I am new to the MVVM pattern and things are coming to me ever so slowly, I want to be able to click a button on my form and then it dynamically create a textbox at runtime. I have a 'Add Title' and also 'Add Question' which both add textboxes but at different locations, you can add as many questions under one title. I have Created a class called Standard in this class it holds:
public class Standard
{
string _title;
ObservableCollection<string> _questions;
public event PropertyChangedEventHandler PropertyChanged;
#region NofiftyPropChnage
protected void NotifyOfPropertyChanged(string name)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(name));
}
}
protected void NotifyOfPropertyChanged<TProperty>(Expression<Func<TProperty>> property)
{
NotifyOfPropertyChanged(property.GetMemberInfo().Name);
}
#endregion
#region Properties
public string Title
{
get { return _title; }
set
{
_title = value;
NotifyOfPropertyChanged(() => Title);
}
}
public ObservableCollection<string> Questions
{
get { return _questions; }
set
{
_questions = value;
NotifyOfPropertyChanged(() => Questions);
}
}
#endregion
}
This class holds a Title property and also a list of Questions property because you can add Questions under a Title.
I also have a ViewModel class which holds:
class ViewModel :INotifyPropertyChanged
{
#region NotifyPropertyChange
public event PropertyChangedEventHandler PropertyChanged;
protected void NotifyOfPropertyChanged(string name)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(name));
}
}
protected void NotifyOfPropertyChanged<TProperty>(Expression<Func<TProperty>> property)
{
NotifyOfPropertyChanged(property.GetMemberInfo().Name);
}
#endregion
private ObservableCollection<Standard> _standardCollection;
public ObservableCollection<Standard> StandardCollection
{
get
{
return _standardCollection;
}
set
{
_standardCollection = value;
NotifyOfPropertyChanged(() => StandardCollection);
}
}
}
This class holds a list of standards, a standard is when you click save with the text boxes and information in the text boxes done. It saves as a Standard
Finally my XAML code:
<Grid>
<button Content="Add Title"/>
<button Content="Add Question"/>
<StackPanel>
<ItemsControl ItemsSource="{Binding StandardCollection}">
<ItemsControl.ItemTemplate>
<DataTemplate DataType="{x:Type local:Standard}">
<Grid>
<TextBox Text="{Binding Title}"/>
<ItemsControl ItemsSource="{Binding Questions}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<TextBox Text="{Binding Questions}"/>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</Grid>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</StackPanel>
</Grid>
Everything runs and there are no errors but when I click 'Add Title' or 'Add Question' no textbox appears, any help?
Ok, I'll have another shot at this one. I've stripped out the Title part and just concentrated on the Questions in order to keep this as a minimal example. First you'll need a base class that implements INotifyPropertyChanged for your view models:
public abstract class ObservableObject : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged<T>(Expression<Func<T>> propertyExpresion)
{
var property = (MemberExpression)propertyExpresion.Body;
this.OnPropertyChanged(property.Member.Name);
}
protected void OnPropertyChanged(string propertyName)
{
if (this.PropertyChanged != null)
{
this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}
Next you'll need a class that implements ICommand for your buttons to bind to which causes handlers to get called when those buttons are pressed:
// by Josh Smith, http://msdn.microsoft.com/en-us/magazine/dd419663.aspx
public class RelayCommand : ICommand
{
#region Fields
readonly Action<object> _execute;
readonly Predicate<object> _canExecute;
#endregion // Fields
#region Constructors
public RelayCommand(Action<object> execute)
: this(execute, null)
{
}
public RelayCommand(Action<object> execute, Predicate<object> canExecute)
{
if (execute == null)
throw new ArgumentNullException("execute");
_execute = execute;
_canExecute = canExecute;
}
#endregion // Constructors
#region ICommand Members
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
}
Those two classes were written by others, if you add MVVM Lite project to your project you'll get them provided for you.
Next we need to create a view model with an ObservableCollection of Questions and a handler that gets called when the user presses the button:
public class MyViewModel : ObservableObject
{
public ICommand AddQuestionCommand {get; private set;}
ObservableCollection<string> _questions = new ObservableCollection<string>();
public ObservableCollection<string> Questions
{
get { return _questions; }
set
{
_questions = value;
OnPropertyChanged(() => Questions);
}
}
public MyViewModel()
{
this.AddQuestionCommand = new RelayCommand(new Action<object>((o) => OnAddQuestion()));
}
private void OnAddQuestion()
{
this.Questions.Add("new item");
}
}
Obviously you'll need to create an instance of this and set it as your window's DataContext. When the command gets triggerd the handler gets called and it in turn adds a new string to the collection. The XAML now needs to bind a button to that command and use the Questions collection to create a list of TextBlocks that display them all:
<StackPanel>
<Button Content="Add Question" Command="{Binding AddQuestionCommand}" HorizontalAlignment="Left"/>
<ItemsControl ItemsSource="{Binding Questions}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<TextBox Text="{Binding .}" Width="200" HorizontalAlignment="Left"/>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</StackPanel>
Hopefully this should give you a starting point. If I've missed something or you need clarification on anything then pls post a follow-up and I'll do my best.
