MVVM way to wire up event handlers in Silverlight

MVVM way to wire up event handlers in Silverlight

Using an MVVM pattern in Silverlight/WPF, how do you wire up event handers? I'm trying to bind the XAML Click property to a delegate in the view model, but can't get it to work.

In other words, I want to replace this:

<Button Content="Test Click" Click="Button_Click" /> 

where Button_Click is:

private void Button_Click(object sender, RoutedEventArgs e)  {      // ... } 

with this:

<Button Content="Test Click" Click="{Binding ViewModel.HandleClick}" /> 

where HandleClick is the handler. Attempting this throws a runtime exception:

Object of type 'System.Windows.Data.Binding' cannot be converted to type 'System.Windows.RoutedEventHandler'.

Answers & Comments...

Answer: 1

The answer is to use the extensions provided by Microsoft in the Prism framework. With the DLLs System.Windows.Interactivity.dll and Microsoft.Expression.Interactions.dll, it's possible to bind an event to a handler method in a view model:

<Button Content="Test Click"     xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"           xmlns:ei="http://schemas.microsoft.com/expression/2010/interactions"     >     <i:Interaction.Triggers>         <i:EventTrigger EventName="Click">             <ei:CallMethodAction TargetObject="{Binding ViewModel}" MethodName="HandleClick" />         </i:EventTrigger>     </i:Interaction.Triggers> </Button> 

by : dbasemanhttp://stackoverflow.com/users/1001985

Answer: 2

The MVVM way to do so is by using commands and the ICommand interface. The Button control has a property named Command which receives an object of type ICommand

A commonly used implementation of ICommand is Prism's DelegateCommand. To use it, you can do this in your view model:

public class ViewModel {     public ICommand DoSomethingCommand { get; private set; }      public ViewModel()     {         DoSomethingCommand = new DelegateCommand(HandleDoSomethingCommand);     }      private void HandleDoSomethingCommand()     {         // Do stuff     } } 

Then in XAML:

<Button Content="Test Click" Command={Binding DoSomethingCommand} /> 

Also, make sure that the viewmodel is set as your view's DataContext. One way to do so is in your view's code-behind:

this.DataContext = new ViewModel(); 

This article is a good place to start if you want to know more about MVVM.

by : Adi Lesterhttp://stackoverflow.com/users/389966

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