.. include:: headings.inc .. _drag and drop overview: =========================================== |phoenix_title| **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 :ref:`wx.DataObject` and identify its format(s) using the :ref:`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 :meth:`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 :meth:`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 :ref:`wx.DropTarget` methods are called - see below. - **Processing the result**: `DoDragDrop()` returns an effect code which is one of the values of :ref:`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 :ref:`wx.DropTarget` object. Normally, you will call :meth:`wx.Window.SetDropTarget` during window creation associating your drop target with it. You must derive a class from :ref:`wx.DropTarget` and override its pure virtual methods. Alternatively, you may derive from :ref:`wx.TextDropTarget` or :ref:`wx.FileDropTarget` and override their `OnDropText()` or `OnDropFiles()` method. - **Drop**: When the user releases the mouse over a window, wxPython asks the associated :ref:`wx.DropTarget` object if it accepts the data. For this, a :ref:`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 :meth:`wx.DropTarget.OnData` will get called and the :ref:`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.