StartupUri gets or sets a UI that is automatically shown when an application starts.
Example
StartUp Window or Page WPF
Open App.xaml file and change StartupUri.
<Application x:Class="DataGrid.App"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
StartupUri="winMain.xaml">
<Application.Resources>
</Application.Resources>
</Application>