Standard needs to implement the INotifyPropertyChanged interface. Generally you shouldn't do this more than once though, just declare one base class that implements that stuff and inherit all your view models from that. Also if you use package manager to add MVVM Lite to your project then you'll get a lot of this stuff provided for you.
I have no idea why these other guys are banging on about the INotifyPropertyChanged interface, as that has so very little to do with ICommand, although it does appear that you have tried to use it without adding it to the Standard class definition.
Either way, it sounds to me like you need to use the RelayCommand, or similar. This is a class that extends the ICommand interface... you can think of it as a delegate command. Instead of defining a separate class for each command, you can simply define the command logic and the canExecute handler inline. Here is a simplified example:
public ICommand SaveCommand
{
get { return new RelayCommand(execute => Save(), canExecute => CanSave()); }
}
...
<Button Content="Save" Command="{Binding SaveCommand}" />
You can find an implementation of it in the RelayCommand.cs page on GitHub and a description of it in the Commands, RelayCommands and EventToCommand page on MDSN Magazine.
You will need to change your code heavily to make it work. Do the following:
Step 1. Add Class RelayCommand:
public class RelayCommand : ICommand
{
public Func<bool> CanExecute { get; set; }
public Action Execute { get; set; }
public RelayCommand()
{
}
public RelayCommand(Action execute)
{
Execute = execute;
}
#region ICommand Members
bool ICommand.CanExecute(object parameter)
{
if (this.CanExecute == null)
{
return true;
}
else
{
return this.CanExecute();
}
}
event EventHandler ICommand.CanExecuteChanged
{
add { CommandManager.RequerySuggested += value; }
remove { CommandManager.RequerySuggested -= value; }
}
void ICommand.Execute(object parameter)
{
this.Execute();
}
#endregion
}
Step 2. Add Commands in ViewModel
public ICommand AddTitle { get; private set; }
public ICommand AddQuestion { get; private set; }
public ViewModel()
{
_standardCollection = new ObservableCollection<Standard>();
AddTitle = new RelayCommand(OnAddTitle);
AddQuestion = new RelayCommand(OnAddQuestion);
}
void OnAddTitle()
{
_standardCollection.Add(new Standard());
}
void OnAddQuestion()
{
_standardCollection.Last().Questions.Add(new Question("Some Question"));
}
Step 3. Bind buttons
<Button Content="Add Title" Command="{Binding AddTitle}"/>
<Button Content="Add Question" Command="{Binding AddQuestion}"/>
You will also have to fix you layount in XAML.
Since the user can change the question text, you should create a separate class Question.
Try implementing INotifyPropertyChanged on class Standard.
public class Standard : INotifyPropertyChanged
{
string _title;
ObservableCollection<string> _questions;
public event PropertyChangedEventHandler PropertyChanged;
#region NofiftyPropChnage
protected void NotifyOfPropertyChanged(string name)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(name));
}
}
protected void NotifyOfPropertyChanged<TProperty>(Expression<Func<TProperty>> property)
{
NotifyOfPropertyChanged(property.GetMemberInfo().Name);
}
#endregion
#region Properties
public string Title
{
get { return _title; }
set
{
_title = value;
NotifyOfPropertyChanged(() => Title);
}
}
public ObservableCollection<string> Questions
{
get { return _questions; }
set
{
_questions = value;
NotifyOfPropertyChanged(() => Questions);
}
}
#endregion
}
Related
What I'm trying to do is: when the textbox contains the value "123" it should enable the button and allow me to click it.
Solution Image &
View Image
I can not find a way to trigger the Button Command (Class called SpecialCommand.cs) based on my Button parameters. Could you support where I'm getting this MVVM pattern wrong?
WPF View [MainWindow.xaml]:
<Window.Resources>
<ViewModel:MainWindowVM x:Key="WindowVm"></ViewModel:MainWindowVM>
</Window.Resources>
<Grid>
<StackPanel>
<TextBox x:Name="textBox" Margin="0, 5" Text="123"/>
<Button Content="Click me!" Margin="0, 5" Command="{Binding SpecialCommand, Source={StaticResource WindowVm}}" CommandParameter="{Binding Text, ElementName=textBox, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}"/>
</StackPanel>
</Grid>
ViewModel [MainWindowVM.cs]:
public class MainWindowVM
{
private SpecialCommand _specialCommand;
public SpecialCommand SpecialCommand { get => _specialCommand; set => _specialCommand = value; }
public MainWindowVM()
{
_specialCommand = new SpecialCommand();
}
}
Command [SpecialCommand.cs]
public class SpecialCommand : ICommand
{
public bool CanExecute(object parameter)
{
if (parameter != null && (parameter as string) == "123")
return true;
return false;
}
public void Execute(object parameter)
{
MessageBox.Show("Button Pressed!");
}
public event EventHandler CanExecuteChanged;
}
What I believe, maybe this is what I'm getting wrong is since Button & Textbox are in the View I don't need add/modify any method in my SpecialCommand implementation. They should be able to see when a property is changed.
