Treeview - Hierarchical Data Template - Binding does not update on source change?
- by ClearsTheScreen
Greetings!
I ran into this problem in my project (Silverlight 3 with C#):
I have a TreeView which is data bound to, well, a tree.
This TreeView has a HierarchicalDataTamplate in a resource dictionary, that defines various controls. Now I want to hide (Visibility.Collapse) some items depending on wether a node has children or not. Other items shall be visible under the same condition.
It works like charm when I first bind the source tree to the TreeView, but when I change the source tree, the visibility in the treeview does not change.
XAML - page:
<controls:TreeView x:Name="SankeyTreeView"
ItemContainerStyle="{StaticResource expandedTreeViewItemStyle}"
ItemTemplate="{StaticResource SankeyTreeTemplate}">
<controls:TreeViewItem IsExpanded="True">
<controls:TreeViewItem.HeaderTemplate>
<DataTemplate>
<TextBlock Text="This is just for loading and will be replaced directly after the data becomes available..."/>
</DataTemplate>
</controls:TreeViewItem.HeaderTemplate>
</controls:TreeViewItem>
</controls:TreeView>
XAML - ResourceDictionary
<!-- Each node in the tree is structurally identical, hence only one Hierarchical
Data Template that'll use itself on the children. -->
<Data:HierarchicalDataTemplate x:Key="SankeyTreeTemplate"
ItemsSource="{Binding Children}">
<Grid Height="24">
<TextBlock x:Name="TextBlockName" Text="{Binding Path=Value.name, Mode=TwoWay}"
VerticalAlignment="Center" Foreground="Black"/>
<TextBox x:Name="TextBoxFlow" Text="{Binding Path=Value.flow, Mode=TwoWay}"
Grid.Column="1" Visibility="{Binding Children,
Converter={StaticResource BoxConverter},
ConverterParameter=\{box\}}"/>
<TextBlock x:Name="TextBlockThroughput" Text="{Binding Path=Value.throughput, Mode=TwoWay}"
Grid.Column="1" Visibility="{Binding Children,
Converter={StaticResource BoxConverter}, ConverterParameter=\{block\}}"/>
<Button x:Name="ButtonAddNode"/>
<Button x:Name="ButtonDeleteNode"/>
<Button x:Name="ButtonEditNode"/>
</Grid>
</Data:HierarchicalDataTemplate>
Now, as you can see, the TextBoxFlow and the TextBlockThroughput share the same space.
What I aim at: The "Throughput" value of a node is how much of something 'flows' through this node from its children. It can't be changed directly, so I want to display a text block. Only leaf nodes have a TextBox to let someone enter the 'flow' that is generated in this leaf node. (I.E.: Node.Throughput = Node.Flow + Sum(Children.Throughput), where Node.Flow = 0 for each non-leaf.)
What the BoxConverter (silly name -.-) does:
public object Convert(object value, Type targetType, object parameter,
System.Globalization.CultureInfo culture)
{
if ((value as NodeList<TreeItem>).Count > 1) // Node has Children?
{
if ((parameter as String) == "{box}")
{
return Visibility.Collapsed;
}
else ((parameter as String) == "{block}")
{
return Visibility.Visible;
}
}
else
{
/*
* As above, just with Collapsed and Visible switched
*/
}
}
The structure of the tree that is bound to the TreeView is essentially stolen from Dan Vanderboom (a bit too much to dump the whole code here), except that I here of course use an ObservableCollection for the children and the value items implement INotifyPropertyChanged.
I would be very grateful if someone could explain to me, why inserting items into the underlying tree does not update the visibility for box and block.
Thank you in advance!
