Application Constructor

If your application class is implemented entirely using code, you must register a handler with the Startup event in the constructor. You can optionally register handlers with the other Application class events in the constructor, including Exit and UnhandledException.

If your application class is implemented using markup and code-behind, you should register your events in markup and call InitializeComponent from the constructor to ensure that your events are hooked up, and any properties you set in markup are applied.

The following code shows the minimum application class implementation in markup and code-behind that calls InitializeComponent.

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

</Application>

using System.Windows; // Application

namespace SilverlightApplication
{
    public partial class App : Application
    {
        public App()
        {
            // Initialize custom properties and events.

            // Merge application class markup implementation with 
            // this object.
            InitializeComponent();
        }
    }
}

Silverlight

Silverlight for Windows Phone

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

Reference