Windows 8 MVVM Animation Control

Overview

As we know Windows 8 Metro apps (or whatever they are called now) don't support trigger or behaviours like Silverlight and WPF apps do, even though they are XAML family. This means that once you have crafted an animation in XAML, you can't actually trigger it without code behind. This article demonstrates how to use an attached property which is toggled by a bool dependency property and controls a pair of animations.

Usage

I have a common settings page which is opened via the charm bar which I was originally showing and hiding using a bool property in the view model and a visibility converter. I wanted to have an animation so that the control would slide in and out but wanted to control it through the view model.

Dependency Property

This dependency property is fairly straight forward, it has 3 dependency properties, the first binds to a boolean property and the other two bind to a pair of opposing animations to control the slide in and out:

/// <summary>

/// This attached property binds to a bool and a pair of StoryboardAnimations

/// When the bool is true, the true animation is started

/// When the bool is false, the fals animation is started

/// </summary>

public class BoolBeginStoryBoardTrigger

{

  #region Bool Property

  public static readonly DependencyProperty BoolProperty =

    DependencyProperty.RegisterAttached("Bool", typeof(bool),   typeof(BoolBeginStoryBoardTrigger), new PropertyMetadata(false, BoolPropertyChanged));

  public static void SetBool(DependencyObject attached, bool value)

  {

    attached.SetValue(BoolProperty, value);

  }

  public static bool GetBool(DependencyObject attached)

  {

    return (bool)attached.GetValue(BoolProperty);

  }

  private static void BoolPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)

  {

    if (GetBool(d))

      GetTrueStoryboard(d).Begin();

    else

      GetFalseStoryboard(d).Begin();

  }

  #endregion

  #region TrueStoryboard Property

  public static readonly DependencyProperty TrueStoryboardProperty =

    DependencyProperty.RegisterAttached("TrueStoryboard", typeof(Storyboard), typeof(BoolBeginStoryBoardTrigger), null);

  public static void SetTrueStoryboard(DependencyObject attached, Storyboard value)

  {

    attached.SetValue(TrueStoryboardProperty, value);

  }

  public static Storyboard GetTrueStoryboard(DependencyObject attached)

  {

    return (Storyboard)attached.GetValue(TrueStoryboardProperty);

  }

  #endregion

  #region FalseStoryboard Property

  public static readonly DependencyProperty FalseStoryboardProperty =

  DependencyProperty.RegisterAttached("FalseStoryboard", typeof(Storyboard), typeof(BoolBeginStoryBoardTrigger), null);

  public static void SetFalseStoryboard(DependencyObject attached, Storyboard value)

  {

    attached.SetValue(FalseStoryboardProperty, value);

  }

  public static Storyboard GetFalseStoryboard(DependencyObject attached)

  {

    return (Storyboard)attached.GetValue(FalseStoryboardProperty);

  }

  #endregion

}

The XAML

The attached property can be put anywhere after where the animations are defined. The 3 properties are set like this:

<Grid Style="{StaticResource LayoutRootStyle}"

        cmd:BoolBeginStoryBoardTrigger.Bool="{Binding IsSettingsVisible}"

        cmd:BoolBeginStoryBoardTrigger.FalseStoryboard="{StaticResource SettingsSlideIn}"

        cmd:BoolBeginStoryBoardTrigger.TrueStoryboard="{StaticResource             SettingsSlideOut}">

If you don't want to bind it to a View Model, it can easily bound to a toggle button in the view like this:

<Grid x:Name="settingsPanel"

          local:BoolBeginStoryBoardTrigger.Bool="{Binding ElementName=toggleButton, Path=IsChecked}"

          local:BoolBeginStoryBoardTrigger.FalseStoryboard="{StaticResource SettingsSlideIn}"

          local:BoolBeginStoryBoardTrigger.TrueStoryboard="{StaticResource SettingsSlideOut}"

Complete Settings Panel XAML

This is bound to the Settings view model which controls the IsSettingsVisible property.