Like the CanExecuteChanged() below, this command raises a lot of times and seems overkill for this small task.
public event EventHandler CanExecuteChanged
{
add { CommandManager.RequerySuggested += value; }
remove { CommandManager.RequerySuggested -= value; }
}
There is no need to make it more complicated than it needs to be.
public class MainWindowVM
{
private string m_OneTwoThree;
public string OneTwoThree{
get { return OneTwoThree; }
set {
if (m_OneTwoThree != value){
m_OneTwoThree = value;
NotifyPropertyChanged(nameof(OneTwoThree)); //if you need this let me know
}
}
}
public MainWindowVM()
{
}
public ICommand RandomCommand { get { return new RelayCommand(OnRandom, IsOneTwoThree); } }
private void OnRandom()
{
//do stuff
}
private bool IsOneTwoThree(){
if (OneTwoThree == "123"){
return true;
}
return false;
}
}
You'll also have to update your xaml I don't think it'll be able to find 'OneTwoThree' so you'll have to bind it yourself, however you usually would.
<StackPanel>
<TextBox x:Name="textBox" Margin="0, 5" Text="{Binding OneTwoThree}"/>
<Button Content="Click me!" Margin="0, 5" Command="{Binding RandomCommand, Source={StaticResource WindowVm}}"/>
</StackPanel>
If you have any questions just ask.
This is my RelayCommand : Use RelayCommand("thing to execute", "if function returns true you can execute");
public class RelayCommand : ICommand
{
public event EventHandler CanExecuteChanged
{
add { CommandManager.RequerySuggested += value; }
remove { CommandManager.RequerySuggested -= value; }
}
private Action methodToExecute;
private Func<bool> canExecuteEvaluator;
public RelayCommand(Action methodToExecute, Func<bool> canExecuteEvaluator)
{
this.methodToExecute = methodToExecute;
this.canExecuteEvaluator = canExecuteEvaluator;
}
public RelayCommand(Action methodToExecute)
: this(methodToExecute, null)
{
}
public bool CanExecute(object parameter)
{
if (this.canExecuteEvaluator == null) {
return true;
}
else {
bool result = this.canExecuteEvaluator.Invoke();
return result;
}
}
public void Execute(object parameter)
{
this.methodToExecute.Invoke();
}
}
You need a way to tell the command that it should check whether it CanExecute. This is done by triggering the event CanExecuteChanged. It tells the button to requery the CanExecute property.
For this to work, I would add a text property to your view model and bind the textbox to it.
In SpecialCommand add the method:
public void TriggerCanExecuteChanged()
{
CanExecuteChanged?.Invoke(this, EventArgs.Empty);
}
In the class MainWindowVM add the property:
private string _text;
public string Text
{
get { return _text; }
set {
if (value != _text) {
_text = value;
_specialCommand.TriggerCanExecuteChanged();
}
}
}
View Model to implementing INotifyPropertyChanged (see comments):
public class MainWindowVM : INotifyPropertyChanged
{
public SpecialCommand SpecialCommand { get; set; } = new SpecialCommand();
private string _text;
public string Text
{
get { return _text; }
set {
if (value != _text) {
_text = value;
OnPropertyChanged(nameof(Text));
SpecialCommand.TriggerCanExecuteChanged();
}
}
}
public event PropertyChangedEventHandler PropertyChanged;
private void OnPropertyChanged(string propertyName)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
I am very new to WPF and relatively new to C# programming (programming in general), and I'm trying to develop a WPF application.
I have tried to go through several posts similar to this, but I can't seem to find the answer of why this is not working.
So, I'm having a hard time understanding the MVVM architecture, how and what it requires to switch between multiple user controls binded to a single <ContentControl />.
From what I understand and read so far, is that I have to bind the view model like this:
<ContentControl Content="{Binding ApplicationViewModel}"/>
So here is what I want to a achieve:
An ApplicationWindow.xaml with sidebar menu on the left side that will be shown at all times when the application is running, and a <ContentControl/> on the remaining space. Buttons shown on the sidebar menu will be:
Main (will show MainView.xaml User Control, should be the default User Control)
Settings (will show SettingsView.xaml User Control)
Exit (will close the application)
I understand that I need to bind the buttons to ICommand commands, and I understand the concept of a RelayCommand.cs class.
So let's jump into the simplified code of my idea and figure out what I need to understand and what I may have misunderstood in the process.
What MainView.xaml and SettingsView.xaml contain are not important right now, as I'm just trying to figure out how to show them in my application.
Here's the ApplicationWindow.xaml:
<Window x:Class="WpfApp1.ApplicationWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:WpfApp1"
xmlns:v="clr-namespace:WpfApp1.View"
xmlns:vm="clr-namespace:WpfApp1.ViewModel"
mc:Ignorable="d"
Title="ApplicationWindow" Height="1080" Width="1920"
WindowStyle="None" WindowState="Maximized">
<Window.Resources>
<DataTemplate DataType="{x:Type vm:MainViewModel}">
<v:MainView/>
</DataTemplate>
<DataTemplate DataType="{x:Type vm:SettingsViewModel}">
<v:SettingsView/>
</DataTemplate>
</Window.Resources>
<DockPanel>
<!--Menu bar on the left-->
<Border DockPanel.Dock="Left">
<StackPanel Orientation="Vertical" Background="Gray" Width="120">
<Button Content="Main" Command="{Binding ShowMainCommand}"/>
<Button Content="Settings" Command="{Binding ShowSettingsCommand}"/>
<Button Content="Exit" Command="{Binding ExitApplicationCommand}"/>
</StackPanel>
</Border>
<!--The content control that view the current view-->
<ContentControl Content="{Binding ApplicationViewModel}"/>
</DockPanel>
</Window>
Note: DataContext is set to ApplicationViewModel.cs in App.xaml.cs by overriding the OnStartup() method.
