How to programmatically set selected node of a treeview in 1803 version

Question

I am using a treeview in my uwp project which supports 1803 version. I need to know how to set the selected node of the treeview programmatically. Also it would be helpful if solution is provided in C#. Thanks in advance.

Answer 1

Hi, try following demo:

XAML:

<Page
    x:Class="App1.Page06"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:App06"
    xmlns:i="using:Microsoft.Xaml.Interactivity"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
  <Page.DataContext>
    <local:ViewModel/>
  </Page.DataContext>
  <StackPanel>
    <Button Content="Select Node" Command="{Binding Cmd}"/>
    <TreeView SelectionMode="Multiple" Height="400">
      <i:Interaction.Behaviors>
        <local:TvBehavior/>
      </i:Interaction.Behaviors>
    </TreeView>
  </StackPanel>
</Page>

and code:

using Microsoft.Xaml.Interactivity;
using System;
using System.Windows.Input;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;

namespace App06
{
  public class ViewModel
  {
    Random rnd = new Random();

    public ICommand Cmd
    {
      get => new RelayCommand((state) =>
      {
        var n = TreeV.RootNodes[rnd.Next(0, TreeV.RootNodes.Count)];
        if (rnd.NextDouble() > .5 && n.HasChildren)
        {
          n.IsExpanded = true;
          n = n.Children[rnd.Next(0, n.Children.Count)];
        }
        //TreeV.SelectedNodes.Clear();
        TreeV.SelectedNodes.Add(n);
      });
    }

    public TreeView TreeV { get; set; }

        internal void LoadTree()
    {
      for (int i = 1; i < 10; i++)
      {
        var n = new TreeViewNode() { Content = $"Node {i}" };
        TreeV.RootNodes.Add(n);
        for (int k = 1; k < 10; k++) n.Children.Add(new TreeViewNode() { Content = $"SubNode {i} {k}" });
      }
    }
  }

  public class TvBehavior : Behavior<TreeView>
  {
    protected override void OnAttached() => AssociatedObject.Loaded += AssociatedObject_Loaded;
    private void AssociatedObject_Loaded(object sender, RoutedEventArgs e)
    {
      var vm = AssociatedObject.DataContext as ViewModel;
      if (vm == null) return;
      vm.TreeV = AssociatedObject;
      vm.LoadTree();
    }
  }

  public class RelayCommand : ICommand
  {
    private readonly Predicate<object> _canExecute;
    private readonly Action<object> _execute;
    public event EventHandler CanExecuteChanged;
    public RelayCommand(Action<object> execute) : this(execute, null) { }
    public RelayCommand(Action<object> execute, Predicate<object> canExecute) { _execute = execute; _canExecute = canExecute; }
    public bool CanExecute(object parameter) => (_canExecute == null) ? true : _canExecute(parameter);
    public void Execute(object parameter) => _execute(parameter);
    public void RaiseCanExecuteChanged() => CanExecuteChanged?.Invoke(this, EventArgs.Empty);
  }
}

Answer 2

Hello,​

Welcome to our Microsoft Q&A platform!

We can usually set TreeView's selected item by binding.

This is a simple idea:

1. Create a data class, which contains a property to control whether it is selected

public class Model : INotifyPropertyChanged
{
    public string Name { get; set; }
    public bool _isSelected;
    public bool IsSelected
    {
        get => _isSelected;
        set
        {
            _isSelected = value;
            OnPropertyChanged();
        }
    }
    public List<Model> Children { get; set; }
    public event PropertyChangedEventHandler PropertyChanged;
    public void OnPropertyChanged([CallerMemberName]string propertyName = "")
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

2. Create a data collection as a data source

private ObservableCollection<SupportTopic> TopicCollection = new ObservableCollection<SupportTopic>();

3. Create the corresponding DataTemplate and bind the corresponding properties

<TreeView x:Name="MyTreeView"
      ItemsSource="{x:Bind TopicCollection}">
    <TreeView.ItemTemplate>
        <DataTemplate x:DataType="local:Model">
            <TreeViewItem Content="{x:Bind Name}"
                          ItemsSource="{x:Bind Children}"
                          IsSelected="{x:Bind IsSelected,Mode=OneWay}"
                          />
        </DataTemplate>
    </TreeView.ItemTemplate>
</TreeView>

---

In this case, if you need to set an item in the list as a selected item, you only need to set the corresponding Model.IsSelected to True.

Thanks.