TextBox in WPF TreeView not updating source - wpf

Question

I cannot tell if I fundamentally don't understand something here, or have just done something silly.
I have a tree view with two types of templates.
Nodes that are HierarchicalDataTemplate with a TextBlock
Leaves that are DataTemplate with a TextBlock and a TextBox3.
The binding from source is working fine in all cases and reading the Name or Name & Value properties from the underlying classes, and updating if from any changes from the code behind.
Both the TreeNode and TreeLeaf class implement INotifyPropertyChanged
However the binding of the TextBox.text property back to the TreeLeaf.Value property (with its getter) does not seem to work.
XAML
<TreeView Name="ItemsTree" Grid.Row="1" Grid.Column="1" ItemsSource="{Binding}">
<TreeView.Resources>
<Color x:Key="detailMark">#FFA1A9B3</Color>
<SolidColorBrush x:Key="detailMarkBrush" Color="{StaticResource ResourceKey=detailMark}" />
<Style x:Key="flatTextBox" TargetType="{x:Type TextBox}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type TextBox}">
<Grid>
<Rectangle Stroke="{StaticResource ResourceKey=detailMarkBrush}" StrokeThickness="0"/>
<TextBox Margin="1" Text="{TemplateBinding Text}" BorderThickness="0"/>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<HierarchicalDataTemplate DataType="{x:Type local:TreeNode}" ItemsSource="{Binding Children, NotifyOnSourceUpdated=True, UpdateSourceTrigger=PropertyChanged}">
<TextBlock Text="{Binding Name, NotifyOnSourceUpdated=True}">
</TextBlock>
</HierarchicalDataTemplate>
<DataTemplate DataType="{x:Type local:TreeLeaf}" >
<StackPanel Orientation="Horizontal">
<TextBlock Width="150" Text="{Binding Name, NotifyOnSourceUpdated=True}"/>
<TextBox Width="150" Text="{Binding Value, NotifyOnSourceUpdated=True, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}" Style="{StaticResource ResourceKey=flatTextBox}"/>
</StackPanel>
</DataTemplate>
</TreeView.Resources>
</TreeView>
And then code behind for adding the items to the tree
ItemsTree.Items.Add(treeRoot)
The TreeLeaf class
Public Class TreeLeaf
Implements INotifyPropertyChanged, IEditableObject
Private m_Key As String
Private m_Value As String
Private m_Parent As TreeNode
Private temp_Item As TreeLeaf = Nothing
Private m_Editing As Boolean = False
Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged
Public Sub New()
m_Key = ""
m_Value = ""
End Sub
Public Sub NotifyPropertyChanged(ByVal propertyName As String)
RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(propertyName))
End Sub
Public Sub BeginEdit() Implements IEditableObject.BeginEdit
If Not m_Editing Then
temp_Item = MemberwiseClone()
m_Editing = True
End If
End Sub
Public Sub EndEdit() Implements IEditableObject.EndEdit
If m_Editing = True Then
temp_Item = Nothing
m_Editing = False
End If
End Sub
Public Sub CancelEdit() Implements IEditableObject.CancelEdit
If m_Editing = True Then
m_Key = temp_Item.m_Key
m_Value = temp_Item.m_Value
m_Editing = False
End If
End Sub
Public Property Parent As TreeNode
Get
Return m_Parent
End Get
Set(value As TreeNode)
m_Parent = value
NotifyPropertyChanged("Parent")
End Set
End Property
Public ReadOnly Property Name As String
Get
Return m_Key & " : "
End Get
End Property
Public Property Key As String
Get
Return m_Key
End Get
Set(ByVal value As String)
If Not value = m_Key Then
m_Key = value
NotifyPropertyChanged("Key")
End If
End Set
End Property
Public Property Value As String
Get
Return m_Value
End Get
Set(ByVal value As String)
If Not value = m_Value Then
m_Value = value
NotifyPropertyChanged("Value")
End If
End Set
End Property
End Class
I have seen mentions of setting the DataContext but I don't understand how that would apply to this situation.

Answer 1

Well, unfortunately figured it out.
The style template for the text box was overriding the binding.
The line with TemplateBinding seems to default to a one way from source
<TextBox Margin="1" Text="{TemplateBinding Text}" BorderThickness="0"/>
and it now works if you change it too
<TextBox Margin="1" Text="{Binding Value, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged, NotifyOnSourceUpdated=True}" BorderThickness="0"/>

Answer 2

It's not possible to tell from your code whether the binding works or not since the ViewModel code is complicated enough and also depends on the treeview viewmodel code etc...
One way to debug these types of problems is to create a Converter and make it part of the binding that should be debugged. Setting a breakpoint within the Converter will show whether the binding is called as expected when the value in the source or destination has changed. The code for the converter is realy simple:
Imports System
Imports System.Globalization
Imports System.Windows.Data
Namespace MyApp.Converters
Public Class DebugConverter
Inherits IValueConverter
Public Function Convert(ByVal value As Object, ByVal targetType As Type, ByVal parameter As Object, ByVal culture As CultureInfo) As Object
Return value
End Function
Public Function ConvertBack(ByVal value As Object, ByVal targetType As Type, ByVal parameter As Object, ByVal culture As CultureInfo) As Object
Return value
End Function
End Class
End Namespace
Its integration into a questionable binding is also simple. Add it via its namespace (eg MyApp.Converters) into the XAML:
xmlns:conv="clr-namespace:MyApp.Converters"
...and create an instance via this statement in the Resource section of your TreeView code listing:
<conv:DebugConverter x:Key="DebugConverter"/>
...and last but not least integrate the converter into a binding you want to debug:
<TextBox
Width="150"
Style="{StaticResource ResourceKey=flatTextBox}"
Text="{Binding Value, NotifyOnSourceUpdated=True, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay, Converter={StaticResource DebugConverter}}" />
Now, when you set a breakpoint in the Convert and ConvertBack method you should see these methods being invoked when you start the application. If you do not see it in either direction you know the binding is either not working or the value is not being updated and you can then search further for the cause.
Hope this helps.