ViewModelBase
{
private PopUpViewModel _PopUp;
public PopUpViewModel PopUp
{
get { return _PopUp; }
set { _PopUp = value; RaisePropertyChanged(() => this.PopUp); }
}
}
public class PopUpViewModel : ViewModelBase
{
private string _Message;
public string Message
{
get { return _Message; }
set { _Message = value; RaisePropertyChanged(() => this.Message); }
}
}
The MainViewModel's PopUp member is initially null, we'll set it to an instance of PopUpViewModel when we want the popup to appear. To do that we create a content control on the main window and set it's content to that member. We also use a data template to specify the type of child control to create when the popup view model has been set:
<Window.Resources>
<DataTemplate DataType="{x:Type local:PopUpViewModel}">
<local:PopUpWindow />
</DataTemplate>
</Window.Resources>
<StackPanel>
<Button Content="Show PopUp" Click="Button_Click_1" HorizontalAlignment="Left"/>
<ContentControl Content="{Binding PopUp}" />
</StackPanel>
I'm doing a big no-no here by creating the view model in the code-behind along with a click handler, but it's just for illustrative purposes:
public partial class MainWindow : Window
{
MainViewModel VM = new MainViewModel();
public MainWindow()
{
InitializeComponent();
this.DataContext = this.VM;
}
private void Button_Click_1(object sender, RoutedEventArgs e)
{
this.VM.PopUp = new PopUpViewModel { Message = "Hello World!" };
}
}
That's it! Click the button, popup window appears underneath it showing the content. Now it may not always be this simple, sometimes you may want to create multiple children on a parent control...in that case you'd set up an ItemsControl, set its panel to a Grid (say) and modify the data templates to set the Margin etc on each element to position them. Or you may not always know what type of view model is going to be created, in which case you need to add multiple data templates for each type you're expecting. Either way you still have good separation of concerns because it is the views that are deciding how to display the content in the view models. The view models themselves still don't know anything about the views and they can be unit-tested etc independently.

Bind a button to a command (Windows Phone 7.5)

I'm working on my windows-phone app which uses some simple data binding. I've already created a app which was based on the MvvM programming method.The app i'm currently working on also works by MvvM method. Because i want to keep my code behind as clean as possible i was looking for a way to make the "button click event" (which normally takes place in the codebehind page) take place in my viewmodel or mainviewmodel.
I have searched the internet in need of a simple explanation for the Icommand interface because i believe that's the way to go. Problem with the explanations I found was that some of them were based on MvvMlight toolkit using the CommandRelay function. I don't want to use the MvvM light toolkit because I want to understand things myself first. The other tutorials I found were written by over enthusiastic developers which give you an overkill of information.
Can someone show me the Most simple version of an Icommand bound to a button works?
In your XAML:
<Button Content="My Button" Command="{Binding MyViewModelCommand}" />
In your view-model:
public class MyViewModel
{
public MyViewModel()
{
MyViewModelCommand = new ActionCommand(DoSomething);
}
public ICommand MyViewModelCommand { get; private set; }
private void DoSomething()
{
// no, seriously, do something here
}
}
INotifyPropertyChanged and other view-model pleasantries elided.
An alternative way to structure the command in your view-model is shown at the bottom of this answer.
Now, you'll need an implementation of ICommand. I suggest starting with something simple like this, and extend or implement other features/commands as necessary:
public class ActionCommand : ICommand
{
private readonly Action _action;
public ActionCommand(Action action)
{
_action = action;
}
public void Execute(object parameter)
{
_action();
}
public bool CanExecute(object parameter)
{
return true;
}
public event EventHandler CanExecuteChanged;
}
Here is an alternative way to layout your view-model:
public class MyViewModel
{
private ICommand _myViewModelCommand;
public ICommand MyViewModelCommand
{
get
{
return _myViewModelCommand
?? (_myViewModelCommand = new ActionCommand(() =>
{
// your code here
}));
}
}
}
To add to Jays answer:
My all time favorite is the DelegateCommand from the Patterns and Practices team # Microsoft. Check out this post for more info.

How should the ViewModel close the form?

I'm trying to learn WPF and the MVVM problem, but have hit a snag.
This question is similar but not quite the same as this one (handling-dialogs-in-wpf-with-mvvm)...
I have a "Login" form written using the MVVM pattern.
