Silverlight 4: Application_Exit

How do I call a webservice in the Application_Exit event?

 private void 开发者_JS百科Application_Exit(object sender, EventArgs e)
    {
        TestWSSoapClient.ReleaseUserCompleted += new EventHandler<System.ComponentModel.AsyncCompletedEventArgs>(TestWSSoapClient_ReleaseUserCompleted);
        TestWSSoapClient.ReleaseUserAsync(UserToken);}

The method below is no longer executed.

void TestWSSoapClient_ReleaseUserCompleted(object sender, System.ComponentModel.AsyncCompletedEventArgs e)
    {

    }

Thank you in advance.

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I finally solved my problem by following this example