WPF TreeView not being populated

Question

I am trying to dynamically populate a WPF tree by using a ViewModel, however, for some reason it's not working. Either the bindings either aren't properly or I am messing up somewhere in code behind.

Here's a sample of what I have. In XAML I define my TreeView like so...

<TreeView DockPanel.Dock="Left" Width="200" DataContext="{Binding MessageTree}" ItemsSource="{Binding MessageTree}">
    <TreeView.ItemContainerStyle>
            <Style TargetType="{x:Type TreeViewItem}">
            <Setter Property="IsExpanded" Value="{Binding IsExpanded, Mode=TwoWay}" />
            <Setter Property="IsSelected" Value="{Binding IsSelected, Mode=TwoWay}" />
            <Setter Property="FontWeight" Value="Normal" />
            <Style.Triggers>
                <Trigger Property="IsSelected" Value="True">
                    <Setter Property="FontWeight" Value="Bold" />
                </Trigger>
            </Style.Triggers>
        </Style>
        </TreeView.ItemContainerStyle>
        <TreeView.ItemTemplate>
            <HierarchicalDataTemplate DataType="viewModel:Mail" ItemsSource="{Binding Children}">
            <TextBlock Text="{Binding Subject}" />
        </HierarchicalDataTemplate>
    </TreeView.ItemTemplate>
</TreeView>

In Code Behing i have...

private Mail MessageTree { get; set; }

And

using (var mail = new MailParser())
{
    int count = mail.GetMessageCount(DateTime.Today.AddDays(-10), DateTime.Today.AddDays(1));
    MessageTree = new Mail();
    for (int i = count - 1; i >= 0; i--)
    {
        MailMessage msg = mail.RetrieveMessage(i);
        if (msg != null)
        {
            MessageTree.Add(msg);
        }
        if (backgroundWorker != null)
        {
            decimal perc = (100.0m - (((i + 1.0m)*100.0m)/count));
            backgroundWorker.ReportProgress((int) perc, "Recebendo mensagens... " + perc.ToString("N2") + "%");
            if (backgroundWorker.CancellationPending)
            {
                e.Cancel = true;
                break;
            }
        }
    }
}

Mail is defined as

public sealed class Mail : INotifyPropertyChanged
{
    private readonly ObservableCollection<Mail> _children;
    private readonly MailMessage _msg;
    private readonly Mail _parent;

    private bool _isExpanded;
    private bool _isSelected;

    public Mail()
    {
        _msg = new MailMessage {Subject = "Empty"};
        _parent = null;
        _children = new ObservableCollection<Mail>();
    }

    public Mail(MailMessage msg, Mail parent = null)
    {
        _msg = msg;
        _parent = parent;
        _children = new ObservableCollection<Mail>();
    }

    public IEnumerable<Mail> Children
    {
        get { return _children; }
    }

    public string Subject
    {
        get { return _msg.Subject; }
    }

    public bool IsExpanded
    {
        get { return _isExpanded; }
        set
        {
            if (value != _isExpanded)
            {
                _isExpanded = value;
                OnPropertyChanged();
            }
            if (_isExpanded && _parent != null)
                _parent.IsExpanded = true;
        }
    }

    public bool IsSelected
    {
        get { return _isSelected; }
        set
        {
            if (value != _isSelected)
            {
                _isSelected = value;
                OnPropertyChanged();
            }
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    public void Add(MailMessage msg)
    {
        _children.Add(new Mail(msg, this));
        OnPropertyChanged("Children");
    }

    private void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        PropertyChangedEventHandler handler = PropertyChanged;
        if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
    }
}

I can't find anything in it so different from examples found online that it wouldn't work. The Add method is incomplete, I still need some logic to decide whether to add them to the collection or to the collection of one of the collection members, but as is all my Mail objecys are beeing added to the collection but not showing up in the TreeView.

What totally obvious thing am i missing? Shouldn't the TreeView automaticly update as I add items to the collection?

What I want is for the TreeView to show The children of the MessageTree property, and those children's children.

Answer 1

Without seeing the entire setup, I'm not positive but my guess would be that since MessageTree is a plain CLR property (rather than something that raises PropertyChanged or a DependencyProperty or something, that the binding is occurring before your MessageTree = new Mail(); call. When you set it to a new instance, the binding system isn't getting notified since it is a plain property.