This form has a ViewModel which holds the Username and Password, which are bound to the view in the XAML using normal data bindings.
It also has a "Login" command which is bound to the "Login" button on the form, agan using normal databinding.
When the "Login" command fires, it invokes a function in the ViewModel which goes off and sends data over the network to log in. When this function completes, there are 2 actions:
The login was invalid - we just show a MessageBox and all is fine
The login was valid, we need to close the Login form and have it return true as its DialogResult...
The problem is, the ViewModel knows nothing about the actual view, so how can it close the view and tell it to return a particular DialogResult?? I could stick some code in the CodeBehind, and/or pass the View through to the ViewModel, but that seems like it would defeat the whole point of MVVM entirely...
Update
In the end I just violated the "purity" of the MVVM pattern and had the View publish a Closed event, and expose a Close method. The ViewModel would then just call view.Close. The view is only known via an interface and wired up via an IOC container, so no testability or maintainability is lost.
It seems rather silly that the accepted answer is at -5 votes! While I'm well aware of the good feelings that one gets by solving a problem while being "pure", Surely I'm not the only one that thinks that 200 lines of events, commands and behaviors just to avoid a one line method in the name of "patterns" and "purity" is a bit ridiculous....
I was inspired by Thejuan's answer to write a simpler attached property. No styles, no triggers; instead, you can just do this:
<Window ...
xmlns:xc="clr-namespace:ExCastle.Wpf"
xc:DialogCloser.DialogResult="{Binding DialogResult}">
This is almost as clean as if the WPF team had gotten it right and made DialogResult a dependency property in the first place. Just put a bool? DialogResult property on your ViewModel and implement INotifyPropertyChanged, and voilĂ , your ViewModel can close the Window (and set its DialogResult) just by setting a property. MVVM as it should be.
Here's the code for DialogCloser:
using System.Windows;
namespace ExCastle.Wpf
{
public static class DialogCloser
{
public static readonly DependencyProperty DialogResultProperty =
DependencyProperty.RegisterAttached(
"DialogResult",
typeof(bool?),
typeof(DialogCloser),
new PropertyMetadata(DialogResultChanged));
private static void DialogResultChanged(
DependencyObject d,
DependencyPropertyChangedEventArgs e)
{
var window = d as Window;
if (window != null)
window.DialogResult = e.NewValue as bool?;
}
public static void SetDialogResult(Window target, bool? value)
{
target.SetValue(DialogResultProperty, value);
}
}
}
I've also posted this on my blog.
From my perspective the question is pretty good as the same approach would be used not only for the "Login" window, but for any kind of window. I've reviewed a lot of suggestions and none are OK for me. Please review my suggestion that was taken from the MVVM design pattern article.
Each ViewModel class should inherit from WorkspaceViewModel that has the RequestClose event and CloseCommand property of the ICommand type. The default implementation of the CloseCommand property will raise the RequestClose event.
In order to get the window closed, the OnLoaded method of your window should be overridden:
void CustomerWindow_Loaded(object sender, RoutedEventArgs e)
{
CustomerViewModel customer = CustomerViewModel.GetYourCustomer();
DataContext = customer;
customer.RequestClose += () => { Close(); };
}
or OnStartup method of you app:
protected override void OnStartup(StartupEventArgs e)
{
base.OnStartup(e);
MainWindow window = new MainWindow();
var viewModel = new MainWindowViewModel();
viewModel.RequestClose += window.Close;
window.DataContext = viewModel;
window.Show();
}
I guess that RequestClose event and CloseCommand property implementation in the WorkspaceViewModel are pretty clear, but I will show them to be consistent:
public abstract class WorkspaceViewModel : ViewModelBase
// There's nothing interesting in ViewModelBase as it only implements the INotifyPropertyChanged interface
{
RelayCommand _closeCommand;
public ICommand CloseCommand
{
get
{
if (_closeCommand == null)
{
_closeCommand = new RelayCommand(
param => Close(),
param => CanClose()
);
}
return _closeCommand;
}
}
public event Action RequestClose;
public virtual void Close()
{
if ( RequestClose != null )
{
RequestClose();
}
}
public virtual bool CanClose()
{
return true;
}
}
And the source code of the RelayCommand:
public class RelayCommand : ICommand
{
#region Constructors
public RelayCommand(Action<object> execute, Predicate<object> canExecute)
{
if (execute == null)
throw new ArgumentNullException("execute");
_execute = execute;
_canExecute = canExecute;
}
#endregion // Constructors
#region ICommand Members
[DebuggerStepThrough]
public bool CanExecute(object parameter)
{
return _canExecute == null ? true : _canExecute(parameter);
}
public event EventHandler CanExecuteChanged
{
add { CommandManager.RequerySuggested += value; }
remove { CommandManager.RequerySuggested -= value; }
}
public void Execute(object parameter)
{
_execute(parameter);
}
#endregion // ICommand Members
#region Fields
readonly Action<object> _execute;
readonly Predicate<object> _canExecute;
#endregion // Fields
}
P.S. Don't treat me badly for those sources! If I had them yesterday that would have saved me a few hours...
