XAML Storyboards
<TextBlock>The the TextBlock below validates its input using the KeyDown event</TextBlock>
<StackPanel Orientation="Horizontal">
<TextBox Width="100" HorizontalAlignment="Left" KeyDown="TextBox_OnKeyDown"></TextBox>
<TextBlock x:Name="msgTextBlock" Text="Invalid Character-numbers only" Opacity="0" Foreground="#FFF51616">
<TextBlock.Resources>
<Storyboard x:Key="errorMessageAnimation">
<DoubleAnimation Storyboard.TargetName="msgTextBlock" Storyboard.TargetProperty="Opacity"
From="0" To="1.0" Duration="00:00:03" AutoReverse="True" >
</DoubleAnimation>
</Storyboard>
</TextBlock.Resources>
</TextBlock>
</StackPanel>