WPF ComboBox GotFocus (MVVM)

Prepare

NuGet
- Microsoft.Xaml.Behaviors.Wpf 1.1.31
- ReactiveProperty 7.8.3

Notes

• Use Behaviors InvokeCommandAction, then set PassEventArgsToCommand="True".
• You can use ICommand. ReactiveCommand includes ICommand.
• Determin focus types of ComboBox or ComboBoxItem.
• .NET5

View

xmlns:bh="http://schemas.microsoft.com/xaml/behaviors"

<ComboBox Width="120" Height="30">
    <bh:Interaction.Triggers>
        <bh:EventTrigger EventName="GotFocus">
            <bh:InvokeCommandAction Command="{Binding ComboBoxFocus}" PassEventArgsToCommand="True" />
        </bh:EventTrigger>
    </bh:Interaction.Triggers>
    <ComboBoxItem>Test Item1</ComboBoxItem>
    <ComboBoxItem>Test Item2</ComboBoxItem>
    <ComboBoxItem>Test Item3</ComboBoxItem>
</ComboBox>

MainManager is model. This code omited model.

ViewModel

public class MainViewModel : INotifyPropertyChanged, IDisposable
{

    private MainManager Model { get; }
    public ReactiveCommand<RoutedEventArgs> ComboBoxFocus { get; } = new();

    public MainViewModel(MainManager model)
    {
        Model = model;
        ComboBoxFocus.Subscribe(e => ComboBox_GotFocus(e)).AddTo(Disposable);
    }

    private void ComboBox_GotFocus(RoutedEventArgs e)
    {
        var type = e.OriginalSource.GetType();
        if (type == typeof(ComboBox))
        {
            Debug.WriteLine("ComboBox Foucus");
        }
        else if (type == typeof(ComboBoxItem))
        {
            Debug.WriteLine("ComboBoxItem Foucus");
            Debug.WriteLine(((ComboBoxItem)e.OriginalSource).Content);
        }
    }

 // INotifyPropertyChanged
 // Dispose