Animate Expander in WPF - animation

Question

How to animate the expanded and collapsed actions of a Wpf expander control?

Answer 1

I've found this article on Code Project : Read Here
The author creates his own SimpleExpander Template, then adds a stretch out animation to it. He even added a nifty rotating arrow to it.

Answer 2

I created a style based on msdn Style and the point in this answer:
<Window x:Class="Test.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:Test"
xmlns:sys="clr-namespace:System;assembly=mscorlib"
xmlns:scm="clr-namespace:System.ComponentModel;assembly=WindowsBase"
mc:Ignorable="d">
<Window.Resources>
<Color x:Key="WindowColor">#FFE8EDF9</Color>
<Color x:Key="ContentAreaColorLight">#FFC5CBF9</Color>
<Color x:Key="ContentAreaColorDark">#FF7381F9</Color>
<Color x:Key="DisabledControlLightColor">#FFE8EDF9</Color>
<Color x:Key="DisabledControlDarkColor">#FFC5CBF9</Color>
<Color x:Key="DisabledForegroundColor">#FF888888</Color>
<Color x:Key="SelectedBackgroundColor">#FFC5CBF9</Color>
<Color x:Key="SelectedUnfocusedColor">#FFDDDDDD</Color>
<Color x:Key="ControlLightColor">White</Color>
<Color x:Key="ControlMediumColor">#FF7381F9</Color>
<Color x:Key="ControlDarkColor">#FF211AA9</Color>
<Color x:Key="ControlMouseOverColor">#FF3843C4</Color>
<Color x:Key="ControlPressedColor">#FF211AA9</Color>
<Color x:Key="GlyphColor">#FF444444</Color>
<Color x:Key="GlyphMouseOver">sc#1, 0.004391443, 0.002428215, 0.242281124</Color>
<!--Border colors-->
<Color x:Key="BorderLightColor">#FFCCCCCC</Color>
<Color x:Key="BorderMediumColor">#FF888888</Color>
<Color x:Key="BorderDarkColor">#FF444444</Color>
<Color x:Key="PressedBorderLightColor">#FF888888</Color>
<Color x:Key="PressedBorderDarkColor">#FF444444</Color>
<Color x:Key="DisabledBorderLightColor">#FFAAAAAA</Color>
<Color x:Key="DisabledBorderDarkColor">#FF888888</Color>
<Color x:Key="DefaultBorderBrushDarkColor">Black</Color>
<!--Control-specific resources.-->
<Color x:Key="HeaderTopColor">#FFC5CBF9</Color>
<Color x:Key="DatagridCurrentCellBorderColor">Black</Color>
<Color x:Key="SliderTrackDarkColor">#FFC5CBF9</Color>
<Color x:Key="NavButtonFrameColor">#FF3843C4</Color>
<LinearGradientBrush x:Key="MenuPopupBrush"
EndPoint="0.5,1"
StartPoint="0.5,0">
<GradientStop Color="{DynamicResource ControlLightColor}"
Offset="0" />
<GradientStop Color="{DynamicResource ControlMediumColor}"
Offset="0.5" />
<GradientStop Color="{DynamicResource ControlLightColor}"
Offset="1" />
</LinearGradientBrush>
<LinearGradientBrush x:Key="ProgressBarIndicatorAnimatedFill"
StartPoint="0,0"
EndPoint="1,0">
<LinearGradientBrush.GradientStops>
<GradientStopCollection>
<GradientStop Color="#000000FF"
Offset="0" />
<GradientStop Color="#600000FF"
Offset="0.4" />
<GradientStop Color="#600000FF"
Offset="0.6" />
<GradientStop Color="#000000FF"
Offset="1" />
</GradientStopCollection>
</LinearGradientBrush.GradientStops>
</LinearGradientBrush>
<ControlTemplate x:Key="ExpanderToggleButton"
TargetType="{x:Type ToggleButton}">
<Border x:Name="Border"
CornerRadius="2,0,0,0"
BorderThickness="0,0,1,0">
<Border.Background>
<LinearGradientBrush EndPoint="0.5,1"
StartPoint="0.5,0">
<GradientStop Color="{DynamicResource ControlLightColor}" />
<GradientStop Color="{DynamicResource ControlMediumColor}"
Offset="1" />
</LinearGradientBrush>
</Border.Background>
<Border.BorderBrush>
<LinearGradientBrush StartPoint="0,0"
EndPoint="0,1">
<LinearGradientBrush.GradientStops>
<GradientStopCollection>
<GradientStop Color="{DynamicResource BorderLightColor}"
Offset="0.0" />
<GradientStop Color="{DynamicResource BorderDarkColor}"
Offset="1.0" />
</GradientStopCollection>
</LinearGradientBrush.GradientStops>
</LinearGradientBrush>
</Border.BorderBrush>