<UserControl

    x:Class="WebberCross.Win8.Demo.View.SettingsPanel"

    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

    xmlns:local="using:WebberCross.Win8.Demo.Settings"

    xmlns:cmd="using:WebberCross.Win8.Demo.Commanding"

    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"

    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"

    Width="346" HorizontalAlignment="Right"

    mc:Ignorable="d"

    d:DesignHeight="300"

    d:DesignWidth="346"   

    x:Name="ThisControl" Visibility="Collapsed"

    DataContext="{Binding Settings, Source={StaticResource Locator}}">

   

    <UserControl.RenderTransform>

        <TranslateTransform x:Name="settingsTranslateX" X="346" />

    </UserControl.RenderTransform>

    <UserControl.Resources>

        <Storyboard x:Key="SettingsSlideOut">

            <DoubleAnimationUsingKeyFrames

                Storyboard.TargetProperty="X"

                Storyboard.TargetName="settingsTranslateX">

                <EasingDoubleKeyFrame KeyTime="0:0:0" Value="346" />

                <EasingDoubleKeyFrame KeyTime="0:0:0.5" Value="0" >

                    <EasingDoubleKeyFrame.EasingFunction>

                        <PowerEase EasingMode="EaseOut"/>

                    </EasingDoubleKeyFrame.EasingFunction>

                </EasingDoubleKeyFrame>

            </DoubleAnimationUsingKeyFrames>

            <ObjectAnimationUsingKeyFrames

                Storyboard.TargetProperty="Visibility"

                Storyboard.TargetName="ThisControl">

                <DiscreteObjectKeyFrame KeyTime="0:0:0" Value="Visible" />                  

            </ObjectAnimationUsingKeyFrames>

        </Storyboard>

        <Storyboard x:Key="SettingsSlideIn">

            <DoubleAnimationUsingKeyFrames

        Storyboard.TargetProperty="X"

        Storyboard.TargetName="settingsTranslateX">

                <EasingDoubleKeyFrame KeyTime="0:0:0" Value="0" />

                <EasingDoubleKeyFrame KeyTime="0:0:0.5" Value="346" >

                    <EasingDoubleKeyFrame.EasingFunction>

                        <PowerEase EasingMode="EaseIn"/>

                    </EasingDoubleKeyFrame.EasingFunction>

                </EasingDoubleKeyFrame>

            </DoubleAnimationUsingKeyFrames>

        </Storyboard>

    </UserControl.Resources>

    <Grid Style="{StaticResource LayoutRootStyle}"

        cmd:BoolBeginStoryBoardTrigger.Bool="{Binding IsSettingsVisible}"

        cmd:BoolBeginStoryBoardTrigger.FalseStoryboard="{StaticResource SettingsSlideIn}"

        cmd:BoolBeginStoryBoardTrigger.TrueStoryboard="{StaticResource SettingsSlideOut}">

        <Grid.RowDefinitions>

            <RowDefinition Height="140"/>

            <RowDefinition Height="*"/>

        </Grid.RowDefinitions>

        <!-- Back button and page title -->

        <Grid>

            <Grid.ColumnDefinitions>

                <ColumnDefinition Width="Auto"/>

                <ColumnDefinition Width="*"/>

            </Grid.ColumnDefinitions>

            <ToggleButton  Style="{StaticResource BackToggleButtonStyle}"

                           IsChecked="{Binding IsSettingsVisible, Mode=TwoWay}"/>

            <TextBlock x:Name="pageTitle" Text="{Binding SettingsTitle}" Style="{StaticResource PageSubheaderTextStyle}" Grid.Column="1"/>

        </Grid>

        <Grid Grid.Row="1" Margin="40,0,20,0">

            <Grid.RowDefinitions>

                <RowDefinition Height="Auto" />

                <RowDefinition Height="20" />

                <RowDefinition Height="Auto" />

                <RowDefinition Height="*" />

            </Grid.RowDefinitions>

            <Grid.ColumnDefinitions>

                <ColumnDefinition Width="*" />

                <ColumnDefinition Width="*" />

            </Grid.ColumnDefinitions>

            <TextBlock Text="{Binding PushNotificationsText, Mode=OneWay}" VerticalAlignment="Center"

                       Style="{StaticResource TitleTextStyle}" />

            <ToggleSwitch Grid.Column="1" IsOn="{Binding IsPushEnabled, Mode=TwoWay}" />

            <TextBlock Grid.Row="2" Text="{Binding FontSizeText, Mode=OneWay}" Style="{StaticResource TitleTextStyle}" />

            <ComboBox Grid.Row="2" Grid.Column="1" ItemsSource="{Binding FontSizes}" DisplayMemberPath="Key"

                                SelectedItem="{Binding SelectedFontSize, Mode=TwoWay}" 

                                Grid.ColumnSpan="2"  >

            </ComboBox>

        </Grid>

    </Grid>

</UserControl>

Settings Service

The next article discusses how to implement the settings service.

http://geoffwebbercross.blogspot.co.uk/2012/08/windows-8-mvvm-settings-service.html