WPF and MVVM - Events

Last time we have seen how to use RelayCommand in ViewModel instead of a click event in View. But what's about all the other events? There is an easy solution where RelayCommand can be used. Therefore we need to add a Reference to the Extension Assembly System.Windows.Interactivity from Blend SDK (for VS2013).

In the XAML part of the View we need to add the namespace that leads to System.Windows.Interactivity from Blend SDK (for VS2013).

<UserControl x:Class="MvvmPassword.LoginView"
             x:Name="This"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity">

Now we can use i:EventTrigger with the property EventName within Interaction.Triggers to define which event should linked to Command. The Command is defined with the property Command within i:InvokeCommandAction.

        <ComboBox x:Name="UserNames"
                  Grid.Row="1"
                  Grid.Column="1"
                  Margin="4"
                  ItemsSource="{Binding UserNames}"
                  DisplayMemberPath="UserName">
            <i:Interaction.Triggers>
                <i:EventTrigger EventName="SelectionChanged">
                    <i:InvokeCommandAction Command="{Binding SelectionCommand}" />
                </i:EventTrigger>
            </i:Interaction.Triggers>
        </ComboBox>

Next we can just use the RelayCommand in ViewModel, as seen in the last post.

SelectionCommand = new RelayCommand(SelectionChanged);

public ICommand SelectionCommand
{
    get;
    private set;
}

private void SelectionChanged(object parameter)
{
    // ...
}

With the ViewModelBase class, the RelayCommand and the EventTrigger our small MVVM Framework can be taken as a good starting point.

Further Posts

1. WPF and MVVM - Fundamentals
2. WPF and MVVM - Commands
3. WPF and MVVM - Events