WPF Launch animation from code-behind in MVVM

问题

I'm looking for the way to code-behind launch an animation on a control contained in an ControlTemplate. In my app I have custom templated buttons (playing menu role) created from an ObservableCollection :

MainMenuViewModel :

/// <summary>
/// Menu items list
/// </summary>
private ObservableCollection<MenuItem> _items;

....

/// <summary>
/// Menu items list property
/// </summary>
public ObservableCollection<MenuItem> Items
{
    get { return _items; }
    set { _items = value; }
}

MainMenuView :

<UserControl x:Class="OfficeTourismeBrantome.Views.MainMenuView"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
         mc:Ignorable="d" 
         d:DesignHeight="800" d:DesignWidth="300">
    <UserControl.Resources>
        <Style x:Key="MenuItemButtonStyle" TargetType="Button">
            <Setter Property="FontSize" Value="60" />
            <Setter Property="FontFamily" Value="Segoe" />
            <Setter Property="FontWeight" Value="UltraLight" />
            <Setter Property="Foreground" Value="#FFEBEDEA" />
            <!--<Setter Property="Height" Value="{Binding MenuLayout.MenuItemSize.Height}" />-->
            <Setter Property="HorizontalContentAlignment" Value="Right" />
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type Button}">
                        <ControlTemplate.Triggers>
                            <EventTrigger RoutedEvent="Button.Click">
                                <EventTrigger.Actions>
                                    <BeginStoryboard>
                                        <Storyboard Name="themeSelectionAnimation">
                                            <DoubleAnimation 
                                                Storyboard.TargetName="coloredRectangle"
                                                Storyboard.TargetProperty="Width"
                                                From="30.0" 
                                                To="250.0" 
                                                Duration="0:0:0.3" />
                                        </Storyboard>
                                    </BeginStoryboard>                                    
                                </EventTrigger.Actions>
                            </EventTrigger>
                        </ControlTemplate.Triggers>
                        <Canvas HorizontalAlignment="Stretch" ClipToBounds="False" >
                            <ContentPresenter Canvas.Left="{Binding MenuLayout.MenuItemLeftMargin}" HorizontalAlignment="Center"                                                  
                                            VerticalAlignment="Center" Canvas.ZIndex="1"/>
                            <TextBlock 
                                Text="{Binding SecondaryText}" 
                                Canvas.Top="50"
                                Canvas.Left="10"
                                FontSize="30"
                                FontWeight="ExtraLight"
                                FontStyle="Italic"
                                Canvas.ZIndex="1"
                                />
                            <Rectangle
                                Canvas.Top="30"
                                Canvas.Left="10"
                                Name="coloredRectangle"
                                Width="30"
                                Height="10"
                                Canvas.ZIndex="0"
                                Fill="{Binding Color}"/>
                        </Canvas>                        
                    </ControlTemplate>                    
                </Setter.Value>
            </Setter>             
        </Style>
        <Storyboard x:Key="themeUnselectionAnimation">
            <DoubleAnimation                 
                Storyboard.TargetProperty="Width"
                From="250.0" 
                To="30.0" 
                Duration="0:0:0.15" />
        </Storyboard>
    </UserControl.Resources>
    <ItemsControl Name="menuButtonContainer" ItemsSource="{Binding Items}" Margin="{Binding MenuLayout.MenuMargin}">
        <ItemsControl.ItemsPanel>
            <ItemsPanelTemplate>
                <StackPanel Orientation="Vertical" />
            </ItemsPanelTemplate>
        </ItemsControl.ItemsPanel>        
        <ItemsControl.ItemTemplate>
            <DataTemplate>
                <Button 
                    Style="{StaticResource ResourceKey=MenuItemButtonStyle}" 
                    Margin="{Binding ElementName=menuButtonContainer, 
                                        Path=DataContext.MenuLayout.MenuItemMargin}"                    
                    Height="{Binding ElementName=menuButtonContainer, 
                                        Path=DataContext.MenuLayout.MenuItemSize.Height}"
                    Content="{Binding Text}"                    
                    Command="{Binding ElementName=menuButtonContainer, 
                                        Path=DataContext.ChangeThemeCommand}"
                    CommandParameter="{Binding Id}"
                    />
            </DataTemplate>
        </ItemsControl.ItemTemplate>
    </ItemsControl>
</UserControl>

As you can see in the code above, I got an animation automatically triggered on button click. I want to play it reverse when another button in the collection is clicked (another menu entry is selected). The animation to play is the one called themeUnselectionAnimation.

First question : is there a way to do it only in XAML? I'm not sure as another button need to be pressed to trigger it.

Below is what I thought :

1. In the Button (which is my menu item) command action, send a message to let subscribers that menu item is changing.
2. Register to it in MainMenuView code-behind.
3. Launch animation from there.

My problem so far is to set the target control for the animation. To do that, I need to find the Rectangle named coloredRectangle in ControlTemplate. How to do that ?

