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325 lines
11 KiB
Python
325 lines
11 KiB
Python
"""Drag-and-drop support for Tkinter.
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This is very preliminary. I currently only support dnd *within* one
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application, between different windows (or within the same window).
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I am trying to make this as generic as possible -- not dependent on
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the use of a particular widget or icon type, etc. I also hope that
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this will work with Pmw.
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To enable an object to be dragged, you must create an event binding
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for it that starts the drag-and-drop process. Typically, you should
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bind <ButtonPress> to a callback function that you write. The function
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should call Tkdnd.dnd_start(source, event), where 'source' is the
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object to be dragged, and 'event' is the event that invoked the call
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(the argument to your callback function). Even though this is a class
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instantiation, the returned instance should not be stored -- it will
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be kept alive automatically for the duration of the drag-and-drop.
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When a drag-and-drop is already in process for the Tk interpreter, the
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call is *ignored*; this normally averts starting multiple simultaneous
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dnd processes, e.g. because different button callbacks all
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dnd_start().
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The object is *not* necessarily a widget -- it can be any
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application-specific object that is meaningful to potential
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drag-and-drop targets.
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Potential drag-and-drop targets are discovered as follows. Whenever
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the mouse moves, and at the start and end of a drag-and-drop move, the
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Tk widget directly under the mouse is inspected. This is the target
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widget (not to be confused with the target object, yet to be
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determined). If there is no target widget, there is no dnd target
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object. If there is a target widget, and it has an attribute
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dnd_accept, this should be a function (or any callable object). The
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function is called as dnd_accept(source, event), where 'source' is the
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object being dragged (the object passed to dnd_start() above), and
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'event' is the most recent event object (generally a <Motion> event;
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it can also be <ButtonPress> or <ButtonRelease>). If the dnd_accept()
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function returns something other than None, this is the new dnd target
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object. If dnd_accept() returns None, or if the target widget has no
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dnd_accept attribute, the target widget's parent is considered as the
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target widget, and the search for a target object is repeated from
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there. If necessary, the search is repeated all the way up to the
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root widget. If none of the target widgets can produce a target
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object, there is no target object (the target object is None).
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The target object thus produced, if any, is called the new target
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object. It is compared with the old target object (or None, if there
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was no old target widget). There are several cases ('source' is the
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source object, and 'event' is the most recent event object):
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- Both the old and new target objects are None. Nothing happens.
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- The old and new target objects are the same object. Its method
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dnd_motion(source, event) is called.
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- The old target object was None, and the new target object is not
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None. The new target object's method dnd_enter(source, event) is
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called.
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- The new target object is None, and the old target object is not
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None. The old target object's method dnd_leave(source, event) is
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called.
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- The old and new target objects differ and neither is None. The old
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target object's method dnd_leave(source, event), and then the new
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target object's method dnd_enter(source, event) is called.
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Once this is done, the new target object replaces the old one, and the
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Tk mainloop proceeds. The return value of the methods mentioned above
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is ignored; if they raise an exception, the normal exception handling
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mechanisms take over.
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The drag-and-drop processes can end in two ways: a final target object
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is selected, or no final target object is selected. When a final
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target object is selected, it will always have been notified of the
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potential drop by a call to its dnd_enter() method, as described
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above, and possibly one or more calls to its dnd_motion() method; its
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dnd_leave() method has not been called since the last call to
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dnd_enter(). The target is notified of the drop by a call to its
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method dnd_commit(source, event).
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If no final target object is selected, and there was an old target
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object, its dnd_leave(source, event) method is called to complete the
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dnd sequence.
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Finally, the source object is notified that the drag-and-drop process
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is over, by a call to source.dnd_end(target, event), specifying either
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the selected target object, or None if no target object was selected.
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The source object can use this to implement the commit action; this is
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sometimes simpler than to do it in the target's dnd_commit(). The
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target's dnd_commit() method could then simply be aliased to
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dnd_leave().
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At any time during a dnd sequence, the application can cancel the
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sequence by calling the cancel() method on the object returned by
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dnd_start(). This will call dnd_leave() if a target is currently
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active; it will never call dnd_commit().
