I have several different ViewModels that I would like to display in the same view (MainPage.xaml).
I'm new to this and don't know how to do it. I have tried to create a MainViewModel:
public class MainViewModel : ViewModelBase, INotifyPropertyChanged
{
WeatherViewModel weatherView = new WeatherViewModel();
ForecastViewModel forecastViewModel = new ForecastViewModel();
DeparturesViewModel departuresViewModel = new DeparturesViewModel();
CalenderViewModel calenderViewModel = new CalenderViewModel();
}
public void GetAllViews()
{
weatherView.GetCurrentTemp();
forecastViewModel.GetForecastTemp();
departuresViewModel.GetDepartures();
calenderViewModel.GetCalender();
}
And in my MainPage.xaml.cs I have this:
public MainPage()
{
this.InitializeComponent();
this.DataContext = new MainViewModel();
}
private void Window_Loaded(object sender, RoutedEventArgs e)
{
var vm = this.DataContext as MainViewModel;
vm.GetAllViews();
}
I manage to display each ViewModel individually like this instead:
this.DataContext = new WeatherViewModel();
but I would like to display everything in the same View.
I think you're on the right track but missed some small but important pieces.
In your example code the MainViewModel class is currently setup with private fields where you really need public properties. Additionally, I would make sure ViewModelBase implements INotifyPropertyChanged if it's not already; that way none of the classes deriving from ViewModelBase need to worry about that part.
public abstract class ViewModelBase : INotifyPropertyChanged
{
/* INotifyPropertyChanged implementation +
whatever other common behavior makes sense
belongs in this class
*/
}
public class MainViewModel : ViewModelBase
{
public WeatherViewModel Weather { get; } = new WeatherViewModel();
public ForecastViewModel Forecast { get; } = new ForecastViewModel();
public DeparturesViewModel Departures { get; } = new DeparturesViewModel();
public CalendarViewModel Calendar { get; } = new CalendarViewModel();
}
In your view code behind file you're setting the data context to 2 different instances of MainViewModel - once in the constructor and once in the Loaded event handler. I'd stick with the constructor version or instead you could set the data context in XAML like this:
<MainPage.DataContext>
<MainViewModel>
</MainPage.DataContext>
Once the data context for the main page is setup and the view models are public properties then you can use bindings to access the state (properties) of the view models perhaps something like this:
<TextBlock Text='{Binding Path=Weather.CurrentTempCelsius, StringFormat='Current Temp: {0}°C'}' />
Multiple ViewModels in same View
You have many ways to approach. Fist way using x:bind. You could initialize each view model in the page resource and give them x:Name, then using x:bind to access specific property like following.
<Page.Resources>
<local:CalenderViewModel x:Name="CalenderViewModel"/>
<local:DeparturesViewModel x:Name="DeparturesViewModel"/>
<local:ForecastViewModel x:Name="ForecastViewModel"/>
<local:WeatherViewModel x:Name="WeatherViewModel"/>
</Page.Resources>
<Grid>
<TextBlock Text="{x:Bind WeatherViewModel.temperature}"/>
</Grid>
Other Way is that integrate all the ViewModels into MainViewModel. And coding.monkey provide the correct solution that you could refer directly.
Here's what I'm trying to do (and there may be a better way):
My application is meant to keep track of players in a game. As players join the game events will be sent (using the event aggregator) to create a user control and add it to a List which is connected to an ItemControl. When they leave the game, events will be sent to remove the user control from the list.
The actual ItemContol looks like this - the Players binding is to the List so that it can show the individual player user controls:
<UserControl>
<Grid>
<ScrollViewer VerticalScrollBarVisibility="Auto">
<ItemsControl ItemsSource="{Binding Players}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<local:PlayerListView />
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</ScrollViewer>
</Grid>
</UserControl>
This is inserted into a grid row/column of the main window view just by using the below command:
<views:PlayerListView />
The issue I am running into is this last line <views:PlayerListView /> as it is saying that "There are no accessible PlayerListView constructors". Here is the code behind with the constructor and I believe the reason I am getting this error is because the constructor isn't parameterless -- here is the code-behind.
public partial class PlayerListView : UserControl
{
public PlayerListView(IEventAggregator eventAggregator)
{
InitializeComponent();
DataContext = new PlayerListViewModel(eventAggregator);
}
}
I need the PlayerListViewModel to have the IEventAggregator in its constructor but am not sure the appropriate way to do it. I've viewed this Stack Overflow post: Prism MVVM - How to pass an IEventAggregator to my ViewModel but am not sure if that is the best way to achieve what I am trying to do or not and am slightly confused on how I would incorporate it.