<VisualStateManager.VisualStateGroups>
<VisualStateGroup x:Name="CommonStates">
<VisualState x:Name="Normal" />
<VisualState x:Name="MouseOver">
<Storyboard>
<ColorAnimationUsingKeyFrames Storyboard.TargetName="Border"
Storyboard.TargetProperty="(Panel.Background).
(GradientBrush.GradientStops)[1].(GradientStop.Color)">
<EasingColorKeyFrame KeyTime="0"
Value="{StaticResource ControlMouseOverColor}" />
</ColorAnimationUsingKeyFrames>
</Storyboard>
</VisualState>
<VisualState x:Name="Pressed">
<Storyboard>
<ColorAnimationUsingKeyFrames Storyboard.TargetName="Border"
Storyboard.TargetProperty="(Panel.Background).
(GradientBrush.GradientStops)[1].(GradientStop.Color)">
<EasingColorKeyFrame KeyTime="0"
Value="{StaticResource ControlPressedColor}" />
</ColorAnimationUsingKeyFrames>
</Storyboard>
</VisualState>
<VisualState x:Name="Disabled">
<Storyboard>
<ColorAnimationUsingKeyFrames Storyboard.TargetName="Border"
Storyboard.TargetProperty="(Panel.Background).
(GradientBrush.GradientStops)[1].(GradientStop.Color)">
<EasingColorKeyFrame KeyTime="0"
Value="{StaticResource DisabledControlDarkColor}" />
</ColorAnimationUsingKeyFrames>
<ColorAnimationUsingKeyFrames Storyboard.TargetName="Border"
Storyboard.TargetProperty="(Border.BorderBrush).
(GradientBrush.GradientStops)[1].(GradientStop.Color)">
<EasingColorKeyFrame KeyTime="0"
Value="{StaticResource DisabledBorderLightColor}" />
</ColorAnimationUsingKeyFrames>
</Storyboard>
</VisualState>
</VisualStateGroup>
<VisualStateGroup x:Name="CheckStates">
<VisualState x:Name="Checked">
<Storyboard>
<ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="(UIElement.Visibility)"
Storyboard.TargetName="CollapsedArrow">
<DiscreteObjectKeyFrame KeyTime="0"
Value="{x:Static Visibility.Hidden}" />
</ObjectAnimationUsingKeyFrames>
<ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="(UIElement.Visibility)"
Storyboard.TargetName="ExpandededArrow">
<DiscreteObjectKeyFrame KeyTime="0"
Value="{x:Static Visibility.Visible}" />
</ObjectAnimationUsingKeyFrames>
</Storyboard>
</VisualState>
<VisualState x:Name="Unchecked" />
<VisualState x:Name="Indeterminate" />
</VisualStateGroup>
</VisualStateManager.VisualStateGroups>
<Grid>
<Path x:Name="CollapsedArrow"
HorizontalAlignment="Center"
VerticalAlignment="Center"
Data="M 0 0 L 4 4 L 8 0 Z">
<Path.Fill>
<SolidColorBrush Color="{DynamicResource GlyphColor}" />
</Path.Fill>
</Path>
<Path x:Name="ExpandededArrow"
HorizontalAlignment="Center"
VerticalAlignment="Center"
Visibility="Collapsed"
Data="M 0 4 L 4 0 L 8 4 Z">
<Path.Fill>
<SolidColorBrush Color="{DynamicResource GlyphColor}" />
</Path.Fill>
</Path>
</Grid>
</Border>
</ControlTemplate>
<Style TargetType="{x:Type Expander}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type Expander}">
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition x:Name="ContentRow" >
<RowDefinition.Resources>
<local:MultiplyConverter x:Key="multiplyConverter"/>
</RowDefinition.Resources>
<RowDefinition.Tag>
<sys:Double>0.0</sys:Double>
</RowDefinition.Tag>
<RowDefinition.Height>
<MultiBinding Converter="{StaticResource multiplyConverter}">
<Binding Path="DesiredSize.Height" ElementName="Content" />
<Binding Path="Tag" RelativeSource="{RelativeSource Self}" />
</MultiBinding>
</RowDefinition.Height>
</RowDefinition>
</Grid.RowDefinitions>
<VisualStateManager.VisualStateGroups>
<VisualStateGroup x:Name="CommonStates">
<VisualState x:Name="Normal" />
<VisualState x:Name="MouseOver" />
<VisualState x:Name="Disabled">
<Storyboard>
<ColorAnimationUsingKeyFrames Storyboard.TargetName="Border"
Storyboard.TargetProperty="(Panel.Background).
(GradientBrush.GradientStops)[1].(GradientStop.Color)">
<EasingColorKeyFrame KeyTime="0"
Value="{StaticResource DisabledControlDarkColor}" />
