WPF tree view how do I add to the selected item

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CharlesHe-MSFT asked Mar 27, '20 AlexLi-MSFT answered Mar 27, '20

WPF tree view how do I add to the selected item

This is a MSDN question asked by WPF tree view how do I add to the selected item, the source is WPF tree view how do I add to the selected item.

         public List<TreeViewList> treelist = new List<TreeViewList>();
    
         private void AddFolder_Click(object sender, RoutedEventArgs e)
         {
             if (list.SelectedItem != null) 
             {
                 try 
                 {
                     var listof = (list.ItemsSource as List<TreeViewList>);
                     int curIndex = listof.IndexOf(list.SelectedItem as TreeViewList);
    
                     listof[curIndex].Children.Add(person);
                 } 
                 catch 
                 {
                     var listof = (list.ItemsSource as List<TreeViewList>);
    
                     for (int a = 0; a < listof.Count; a++) 
                     {
                         for (int b = 0; b < listof[a].Children.Count; b++)
                         {
                             if (list.SelectedItem == listof[a].Children[b]) 
                             {
                                 listof[a].Children[b].Children.Add(person);
                             }
                         }
                     }
                 }
             }
         }
    
         public class TreeViewList
         {
             public string Name { get; set; }
             public TreeViewList()
             {
                 Children = new ObservableCollection<TreeViewList>();   
             }        
             public ObservableCollection<TreeViewList> Children { get; set; }      
         }

windows-wpf

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Answer 1 · 2020-03-27T08:56:58.087Z

AlexLi-MSFT answered Mar 27, '20

Hi,

Welcome to our Q&A platform!

The reply from Peter Fleischer

you can simplified your code.

use ObservableCollection instead of list,
use SelectedItemChanged event to get SelectedItem.

Try following demo. Demo use Interaction and MVVM.

XAML:

 <Window x:Class="WpfApp1.Window13"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
         xmlns:local="clr-namespace:WpfApp13"
         xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"
         mc:Ignorable="d"
         Title="Window13" Height="450" Width="800">
   <Window.DataContext>
     <local:ViewModel/>
   </Window.DataContext>
   <StackPanel>
     <Button Content="Add new person" Command="{Binding Cmd}"/>
     <TreeView ItemsSource="{Binding View}" Margin="5">
       <i:Interaction.Behaviors>
         <local:TreeViewBehavior/>
       </i:Interaction.Behaviors>
       <TreeView.Resources>
         <HierarchicalDataTemplate DataType="{x:Type local:TreeViewList}"
                                   ItemsSource="{Binding Children}">
           <Label Content="{Binding Name}"/>
         </HierarchicalDataTemplate>
       </TreeView.Resources>
     </TreeView>
   </StackPanel>
 </Window>

Code:

 using System;
 using System.Collections.ObjectModel;
 using System.Windows;
 using System.Windows.Controls;
 using System.Windows.Input;
 using System.Windows.Interactivity;
    
 namespace WpfApp13
 {
   public class ViewModel
   {
     public ObservableCollection<TreeViewList> treelist = new ObservableCollection<TreeViewList>();
     public ObservableCollection<TreeViewList> View { get => treelist; }
    
     public TreeViewList SelectedItem { get; set; }
    
     public ICommand Cmd { get => new RelayCommand(AddFolder_Click); }
    
     private int nr = 1;
     private TreeViewList person { get => new TreeViewList() { Name = $"Name {nr++}" }; }
    
     private void AddFolder_Click(object state)
     {
       if (SelectedItem == null) treelist.Add(person); else SelectedItem.Children.Add(person);
     }
   }
    
   public class TreeViewList
   {
     public string Name { get; set; }
     public ObservableCollection<TreeViewList> Children { get; set; } = new ObservableCollection<TreeViewList>();
   }
    
   public class TreeViewBehavior : Behavior<TreeView>
   {
     protected override void OnAttached()
     {
       AssociatedObject.SelectedItemChanged += AssociatedObject_SelectedItemChanged;
     }
    
     private void AssociatedObject_SelectedItemChanged(object sender, RoutedPropertyChangedEventArgs<object> e)
     {
       var tv = sender as TreeView;
       if (tv == null) return;
       var vm = tv.DataContext as ViewModel;
       if (vm == null) return;
       vm.SelectedItem = tv.SelectedItem as TreeViewList;
     }
   }
    
   public class RelayCommand : ICommand
   {
     private readonly Predicate<object> _canExecute;
     private readonly Action<object> _action;
     public RelayCommand(Action<object> action) { _action = action; _canExecute = null; }
     public void Execute(object o) => _action(o);
     public bool CanExecute(object o) => _canExecute == null ? true : _canExecute(o);
     public event EventHandler CanExecuteChanged
     {
       add { CommandManager.RequerySuggested += value; }
       remove { CommandManager.RequerySuggested -= value; }
     }
   }
 }

Thanks.

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