Another potential issue is that you say that code is in the code-behind. Just using that Binding syntax won't pick up a property from the code-behind. It's possible that you're setting that up somewhere else in the code that you didn't show us. But generally you aren't going to be binding from the View to the code-behind, you'd be binding to a ViewModel that was used as the DataContext for the view itself.

Answer 2

EDIT: Couldn't see the whole thing on my phone - amended answer based on ability to actually see everything. :)

MOREEDIT: updated based on comments, let's start from scratch!

First off, if you're set on using the window/whatever as the datacontext, let's make it `INotifyPropertyChange...next, let's make "MessageTree" a collection of mails, not just a single one (it'll make binding semantics easier, trust me)

public class WhateverContainsTheTree : Window, INotifyPropertyChanged
{
    public WhateverContainsTheTree()
    {
        this.Loaded += OnLoaded;
        this._messageTree = new ObservableCollection<Mail>();
        this.DataContext = this;
    }

    private void OnLoaded(object sender, RoutedEventArgs e)
    {
        _worker = new BackgroundWorker();
        _worker.DoWork += WorkerWorkin;
        _worker.RunWorkerAsync();
    }

    private BackgroundWorker _worker;
    private ObservableCollection<Mail> _messageTree;    
    public ObservableCollection<Mail> MessageTree 
    { 
        get { return _messageTree; }  
        set { _messageTree = value; RaisePropertyChanged("MessageTree"); } 
    }

    public event PropertyChangedEventHandler PropertyChanged = delegate {};
    private void RaisePropertyChanged(string propertyName)
    {
        PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }

    private void WorkerWorkin(object sender, DoWorkEventArgs e)
    {
                // obviously, change this to your stuff; I added a ctor so I could pass a string
        Thread.Sleep(3000);
        Console.WriteLine("Ok, setting message tree");
        Dispatcher.Invoke(
            System.Windows.Threading.DispatcherPriority.Normal,
            (Action)(() => 
            { 
                var mail1 = new Mail("Mail#1:Changed from background thread");
                var mail2 = new Mail("Mail#2:Submail of mail #1");
                var mail3 = new Mail("Mail#3:Submail of mail #2");
                var mail4 = new Mail("Mail#4:Submail of mail #1");
                var mail5 = new Mail("Mail#5:Submail of mail #4");
                mail1.Children.Add(mail2);
                mail1.Children.Add(mail4);
                mail2.Children.Add(mail3);
                mail4.Children.Add(mail5);
                MessageTree.Add(mail1);
            })
        );
    }
}

Also, like I'd said in the original response, let's slightly tweak Mail.Children:

public ObservableCollection<Mail> Children
{
    get { return _children; }
}

And here's what I used for the treeview xaml:

<TreeView DockPanel.Dock="Left" Width="200" ItemsSource="{{Binding MessageTree}}">
    <TreeView.ItemContainerStyle>
            <Style TargetType="{{x:Type TreeViewItem}}">
            <Setter Property="IsExpanded" Value="{{Binding IsExpanded, Mode=TwoWay}}" />
            <Setter Property="IsSelected" Value="{{Binding IsSelected, Mode=TwoWay}}" />
            <Setter Property="FontWeight" Value="Normal" />
            <Style.Triggers>
                <Trigger Property="IsSelected" Value="True">
                    <Setter Property="FontWeight" Value="Bold" />
                </Trigger>
            </Style.Triggers>
        </Style>
        </TreeView.ItemContainerStyle>
        <TreeView.ItemTemplate>
            <HierarchicalDataTemplate DataType="viewModel:Mail" ItemsSource="{{Binding Children}}">
                <TextBlock Text="{{Binding Subject}}" />
            </HierarchicalDataTemplate>
    </TreeView.ItemTemplate>
</TreeView>

If this STILL doesn't work, I'll just paste in the whole LINQPad blob I put together to test this.

Answer 3

Had to give a name to the TreeView (Tree) and then after

MessageTree = new Mail();

insert

Tree.ItemSource = MessageTree.Children;

I find this ugly but at least it works now. Thank you all for trying to help.