Introduction

• Drag and drop support within wxPython is a conversation between a "drop source" and a "drop target". The conversation is accomplished by sharing a "data object" which includes certain pieces of metadata (primarily the data types available from the drop source) as well as the actual shared data.

What Objects are Involved

• Source window -- Interprets an event as the beginning of a new drag-and-drop request. Instantiates a new drop source

  and triggers the drag-and-drop sequence by calling DoDragDrop on the drop source object. Responds to the result code of the drag-and-drop sequence (move/copy/cancel/fail).

• wxDropSource -- Provides common functionality for drag-and-drop source windows (UI interactions, data object storage)

• Destination window -- Advertises acceptable data types by

  calling SetDropTarget with a configured drop target object.

• wxDropTarget -- Responds to various "pseudo-events" during the drag-and-drop process, most importantly the OnData "event" which indicates that an object has been dropped on the associated window.

• wxDataObject -- Provides storage and metadata relating to the data being transferred during a drag-and-drop operation. May support one of the built-in data types (text, bitmap, file), a single declared data type, or multiple data types. Includes: wxTextDataObject, wxBitmapDataObject, wxFileDataObject, wxDataObjectSimple, wxDataObjectComposite, wxDataObject

Process Overview

• Create or choose a wxDataObject subclass appropriate to the data being shared

  • Provide OnData method to handle incoming data and update your application with the results of the drag-and-drop operation.

  • If you are not using a built-in data type, choose a type specifier (a unique string used to identify the datatype). Only targets whose type specifiers include one of the current data source specifiers will be eligible for drops.

• Create a wxPyDropTarget subclass (and instance)

  • Provide an OnData method to handle a drop "event"

    • Call self.GetData() to transfer data to the target's wxDataObject instance

    • Call wxDataObject.GetData() to retrieve the actual shared data

    • Update your application to reflect drag-and-drop operation (in many cases you will need a pointer to the target window within the drop target instance to accomplish this).

  • Instantiate an instance of your wxDataObject class

  • Bind a wxDataObject to the drop target by calling SetDataObject. You will also want to keep a pointer to the wxDataObject in the drop target instance, so that you can call wxDataObject.GetData() within the OnData method.

  • Bind the drop target to the target window using wxWindow.SetDropTarget

• Handle an event on the source window which signals the start of the drag-and-drop cycle

  • Create a wxDropSource

  • Set the data object of the drop source to another instance of your wxDataObject class

  • Call the drop source DoDragDrop() method to begin the drag-and-drop operation

  • Respond to the result code of the DoDragDrop method as appropriate to your application

wxDataObjects

• Discuss the various concerns relating to the data object. Python pickling options Multiple formats -- currently only works for source in Python (as far as I can see) Format specifiers, do these need to be discussed? Special Data Types

Code Samples

• Simple drag-and-drop
• File/bitmap/text

Comments...

I will add a example for dragging items in a wxTreeCtrl and what is more interresting how to drag a branch in a wxTreeCtrl. if added it will be found under "ListAndTreeControls".

--René Freund