#2782

Gotchas: Debugging WPF Data Binding

I’ve been playing around with WPF data binding recently and was struggling a bit with how to debug it when things weren’t working right. Translation: cursing a lot when everything was hawked and I couldn’t figure out why.

Suppose I have the following binding that doesn’t work the way I expect.

    <TextBox Height="23" Name="textBox3" Width="52" 
             Text="{Binding Path=Radius}"
             ToolTip="Initial radius." />

What I’d like is some debug output from WPF to tell me what I messed up.

Turns out that .NET 3.5 has a new TraceLevel attached property that can really help out. The fact that this is gets a tiny mention at the very end of the data binding overview article on MSDN is a mystery but there you go. Simply set this as part of the binding configuration. Don’t forget to include the diagnostics namespace in the root XAML element.

  <UserControl x:Class="NBody.Viewer.Modules.Configurator.ConfiguratorView"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:diagnostics="clr-namespace:System.Diagnostics;assembly=WindowsBase"
    Height="86" Width="400">

  ...

  <TextBox Height="23" Name="textBox3" Width="52"
     Text="{Binding Path=Radius,
       diagnostics:PresentationTraceSources.TraceLevel=High}"
     ToolTip="Initial radius." />

Easy! The debug window will now contain output like this:

System.Windows.Data Warning: 56 :
BindingExpression (hash=30474330): Default mode resolved to TwoWay
System.Windows.Data Warning: 63 :
BindingExpression (hash=30474330): Resolving source

Here’s another post by Beatriz Stollnitz on some other debugging strategies. The configuration in the Trace Sources section didn’t work for me and I haven’t had time fit it but the article does include some other ideas.