Question

I am having trouble databinding a TextBox.Text property to a object’s method. The idea is allowing the user to write in a TextBox a file name and then have a TextBlock output that file’s extension.

class GetFileInfo
{
    public string GetFileExtension(string fileName)
    {
        return Path.GetExtension(fileName);
    }
}

Here is my XAML:

<Window.Resources>
    <ObjectDataProvider x:Key="getFileInfo" MethodName="GetFileExtension" ObjectType="{x:Type local:GetFileInfo}">
        <ObjectDataProvider.MethodParameters>
            <sys:String>abc.text</sys:String>
        </ObjectDataProvider.MethodParameters>
    </ObjectDataProvider>
</Window.Resources>

<StackPanel>
    <TextBox Name="textBox1">
        <TextBox.Text>
            <Binding Source="{StaticResource getFileInfo}" Path="MethodParameters[0]" BindsDirectlyToSource="True" UpdateSourceTrigger="PropertyChanged" />
        </TextBox.Text>
    </TextBox>
    <TextBlock Name="textBlock1" Text="{Binding Source={StaticResource getFileInfo}}"/>
</StackPanel>

For some reason it is not doing anything. Anyknow could point out what may be the reasons?
Here is what I see on the designer and when I run the application:

And here is what happens when I try setting other text at run-time:

Here is the error given by de debugger when trying to set other text at run-time:

System.Windows.Data Error: 8 : Cannot save value from target back to source. BindingExpression:Path=MethodParameters[0]; DataItem=’ObjectDataProvider’ (HashCode=2207369); target element is ‘TextBox’ (Name=’textBox1′); target property is ‘Text’ (type ‘String’) ArgumentException:’System.ArgumentException: Object of type ‘MS.Internal.Data.PropertyPathWorker+IListIndexerArg’ cannot be converted to type ‘System.Int32′.
at System.RuntimeType.TryChangeType(Object value, Binder binder, CultureInfo culture, Boolean needsSpecialCast)
at System.RuntimeType.CheckValue(Object value, Binder binder, CultureInfo culture, BindingFlags invokeAttr)
at System.Reflection.MethodBase.CheckArguments(Object[] parameters, Binder binder, BindingFlags invokeAttr, CultureInfo culture, Signature sig)
at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, Boolean skipVisibilityChecks)
at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
at System.Reflection.RuntimePropertyInfo.SetValue(Object obj, Object value, BindingFlags invokeAttr, Binder binder, Object[] index, CultureInfo culture)
at MS.Internal.Data.PropertyPathWorker.SetValue(Object item, Object value)
at MS.Internal.Data.ClrBindingWorker.UpdateValue(Object value)
at System.Windows.Data.BindingExpression.UpdateSource(Object value)’

Answer 1

Ok, seems like this a bug when running WPF 4.0, as can be seen in comments here.

Woops, I was a bit hasty .. the example works perfectly as long you compile it for the 3.5 framework (in VS 2010).
But if you convert it to WPF 4.0 project the method WeightOnPlanet on ObjectDataProvider is nolonger invoked on odp2 when you edit the textbox.
I have tried to find any new Attributes on either the Binding or the ObjectDataProvider – but nothing has worked out so far …

When compiling in 3.5, it works fine here.