Question

I’m working on some code that has a Button that contains an image and some text, and which should display either the image, the text, or both, depending upon the value of a bound property. The code is currently using Styles and DataTriggers:

public enum ButtonStyle { Image, Text, Both };

public class ViewModel : INotifyPropertyChanged
{
    private ButtonStyle _buttonStyle;
    public ButtonStyle buttonStyle
    {
        get { return this._buttonStyle; }
        set
        {
            this._buttonStyle = value;
            notifyPropertyChanged("buttonStyle");
        }
}

And:

<UserControl.Resources>
    <Style x:Key="buttonTextStyle" TargetType="{x:Type Label}">
        <Style.Triggers>
            <DataTrigger Binding="{Binding Path=buttonStyle}"
                    Value="{x:Static local:ButtonStyle.Text}">
                <Setter Property="Visibility" Value="Collapsed" />
            </DataTrigger>
        </Style.Triggers>
    </Style>
    <Style x:Key="buttonImageStyle" TargetType="{x:Type Image}">
        <Style.Triggers>
            <DataTrigger Binding="{Binding Path=buttonStyle}"
                    Value="{x:Static local:ButtonStyle.Image}">
                <Setter Property="Visibility" Value="Collapsed" />
            </DataTrigger>
        </Style.Triggers>
    </Style>
</UserControl.Resources>


<Button>
    <StackPanel>
        <Image Source="..." Style="{StaticResource buttonImageStyle} />
        <Label Style={StaticResource buttonTextStyle}>My Text</Label>
    </StackPanel>
</Button>

My problem? The button doesn’t change when I change the value of the buttonStyle property in the view model. This control is in a tab, and if I switch to another tab and then switch back, the button updates to reflect the current value of the buttonStyle property, but it does not change until I do.

It looks like the DataTrigger is processed only when the control is rendered, and does not re-render when the bound value is modified, despite the bound value raising a PropertyChanged event.

Any ideas?

Answer 1

Here’s an idea – any time you have a binding problem and it looks like INotifyPropertyChanged isn’t working, check and double check and make damned sure that you spelled the name of the property right, in your PropertyChangedEventArgs().

Sorry for the trouble.