public partial class App : Application
{
protected override void OnStartup(StartupEventArgs e)
{
base.OnStartup(e);
ApplicationWindow app = new ApplicationWindow
{
DataContext = new ApplicationViewModel()
};
app.Show();
}
}
Here's the ApplicationViewModel.cs:
public class ApplicationViewModel : ViewModelBase
{
#region Fields
private List<ViewModelBase> _viewModels;
private ViewModelBase _currentViewModel;
private ICommand _showMainCommand;
private ICommand _showSettingsCommand;
private ICommand _exitApplicationCommmand;
#endregion
#region Constructor
public ApplicationViewModel()
{
ViewModels = new List<ViewModelBase>
{
new MainViewModel(),
new SettingsViewModel()
};
CurrentViewModel = ViewModels[0];
}
#endregion
#region Public Properties
public List<ViewModelBase> ViewModels
{
get
{
return _viewModels;
}
set
{
if (_viewModels != value)
{
_viewModels = value;
OnPropertyChanged(nameof(ViewModels));
}
}
}
public ViewModelBase CurrentViewModel
{
get
{
return _currentViewModel;
}
set
{
if(_currentViewModel != value)
{
_currentViewModel = value;
OnPropertyChanged(nameof(CurrentViewModel));
}
}
}
#endregion
#region Commands
public ICommand ShowMainCommand
{
get
{
if(_showMainCommand == null)
{
_showMainCommand = new RelayCommand(action => ShowMain());
}
return _showMainCommand;
}
}
public ICommand ShowSettingsCommand
{
get
{
if (_showSettingsCommand == null)
{
_showSettingsCommand = new RelayCommand(action => ShowSettings());
}
return _showSettingsCommand;
}
}
public ICommand ExitApplicationCommand
{
get
{
if (_exitApplicationCommmand == null)
{
_exitApplicationCommmand = new RelayCommand(action => ExitApplication());
}
return _exitApplicationCommmand;
}
}
#endregion
#region Private Methods
private void ShowMain()
{
CurrentViewModel = ViewModels[0];
}
private void ShowSettings()
{
CurrentViewModel = ViewModels[1];
}
private void ExitApplication()
{
MessageBoxResult result = MessageBox.Show("Are you sure you want to exit?", "Exit", MessageBoxButton.YesNo);
if (result == MessageBoxResult.Yes)
{
System.Windows.Application.Current.Shutdown();
}
}
#endregion
}
So, from what I understand, the ApplicationWindow.xaml should be able to determine which view to show out from what the CurrentViewModel is set to.
For the sake of information (or miss-information), here are ViewModelBase.cs:
public class ViewModelBase : INotifyPropertyChanged
{
#region INotifyPropertyChanged
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
#endregion
}
And RelayCommand.cs:
public class RelayCommand : ICommand
{
#region Fields
private readonly Action<object> _execute;
private readonly Predicate<object> _canExecute;
#endregion
#region Constructors
public RelayCommand(Action<object> execute, Predicate<object> canExecute)
{
if (execute == null)
throw new ArgumentNullException("execute");
_execute = execute;
_canExecute = canExecute;
}
public RelayCommand(Action<object> execute) : this(execute, null)
{
}
#endregion
#region ICommand
public bool CanExecute(object parameters)
{
return _canExecute == null ? true : _canExecute(parameters);
}
public event EventHandler CanExecuteChanged
{
add { CommandManager.RequerySuggested += value; }
remove { CommandManager.RequerySuggested -= value; }
}
public void Execute(object parameters)
{
_execute(parameters);
}
#endregion
}
I hope my thought process on this was clear to you, and that one of you smart programmers out there can help solving this, and help me understand why this isn't turning out as I want it to.
In case of what I'm trying to do is harder than Elon Musk's project on making life multiplanetary, feel free to explain why and suggest me a better way to
Your Content control binding should be pointed at the actual property you change when switching ViewModels
<ContentControl Content="{Binding CurrentViewModel}"/>
I have a TextBox in a UserControl which is binded to a property in the MainWindow's ViewModel.
Now when I type something in the Textbox, it updates the property in the viewmodel but if I change Textbox's text in code behind, the viewmodel property isn't updating.
Actually the textbox is getting the value from FileDialog which is opened when I click the button, so Textbox is getting its text from code behind.
