WPF Start-up

StartupUri Property

<Application x:Class="StartupShutdownDemo.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             StartupUri="MainWindow.xaml">
    <Application.Resources>
          
    </Application.Resources>
</Application>

OnStartup

protected override async void OnStartup(StartupEventArgs e)
{
await Init();
}

References
http://www.blackwasp.co.uk/WPFStartupShutdown.aspx