How to have drag-and-drop and sorted GtkTreeView in GTK3?

Firstly, the error you get seems related to version of PyGObject. I do reproduce similar error info before reinstall my laptop with latest Ubuntu 13.04 beta. But after the upgrading, the error callback changes to something like

on_drag_data_get( <TreeView object at 0x1765870 (GtkTreeView at 0x19120a0)> <gtk.gdk.X11DragContext object at 0x1765aa0 (GdkX11DragContext at 0x1988820)> <GtkSelectionData at 0x7fffb106b760> 0 21962912Traceback (most recent call last):  File "dnd_gtk3_org.py", line 116, in on_drag_data_get    selection.set(dnd_internal_target, 0, iter_str)  File "/usr/lib/python2.7/dist-packages/gi/types.py", line 113, in function    return info.invoke(*args, **kwargs)TypeError: argument type: Expected Gdk.Atom, but got stron_drag_data_received <TreeView object at 0x1765870 (GtkTreeView at 0x19120a0)> <gtk.gdk.X11DragContext object at 0x1765be0 (GdkX11DragContext at 0x1988940)> 45 77 <GtkSelectionData at 0x7fffb106b6e0> 0 21962912Traceback (most recent call last):  File "dnd_gtk3_org.py", line 151, in on_drag_data_received    if selection.data == '':AttributeError: 'SelectionData' object has no attribute 'data'

There are only two little problems:

• the first parameter of SelectionData.set() seems only can be Gtk.gdk.Atom but not a string that specifies that as in pygtk.
• SelectionData has no data attributes but has a get_data() method instead.

A working code snippet listed below

#!/usr/bin/python# -*- coding: utf-8 -*-from gi.repository import Gtk, Gdkwindow = Gtk.Window()window.set_size_request(300, 200)window.connect('delete_event', Gtk.main_quit)# Define Liblarch Treestore = Gtk.TreeStore(str, str)store.insert(None, -1, ["A", "Task A"])store.insert(None, -1, ["B", "Task B"])store.insert(None, -1, ["C", "Task C"])d_parent = store.insert(None, -1, ["D", "Task D"])store.insert(d_parent, -1, ["E", "Task E"])# Define TreeView in similar way as it happens in GTG/Liblarch_gtktv = Gtk.TreeView()col = Gtk.TreeViewColumn()col.set_title("Title")render_text = Gtk.CellRendererText()col.pack_start(render_text, expand=True)col.add_attribute(render_text, 'markup', 1)col.set_resizable(True)col.set_expand(True)col.set_sort_column_id(0)tv.append_column(col)tv.set_property("expander-column", col)treemodel = storedef _sort_func(model, iter1, iter2):    """ Sort two iterators by function which gets node objects.    This is a simple wrapper which prepares node objects and then    call comparing function. In other case return default value -1    """    node_a = model.get_value(iter1, 0)    node_b = model.get_value(iter2, 0)    if node_a and node_b:        sort = cmp(node_a, node_b)    else:        sort = -1    return sorttreemodel.set_sort_func(1, _sort_func)tv.set_model(treemodel)def on_child_toggled(treemodel2, path, iter, param=None):    """ Expand row """    if not tv.row_expanded(path):        tv.expand_row(path, True)treemodel.connect('row-has-child-toggled', on_child_toggled)tv.set_search_column(1)tv.set_property("enable-tree-lines", False)tv.set_rules_hint(False)#### Drag and drop stuffdnd_internal_target = ''dnd_external_targets = {}def on_drag_fail(widget, dc, result):    print "Failed dragging", widget, dc, resultdef __init_dnd():    """ Initialize Drag'n'Drop support    Firstly build list of DND targets:        * name        * scope - just the same widget / same application        * id    Enable DND by calling enable_model_drag_dest(),     enable_model-drag_source()    It didnt use support from Gtk.Widget(drag_source_set(),    drag_dest_set()). To know difference, look in PyGTK FAQ:    http://faq.pygtk.org/index.py?file=faq13.033.htp&req=show    """    #defer_select = False    if dnd_internal_target == '':        error = 'Cannot initialize DND without a valid name\n'        error += 'Use set_dnd_name() first'        raise Exception(error)    dnd_targets = [(dnd_internal_target, Gtk.TargetFlags.SAME_WIDGET, 0)]    for target in dnd_external_targets:        name = dnd_external_targets[target][0]        dnd_targets.append((name, Gtk.TARGET_SAME_APP, target))    tv.enable_model_drag_source( Gdk.ModifierType.BUTTON1_MASK,        dnd_targets, Gdk.DragAction.DEFAULT | Gdk.DragAction.MOVE)    tv.enable_model_drag_dest(\        dnd_targets, Gdk.DragAction.DEFAULT | Gdk.DragAction.MOVE)def on_drag_data_get(treeview, context, selection, info, timestamp):    """ Extract data from the source of the DnD operation.    Serialize iterators of selected tasks in format     <iter>,<iter>,...,<iter> and set it as parameter of DND """    print "on_drag_data_get(", treeview, context, selection, info, timestamp    treeselection = treeview.get_selection()    model, paths = treeselection.get_selected_rows()    iters = [model.get_iter(path) for path in paths]    iter_str = ','.join([model.get_string_from_iter(iter) for iter in iters])    selection.set(selection.get_target(), 0, iter_str)    print "Sending", iter_strdef on_drag_data_received(treeview, context, x, y, selection, info,\                          timestamp):    """ Handle a drop situation.    First of all, we need to get id of node which should accept    all draged nodes as their new children. If there is no node,    drop to root node.    Deserialize iterators of dragged nodes (see self.on_drag_data_get())    Info parameter determines which target was used:        * info == 0 => internal DND within this TreeView        * info > 0 => external DND    In case of internal DND we just use Tree.move_node().    In case of external DND we call function associated with that DND    set by self.set_dnd_external()    """    print "on_drag_data_received", treeview, context, x, y, selection, info, timestamp    model = treeview.get_model()    destination_iter = None    destination_tid = None    drop_info = treeview.get_dest_row_at_pos(x, y)    if drop_info:        path, position = drop_info        destination_iter = model.get_iter(path)        if destination_iter:            destination_tid = model.get_value(destination_iter, 0)    # Get dragged iter as a TaskTreeModel iter    # If there is no selected task (empty selection.data),     # explictly skip handling it (set to empty list)    data = selection.get_data()    if data == '':        iters = []    else:        iters = data.split(',')    dragged_iters = []    for iter in iters:        print "Info", info        if info == 0:            try:                dragged_iters.append(model.get_iter_from_string(iter))            except ValueError:                #I hate to silently fail but we have no choice.                #It means that the iter is not good.                #Thanks shitty Gtk API for not allowing us to test the string                print "Shitty iter", iter                dragged_iter = None        elif info in dnd_external_targets and destination_tid:            f = dnd_external_targets[info][1]            src_model = context.get_source_widget().get_model()            dragged_iters.append(src_model.get_iter_from_string(iter))    for dragged_iter in dragged_iters:        if info == 0:            if dragged_iter and model.iter_is_valid(dragged_iter):                dragged_tid = model.get_value(dragged_iter, 0)                try:                    row = []                    for i in range(model.get_n_columns()):                        row.append(model.get_value(dragged_iter, i))                    #tree.move_node(dragged_tid, new_parent_id=destination_tid)                    print "move_after(%s, %s) ~ (%s, %s)" % (dragged_iter, destination_iter, dragged_tid, destination_tid)                    #model.move_after(dragged_iter, destination_iter)                    model.insert(destination_iter, -1, row)                    model.remove(dragged_iter)                except Exception, e:                    print 'Problem with dragging: %s' % e        elif info in dnd_external_targets and destination_tid:                source = src_model.get_value(dragged_iter,0)            # Handle external Drag'n'Drop            f(source, destination_tid)dnd_internal_target = 'gtg/task-iter-str'__init_dnd()tv.connect('drag_data_get', on_drag_data_get)tv.connect('drag_data_received', on_drag_data_received)tv.connect('drag_failed', on_drag_fail)window.add(tv)window.show_all()tv.expand_all()Gtk.main()# vim: tabstop=4 expandtab shiftwidth=4 softtabstop=4