UserControl XAML:
<StackPanel Orientation="Horizontal" Grid.Row="1" HorizontalAlignment="Left">
<TextBox x:Name="TextBoxFileOrFolder" Text="{Binding FolderOrFileName}" Grid.Row="1" Width="200" Height="100" HorizontalAlignment="Left"></TextBox>
<Button x:Name="ButtonRun" Content="Run" Click="ButtonRun_OnClick" Width="200" Height="100" Margin="10"></Button>
</StackPanel>
UserControl code behind
private void ButtonRun_OnClick(object sender, RoutedEventArgs e)
{
TextBoxFileOrFolder.Text = "FileName" + new Random().Next();
}
ViewModel:
public class MainViewModel: INotifyPropertyChanged
{
public MainViewModel()
{ }
private string folderOrFileName;
public string FolderOrFileName
{
get { return folderOrFileName; }
set
{
if (folderOrFileName!=value)
{
folderOrFileName = value;
RaisePropertyChanged();
}
}
}
#region INotifyPropertyChanged
public event PropertyChangedEventHandler PropertyChanged;
/// <summary>
/// Raises the property changed.
/// </summary>
/// <param name="propertyName">Name of the property.</param>
protected virtual void RaisePropertyChanged([CallerMemberName] string propertyName = null)
{
var handler = PropertyChanged;
if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
}
# endregion
}
but if I change Textbox's text in code behind, the viewmodel property isn't updating.
That’s because if you set the Text property of the text box in the code-behind, you are overwriting the binding. So while you update the view, the link to your view model is gone, so there is nothing that will update it. And also, when the view model update the values, the view also will not be updated.
To solve this, simply don’t set properties that have a binding in the code-behind.
Instead of handling the button event in the code-behind and updating the view, you should have your button command bind to your view model and update the FolderOrFileName in the view model.
If you binding to Text property you should set property in the ViewModel to change value of TextBox:
public partial class MainWindow : Window
{
private MainViewModel _vm;
public MainWindow()
{
InitializeComponent();
_vm = new MainViewModel();
DataContext = _vm;
}
private void ButtonRun_OnClick(object sender, RoutedEventArgs e)
{
_vm.FolderOrFileName = "FileName" + new Random().Next();
}
}
In your case you should use command to modify data.
1) You should create class which inherit from ICommand:
public class DelegateCommand : ICommand
{
private readonly Predicate<object> _canExecute;
private readonly Action<object> _execute;
public event EventHandler CanExecuteChanged;
public DelegateCommand(Action<object> execute)
: this(execute, null)
{
}
public DelegateCommand(Action<object> execute,
Predicate<object> canExecute)
{
_execute = execute;
_canExecute = canExecute;
}
public bool CanExecute(object parameter)
{
if (_canExecute == null)
{
return true;
}
return _canExecute(parameter);
}
public void Execute(object parameter)
{
_execute(parameter);
}
public void RaiseCanExecuteChanged()
{
if (CanExecuteChanged != null)
{
CanExecuteChanged(this, EventArgs.Empty);
}
}
}
2) Next you should create command in ViewModel:
public class MainViewModel : INotifyPropertyChanged
{
public MainViewModel()
{
ChangeFileName = new DelegateCommand(OnChangeFileName);
}
public ICommand ChangeFileName { get; private set; }
private void OnChangeFileName(object param)
{
FolderOrFileName = "FileName" + new Random().Next();
}
private string folderOrFileName;
...
3) And finally you should add binding to Button.Command property in View:
<Button x:Name="ButtonRun" Content="Run" Command="{Binding ChangeFileName}" Width="200" Height="100" Margin="10"></Button>
Make sure your binding is set up as "TwoWay" - UI -> VM and VM -> UI
<TextBox x:Name="TextBoxFileOrFolder" Text="{Binding FolderOrFileName, Mode=TwoWay}" Grid.Row="1" Width="200" Height="100" HorizontalAlignment="Left"></TextBox>
I'm trying to send a variable from the ViewModel as a parameter to a command. The command looks like this:
public class EditPersonCommand : ICommand
{
private bool _CanExecute = false;
public bool CanExecute(object parameter)
{
PersonModel p = parameter as PersonModel;
CanExecuteProperty = (p != null) && (p.Age > 0);
return CanExecuteProperty;
}
public event EventHandler CanExecuteChanged;
public void Execute(object parameter) { }
private bool CanExecuteProperty
{
get { return _CanExecute; }
set
{
if (_CanExecute != value)
{
_CanExecute = value;
EventHandler can_execute = CanExecuteChanged;
if (can_execute != null)
{
can_execute.Invoke(this, EventArgs.Empty);
}
}
}
}
}
The ViewModel looks like this:
public class PersonViewModel : ViewModelBase
{
private PersonModel _PersonModel;
private EditPersonCommand _EditPersonCommand;
///<remarks>
/// must use the parameterless constructor to satisfy <Window.Resources>
///</remarks>
public PersonViewModel()
: this(new PersonModel())
{
}
public PersonViewModel(PersonModel personModel)
{
_PersonModel = personModel;
}
public ICommand EditPersonCommand
{
get
{
if (_EditPersonCommand == null)
{
_EditPersonCommand = new EditPersonCommand();
}
return _EditPersonCommand;
}
}
}
The xaml looks like this:
<Button Content="Edit" HorizontalAlignment="Right" Height="20" Width="80"
Command="{Binding EditPersonCommand}"
CommandParameter="{Binding _PersonModel}" />
I've tried creating a property in the ViewModel instead of using the private local variable name, but that didnt work either. The object parameter always shows null in the call to CanExecute and the button is never enabled. If I change the CommandParameter value to Hello, then I receive Hello in the call to CanExecute, so I'm not sure why the variable doesnt work. Any help would be appreciated.
