In your Loaded handler you can post the UI altering operation ( e.g. void ChangeOpacity()
) on the dispatcher:
Dispatcher.BeginInvoke(DispatcherPriority.Loaded, new Action(ChangeOpacity));
It will execute after the rendering is done.
Edit
I see you simply need an animation to start when the window opens. It's easily done in XAML, here's a working example generated in Blend:
<Window x:Class="WpfApplication3.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="100" Width="200">
<Window.Resources>
<Storyboard x:Key="myStoryboard">
<DoubleAnimationUsingKeyFrames
Storyboard.TargetProperty="(UIElement.Opacity)"
Storyboard.TargetName="myControl">
<EasingDoubleKeyFrame KeyTime="0:0:2" Value="0"/>
</DoubleAnimationUsingKeyFrames>
</Storyboard>
</Window.Resources>
<Window.Triggers>
<EventTrigger RoutedEvent="FrameworkElement.Loaded">
<BeginStoryboard Storyboard="{StaticResource myStoryboard}"/>
</EventTrigger>
</Window.Triggers>
<StackPanel>
<TextBox x:Name="myControl" Text="I'm disappearing..." />
</StackPanel>
</Window>