回答編集履歴

  こうですかね？（いまだにこの長ったらしいプロパティパス？よくわからんですね^^;

 

  <Window

  x:Class="Questions374901.MainWindow"

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

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

  Width="800"

  Height="450">

  <Window.Resources>

  <RotateTransform x:Key="ResourceAnimatedTransform" />

  </Window.Resources>

  <StackPanel Margin="50">

 

  <Button

  HorizontalAlignment="Left"

  RenderTransformOrigin="0.5,0.5">

  <Button.Triggers>

  <EventTrigger RoutedEvent="Button.Click">

  <BeginStoryboard>

  <Storyboard>

  <DoubleAnimation

  From="0.0"

  To="360"

  Duration="0:0:1" />

  </Storyboard>

  </BeginStoryboard>

  </EventTrigger>

  </Button.Triggers>

  </Button>

 

  RenderTransform="{StaticResource ResourceAnimatedTransform}"

  <Rectangle

  Width="50"

  Height="50"

  RenderTransform="{StaticResource ResourceAnimatedTransform}"

  RenderTransformOrigin="0.5,0.5" />

  </StackPanel>

  </Window>

  ```