The diff between the snippet above with the one in your question is

116c116<     selection.set(selection.get_target(), 0, iter_str)--->     selection.set(dnd_internal_target, 0, iter_str)151,152c151<     data = selection.get_data()<     if data == '':--->     if selection.data == '':155c154<         iters = data.split(',')--->         iters = selection.data.split(',')

Besides, there is another example for GTK+3 version Drag and Drop of TreeView in another thread: unresponsive drag and drop in pygobject

GTG is a great piece of software! But it's far too slow, at least on my computer. So I've been writing a C++ library which displays a directed acyclic graph using a Gtk::TreeView, and I looked at the LibLarch source code a lot.

As far as I know, Python and C++ bindings of GTK share the same limitation, coming from GTK itself (I once looked at GTK source code to find exactly why it works like that): If you turn of drag-and-drop and sorting, drag-and-drop won't work. I offer three things you can do about it:

1. Make a patch to GTK which limits dnd when sorting is enabled, instead of completely blocking it

2. Implement sorting by yourself. It easy: start by loading your data to a sorted treeview. Now, every time the user drags and drops, move the dragged row to the new position using your sorting function. But leave GTK sorting off.

3. This can be done in addition to 2, it's a GUI design issue: In GtkTreeView you can insert an item between to sibling items, which doesn't make much sense in sorted trees. In terms of UI it's better to allow dropping only ON rows, not BETWEEN them. Example: Nautilus list-view works like this. The solution is either override the TreeView drag_data_received() default handler, or better than that in terms of maintainability: send your model a hint from the view telling the model whether the drop position is ON or BEFORE. If the position is BEFORE, make your tree's drop_possible() virtual override return false, and then you don't see the treeview's "you can drop here" didplay", thus you get a cleaner GUI.

2 and 3 is what I do in C++, you should be able to do that in Python easily :)

Also, a note regarding option 1: GtktreeView (or was is GtkTreeStore? I forgot) simply blocks any drop if sorting is enabled. If someone just fixes that (you... or me...), or at least writes a derived view class, we'll have a default clean GUI for sorted trees with dnd support.