WPF Binding default mode

Question

in one of my apps I have a code like this:

<ProgressBar Grid.Column="0" Grid.Row="0" HorizontalAlignment="Stretch" Height="27" Margin="5,0,5,0" Maximum="{Binding TabuProgressEnd}" Value="{Binding TabuProgress}" />

While I was testing this everything is ok, but when my client opened this under VS and run this code threw an exception:

An unhandled exception of type 'System.InvalidOperationException' occurred in PresentationFramework.dll

Additional information: A TwoWay or OneWayToSource binding cannot work on the read-only property 'TabuProgress' of type 'TSPLib.TabuEngine'.

Usually I would think this is some kind of hoax, but I know that the guy has no idea about coding and making the "Mode=OneWay" explicit helped. How is it possible that the default binding mode differs on different machines?

Answer 1

The Value property in ProgressBar binds TwoWay by default so the exception should occur unless you explicitly set Mode to OneWay. However I can't explain why it doesn't occur on your machine. I tried using Reflector with .NET versions 4.0, 3.5 and 3.0 and as far as I can tell, the default binding mode hasn't changed in a while.

If you have Reflector installed, it would be interesting to see what the ValueProperty (inherited from RangeBase) looks like on your machine

public static readonly DependencyProperty ValueProperty =
    DependencyProperty.Register(
        "Value",
        typeof(double),
        typeof(RangeBase),
        new FrameworkPropertyMetadata(
            0.0,
            FrameworkPropertyMetadataOptions.Journal | 
            FrameworkPropertyMetadataOptions.BindsTwoWayByDefault,
            new PropertyChangedCallback(RangeBase.OnValueChanged),
            new CoerceValueCallback(RangeBase.ConstrainToRange)),
        new ValidateValueCallback(RangeBase.IsValidDoubleValue));