StartupUri
property gets or sets a UI that is automatically shown when an application
starts.
You can change StartupUri of an application to a window you want to display when your application starts.
<Application x:Class="WPFSample.App"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
StartupUri="Window1.xaml"
>
</Application>
Listing 1 sets the StartupUri of application to SecondWindow.xaml in code behind.
Application
curApp = Application.Current;
curApp.StartupUri = new Uri("SecondWindow.xaml",
UriKind.RelativeOrAbsolute );
Listing 1