P.P.S. Any comments or suggestions are welcome.
There are a lot of comments arguing the pros and cons of MVVM here. For me, I agree with Nir; it's a matter of using the pattern appropriately and MVVM doesn't always fit. People seems to have become willing to sacrifice all of the most important principles of software design JUST to get it to fit MVVM.
That said,..i think your case could be a good fit with a bit of refactoring.
In most cases I've come across, WPF enables you to get by WITHOUT multiple Windows. Maybe you could try using Frames and Pages instead of Windows with DialogResults.
In your case my suggestion would be have LoginFormViewModel handle the LoginCommand and if the login is invalid, set a property on LoginFormViewModel to an appropriate value (false or some enum value like UserAuthenticationStates.FailedAuthentication). You'd do the same for a successful login (true or some other enum value). You'd then use a DataTrigger which responds to the various user authentication states and could use a simple Setter to change the Source property of the Frame.
Having your login Window return a DialogResult i think is where you're getting confused; that DialogResult is really a property of your ViewModel. In my, admittedly limited experience with WPF, when something doesn't feel right it usually because I'm thinking in terms of how i would've done the same thing in WinForms.
Hope that helps.
Assuming your login dialog is the first window that gets created, try this inside your LoginViewModel class:
void OnLoginResponse(bool loginSucceded)
{
if (loginSucceded)
{
Window1 window = new Window1() { DataContext = new MainWindowViewModel() };
window.Show();
App.Current.MainWindow.Close();
App.Current.MainWindow = window;
}
else
{
LoginError = true;
}
}
This is a simple and clean solution - You add an event to the ViewModel and instruct the Window to close itself when that event is fired.
For more details see my blog post, Close window from ViewModel.
XAML:
<Window
x:Name="this"
xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
xmlns:ei="http://schemas.microsoft.com/expression/2010/interactions">
<i:Interaction.Triggers>
<i:EventTrigger SourceObject="{Binding}" EventName="Closed">
<ei:CallMethodAction
TargetObject="{Binding ElementName=this}"
MethodName="Close"/>
</i:EventTrigger>
</i:Interaction.Triggers>
<Window>
ViewModel:
private ICommand _SaveAndCloseCommand;
public ICommand SaveAndCloseCommand
{
get
{
return _SaveAndCloseCommand ??
(_SaveAndCloseCommand = new DelegateCommand(SaveAndClose));
}
}
private void SaveAndClose()
{
Save();
Close();
}
public event EventHandler Closed;
private void Close()
{
if (Closed != null) Closed(this, EventArgs.Empty);
}
Note: The example uses Prism's DelegateCommand (see Prism: Commanding), but any ICommand implementation can be used for that matter.
You can use behaviors from this official package.
The way I would handle it is to add an event handler in my ViewModel. When the user was successfully logged in I would fire the event. In my View I would attach to this event and when it fired I would close the window.
Here's what I initially did, which does work, however it seems rather long-winded and ugly (global static anything is never good)
1: App.xaml.cs
public partial class App : Application
{
// create a new global custom WPF Command
public static readonly RoutedUICommand LoggedIn = new RoutedUICommand();
}
2: LoginForm.xaml
// bind the global command to a local eventhandler
<CommandBinding Command="client:App.LoggedIn" Executed="OnLoggedIn" />
3: LoginForm.xaml.cs
// implement the local eventhandler in codebehind
private void OnLoggedIn( object sender, ExecutedRoutedEventArgs e )
{
DialogResult = true;
Close();
}
4: LoginFormViewModel.cs
// fire the global command from the viewmodel
private void OnRemoteServerReturnedSuccess()
{
App.LoggedIn.Execute(this, null);
}
I later on then removed all this code, and just had the LoginFormViewModel call the Close method on it's view. It ended up being much nicer and easier to follow. IMHO the point of patterns is to give people an easier way to understand what your app is doing, and in this case, MVVM was making it far harder to understand than if I hadn't used it, and was now an anti-pattern.