Update: I've also tried making a public property to the model (which I dont really want to expose the model, but just tried it to see if it works, but it doesnt).
// Added this to the ViewModel
public PersonModel PersonModelProp
{
get
{
return _PersonModel;
}
set
{
_PersonModel = value;
OnPropertyChanged("PersonModelProp");
}
}
And changed the xaml to this:
<Button Content="Edit" HorizontalAlignment="Right" Height="20" Width="80"
Command="{Binding EditPersonCommand}"
CommandParameter="{Binding PersonModelProp}" />
But still no luck. The ViewModel does implement INotifyPropertyChanged
Is the CommandParameter always null or are you only checking the first time it is being executed?
It appears that the order in which you declare your properties matters in this case since setting the Command property causes the CanExecute to fire immediately before the CommandParameter has been set.
Try moving the CommandParameter property before the Command property:
<Button Content="Edit" HorizontalAlignment="Right" Height="20" Width="80"
CommandParameter="{Binding PersonModelProp}"
Command="{Binding EditPersonCommand}" />
Also, see here and here.
Edit
To ensure that your events are being raised properly you should raise the CanExecuteChanged event when the PersonModelProp value changes.
The Command:
public class EditPersonCommand : ICommand
{
public bool CanExecute(object parameter)
{
PersonModel p = parameter as PersonModel;
return p != null && p.Age > 0;
}
public event EventHandler CanExecuteChanged;
public void Execute(object parameter)
{
//command implementation
}
public void RaiseCanExecuteChanged()
{
var handler = CanExecuteChanged;
if(handler != null)
{
handler(this, EventArgs.Empty);
}
}
}
And the view model:
public class PersonViewModel : ViewModelBase
{
private PersonModel _PersonModel;
private EditPersonCommand _EditPersonCommand;
///<remarks>
/// must use the parameterless constructor to satisfy <Window.Resources>
///</remarks>
public PersonViewModel()
: this(new PersonModel())
{
_EditPersonCommand = new EditPersonCommand();
}
public PersonViewModel(PersonModel personModel)
{
_PersonModel = personModel;
}
public ICommand EditPersonCommand
{
get
{
return _EditPersonCommand;
}
}
public PersonModel PersonModelProp
{
get
{
return _PersonModel;
}
set
{
_PersonModel = value;
OnPropertyChanged("PersonModelProp");
EditPersonCommand.RaiseCanExecuteChanged();
}
}
}
Two points to the answer:
First, as #akton mentioned, you can only bind to public properties. It doesn't have to be a DependencyProperty though.
Second, which took me some tome to figure out, is that you have to set the binding for the CommandParameter before the Command property. i.e.
<Button Content="Edit" HorizontalAlignment="Right" Height="20" Width="80"
CommandParameter="{Binding PersonModelProp}"
Command="{Binding EditPersonCommand}" />
Hope this helps :)
_PersonModel is private and so cannot be accessed. Create a public property that exposes it and bind to that in the CommandParameter. Remember to make the property a dependency property (technically not required but it helps) and the ViewModel should implement INotifyProperty changed and fire the PropertyChanged event so the binding is updated.
I think you have a problem in your EditPersonCommand (it not fired ok).I check it with relayCommand and it work!
This is the code:
ViewModel:
public class PersonViewModel : ViewModelBase
{
private PersonModel _PersonModel;
private ICommand _EditPersonCommand;
///<remarks>
/// must use the parameterless constructor to satisfy <Window.Resources>
///</remarks>
public PersonViewModel()
: this(new PersonModel())
{
}
public PersonViewModel(PersonModel personModel)
{
PersonModelProp = personModel;
}
public ICommand EditPersonCommand
{
get
{
if (_EditPersonCommand == null)
{
_EditPersonCommand = new RelayCommand(ExecuteEditPerson,CanExecuteEditPerson);
}
return _EditPersonCommand;
}
}
private bool CanExecuteEditPerson(object parameter)
{
PersonModel p = parameter as PersonModel;
return (p != null) && (p.Age > 0);
}
private void ExecuteEditPerson(object o)
{
}
public PersonModel PersonModelProp
{
get
{
return _PersonModel;
}
set
{
_PersonModel = value;
NotifyPropertyChanged("PersonModelProp");
}
}
}
And this RelayCommand (Fire events ok!)
public class RelayCommand : ICommand
{
#region Constants and Fields
private readonly Predicate<object> canExecute;
private readonly Action<object> execute;
#endregion
#region Constructors and Destructors
public RelayCommand(Action<object> execute)
: this(execute, null)
{
}
public RelayCommand(Action<object> execute, Predicate<object> canExecute)
{
if (execute == null)
{
throw new ArgumentNullException("execute");
}
this.execute = execute;
this.canExecute = canExecute;
}
#endregion
#region Events
public event EventHandler CanExecuteChanged
{
add
{
CommandManager.RequerySuggested += value;
}
remove
{
CommandManager.RequerySuggested -= value;
}
}
#endregion
#region Implemented Interfaces
#region ICommand
[DebuggerStepThrough]
public bool CanExecute(object parameter)
{
return this.canExecute == null || this.canExecute(parameter);
}
public void Execute(object parameter)
{
this.execute(parameter);
}
#endregion
#endregion
}
Xmal:
<Button Content="Edit" HorizontalAlignment="Right" Height="20" Width="80"
CommandParameter="{Binding PersonModelProp}"
Command="{Binding EditPersonCommand}" />
Binding checkbox in WPF is common issue, but I am still not finding example code which is easy to follow for beginners. I have check box list in WPF to select favorite sports’ name. The number of checkboxes is static in my case. Can anyone show me how to implement ViewModel for this issue?
