wpf treeview blues. I want to select an item

Question

I'm trying to select a TreeViewItem. Now, I have access to the containing TreeViewItem and have told it to expand so I can select its kid. If it's already expanded all is well, if it's not then I run this code:

EventHandler selector = new EventHandler(delegate
    {
        if (selectedDirectoryTreeItem.ItemContainerGenerator.Status == GeneratorStatus.ContainersGenerated)
        {
            TreeViewItem want = selectedDirectoryTreeItem.ItemContainerGenerator.ContainerFromItem(dirWeWantSelected) as TreeViewItem;
            if (want == null)
                return;

                want.IsSelected = true;
            // selectedDirectoryTreeItem.ItemContainerGenerator.StatusChanged -= selector;
        }
    });
selectedDirectoryTreeItem.ItemContainerGenerator.StatusChanged += selector;  

So my question is, why wont it select? want is always null. I'm scouring the interwebs looking for another way of doing this but it would be cool if somebody could explain this to me

Answer 1

Thanks for the help, I figured it out. Well it works anyway but i'm not entirely sure why it didn't before... if anyone can tell me it would be lovely... I kinda combined elements of the two responses above and then added on a little bit to make it work. For some reason, no matter what i do I cant select the TVI (TreeViewElement) if its parent wasn't already expanded, even if the parent TVI said its contents were generated and, in fact, had contents i could iterate through. My solution was thus to wait for the contents to be generated and then itrate through them and find the one i wanted. It's really weird to me that I couldn't just grab a container given its contents. Meh. My code could stand to be refactored a little bit but here it is: (works perfectly)

public void listItemClickClick(object sender, RoutedEventArgs e) 
    {
        try
        {
            UserFile fil = (UserFile)(sender as ListBoxItem).DataContext;
            MessageBox.Show("to do: download stuff");
            return;
        }
        catch (InvalidCastException)
        {
        }
        try
        {
            dirWeWantSelected = (Directory)(sender as ListBoxItem).DataContext;
        }
        catch (InvalidCastException)
        {
            MessageBox.Show("this should never happen");
        }
        selectedDirectoryTreeItem.IsExpanded = true;
        TreeViewItem want = null;
        try
        {
            want = selectedDirectoryTreeItem.ItemContainerGenerator.ContainerFromItem(dirWeWantSelected) as TreeViewItem;
        }
        catch
        {
            MessageBox.Show("weird error");
        }
        if (want != null)
        {
            want.IsSelected = true;
        }
        else
        {
            selectedDirectoryTreeItem.ItemContainerGenerator.StatusChanged += ItemContainerGenerator_StatusChanged;
        }
    }

    void ItemContainerGenerator_StatusChanged(object sender, EventArgs e)
    {
        if (selectedDirectoryTreeItem.ItemContainerGenerator.Status
            == System.Windows.Controls.Primitives.GeneratorStatus.ContainersGenerated)
        {
            selectedDirectoryTreeItem.ItemContainerGenerator.StatusChanged
                -= ItemContainerGenerator_StatusChanged;
            Dispatcher.BeginInvoke(System.Windows.Threading.DispatcherPriority.Input,
                new Action(DelayedAction));
        }
    }

    void DelayedAction()
    {
        selectedDirectoryTreeItem.Items.MoveCurrentToFirst();
        Directory curr;
        do
        {
            curr = (Directory)selectedDirectoryTreeItem.Items.CurrentItem;
            if (curr.id == dirWeWantSelected.id)
            {
                curr.Selected = true;
                return;
            }
            selectedDirectoryTreeItem.Items.MoveCurrentToNext();
        }
        while (selectedDirectoryTreeItem.Items.CurrentItem != null);
    }

Answer 2

I've personally always found it easiest to stick a Selected property into my model object and then just bind the TreeViewItem Selected property to the Selected property of the model. Here is some code:

Model

public class Data : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    public Data()
    {
        DataItems = new List<Data>();
    }

    public string Name { get; set; }

    private bool _selected;
    public bool Selected
    {
        get { return _selected; }
        set
        {
            _selected = value;
            OnPropertyChanged("Selected");
        }
    }

    public List<Data> DataItems { get; set; }

    private void OnPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }
}

XAML

<Window x:Class="WpfApplication1.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:WpfApplication1"
    xmlns:controls="clr-namespace:MyControls;assembly=MyControls"
    Title="Window1">  
    <Window.Resources>
        <Style x:Key="CustomTreeViewItem" TargetType="TreeViewItem">
            <Setter Property="IsSelected" Value="{Binding Path=Selected, Mode=TwoWay}" />
            <Setter Property="IsExpanded" Value="True" />
        </Style>
    </Window.Resources>
    <DockPanel Background="Transparent">   
        <TreeView x:Name="_tvTest" DockPanel.Dock="Left" ItemContainerStyle="{StaticResource CustomTreeViewItem}" Width="300" >
            <TreeView.ItemTemplate>
                <HierarchicalDataTemplate DataType="{x:Type local:Data}" ItemsSource="{Binding DataItems}">
                    <TextBlock Text="{Binding Name}" Padding="2" />
                    <HierarchicalDataTemplate.ItemTemplate>
                        <DataTemplate>
                            <TextBlock Text="{Binding Name}" Padding="2" />
                        </DataTemplate>
                    </HierarchicalDataTemplate.ItemTemplate>
                </HierarchicalDataTemplate>
            </TreeView.ItemTemplate>
        </TreeView>

        <Button Content="Select Random TreeView Item" Click="Button_Click" Height="50" Width="200" />
    </DockPanel>
</Window>

Code behind

public partial class Window1 : Window
{
    private Random _random;
    private List<Data> _dataItems;

    public Window1()
    {
        InitializeComponent();
        _dataItems = Init();
        _tvTest.ItemsSource = _dataItems;
        _random = new Random(5);
    }

    private List<Data> Init()
    {
        List<Data> dataItems = new List<Data>();
        for (int i = 1; i <= 10; i++)
        {
            Data d1 = new Data();
            d1.Name = "Data:" + i.ToString();
            for (int j = 1; j <= 4; j++)
            {
                Data d2 = new Data();
                d2.Name = "Data:" + i.ToString() + j.ToString();
                d1.DataItems.Add(d2);
            }
            dataItems.Add(d1);
        }
        return dataItems;
    }

    private void Button_Click(object sender, RoutedEventArgs e)
    {
        int index = _random.Next(0, 9);
        int subIndex = _random.Next(0, 3);

        if (subIndex == 0)
            _dataItems[index].Selected = true;
        else
            _dataItems[index].DataItems[subIndex - 1].Selected = true;
    }
}

Answer 3

In my opinion, this is a bug in WPF, but I have run into the same issue several times. I never trust the ItemContainerGenerator's Status and instead loop on separate thread as such:

private void _selectTreeViewHelper(object directory) {
    TreeViewItem want = null;
    bool broke = false;  //probably some sort of wait timeout instead, but works for sake of example
    while (true) {
       Dispatcher.Invoke(new Action(delegate {
          want = selectedDirectoryTreeItem.ItemContainerGenerator.ContainerFromItem(directory) as TreeViewItem;
          if (want != null && want.IsLoaded) {
               want.IsSelected = true;
               broke = true;
          }
       }));
       if (broke) { break; }
       Thread.Sleep(100); 
    }
}

Then call it:

var thread = new Thread(new ParameterizedThreadStart(_selectTreeViewHelper));
thread.Start(dirWeWantSelected);

Pain I know, but it works.