Ok, so this question is nearly 6 years old and I still can't find in here what I think it's the proper answer, so allow me to share my "2 cents"...
I actually have 2 ways of doing it, first one is the simple one...the second on the right one, so if you are looking for the right one, just skip #1 and jump to #2:
1. Quick and Easy (but not complete)
If I have just a small project I sometimes just create a CloseWindowAction in the ViewModel:
public Action CloseWindow { get; set; } // In MyViewModel.cs
And whoever crates the View, or in the View's code behind I just set the Method the Action will call:
(remember MVVM is about separation of the View and the ViewModel...the View's code behins is still the View and as long as there is proper separation you are not violating the pattern)
If some ViewModel creates a new window:
private void CreateNewView()
{
MyView window = new MyView();
window.DataContext = new MyViewModel
{
CloseWindow = window.Close,
};
window.ShowDialog();
}
Or if you want it in your Main Window, just place it under your View's constructor:
public MyView()
{
InitializeComponent();
this.DataContext = new MainViewModel
{
CloseWindow = this.Close
};
}
when you want to close the window, just call the Action on your ViewModel.
2. The right way
Now the proper way of doing it is using Prism (IMHO), and all about it can be found here.
You can make an Interaction Request, populate it with whatever data you will need in your new Window, lunch it, close it and even receive data back. All of this encapsulated and MVVM approved. You even get a status of how the Window was closed, like if the User Canceled or Accepted (OK button) the Window and data back if you need it. It's a bit more complicated and Answer #1, but it's a lot more complete, and a Recommended Pattern by Microsoft.
The link I gave have all the code snippets and examples, so I won't bother to place any code in here, just read the article of download the Prism Quick Start and run it, it's really simple to understad just a little more verbose to make it work, but the benefits are bigger than just closing a window.
public partial class MyWindow: Window
{
public ApplicationSelection()
{
InitializeComponent();
MyViewModel viewModel = new MyViewModel();
DataContext = viewModel;
viewModel.RequestClose += () => { Close(); };
}
}
public class MyViewModel
{
//...Your code...
public event Action RequestClose;
public virtual void Close()
{
if (RequestClose != null)
{
RequestClose();
}
}
public void SomeFunction()
{
//...Do something...
Close();
}
}
FYI, I ran into this same problem and I think I figured out a work around that doesn't require globals or statics, although it may not be the best answer. I let the you guys decide that for yourself.
In my case, the ViewModel that instantiates the Window to be displayed (lets call it ViewModelMain) also knows about the LoginFormViewModel (using the situation above as an example).
So what I did was to create a property on the LoginFormViewModel that was of type ICommand (Lets call it CloseWindowCommand). Then, before I call .ShowDialog() on the Window, I set the CloseWindowCommand property on the LoginFormViewModel to the window.Close() method of the Window I instantiated. Then inside the LoginFormViewModel all I have to do is call CloseWindowCommand.Execute() to close the window.
It is a bit of a workaround/hack I suppose, but it works well without really breaking the MVVM pattern.
Feel free to critique this process as much as you like, I can take it! :)
This is probably very late, but I came across the same problem and I found a solution that works for me.
I can't figure out how to create an app without dialogs(maybe it's just a mind block). So I was at an impasse with MVVM and showing a dialog. So I came across this CodeProject article:
http://www.codeproject.com/KB/WPF/XAMLDialog.aspx
Which is a UserControl that basically allows a window to be within the visual tree of another window(not allowed in xaml). It also exposes a boolean DependencyProperty called IsShowing.
