added images for topic overviews

[wxWidgets.git] / docs / doxygen / overviews / dnd.h

/////////////////////////////////////////////////////////////////////////////
// Name:        dnd.h
// Purpose:     topic overview
// Author:      wxWidgets team
// RCS-ID:      $Id$
// Licence:     wxWindows license
/////////////////////////////////////////////////////////////////////////////

/*!

 @page overview_dnd Drag and drop overview

 Classes: #wxDataObject, #wxTextDataObject, #wxDropSource, #wxDropTarget,
          #wxTextDropTarget, #wxFileDropTarget

 Note that @c wxUSE_DRAG_AND_DROP must be defined in @c setup.h in order
 to use drag and drop in wxWidgets.

 See also: @ref overview_dataobject and @ref samplednd_overview.

 It may be noted that data transfer to and from the clipboard is quite
 similar to data transfer with drag and drop and the code to implement
 these two types is almost the same. In particular, both data transfer
 mechanisms store data in some kind of #wxDataObject and identify its format(s)
 using the #wxDataFormat class.

 To be a @e drag source, i.e. to provide the data which may be dragged by
 the user elsewhere, you should implement the following steps:

 @li @b Preparation: First of all, a data object must be created and
     initialized with the data you wish to drag. For example:
    
     @code
     wxTextDataObject my_data("This text will be dragged.");
     @endcode

 @li <b>Drag start</b>: To start the dragging process (typically in response to a
     mouse click) you must call wxDropSource::DoDragDrop like this:
    
     @code
     wxDropSource dragSource( this );
     dragSource.SetData( my_data );
     wxDragResult result = dragSource.DoDragDrop( true );
     @endcode

 @li @b Dragging: The call to DoDragDrop() blocks the program until the user releases 
     the mouse button (unless you override the #GiveFeedback function to do something 
     special). When the mouse moves in a window of a program which understands the
     same drag-and-drop protocol (any program under Windows or any program supporting
     the XDnD protocol under X Windows), the corresponding #wxDropTarget methods
     are called - see below.

 @li <b>Processing the result</b>: DoDragDrop() returns an @e effect code which
     is one of the values of @c wxDragResult enum (explained #here):

     @code
     switch (result)
     {
        case wxDragCopy: 
            // copy the data
            break;
        case wxDragMove:
            // move the data
            break;
        default:
            // do nothing
            break;
     }
     @endcode


 To be a @e drop target, i.e. to receive the data dropped by the user you should
 follow the instructions below:

 @li @b Initialization: For a window to be a drop target, it needs to have
     an associated #wxDropTarget object. Normally, you will call wxWindow::SetDropTarget 
     during window creation associating your drop target with it. You must derive a class from
     wxDropTarget and override its pure virtual methods. Alternatively, you may
     derive from #wxTextDropTarget or #wxFileDropTarget and override their OnDropText()
     or OnDropFiles() method.

 @li @b Drop: When the user releases the mouse over a window, wxWidgets
     asks the associated wxDropTarget object if it accepts the data. For this,
     a #wxDataObject must be associated with the drop target and this data object will
     be responsible for the format negotiation between the drag source and the drop target.
     If all goes well, then #OnData will get called and the wxDataObject belonging to 
     the drop target can get filled with data.

 @li <b>The end</b>: After processing the data, DoDragDrop() returns either
     wxDragCopy or wxDragMove depending on the state of the keys Ctrl, Shift
     and Alt at the moment of the drop. There is currently no way for the drop
     target to change this return code.

*/