Question

I am trying to translate WPF CodeBehid events like Event, Handler, EventSetter to MVVM pattern. I am not allowed to use System.Windows.Controls since I am using MVVM. And I am also avoiding 3rd party library to solve this issue.

Can somebody explain how to convert the following CodeBehind Event Handler to MVVM Event-Handler? Please explain as much as you can while writing answer.

XAML Code

<DataGridCheckBoxColumn Header="Select" Binding="{Binding Path=IsSelected}"> 
  <DataGridCheckBoxColumn.CellStyle> 
    <Style TargetType="DataGridCell"> 
      <EventSetter Event="MouseLeftButtonUp" Handler="ApprovedMouseUp"></EventSetter> 
    </Style> 
  </DataGridCheckBoxColumn.CellStyle> 
</DataGridCheckBoxColumn> 

Code Behind

private void ApprovedMouseUp(object sender, MouseButtonEventArgs e) 
{ 
    if(sender is DataGridCell) 
    { 
        var temp = (sender as DataGridCell).Content; 
        if(temp is CheckBox) (temp as CheckBox).IsChecked = !(temp as CheckBox).IsChecked; 
    } 
} 

Answer 1

There are few thumb rules regarding MVVM….

1. Your Models and ViewModles should not refer System.Windows.Controls namespace.
2. Your Models and ViewModles should not handle events. Use ICommand interface for that.
3. RoutedCommand is not valid in Models / ViewModels (due to point 2). Hence use DelegateCommand / RelayCommand

Having said that, all the above points are perfectly allowed if you have written an Attached Behavior in MVVM.