You can set a style like,typically in a resourcedictionary, that basically displays the dialog whenever the Content property of the control != null via triggers:
<Style TargetType="{x:Type d:Dialog}">
<Style.Triggers>
<Trigger Property="HasContent" Value="True">
<Setter Property="Showing" Value="True" />
</Trigger>
</Style.Triggers>
</Style>
In the view where you want to display the dialog simply have this:
<d:Dialog Content="{Binding Path=DialogViewModel}"/>
And in your ViewModel all you have to do is set the property to a value(Note: the ViewModel class must support INotifyPropertyChanged for the view to know something happened ).
like so:
DialogViewModel = new DisplayViewModel();
To match the ViewModel with the View you should have something like this in a resourcedictionary:
<DataTemplate DataType="{x:Type vm:DisplayViewModel}">
<vw:DisplayView/>
</DataTemplate>
With all of that you get a one-liner code to show dialog. The problem you get is you can't really close the dialog with just the above code. So that's why you have to put in an event in a ViewModel base class which DisplayViewModel inherits from and instead of the code above, write this
var vm = new DisplayViewModel();
vm.RequestClose += new RequestCloseHandler(DisplayViewModel_RequestClose);
DialogViewModel = vm;
Then you can handle the result of the dialog via the callback.
This may seem a little complex, but once the groundwork is laid, it's pretty straightforward. Again this is my implementation, I'm sure there are others :)
Hope this helps, it saved me.
You could have the ViewModel expose an event that the View registers to. Then, when the ViewModel decides its time to close the view, it fires that event which causes the view to close. If you want a specific result value passed back, then you would have a property in the ViewModel for that.
Why not just pass the window as a command parameter?
C#:
private void Cancel( Window window )
{
window.Close();
}
private ICommand _cancelCommand;
public ICommand CancelCommand
{
get
{
return _cancelCommand ?? ( _cancelCommand = new Command.RelayCommand<Window>(
( window ) => Cancel( window ),
( window ) => ( true ) ) );
}
}
XAML:
<Window x:Class="WPFRunApp.MainWindow"
x:Name="_runWindow"
...
<Button Content="Cancel"
Command="{Binding Path=CancelCommand}"
CommandParameter="{Binding ElementName=_runWindow}" />
Just to add to the massive number of answers, I want to add the following. Assuming that you have a ICommand on your ViewModel, and you want that command to close its window (or any other action for that matter), you can use something like the following.
var windows = Application.Current.Windows;
for (var i=0;i< windows.Count;i++ )
if (windows[i].DataContext == this)
windows[i].Close();
It's not perfect, and might be difficult to test (as it is hard to mock/stub a static) but it is cleaner (IMHO) than the other solutions.
Erick
I implemented Joe White's solution, but ran into problems with occasional "DialogResult can be set only after Window is created and shown as dialog" errors.
I was keeping the ViewModel around after the View was closed and occasionally I later opened a new View using the same VM. It appears that closing the new View before the old View had been garbage collected resulted in DialogResultChanged trying to set the DialogResult property on the closed window, thus provoking the error.
My solution was to change DialogResultChanged to check the window's IsLoaded property:
private static void DialogResultChanged(
DependencyObject d,
DependencyPropertyChangedEventArgs e)
{
var window = d as Window;
if (window != null && window.IsLoaded)
window.DialogResult = e.NewValue as bool?;
}
After making this change any attachments to closed dialogs are ignored.
I ended up blending Joe White's answer and some code from Adam Mills's answer, since I needed to show a user control in a programmatically created window. So the DialogCloser need not be on the window, it can be on the user control itself
<UserControl ...
xmlns:xw="clr-namespace:Wpf"
xw:DialogCloser.DialogResult="{Binding DialogResult}">
And the DialogCloser will find the window of the user control if it was not attached to the window itself.
namespace Wpf
{
public static class DialogCloser
{
public static readonly DependencyProperty DialogResultProperty =
DependencyProperty.RegisterAttached(
"DialogResult",
typeof(bool?),
typeof(DialogCloser),
new PropertyMetadata(DialogResultChanged));
private static void DialogResultChanged(
DependencyObject d,
DependencyPropertyChangedEventArgs e)
{
var window = d.GetWindow();
if (window != null)
window.DialogResult = e.NewValue as bool?;
}
public static void SetDialogResult(DependencyObject target, bool? value)
{
target.SetValue(DialogResultProperty, value);
}
}
public static class Extensions
{
public static Window GetWindow(this DependencyObject sender_)
{
Window window = sender_ as Window;
return window ?? Window.GetWindow( sender_ );
}
}
}
Behavior is the most convenient way here.
