How to get the control that has the focus in Silverlight?

Is very simple. To get the control with the focus do something just use the FocusManager.GetFocusedElement()

See: http://msdn.microsoft.com/en-us/library/system.windows.input.focusmanager(v=VS.95).aspx

You can also add an extension method like:

public static class FocusExtensionMethods
{

public static bool HasFocus(this Control c)
{
     return FocusManager.GetFocusedElement() == c;
}

}