Question

I would like to call a Command when a TabItem of my TabControl is selected.

Is there a way to do it without breaking the MVVM pattern ?

Answer 1

Use an AttachedCommand Behavior, which will let you bind a Command to WPF events

<TabControl ...
    local:CommandBehavior.Event="SelectionChanged"  
    local:CommandBehavior.Command="{Binding TabChangedCommand}" />

Of course, if you’re using the MVVM design pattern and binding SelectedItem or SelectedIndex, you could also run the command in the PropertyChanged event

void MyViewModel_PropertyChanged(object sender, PropertyChangedEventArgs e)
{
    if (e.PropertyName == "SelectedIndex")
        RunTabChangedLogic();
}