Adding PlayerListViewModel
namespace PlayerTools.ViewModels
{
class PlayerListViewModel
{
#region Private Fields
IEventAggregator _eventAggregator;
#endregion
#region Public Commands
ICommand AddPlayerToListCommand { get; set; }
ICommand RemovePlayerFromListCommand { get; set; }
#endregion
public List<PlayerStackPanelViewModel> Players = new List<PlayerStackPanelViewModel>();
#region Constructor
public PlayerListViewModel(IEventAggregator eventAggregator)
{
_eventAggregator = eventAggregator;
Players.Add(new PlayerStackPanelViewModel()
{
PlayerName = "Steven",
PlayerClass = "Tennis",
CurrentLevel = 10,
NumberOfDeaths = 0
});
Players.Add( new PlayerStackPanelViewModel()
{
PlayerName = "Steven",
PlayerClass = "Soccer",
CurrentLevel = 17,
NumberOfDeaths = 1
});
//Commands
AddPlayerToListCommand = new DelegateCommand<PlayerStackPanelViewModel>(AddPlayerToList);
RemovePlayerFromListCommand = new DelegateCommand<string>(RemovePlayerFromList);
}
#endregion
public void AddPlayerToList(PlayerStackPanelViewModel player)
{
Players.Add(player);
}
public void RemovePlayerFromList(string playerName)
{
Players.Remove(Players.Single(s => s.PlayerName == playerName));
}
}
}
You could use the ViewModelLocator to wire the DataContext of a view to an instance of your view model:
PlayerListView.xaml.cs:
public partial class PlayerListView : UserControl
{
public PlayerListView()
{
InitializeComponent();
}
}
PlayerListView.xaml:
<UserControl ... prism:ViewModelLocator.AutoWireViewModel="True" />
Your use of the event aggregator should be implemented in the view model and not in the view.
I've a question on VM communication.
Here's my code in C#/WPF app.On my MainWindow.xam,I've a button.
On click of this button,
I need to access and modify the ProductList collection from within another ViewModel.
How do I achieve this please?
public List<ProductInfo> ProductList { get; private set; }
private MainWindow m_mvWindow = null;
public MainWindowViewModel(MainWindow window)
{
this.m_mvWindow = window;
}
MainWindow.xaml.cs
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
this.DataContext = new MainWindowViewModel(this);
}
}
Thanks.
The simplest solution would be to expose your other VM as a property of MainWindowViewModel, pass the child VM a reference to the ProductList collection and have an ICommand on the child VM which is bound to the button in your XAML and which handles the collection modifications.
Something like this:
Main VM
public class MainViewModel
{
<!-- Your stuff ->
public ChildViewModel ChildViewModel
{
if(_childViewModel == null)
{
_childViewModel = new ChildViewModel(ProductList)
}
return _childViewModel;
}
}
Child VM
public class ChildViewModel
{
private List<ProductInfo> _products;
public DelegateCommand ClearCollection {get; set;}
public ChildViewModel(List<ProductInfo> products)
{
_products = products;
ClearCollection = new DelegateCommand(OnClearCollection);
}
private void OnClearCollection()
{
_products.Clear();
}
}
And in the xaml...
<Button Command={Binding ChildViewModel.ClearCommand} Content="..." />
You can use either of these ways:
Create an event in the other view model and handle it in the main view model. That would be the preferred way, since it does avoid coupling your child VM to the main VM, which is poor design.
Pass the collection to the child VM in a constructor. Try to avoid passing the full main VM, again to avoid coupling.
I'm trying to develop an easy MVVM project that it has two windows:
The first window is a text editor, where I bind some properties such as FontSize or BackgroundColor:
<TextBlock FontSize="{Binding EditorFontSize}"></TextBlock>
its DataContext is MainWindowViewModel:
public class MainWindowViewModel : BindableBase
{
public int EditorFontSize
{
get { return _editorFontSize; }
set { SetProperty(ref _editorFontSize, value); }
}
.....
The second window is the option window, where I have an slider for changing the font size:
<Slider Maximum="30" Minimum="10" Value="{Binding EditorFontSize }" ></Slider>
its DataContext is OptionViewModel:
public class OptionViewModel: BindableBase
{
public int EditorFontSize
{
get { return _editorFontSize; }
set { SetProperty(ref _editorFontSize, value); }
}
.....
My problem is that I have to get the value of the slider in the option window and then I have to modify the FontSize property of my TextBlock with this value. But I don't know how to send the font size from OptionViewModel to MainViewModel.
I think that I should use:
A shared model
A model in MainWindowViewModel and a ref of this model in OptionViewModel
Other systems like notifications, messages ...