From one hand, it can be binded to the given viewmodel (that can
signal "close the form!")
From another hand, it has access to the form itself so can subscribe to necessary form-specific events, or show confirmation dialog, or anything else.
Writing necessary behavior can be seen boring very first time. However, from now on, you can reuse it on every single form you need by exact one-liner XAML snippet. And if necessary, you can extract it as a separate assembly so it can be included into any next project you want.
Another solution is to create property with INotifyPropertyChanged in View Model like DialogResult, and then in Code Behind write this:
public class SomeWindow: ChildWindow
{
private SomeViewModel _someViewModel;
public SomeWindow()
{
InitializeComponent();
this.Loaded += SomeWindow_Loaded;
this.Closed += SomeWindow_Closed;
}
void SomeWindow_Loaded(object sender, RoutedEventArgs e)
{
_someViewModel = this.DataContext as SomeViewModel;
_someViewModel.PropertyChanged += _someViewModel_PropertyChanged;
}
void SomeWindow_Closed(object sender, System.EventArgs e)
{
_someViewModel.PropertyChanged -= _someViewModel_PropertyChanged;
this.Loaded -= SomeWindow_Loaded;
this.Closed -= SomeWindow_Closed;
}
void _someViewModel_PropertyChanged(object sender, PropertyChangedEventArgs e)
{
if (e.PropertyName == SomeViewModel.DialogResultPropertyName)
{
this.DialogResult = _someViewModel.DialogResult;
}
}
}
The most important fragment is _someViewModel_PropertyChanged.
DialogResultPropertyName can be some public const string in SomeViewModel.
I use this kind of trick to make some changes in View Controls in case when this is hard to do in ViewModel. OnPropertyChanged in ViewModel you can do anything you want in View. ViewModel is still 'unit testable' and some small lines of code in code behind makes no difference.
I would go this way:
using GalaSoft.MvvmLight;
using GalaSoft.MvvmLight.Command;
using GalaSoft.MvvmLight.Messaging;
// View
public partial class TestCloseWindow : Window
{
public TestCloseWindow() {
InitializeComponent();
Messenger.Default.Register<CloseWindowMsg>(this, (msg) => Close());
}
}
// View Model
public class MainViewModel: ViewModelBase
{
ICommand _closeChildWindowCommand;
public ICommand CloseChildWindowCommand {
get {
return _closeChildWindowCommand?? (_closeChildWindowCommand = new RelayCommand(() => {
Messenger.Default.Send(new CloseWindowMsg());
}));
}
}
}
public class CloseWindowMsg
{
}
I've read all the answers but I must say, most of them are just not good enough or even worse.
You could handle this beatifully with DialogService class which responsibility is to show dialog window and return dialog result. I have create sample project demonstrating it's implementation and usage.
here are most important parts:
//we will call this interface in our viewmodels
public interface IDialogService
{
bool? ShowDialog(object dialogViewModel, string caption);
}
//we need to display logindialog from mainwindow
public class MainWindowViewModel : ViewModelBase
{
public string Message {get; set;}
public void ShowLoginCommandExecute()
{
var loginViewModel = new LoginViewModel();
var dialogResult = this.DialogService.ShowDialog(loginViewModel, "Please, log in");
//after dialog is closed, do someting
if (dialogResult == true && loginViewModel.IsLoginSuccessful)
{
this.Message = string.Format("Hello, {0}!", loginViewModel.Username);
}
}
}
public class DialogService : IDialogService
{
public bool? ShowDialog(object dialogViewModel, string caption)
{
var contentView = ViewLocator.GetView(dialogViewModel);
var dlg = new DialogWindow
{
Title = caption
};
dlg.PART_ContentControl.Content = contentView;
return dlg.ShowDialog();
}
}
Isn't this just simpler? more straitforward, more readable and last but not least easier to debug than EventAggregator or other similar solutions?
as you can see, In my view models I'm have used ViewModel first approach described in my post here: Best practice for calling View from ViewModel in WPF
Of course, in real world, the DialogService.ShowDialog must have more option to configure the dialog, e.g. buttons and commands they should execute. There are different way of doing so, but its out of scope :)
While this doesn't answer the question of how to do this via the viewmodel, this does show how to do it using only XAML + the blend SDK.
