WPF TextBlock Binding to DependencyProperty

Question

Hi, I have what I believe to be about one of the most simple cases of attempting to bind a view to a dependencyproperty in the view model. It seems that the initial changes are reflected in the view but other changes to the DP do not update the view's TextBlock. I'm probably just missing something simple but I just can't see what it is. Please take a look...

My XAML has a status bar on the bottom of the window. I want to bind to the DP "VRAStatus".

        <StatusBar x:Name="sbar" Grid.Column="0" Grid.Row="2" Grid.ColumnSpan="2" 
               VerticalAlignment="Bottom" Background="LightBlue" Opacity="0.4" DockPanel.Dock="Bottom" >
            <StatusBarItem>
                <TextBlock x:Name="statusBar" Text="{Binding VRAStatus}" />
            </StatusBarItem>
            <StatusBarItem>
                <Separator Style="{StaticResource StatusBarSeparatorStyle}"/>
            </StatusBarItem>
        </StatusBar>

My viewmodel has the DP defined:

    public string VRAStatus
    {
        get { return (string)GetValue(VRAStatusProperty); }
        set { SetValue(VRAStatusProperty, value); }
    }

    // Using a DependencyProperty as the backing store for VRAStatus. 
    public static readonly DependencyProperty VRAStatusProperty =
        DependencyProperty.Register("VRAStatus", typeof(string), typeof(PenskeRouteAssistViewModel),new PropertyMetadata(string.Empty));

Then, in my code I set the DP:

        VRAStatus = "Test Message...";

Is there something obvious here that I am missing? In my constructor for the viewmodel I set the DP like this:

        VRAStatus = "Ready";

I never get the Test Message to display. Please Help.

thanks in advance! Bill

Answer 1

Try specifying the name of the DP with the Path flag in the binding like this:

<TextBlock x:Name="statusBar" Text="{Binding Path=VRAStatus}">

Answer 2

Bill,

When and where do you set the DataContext? I had problems in the past that when I set the DataContext before the InitializeComponent, my Bindings never executed properly.

Also, for curiosity's sake: why do you use a DP in your ViewModel instead of just a Property?

Answer 3

Hi,

As it turns out things were a little more complicated than I had thought (like, when is that NOT the case :) My RibbonControl was in a UserControl to get all of that XAML out of the MainWindow. It was the fact that it was in a UserControl that made it work differently with the ViewModel. I don't know why - probably one of those mysteries that won't ever be solved. But by putting my RibbonControl directly on the MainWindow, everything works as expected - both with a DP and a C# Property. Interesting. (Wish I could get back those two days of my life!)

thanks, Bill

Answer 4

Try to specify the UpdateSourceTrigger property of the Binding:

<StatusBar x:Name="sbar" Grid.Column="0" Grid.Row="2" Grid.ColumnSpan="2" 
           VerticalAlignment="Bottom" Background="LightBlue" Opacity="0.4" DockPanel.Dock="Bottom" >
        <StatusBarItem>
            <TextBlock x:Name="statusBar" Text="{Binding VRAStatus, UpdateSourceTrigger=PropertyChanged}" />
        </StatusBarItem>
        <StatusBarItem>
            <Separator Style="{StaticResource StatusBarSeparatorStyle}"/>
        </StatusBarItem>
    </StatusBar>