DataViewCtrl drag-and-drop non-functional on GTK: GetDataBuffer() returns opaque void*; GetDataObject() returns None in drop handler

[maxfritzler]

Environment

• wxPython 4.2.5 gtk3 (Phoenix) / wxWidgets 3.2.9
• Linux / GTK3

Summary

wx.dataview.DataViewCtrl drag-and-drop is non-functional on GTK from Python because
the SWIG bindings do not expose drop payload data in a usable form.

Bug 1: GetDataBuffer() returns opaque C pointer

In EVT_DATAVIEW_ITEM_DROP, event.GetDataBuffer() returns a raw SWIG void*
pointer (<Swig Object of type 'void *' at 0x...>) rather than a Python bytes
object. It is impossible to read the dragged data.

def on_drop(self, event):
    buf = event.GetDataBuffer()
    # buf is a void* — cannot call .decode(), bytes(), memoryview(), etc.
    # No way to reconstruct what was dragged

Bug 2: GetDataObject() returns None in drop handler

Users also report event.GetDataObject() returns None inside the drop handler,
providing no alternative route to the data.

Bug 3 (possibly fixed in Phoenix): double-free on SetDataObject()

The original wxWidgets issue #16881 (closed "outdated" in 2017 with a redirect to
Phoenix) documented a crash when calling event.SetDataObject(obj) in
EVT_DATAVIEW_ITEM_BEGIN_DRAG on GTK because Python and C++ both attempt to free
the object. The workaround was obj.this.disown(). It is unclear whether Phoenix's
ownership model has resolved this.

Related

• wxWidgets issue #16881 (closed outdated, never fixed in Phoenix): wx.dataview.DataViewCtrl's Drag-and-Drop unusable in wxPython wxWidgets#16881
• wxPython Discuss thread (no resolution): https://discuss.wxpython.org/t/dataviewctrl-dataviewtreectrl-issue-on-gtk-with-drag-drop-any-workaround/27826
• Phoenix issue Add DnD in DataViewCtrl demo #309 ("Add DnD in DataViewCtrl demo") notes the binding gap but is a
  todo item, not a bug report

Impact

DataViewCtrl with PyDataViewModel would be a clean MVC alternative to wx.TreeCtrl
for tree UIs on GTK, but the broken DnD bindings make it unusable for any application
requiring drag-and-drop reordering on Linux.