WPF DataTrigger on any data (binding) change

Question

Hi,

I want to begin a storyboard, every time my Image source changes. I have implemented INotifyPropertyChanged.

Can anyone help me achieve this?

Thanks,

<Image Name="pic" HorizontalAlignment="Center" VerticalAlignment="Center" Source="{Binding ElementName=uc, Path=Image}">
        <Image.Resources>
            <Storyboard x:Key="picStory" x:Name="picStory">
                <DoubleAnimation 
                Storyboard.TargetProperty="(Image.RenderTransform).(TransformGroup.Children)[0].(RotateTransform.Angle)"
                From="0" To="20" Duration="0:0:0.7" />
                <DoubleAnimation Storyboard.TargetProperty="(Image.RenderTransform).(TransformGroup.Children)[1].(TranslateTransform.Y)" From="100" To="0" Duration="0:0:0.7" />
            </Storyboard>
        </Image.Resources>
        <Image.Style>
            <Style TargetType="{x:Type Image}" BasedOn="{StaticResource {x:Type Image}}">
                <Style.Triggers>
                    <DataTrigger Binding="{Binding Path=Source}">
                        <DataTrigger.EnterActions>
                            <BeginStoryboard Storyboard="{StaticResource picStory}"/>
                        </DataTrigger.EnterActions>                            
                    </DataTrigger>
                </Style.Triggers>
            </Style>
        </Image.Style>
        <Image.RenderTransform>
            <TransformGroup>
                <RotateTransform/>
                <TranslateTransform/>
            </TransformGroup>
        </Image.RenderTransform>  
    </Image>

Code bound to "uc":

        private BitmapImage image;
        public BitmapImage Image
        {
            get { return image; }
            set
            {
                image = value;
                OnPropertyChanged("Image");
            }
        }

        public event PropertyChangedEventHandler PropertyChanged;
        protected void OnPropertyChanged(string propertyName)
        {
            if (PropertyChanged != null) PropertyChanged(this, new System.ComponentModel.PropertyChangedEventArgs(propertyName));
        }

Answer 1

Hey Arne,

you can achieve this in another simple way by building a very basic custom control, which inherits from Image.

Here the code for "MyImage":

public class MyImage : Image
{
    public static readonly RoutedEvent ImageUpdatedEvent =
       EventManager.RegisterRoutedEvent("ImageUpdated", RoutingStrategy.Bubble, typeof(RoutedEventHandler), typeof(MyImage));

    public event RoutedEventHandler ImageUpdated
    {
        add { this.AddHandler(ImageUpdatedEvent, value); }
        remove { this.RemoveHandler(ImageUpdatedEvent, value); }
    }

    public static readonly DependencyProperty MyImageSourceProperty = DependencyProperty.Register(
        "MyImageSource",
        typeof(ImageSource),
        typeof(MyImage),
        new PropertyMetadata(null, new PropertyChangedCallback(OnMyImageSourceChanged)));

    public ImageSource MyImageSource
    {
        get { return (ImageSource)GetValue(MyImageSourceProperty); }
        set
        {
            Source = value;
            SetValue(MyImageSourceProperty, value);
        }
    }

    private static void OnMyImageSourceChanged(DependencyObject obj, DependencyPropertyChangedEventArgs args)
    {
        MyImage img = obj as MyImage;
        img.Source = args.NewValue as ImageSource;
        img.RaiseEvent(new RoutedEventArgs(ImageUpdatedEvent));
    }
}

The MyImage control has it's own image source property and an own routed event called "ImageUpdated", which will later cause the storyboard to be triggerd. I have simplified your image code:

<Button Click="Button_Click" Grid.Row="0">Set Image through view model</Button>

    <local:MyImage Grid.Row="1"  x:Name="pic" MyImageSource="{Binding MySource}">
        <Image.Triggers>
            <EventTrigger RoutedEvent="local:MyImage.ImageUpdated">
                <BeginStoryboard >
                    <Storyboard >
                        <DoubleAnimation Storyboard.TargetProperty="(Image.Opacity)" From="0" To="1" Duration="0:0:1" />
                    </Storyboard>
                </BeginStoryboard>
            </EventTrigger>
        </Image.Triggers>
    </local:MyImage>

The button sets a new value for the image source property of the bound viewmodel, which implements INotifyPropertyChanged:

 private void Button_Click(object sender, RoutedEventArgs e)
    {
        int randomValue = new Random(DateTime.Now.Second).Next(0, 2);

        if (randomValue == 0)
        {
            _viewModel.MySource = new BitmapImage(new Uri(@"test.bmp", UriKind.Relative));
        }
        else
        {
            _viewModel.MySource = new BitmapImage(new Uri(@"test2.bmp", UriKind.Relative));
        }
    }

The setter in the viewmodel updates the MyImage with property changed pattern:

public ImageSource MySource
    {
        get { return _mySource; }
        set
        {
            _mySource = value;
            RaisePropertyChanged("MySource");
        }
    }

In my example, the opacity property is animated.

Hope this was helpful

Jan

Answer 2

You have no Value-tag defined in your DataTrigger.

The DataTrigger is listening to updates to find the value you define in the Value-Tag - since you haven't set it - it defaults to null (and I'm guessing your image is never null).

If you want it to fire everytime it changes - just put a valueconverter in the Binding tag that always returns True and set Value="True".