I chose to download and use two files from the Blend SDK, both of which you can as a package from Microsoft through NuGet. The files are:
System.Windows.Interactivity.dll and Microsoft.Expression.Interactions.dll
Microsoft.Expression.Interactions.dll gives you nice capabilities such as the ability to set property or invoke a method on your viewmodel or other target and has other widgets inside as well.
Some XAML:
<Window x:Class="Blah.Blah.MyWindow"
...
xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
xmlns:ei="http://schemas.microsoft.com/expression/2010/interactions"
...>
<StackPanel>
<Button x:Name="OKButton" Content="OK">
<i:Interaction.Triggers>
<i:EventTrigger EventName="Click">
<ei:ChangePropertyAction
TargetObject="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Window}}}"
PropertyName="DialogResult"
Value="True"
IsEnabled="{Binding SomeBoolOnTheVM}" />
</i:EventTrigger>
</Button>
<Button x:Name="CancelButton" Content="Cancel">
<i:Interaction.Triggers>
<i:EventTrigger EventName="Click">
<ei:ChangePropertyAction
TargetObject="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Window}}}"
PropertyName="DialogResult"
Value="False" />
</i:EventTrigger>
</Button>
<Button x:Name="CloseButton" Content="Close">
<i:Interaction.Triggers>
<i:EventTrigger EventName="Click">
<!-- method being invoked should be void w/ no args -->
<ei:CallMethodAction
TargetObject="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Window}}}"
MethodName="Close" />
</i:EventTrigger>
</i:Interaction.Triggers>
</Button>
<StackPanel>
</Window>
Note that if you're just going for simple OK/Cancel behavior, you can get away w/ using the IsDefault and IsCancel properties as long as the window is shown w/ Window.ShowDialog().
I personally had problems w/ a button that had the IsDefault property set to true, but it was hidden when the page is loaded. It didn't seem to want to play nicely after it was shown, so I just am setting the Window.DialogResult property as shown above instead and it works for me.
Here is the simple bug free solution (with source code), It is working for me.
Derive your ViewModel from INotifyPropertyChanged
Create a observable property CloseDialog in ViewModel
public void Execute()
{
// Do your task here
// if task successful, assign true to CloseDialog
CloseDialog = true;
}
private bool _closeDialog;
public bool CloseDialog
{
get { return _closeDialog; }
set { _closeDialog = value; OnPropertyChanged(); }
}
public event PropertyChangedEventHandler PropertyChanged;
private void OnPropertyChanged([CallerMemberName]string property = "")
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(property));
}
}
}
Attach a Handler in View for this property change
_loginDialogViewModel = new LoginDialogViewModel();
loginPanel.DataContext = _loginDialogViewModel;
_loginDialogViewModel.PropertyChanged += OnPropertyChanged;
Now you are almost done. In the event handler make DialogResult = true
protected void OnPropertyChanged(object sender, PropertyChangedEventArgs args)
{
if (args.PropertyName == "CloseDialog")
{
DialogResult = true;
}
}
Create a Dependency Property in your View/any UserControl(or Window you want to close). Like below:
public bool CloseTrigger
{
get { return (bool)GetValue(CloseTriggerProperty); }
set { SetValue(CloseTriggerProperty, value); }
}
public static readonly DependencyProperty CloseTriggerProperty =
DependencyProperty.Register("CloseTrigger", typeof(bool), typeof(ControlEventBase), new PropertyMetadata(new PropertyChangedCallback(OnCloseTriggerChanged)));
private static void OnCloseTriggerChanged(DependencyObject dp, DependencyPropertyChangedEventArgs e)
{
//write Window Exit Code
}
And bind it from your ViewModel's property:
<Window x:Class="WpfStackOverflowTempProject.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Width="525"
CloseTrigger="{Binding Path=CloseWindow,Mode=TwoWay}"
Property In VeiwModel:
private bool closeWindow;
public bool CloseWindow
{
get { return closeWindow; }
set
{
closeWindow = value;
RaiseChane("CloseWindow");
}
}
Now trigger the close operation by changing the CloseWindow value in ViewModel. :)
Where you need to close the window, simply put this in the viewmodel:
ta-da
foreach (Window window in Application.Current.Windows)
{
if (window.DataContext == this)
{
window.Close();
return;
}
}
Application.Current.MainWindow.Close()
Thats enough!

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