如何从后面的代码委派对ViewModel的调用

Question

I have a listbox and I need to do something on DoubleClick event. I am able achieve this by simply using the "MouseDoubleClick" event of ListBox.

XAML

<ListBox x:Name="lbSelectedTables" AllowDrop="true" ItemsSource="{Binding SelectedTablesCollection, Mode=TwoWay}" DisplayMemberPath="Name" ItemContainerStyle="{StaticResource DraggableListBoxItem}" MouseDoubleClick="ListBox_MouseDoubleClick" SelectionMode="Multiple"></ListBox>

Code Behind

private void ListBox_MouseDoubleClick(object sender, MouseButtonEventArgs e)
{
    .....
    My stuff here....
}

Now I would like to delegate this call to the ViewModel. How can I achieve this.

Regards, Deepak

Answer 1

You can use the control's DataContext :

private void ListBox_MouseDoubleClick(object sender, MouseButtonEventArgs e)
{
    (this.DataContext as ViewModel).HandleClick(...);
}

This works if the ViewModel you want to call is the Control's ViewModel, if you want the ViewModel on which the ListBox is bound use:

private void ListBox_MouseDoubleClick(object sender, MouseButtonEventArgs e)
{
    (lbSelectedTables.DataContext as ViewModel).HandleClick(...);
}

Answer 2

You may use galasoft MVVM light and System.Windows.Interactivity and couple the delegate directly as a command to your viewmodel, the following way. (Get MVVMLight lib only through nuget).

...
xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
xmlns:command="http://www.galasoft.ch/mvvmlight"
xmlns:local="clr-namespace:yournamespace"
...

<UserControl.DataContext>
   <local:YourViewModel />
<UserControl.DataContext/>

<ListBox AllowDrop="true" ItemsSource="{Binding SelectedTablesCollection, Mode=TwoWay}" DisplayMemberPath="Name" ItemContainerStyle="{StaticResource DraggableListBoxItem}" SelectionMode="Multiple">
 <i:Interaction.Triggers>
                <i:EventTrigger EventName="MouseDoubleClick">
                    <command:EventToCommand Command="{Binding YourCommand}" PassEventArgsToCommand="True"/>
                </i:EventTrigger>
            </i:Interaction.Triggers>
</ListBox>

In your viewmodel:

public class YourViewModel: YourViewModelBaseClass {
   public ICommand YourCommand{ get; set; }

   public ViewModelOrCodeBehind() {
      InitStuff();
   }

   void  InitStuff(){
      YourCommand = new RelayCommand<MouseButtonEventArgs>(YourMethod);
   }

   void YourMethod(MouseButtonEventArgs e)
   {
       // Do your magic here
   }
}

Nice and clean with no codebehind.