WPF Binding to Grid Column Width

Well I have got a bit of a kludge working, I'll explain how for future generations:

Essentially I have a 2 column, multi row grid with a splitter right aligned in the first column so it can be resized by the user if the content it contains requires more space. To complicate things I have a user control being loaded programatically into some of the rows which has a columnSpan of 2 for rendering purposes (content 'bleeds' from one cell into the next).

When the first column is resized I need this to be reflected in the usercontrol. Firstly I tried binding to the ColumnDefinition but it really wasn't playing ball.

How I fixed/Kludged it

In a spare cell in the first column I added a <Label> with an x:Name to make it accessible. As it is in a cell it has default properties of 'Stretch' and fills the cell completely. It gets resized as the column is resized using the splitter. Binding to the Label's ActualWidth property means that changes to the size of the column are communicated to the DependancyProperty in my columnSpanned usercontrol correctly.

Thoughts

Obviously, despite ColumnDefinition having an ActualWidth property when it changes it doesn't appear to fire the PropertyChanged event internally (or thats my best guess). This may be a bug, or by design, but for me it means I've had to use a less clean solution.

ColumnDefinition.Width is not an integer - it is a GridLength. You can't bind the GridLength directly to the Integer, you need a converter.

This is also the reason, why you can't bind any Control's Width property (double) to a ColumnDefinition's Width property (GridLength) without a converter.

Have you tried setting up the binding in xaml, the following should work for you.

<ColumnDefinition 
    x:Name="TitleSection" 
    Width="{Binding 
                Path=TitleWidth, 
                RelativeSource={RelativeSource AncestorType=MyUserControl}}" 
    />

Otherwise, looking at the binding code you've supplied, it looks the wrong way around to me, the target of the binding should be the grid column and the source should be your dependency property.

The equivalent code for the above xaml is

BindingOperations.SetBinding(TitleSection, ColumnDefinition.WidthProperty,
    new Binding()
    {
        RelativeSource= new RelativeSource(RelativeSourceMode.FindAncestor, typeof(MyUserControl),1),
        Path = new PropertyPath("TitleWidth"),
    });

On a related note, using a GridSplitter and binding the Width property are mutally exclusive. As soon as you resize the column using the splitter, your binding will be replaced with the value from the splitter.

This is similar to what you would experience by updating any property that is the target of a binding. When you set the targets value directly in code, you are esentially replacing the binding object with the value you supply.