</ColorAnimationUsingKeyFrames>
<ColorAnimationUsingKeyFrames Storyboard.TargetName="Border"
Storyboard.TargetProperty="(Border.BorderBrush).
(GradientBrush.GradientStops)[1].(GradientStop.Color)">
<EasingColorKeyFrame KeyTime="0"
Value="{StaticResource DisabledBorderLightColor}" />
</ColorAnimationUsingKeyFrames>
</Storyboard>
</VisualState>
</VisualStateGroup>
</VisualStateManager.VisualStateGroups>
<Border x:Name="Border" Grid.Row="0" BorderThickness="1" CornerRadius="2,2,0,0">
<Border.BorderBrush>
<LinearGradientBrush EndPoint="0,1"
StartPoint="0,0">
<GradientStop Color="{DynamicResource BorderLightColor}"
Offset="0" />
<GradientStop Color="{DynamicResource BorderDarkColor}"
Offset="1" />
</LinearGradientBrush>
</Border.BorderBrush>
<Border.Background>
<LinearGradientBrush StartPoint="0,0"
EndPoint="0,1">
<LinearGradientBrush.GradientStops>
<GradientStopCollection>
<GradientStop Color="{DynamicResource ControlLightColor}"
Offset="0.0" />
<GradientStop Color="{DynamicResource ControlMediumColor}"
Offset="1.0" />
</GradientStopCollection>
</LinearGradientBrush.GradientStops>
</LinearGradientBrush>
</Border.Background>
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="20" />
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<ToggleButton OverridesDefaultStyle="True"
Template="{StaticResource ExpanderToggleButton}"
IsChecked="{Binding IsExpanded, Mode=TwoWay,
RelativeSource={RelativeSource TemplatedParent}}">
<ToggleButton.Background>
<LinearGradientBrush EndPoint="0.5,1"
StartPoint="0.5,0">
<GradientStop Color="{DynamicResource ControlLightColor}"
Offset="0" />
<GradientStop Color="{DynamicResource ControlMediumColor}"
Offset="1" />
</LinearGradientBrush>
</ToggleButton.Background>
</ToggleButton>
<ContentPresenter Grid.Column="1" Margin="4" ContentSource="Header" RecognizesAccessKey="True" />
</Grid>
</Border>
<Border x:Name="Content" Grid.Row="1" BorderThickness="1,0,1,1" CornerRadius="0,0,2,2">
<Border.BorderBrush>
<SolidColorBrush Color="{DynamicResource BorderMediumColor}" />
</Border.BorderBrush>
<Border.Background>
<SolidColorBrush Color="{DynamicResource ContentAreaColorDark}" />
</Border.Background>
<ContentPresenter Margin="4" />
</Border>
</Grid>
<ControlTemplate.Triggers>
<Trigger Property="IsExpanded" Value="True">
<Trigger.EnterActions>
<BeginStoryboard>
<Storyboard>
<DoubleAnimation Storyboard.TargetName="ContentRow" Storyboard.TargetProperty="Tag" From="0" To="1" Duration="0:0:1"/>
</Storyboard>
</BeginStoryboard>
</Trigger.EnterActions>
<Trigger.ExitActions>
<BeginStoryboard>
<Storyboard>
<DoubleAnimation Storyboard.TargetName="ContentRow" Storyboard.TargetProperty="Tag" From="1" To="0" Duration="0:0:1"/>
</Storyboard>
</BeginStoryboard>
</Trigger.ExitActions>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</Window.Resources>
<StackPanel>
<Expander Header="Canny" >
<StackPanel>
<Button Content="A" />
<Button Content="B" />
<Button Content="C" />
</StackPanel>
</Expander>
<Expander Header="Sobel" >
<StackPanel>
<Button Content="A" />
<Button Content="B" />
<Button Content="C" />
</StackPanel>
</Expander>
<Expander Header="LoG" >
<StackPanel>
<Button Content="A" />
<Button Content="B" />
<Button Content="C" />
</StackPanel>
</Expander>
</StackPanel>
</Window>
Which requires this converter:
public class MultiplyConverter : IMultiValueConverter
{
public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
{
return new GridLength((double)values[0] * (double)values[1], GridUnitType.Pixel);
}
public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
The main point is to set DoubleAnimation on ContentRow.Height in the template. However, you need to use a MultiBinding to bind the To property of this animation.