Assembly: System.Windows (in System.Windows.dll)
The method is called before any event handler for the MouseLeftButtonDown event is called. This method allows derived classes to handle the MouseLeftButtonDown event without attaching a delegate. This is the preferred technique for handling the event in a derived class.
TextBox handles cursor placement and selection in MouseLeftButtonDown event. Derived classes can prevent the TextBox from processing the TextBox event by setting the Handled property of the event data to true.Notes to Inheritors
When overriding method in a derived class, be sure to call the base class’s method so that registered delegates receive the event.