I hope that you can help me. It's my first MVVM project and English isn't my main language :S
Thanks
Another option is to store such "shared" variables in a SessionContext-class of some kind:
public interface ISessionContext: INotifyPropertyChanged
{
int EditorFontSize { get;set; }
}
Then, inject this into your viewmodels (you are using Dependency Injection, right?) and register to the PropertyChanged event:
public class MainWindowViewModel
{
public MainWindowViewModel(ISessionContext sessionContext)
{
sessionContext.PropertyChanged += OnSessionContextPropertyChanged;
}
private void OnSessionContextPropertyChanged(object sender, PropertyChangedEventArgs e)
{
if (e.PropertyName == "EditorFontSize")
{
this.EditorFontSize = sessionContext.EditorFontSize;
}
}
}
There are many ways to communicate between view models and a lot of points what the point is the best. You can see how it is done:
using MVVMLight
in Prism
by Caliburn
In my view, the best approach is using EventAggregator pattern of Prism framework. The Prism simplifies MVVM pattern. However, if you have not used Prism, you can use Rachel Lim's tutorial - simplified version of EventAggregator pattern by Rachel Lim.. I highly recommend you Rachel Lim's approach.
If you use Rachel Lim's tutorial, then you should create a common class:
public static class EventSystem
{...Here Publish and Subscribe methods to event...}
And publish an event into your OptionViewModel:
eventAggregator.GetEvent<ChangeStockEvent>().Publish(
new TickerSymbolSelectedMessage{ StockSymbol = “STOCK0” });
then you subscribe in constructor of another your MainViewModel to an event:
eventAggregator.GetEvent<ChangeStockEvent>().Subscribe(ShowNews);
public void ShowNews(TickerSymbolSelectedMessage msg)
{
// Handle Event
}
The Rachel Lim's simplified approach is the best approach that I've ever seen. However, if you want to create a big application, then you should read this article by Magnus Montin and at CSharpcorner with an example.
Update: For versions of Prism later than 5 CompositePresentationEvent is depreciated and completely removed in version 6, so you will need to change it to PubSubEvent everything else can stay the same.
I have done a big MVVM application with WPF. I have a lot of windows and I had the same problem. My solution maybe isn't very elegant, but it works perfectly.
First solution: I have done one unique ViewModel, splitting it in various file using a partial class.
All these files start with:
namespace MyVMNameSpace
{
public partial class MainWindowViewModel : DevExpress.Mvvm.ViewModelBase
{
...
}
}
I'm using DevExpress, but, looking your code you have to try:
namespace MyVMNameSpace
{
public partial class MainWindowViewModel : BindableBase
{
...
}
}
Second solution: Anyway, I have also a couple of different ViewModel to manage some of these windows. In this case, if I have some variables to read from one ViewModel to another, I set these variables as static.
Example:
public static event EventHandler ListCOMChanged;
private static List<string> p_ListCOM;
public static List<string> ListCOM
{
get { return p_ListCOM; }
set
{
p_ListCOM = value;
if (ListCOMChanged != null)
ListCOMChanged(null, EventArgs.Empty);
}
}
Maybe the second solution is simplier and still ok for your need.
I hope this is clear. Ask me more details, if you want.
I'm not a MVVM pro myself, but what I've worked around with problems like this is,
having a main class that has all other view models as properties, and setting this class as data context of all the windows, I don't know if its good or bad but for your case it seems enough.
For a more sophisticated solution see this
For the simpler one,
You can do something like this,
public class MainViewModel : BindableBase
{
FirstViewModel firstViewModel;
public FirstViewModel FirstViewModel
{
get
{
return firstViewModel;
}
set
{
firstViewModel = value;
}
}
public SecondViewModel SecondViewModel
{
get
{
return secondViewModel;
}
set
{
secondViewModel = value;
}
}
SecondViewModel secondViewModel;
public MainViewModel()
{
firstViewModel = new FirstViewModel();
secondViewModel = new SecondViewModel();
}
}
now you have to make another constructor for your OptionWindow passing a view model.
public SecondWindow(BindableBase viewModel)
{
InitializeComponent();
this.DataContext = viewModel;
}
this is to make sure that both windows work on the same instance of a view model.
Now, just wherever you're opening the second window use these two lines
var window = new SecondWindow((ViewModelBase)this.DataContext);
window.Show();
now you're passing the First Window's view model to the Second window, so that they work on the same instance of the MainViewModel.