FavoriteSportsView.xaml:
<StackPanel Height="50" HorizontalAlignment="Left" VerticalAlignment="Top"
Width="150">
<CheckBox IsChecked="{Binding IsChecked, Mode=TwoWay}"
Command="{Binding Path=SportsResponseCommand}"
CommandParameter="Football"
Content="Football"
Margin="5" />
<CheckBox IsChecked="{Binding IsChecked, Mode=TwoWay}"
Command="{Binding Path=SportsResponseCommand}"
CommandParameter="Hockey"
Content="Hockey"
Margin="5" />
<CheckBox IsChecked="{Binding IsChecked, Mode=TwoWay}"
Command="{Binding Path=SportsResponseCommand}"
CommandParameter="Golf"
Content="Golf"
Margin="5" />
</StackPanel>
FavoriteSportsViewModel.cs
public class FavoriteSportsViewModel.cs {
//Since I am using the same IsChecked in all check box options, I found all check
//boxes gets either checked or unchecked when I just check or uncheck one option.
//How do i resolve this issue? I don't think i need seprate IsChecked for each
//check box option.
private bool _isChecked;
public bool IsChecked{
get {
return _isChecked;
}
set { if (value != _isChecked)
_isChecked = value;
this.OnPropertyChanged("IsChecked");
}
}
//How do i detect parameter in this method?
private ICommand _sportsResponseCommand;
public ICommand SportsResponseCommand
{
get
{
if (_sportsResponseCommand== null)
_sportsResponseCommand= new
RelayCommand(a => DoCollectSelectedGames(), p => true);
return _sportsResponseCommand;
}
set
{
_sportsResponseCommand= value;
}
}
private void DoCollectSelectedGames(){
//Here i push all selected games in an array
}
public abstract class ViewModelBase : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}
I'm not sure how to do the following in above ViewModel:
1. How do I implement single method to handle all my options?
2. how do I detect each one of the checkboxes to see whether checked or not
3. How do i utlize CommandParameter?
4. How do i implement SportsResponseCommand correctly
Your view model should look something like this:
public class MyViewModel : INotifyPropertyChanged
{
//INotifyPropertyChanged implementation
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged(string propertyName)
{
if (this.PropertyChanged != null)
this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
//bindable property
private bool _football;
public bool Football
{
get { return _football; }
set
{
if (value != _football)
{
_football = value;
this.OnPropertyChanged("Football");
}
}
}
//... and the same for Golf and Hockey
}
Then you associate your view model with the view by setting the DataContext property (this will most likely be in the Window or UserControl code behind, though there are a lot of ways to achieve this).
Finally, update your bindings so that they look like:
<CheckBox IsChecked="{Binding Football, Mode=TwoWay}"
Content="Football"
Margin="5" />
<CheckBox IsChecked="{Binding Golf, Mode=TwoWay}"
Content="Football"
Margin="5" />
As a final comment, you shouldn't really need to bind the Command property - you can just write whatever code you need to run in the property setter on the view model.
I highly recommend you to read this http://msdn.microsoft.com/en-us/magazine/dd419663.aspx
I describe a solution below I tried to not modify your XAML code but it is not the only way (or the best approach) but contains all necessary elements!
