[Silverlight] 改进 Nikhil Kothari 的换肤方案：允许自定义控件的皮肤定义

在 public string GetXml() {
    string resourceDictionaryFormat =
@"<UserControl 
xmlns=""http://schemas.microsoft.com/winfx/2006/xaml/presentation""
xmlns:x=""http://schemas.microsoft.com/winfx/2006/xaml""
xmlns:vsm=""clr-namespace:System.Windows;assembly=System.Windows"">
<UserControl.Resources>
{0}
</UserControl.Resources>
</UserControl>";

    _content.Replace(@"xmlns=""http://schemas.microsoft.com/winfx/2006/xaml/presentation""", "");
    _content.Replace(@"xmlns:x=""http://schemas.microsoft.com/winfx/2006/xaml""", "");
    _content.Replace(@"xmlns:vsm=""clr-namespace:System.Windows;assembly=System.Windows""", "");

    return String.Format(resourceDictionaryFormat, _content.ToString());
 }