How to Convert Event to Command in MVVM Pattern in WPF TreeView?

This repository describes how to convert event to command in MVVM pattern in WPF TreeView (SfTreeView).

The TreeView event can be converted into commands using Behaviors. To achieve this, create a command in the ViewModel class and associate it to the TreeView event using Behaviors.

XAML

<syncfusion:SfTreeView 
            x:Name="sfTreeView"
            Margin="20"
            BorderThickness="1"
            SelectionMode="Multiple"
            AutoExpandMode="AllNodes"
            BorderBrush="LightGray"   
            ChildPropertyName="Models"
            ItemTemplateDataContextType="Node"
            ItemsSource="{Binding Items}">
    <syncfusion:SfTreeView.ItemTemplate>
        <DataTemplate>
            <Grid>
                <TextBlock FontSize="12" VerticalAlignment="Center" Text="{Binding Content.State}" />
            </Grid>
        </DataTemplate>
    </syncfusion:SfTreeView.ItemTemplate>
    <I:Interaction.Triggers>
        <I:EventTrigger EventName="SelectionChanged" >
            <cmd:EventToCommand Command="{Binding SelectionChangedCommand}" PassEventArgsToCommand="True" />
        </I:EventTrigger>
    </I:Interaction.Triggers>
</syncfusion:SfTreeView>

C#

public class ViewModel : NotificationObject
{
    public ObservableCollection<Model> Items { get; set; }

    private ICommand selectionChangedCommand;

    public ICommand SelectionChangedCommand
    {
        get
        {
            return selectionChangedCommand;
        }
        set
        {
            selectionChangedCommand = value;
        }
    }
   
    public ViewModel()
    {
        Items = new ObservableCollection<Model>();

        SelectionChangedCommand = new BaseCommand(OnSelectionChanged);

        var country1 = new Model { State = "Australia" };
        var country2 = new Model { State = "Brazil" };
        var country3 = new Model { State = "China" };
        var country4 = new Model { State = "France" };            

        var aus_state1 = new Model { State = "New South Wales" };
        var aus_state2 = new Model { State = "Victoria" };
        var aus_state3 = new Model { State = "South Autralia" };
        var aus_state4 = new Model { State = "Western Australia" };

        var brazil_state1 = new Model { State = "Parana" };
        var brazil_state2 = new Model { State = "Ceara" };
        var brazil_state3 = new Model { State = "Acre" };

        var china_state1 = new Model { State = "Guangzhou" };
        var china_state2 = new Model { State = "Shanghai" };
        var china_state3 = new Model { State = "Beijing" };
        var china_state4 = new Model { State = "Shantou" };

        var france_state1 = new Model { State = "Pays de la Loire" };
        var france_state2 = new Model { State = "Aquitaine" };
        var france_state3 = new Model { State = "Brittany" };
        var france_state4 = new Model { State = "Lorraine" };
      
        country1.Models.Add(aus_state1);
        country1.Models.Add(aus_state2);
        country1.Models.Add(aus_state3);
        country1.Models.Add(aus_state4);

        country2.Models.Add(brazil_state1);
        country2.Models.Add(brazil_state2);
        country2.Models.Add(brazil_state3);

        country3.Models.Add(china_state1);
        country3.Models.Add(china_state2);
        country3.Models.Add(china_state3);
        country3.Models.Add(china_state4);

        country4.Models.Add(france_state1);
        country4.Models.Add(france_state2);
        country4.Models.Add(france_state3);
        country4.Models.Add(france_state4);

        Items.Add(country1);
        Items.Add(country2);
        Items.Add(country3);
        Items.Add(country4);
    }

    private void OnSelectionChanged(object obj)
    {
        var args = obj as ItemSelectionChangedEventArgs;
        if (args.AddedItems.Count > 0)
            MessageBox.Show("Selected State: " + (args.AddedItems[0] as Model).State.ToString());
    }
}