Here below is my code corresponding to above steps :

Step 1 : send message (I'm using MVVM Light framework)

/// <summary>
/// Delegates that handles theme change process and tasks
/// </summary>
/// <param name="themeId">the new active theme</param>
private void ChangeTheme(int themeId)
{
    // Set current active theme as inactive, if one is selected.
    // Exception use because of Single implementation that throw an InvalidOperationException if not item is found
    try
    {
        MenuItem currentTheme = Items.Single(x => x.IsActive == true);

        // Check if this is current theme. If it is, we do nothing.
        if(currentTheme.Id == themeId)
            return;

        // If current theme is set and new theme id is not the same, disable the old one
        currentTheme.IsActive = false;
        // Set new theme as active
        Items.Single(x => x.Id == themeId).IsActive = true;

        // Finally, launch unselection animation

        // Send message and register to it in view code behind
        // Create inner message
        ThemeChangeNotification innerMessage = new ThemeChangeNotification();
        innerMessage.NewThemeId = themeId;
        innerMessage.OldThemeId = currentTheme.Id;

        NotificationMessage<ThemeChangeNotification> message =
            new NotificationMessage<ThemeChangeNotification>(innerMessage, "");
        // Send message
        Messenger.Default.Send(message);                
    }
    catch (InvalidOperationException exception)
    {
        // Set first theme selection as active
        Items.Single(x => x.Id == themeId).IsActive = true;
    }                                    
}

Step 2 : Register to message

Messenger.Default.Register<NotificationMessage<ThemeChangeNotification>>(this, ChangeThemeAnimation);

Step 3 : reach Button from index/id and launch animation (not working)

/// <summary>
/// Theme change message delegate
/// </summary>
/// <param name="e">The ThemeChangeNotification message</param>
private void ChangeThemeAnimation(NotificationMessage<ThemeChangeNotification> message)
{
    var buttonTheme = menuButtonContainer.ItemContainerGenerator.ContainerFromIndex(message.Content.OldThemeId) as FrameworkElement;
    var rectangle = buttonTheme.FindName("coloredRectangle") as Rectangle;
    Storyboard sb = this.FindResource("themeUnselectionAnimation") as Storyboard;
    Storyboard.SetTarget(sb, rectangle);
    sb.Begin();
}

Thank you very much for your answers !

回答1:

Surely, you can just create another Style based on the first one that uses the other Storyboard instead... then you could just apply the reverse Style on whichever Button(s) that you want to start that Storyboard:

<Style x:Key="ReverseMenuItemButtonStyle" TargetType="Button">
    <Setter Property="FontSize" Value="60" />
    <Setter Property="FontFamily" Value="Segoe" />
    <Setter Property="FontWeight" Value="UltraLight" />
    <Setter Property="Foreground" Value="#FFEBEDEA" />
    <Setter Property="HorizontalContentAlignment" Value="Right" />
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type Button}">
                <ControlTemplate.Triggers>
                    <EventTrigger RoutedEvent="Button.Click">
                        <EventTrigger.Actions>
                            <BeginStoryboard>
                                <Storyboard Name="themeUnselectionAnimation">
                                    <DoubleAnimation 
                                        Storyboard.TargetName="coloredRectangle"
                                        Storyboard.TargetProperty="Width"
                                        From="30.0" 
                                        To="250.0" 
                                        Duration="0:0:0.3" />
                                </Storyboard>
                            </BeginStoryboard>                                    
                        </EventTrigger.Actions>
                    </EventTrigger>
                </ControlTemplate.Triggers>
                ...
            </ControlTemplate>                    
        </Setter.Value>
    </Setter>             
</Style>

I've got to be fully honest... I didn't totally understand your question, so if that didn't answer it, it seems as though you also want to know how to start a Storyboard from a view model. In this case, you just need a bool property which will start the animation when set to true in the view model. You can do that using the DataTrigger.EnterActions:

<Style>
    <Style.Triggers>
        <DataTrigger Binding="{Binding SomeBooleanPropertyInViewModel}" Value="True">
            <DataTrigger.EnterActions>
                <BeginStoryboard>
                    <Storyboard ... />
                </BeginStoryboard>
            </DataTrigger.EnterActions>
        </DataTrigger>
    </Style.Triggers>
</Style>

---

UPDATE >>>

Again... I still don't really know what you're after... I'd suggest working on your question asking skills before posting another one. However, this much I could work out:

You're getting an TargetName cannot be used on Style Setter error and you want to target your coloredRectangle element.

The usual fix for this error is simply to move your Trigger to the element that you are trying to target. So try this instead:

<Rectangle Canvas.Top="30" Canvas.Left="10" Name="coloredRectangle" ... >
    <Rectangle.Style>
        <Style>
            <Style.Triggers>
                <DataTrigger Binding="{Binding SomeBooleanProperty}" Value="True">
                    <DataTrigger.EnterActions>
                        <BeginStoryboard>
                            <Storyboard ... />
                        </BeginStoryboard>
                    </DataTrigger.EnterActions>
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </Rectangle.Style>
</Rectangle>

来源：https://stackoverflow.com/questions/22203095/wpf-launch-animation-from-code-behind-in-mvvm