Drag and Drop 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 wx.DataObject and identify its format(s) using the wx.DataFormat class.
To be a drag source, i.e. to provide the data which may be dragged by the user elsewhere, you should implement the following steps:
Preparation: First of all, a data object must be created and initialized with the data you wish to drag. For example:
my_data = wx.TextDataObject("This text will be dragged.")
Drag start: To start the dragging process (typically in response
to a mouse click) you must call wx.DropSource.DoDragDrop like
this:
dragSource = wx.DropSource(self)
dragSource.SetData(my_data)
result = dragSource.DoDragDrop(True)
Dragging: The call to DoDragDrop() blocks the program until
the user releases the mouse button (unless you override the
wx.DropSource.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 wx.DropTarget methods are called -
see below.
Processing the result: DoDragDrop() returns an effect code which is one of the values of wx.DragResult:
if result == wx.DragCopy:
# Copy the data
CopyMyData()
elif result == wx.DragMove:
# Move the data
MoveMyData()
else:
# Default, do nothing
pass
To be a drop target, i.e. to receive the data dropped by the user you should follow the instructions below:
Initialization: For a window to be a drop target, it needs to
have an associated wx.DropTarget object. Normally, you will
call wx.Window.SetDropTarget during window creation
associating your drop target with it. You must derive a class from
wx.DropTarget and override its pure virtual
methods. Alternatively, you may derive from wx.TextDropTarget
or wx.FileDropTarget and override their OnDropText() or
OnDropFiles() method.
Drop: When the user releases the mouse over a window, wxPython
asks the associated wx.DropTarget object if it accepts the
data. For this, a wx.DataObject 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 wx.DropTarget.OnData will get called and the
wx.DataObject belonging to the drop target can get filled
with data.
The end: After processing the data, DoDragDrop() returns
either wx.DragCopy or wx.DragMove 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.