Everything is done, just you've to address to binding as
<TextBlock FontSize="{Binding FirstViewModel.EditorFontSize}"></TextBlock>
<TextBlock FontSize="{Binding SecondViewModel.EditorFontSize}"></TextBlock>
and no need to say that the data context of First window is MainViewModel
In MVVM, models are the shared data store. I would persist the font size in the OptionsModel, which implements INotifyPropertyChanged. Any viewmodel interested in font size subscribes to PropertyChanged.
class OptionsModel : BindableBase
{
public int FontSize {get; set;} // Assuming that BindableBase makes this setter invokes NotifyPropertyChanged
}
In the ViewModels that need to be updated when FontSize changes:
internal void Initialize(OptionsModel model)
{
this.model = model;
model.PropertyChanged += ModelPropertyChanged;
// Initialize properties with data from the model
}
private void ModelPropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
{
if (e.PropertyName == nameof(OptionsModel.FontSize))
{
// Update properties with data from the model
}
}
I'm new to WPF and I've come up with a solution to this and I'm curious of more knowledgeable people's thoughts about what's right and wrong with it.
I have an Exams tab and a Templates tab. In my simple proof of concept, I want each tab to "own" an Exam object, and to be able to access the other tab's Exam.
I define the ViewModel for each tab as static because if it's a normal instance property, I don't know how one tab would get the actual instance of the other tab. It feels wrong to me, though it's working.
namespace Gui.Tabs.ExamsTab {
public class GuiExam: INotifyPropertyChanged {
private string _name = "Default exam name";
public string Name {
get => _name;
set {
_name = value;
OnPropertyChanged();
}
}
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged([CallerMemberName] string propertyName="") {
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
public partial class ExamsHome : Page {
public ExamsHome() {
InitializeComponent();
DataContext = ViewModel;
}
public static readonly ExamsTabViewModel ViewModel = new ExamsTabViewModel();
}
public class ExamsTabViewModel {
public GuiExam ExamsTabExam { get; set; } = new GuiExam() { Name = "Exam from Exams Tab" };
public GuiExam FromTemplatesTab { get => TemplatesHome.ViewModel.TemplatesTabExam; }
}
}
namespace Gui.Tabs.TemplatesTab {
public partial class TemplatesHome : Page {
public TemplatesHome() {
InitializeComponent();
DataContext = ViewModel;
}
public static readonly TemplatesTabViewModel ViewModel = new TemplatesTabViewModel();
}
public class TemplatesTabViewModel {
public GuiExam TemplatesTabExam { get; set; } = new GuiExam() { Name = "Exam from Templates Tab" };
public GuiExam FromExamTab { get => ExamsHome.ViewModel.ExamsTabExam; }
}
}
And then everything is accessible in the xaml:
TemplatesHome.xaml (excerpt)
<StackPanel Grid.Row="0">
<Label Content="From Exams Tab:"/>
<Label FontWeight="Bold" Content="{Binding FromExamTab.Name}"/>
</StackPanel>
<StackPanel Grid.Row="1">
<Label Content="Local Content:"/>
<TextBox Text="{Binding TemplatesTabExam.Name, UpdateSourceTrigger=PropertyChanged}"
HorizontalAlignment="Center" Width="200" FontSize="16"/>
</StackPanel>
ExamsHome.xaml (excerpt)
<StackPanel Grid.Row="0">
<Label Content="Local Content:"/>
<TextBox Text="{Binding ExamsTabExam.Name, UpdateSourceTrigger=PropertyChanged}"
HorizontalAlignment="Center" Width="200" FontSize="16"/>
</StackPanel>
<StackPanel Grid.Row="1">
<Label Content="From Templates Tab:"/>
<Label FontWeight="Bold" Content="{Binding FromTemplatesTab.Name}"/>
</StackPanel>
I'm struggling to find a solution to the problem of having to maintain two lists.
I'm using MVVM, but don't want my model to use ObservableCollection. I feel this is best to encapsulate and allows me to use different views/patterns (a console for example). Instead of setting up my structure like this:
public class MainWindow {
// handled in XAML file, no code in the .cs file
}
public abstract class ViewModelBase : INotifyPropertyChanged {
// handles typical functions of a viewmodel base class
}
public class MainWindowViewModel : ViewModelBaseClass {
public ObservableCollection<Account> accounts { get; private set; }
}
public class Administrator {
public List<Account> accounts { get; set; }
public void AddAccount(string username, string password) {
// blah blah
}
}
I would like to avoid having two different collections/lists in the case above. I want only the model to handle the data, and the ViewModel to responsible for the logic of how its rendered.
what you could do is to use a ICollectionView in your Viewmodel to show your Model Data.
public class MainWindowViewModel : ViewModelBaseClass {
public ICollectionView accounts { get; private set; }
private Administrator _admin;
//ctor
public MainWindowViewModel()
{
_admin = new Administrator();
this.accounts = CollectionViewSource.GetDefaultView(this._admin.accounts);
}
//subscribe to your model changes and call Refresh
this.accounts.Refresh();
xaml
<ListBox ItemsSource="{Binding accounts}" />