XAML Storyboard.IsPlaying Attached Property

By Fons Sonnemans, 24-feb-2017

XAML is very powerful. I have blogged about behaviors a lot. They are great but also have limitations. You can only drag them on Controls, not on Storyboards. To "fix" this I came up with a solution using Attached Properties. The designer support isn't as good with Behaviors but who needs that if we have IntelliSense.

IsPlaying Attached Property

I have created a StoryboardServices class which contains the IsPlaying attached property of the type boolean. In the OnIsPlayingChanged() method I Begin() or Resume() the Storyboard if it is set to True, I Pause() it when it is set to False.

using System;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Media.Animation;

namespace AnimationDemo {
    public class StoryboardServices {

        #region IsPlaying Attached Property

        /// <summary> 
        /// Identifies the IsPlaying attachted property. This enables animation, styling, binding, etc...
        /// </summary>
        public static readonly DependencyProperty IsPlayingProperty =
            DependencyProperty.RegisterAttached("IsPlaying",
                typeof(bool),
                typeof(StoryboardServices),
                new PropertyMetadata(false, OnIsPlayingChanged));

        /// <summary>
        /// IsPlaying changed handler. 
        /// </summary>
        /// <param name="d">FrameworkElement that changed its IsPlaying attached property.</param>
        /// <param name="e">DependencyPropertyChangedEventArgs with the new and old value.</param> 
        private static void OnIsPlayingChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) {
            var source = d as Storyboard;
            if (source != null) {
                var value = (bool)e.NewValue;
                if (value) {
                    if (source.GetCurrentState() == ClockState.Stopped) {
                        source.Begin();
                    } else {
                        source.Resume();
                    }
                } else {
                    source.Pause();
                }
            }
        }

        /// <summary>
        /// Gets the value of the IsPlaying attached property from the specified FrameworkElement.
        /// </summary>
        public static bool GetIsPlaying(DependencyObject obj) {
            return (bool)obj.GetValue(IsPlayingProperty);
        }


        /// <summary>
        /// Sets the value of the IsPlaying attached property to the specified FrameworkElement.
        /// </summary>
        /// <param name="obj">The object on which to set the IsPlaying attached property.</param>
        /// <param name="value">The property value to set.</param>
        public static void SetIsPlaying(DependencyObject obj, bool value) {
            obj.SetValue(IsPlayingProperty, value);
        }

        #endregion IsPlaying Attached Property

    }
}

Example

In this example I have a Storyboard1 which plays when the checkbox on the page is checked. I databound the IsPlaying attached property to the IsChecked property of the checkbox (see line 10). The animation is really simple but you get the idea.

<Page x:Class="AnimationDemo.MainPage"
      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
      xmlns:local="using:AnimationDemo"
      xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
      xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
      mc:Ignorable="d">
    <Page.Resources>
        <Storyboard x:Name="Storyboard1"
             local:StoryboardServices.IsPlaying="{Binding IsChecked, ElementName=checkBoxIsAnimated, Mode=OneWay}"
             RepeatBehavior="Forever">
            <ColorAnimationUsingKeyFrames
                    Storyboard.TargetProperty="(Border.Background).(SolidColorBrush.Color)"
                   Storyboard.TargetName="myBorder">
                <EasingColorKeyFrame KeyTime="0:0:1"
                                     Value="Blue" />
                <EasingColorKeyFrame KeyTime="0:0:2"
                                     Value="Red" />
            </ColorAnimationUsingKeyFrames>
        </Storyboard>
    </Page.Resources>

    <Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="1*" />
            <ColumnDefinition Width="2*" />
            <ColumnDefinition Width="1*" />
        </Grid.ColumnDefinitions>

        <CheckBox x:Name="checkBoxIsAnimated"
                  Content="Animate"
                  IsChecked="True"
                  VerticalAlignment="Top"
                  HorizontalAlignment="Center"
                  Grid.Column="1" />

        <Border x:Name="myBorder"
                Height="100"
                Grid.Column="1"
                Background="Red" />
    </Grid>
</Page>

The code

I have published my code on GitHub. I hope you like it.

Fons

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