At first step you need your model I call it Model_Sport
public class Model_Sport : INotifyPropertyChanged
{
#region Constructor
public Model_Sport(string name, ICommand command)
{
Name = name;
SportsResponseCommand = command;
}
#endregion
static readonly PropertyChangedEventArgs _NameEventArgs = new PropertyChangedEventArgs("Name");
private string _Name = null;
public string Name
{
get { return _Name; }
set
{
_Name = value;
OnPropertyChanged(_NameEventArgs);
}
}
static readonly PropertyChangedEventArgs _SportsResponseCommandEventArgs = new PropertyChangedEventArgs("SportsResponseCommand");
private ICommand _SportsResponseCommand = null;
public ICommand SportsResponseCommand
{
get { return _SportsResponseCommand; }
set
{
_SportsResponseCommand = value;
OnPropertyChanged(_SportsResponseCommandEventArgs);
}
}
static readonly PropertyChangedEventArgs _IsCheckedEventArgs = new PropertyChangedEventArgs("IsChecked");
private bool _IsChecked = false;
public bool IsChecked
{
get { return _IsChecked; }
set
{
_IsChecked = value;
OnPropertyChanged(_IsCheckedEventArgs);
}
}
#region INotifyPropertyChanged Members
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(PropertyChangedEventArgs eventArgs)
{
if (PropertyChanged != null)
{
PropertyChanged(this, eventArgs);
}
}
#endregion
}
Now you need a way to delegate your command “SportsResponseCommand”, DelegateCommand object will help you to do that
public class DelegateCommand : ICommand
{
private readonly Action<object> _ExecuteMethod;
private readonly Func< object, bool> _CanExecuteMethod;
#region Constructors
public DelegateCommand(Action<object>executeMethod, Func<object, bool> canExecuteMethod)
{
if (null == executeMethod)
{
throw new ArgumentNullException("executeMethod", "Delegate Command Delegates Cannot Be Null");
}
_ExecuteMethod = executeMethod;
_CanExecuteMethod = canExecuteMethod;
}
public DelegateCommand(Action<object>executeMethod) : this(executeMethod, null) { }
#endregion
#region Methods
public bool CanExecute(object parameter)
{
if (_CanExecuteMethod == null) return true;
return _CanExecuteMethod(parameter);
}
public void Execute(object parameter)
{
if (_ExecuteMethod == null) return;
_ExecuteMethod(parameter);
}
bool ICommand.CanExecute(object parameter)
{
return CanExecute(parameter);
}
public event EventHandler CanExecuteChanged
{
add { CommandManager.RequerySuggested += value; }
remove { CommandManager.RequerySuggested -= value; }
}
void ICommand.Execute(object parameter)
{
Execute(parameter);
}
#endregion
}
Now “ViewModel”
public class ViewModel
{
#region property
public Dictionary<string, Model_Sport> Sports { get; set; }
public DelegateCommand SportsResponseCommand { get; set; }
#endregion
public ViewModel()
{
Sports = new Dictionary<string, Model_Sport>();
SportsResponseCommand = new DelegateCommand(p => execute_SportsResponseCommand(p));
buildSports();
}
private void buildSports()
{
Model_Sport football = new Model_Sport("Football", SportsResponseCommand);
Model_Sport golf = new Model_Sport("Golf", SportsResponseCommand);
Model_Sport hockey = new Model_Sport("Hockey", SportsResponseCommand);
football.IsChecked = true; // just for test
Sports.Add(football.Name, football);
Sports.Add(golf.Name, golf);
Sports.Add(hockey.Name, hockey);
}
private void execute_SportsResponseCommand(object p)
{
// TODO :what ever you want
MessageBox.Show(p.ToString());
}
}
Now View
Remember to set datacontext for your Window
public MainWindow()
{
InitializeComponent();
this.DataContext = new ViewModel();
}
Then in XAML
<StackPanel HorizontalAlignment="Left" VerticalAlignment="Top" >
<CheckBox DataContext="{Binding Path=Sports[Football]}"
IsChecked="{Binding IsChecked, Mode=TwoWay}"
Command="{Binding Path=SportsResponseCommand}"
CommandParameter="Football"
Content="Football"
Margin="5" />
<CheckBox DataContext="{Binding Path=Sports[Hockey]}"
IsChecked="{Binding IsChecked, Mode=TwoWay}"
Command="{Binding Path=SportsResponseCommand}"
CommandParameter="Hockey"
Content="Hockey"
Margin="5" />
<CheckBox DataContext="{Binding Path=Sports[Golf]}" IsChecked="{Binding IsChecked, Mode=TwoWay}"
Command="{Binding Path=SportsResponseCommand}"
CommandParameter="Golf"
Content="Golf"
Margin="5" />
</StackPanel>
If you just want a property in your ViewModel to get updated when the IsChecked changes, replace the Binding for IsChecked to a boolean property in your ViewModel that raises NotifyPropertyChanged on its "set".
Now if you want to perform an action everytime IsChecked changes for one of the 3 CheckBoxes:
First of all, replace your CommandParameter with "{Binding RelativeSource={RelativeSource Mode=Self}}"
In your ViewModel (that should implement INotifyPropertyChanged), create an ICommand (SportsResponseCommand) that takes a CheckBox in parameter.
In the command's method, check for the Content of your CheckBox, and for the "IsChecked" property then do your stuff with them.
If you have further questions let me know.
You can assign a view model by using this
//for the view
partial class MainView:Window
{
InitializeComponent();
this.DataContext=new MainViewModel();
}
//ViewModel Code
public class MainViewModel: INotifyPropertyChanged
{
//INotifyPropertyChanged implementation
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged(string propertyName)
{
if (this.PropertyChanged != null)
this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
//bindable property
private bool _football;
public bool Football
{
get { return _football; }
set
{
if (value != _football)
{
_football = value;
this.OnPropertyChanged("Football");
}
}
}
//... and the same for Golf and Hockey
}`
and then you can implement Binding in XAML as
<CheckBox IsChecked="{Binding Football, Mode=TwoWay}"
Command="{Binding Path=SportsResponseCommand}"
CommandParameter="Football"
Content="Football"
Margin="5" />
<CheckBox IsChecked="{Binding Golf, Mode=TwoWay}"
Command="{Binding Path=SportsResponseCommand}"
CommandParameter="Football"
Content="Football"
Margin="5" />