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"""
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import tkinter
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__all__ = ["dnd_start", "DndHandler"]
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# The factory function
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def dnd_start(source, event):
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h = DndHandler(source, event)
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if h.root is not None:
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return h
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else:
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return None
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# The class that does the work
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class DndHandler:
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root = None
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def __init__(self, source, event):
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if event.num > 5:
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return
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root = event.widget._root()
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try:
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root.__dnd
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return # Don't start recursive dnd
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except AttributeError:
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root.__dnd = self
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self.root = root
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self.source = source
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self.target = None
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self.initial_button = button = event.num
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self.initial_widget = widget = event.widget
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self.release_pattern = "<B%d-ButtonRelease-%d>" % (button, button)
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self.save_cursor = widget['cursor'] or ""
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widget.bind(self.release_pattern, self.on_release)
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widget.bind("<Motion>", self.on_motion)
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widget['cursor'] = "hand2"
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def __del__(self):
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root = self.root
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self.root = None
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if root is not None:
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try:
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del root.__dnd
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except AttributeError:
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pass
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def on_motion(self, event):
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x, y = event.x_root, event.y_root
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target_widget = self.initial_widget.winfo_containing(x, y)
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source = self.source
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new_target = None
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while target_widget is not None:
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try:
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attr = target_widget.dnd_accept
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except AttributeError:
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pass
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else:
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new_target = attr(source, event)
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if new_target is not None:
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break
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target_widget = target_widget.master
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old_target = self.target
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if old_target is new_target:
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if old_target is not None:
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old_target.dnd_motion(source, event)
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else:
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if old_target is not None:
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self.target = None
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old_target.dnd_leave(source, event)
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if new_target is not None:
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new_target.dnd_enter(source, event)
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self.target = new_target
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def on_release(self, event):
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self.finish(event, 1)
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def cancel(self, event=None):
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self.finish(event, 0)
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def finish(self, event, commit=0):
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target = self.target
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source = self.source
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widget = self.initial_widget
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root = self.root
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try:
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del root.__dnd
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self.initial_widget.unbind(self.release_pattern)
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self.initial_widget.unbind("<Motion>")
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widget['cursor'] = self.save_cursor
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self.target = self.source = self.initial_widget = self.root = None
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if target is not None:
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if commit:
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target.dnd_commit(source, event)
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else:
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target.dnd_leave(source, event)
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finally:
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source.dnd_end(target, event)
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# ----------------------------------------------------------------------
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# The rest is here for testing and demonstration purposes only!
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class Icon:
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def __init__(self, name):
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self.name = name
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self.canvas = self.label = self.id = None
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def attach(self, canvas, x=10, y=10):
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if canvas is self.canvas:
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self.canvas.coords(self.id, x, y)
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return
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if self.canvas is not None:
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self.detach()
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if canvas is None:
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return
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label = tkinter.Label(canvas, text=self.name,
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borderwidth=2, relief="raised")
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id = canvas.create_window(x, y, window=label, anchor="nw")
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self.canvas = canvas
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self.label = label
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self.id = id
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label.bind("<ButtonPress>", self.press)
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def detach(self):
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canvas = self.canvas
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if canvas is None:
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return
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id = self.id
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label = self.label
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self.canvas = self.label = self.id = None
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canvas.delete(id)
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label.destroy()
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def press(self, event):
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if dnd_start(self, event):
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# where the pointer is relative to the label widget:
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self.x_off = event.x
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self.y_off = event.y
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# where the widget is relative to the canvas:
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self.x_orig, self.y_orig = self.canvas.coords(self.id)
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def move(self, event):
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x, y = self.where(self.canvas, event)
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self.canvas.coords(self.id, x, y)
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def putback(self):
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self.canvas.coords(self.id, self.x_orig, self.y_orig)
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def where(self, canvas, event):
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# where the corner of the canvas is relative to the screen:
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x_org = canvas.winfo_rootx()
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y_org = canvas.winfo_rooty()
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# where the pointer is relative to the canvas widget:
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x = event.x_root - x_org
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y = event.y_root - y_org
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# compensate for initial pointer offset
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return x - self.x_off, y - self.y_off
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def dnd_end(self, target, event):
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pass
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class Tester:
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def __init__(self, root):
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self.top = tkinter.Toplevel(root)
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self.canvas = tkinter.Canvas(self.top, width=100, height=100)
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self.canvas.pack(fill="both", expand=1)
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self.canvas.dnd_accept = self.dnd_accept
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def dnd_accept(self, source, event):
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return self
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def dnd_enter(self, source, event):
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self.canvas.focus_set() # Show highlight border
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x, y = source.where(self.canvas, event)
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x1, y1, x2, y2 = source.canvas.bbox(source.id)
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dx, dy = x2-x1, y2-y1
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self.dndid = self.canvas.create_rectangle(x, y, x+dx, y+dy)
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self.dnd_motion(source, event)
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def dnd_motion(self, source, event):
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x, y = source.where(self.canvas, event)
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x1, y1, x2, y2 = self.canvas.bbox(self.dndid)
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self.canvas.move(self.dndid, x-x1, y-y1)
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def dnd_leave(self, source, event):
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self.top.focus_set() # Hide highlight border
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self.canvas.delete(self.dndid)
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self.dndid = None
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def dnd_commit(self, source, event):
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self.dnd_leave(source, event)
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x, y = source.where(self.canvas, event)
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source.attach(self.canvas, x, y)
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def test():
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root = tkinter.Tk()
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root.geometry("+1+1")
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tkinter.Button(command=root.quit, text="Quit").pack()
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t1 = Tester(root)
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t1.top.geometry("+1+60")
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t2 = Tester(root)
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t2.top.geometry("+120+60")
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t3 = Tester(root)
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t3.top.geometry("+240+60")
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i1 = Icon("ICON1")
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i2 = Icon("ICON2")
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i3 = Icon("ICON3")
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i1.attach(t1.canvas)
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i2.attach(t2.canvas)
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i3.attach(t3.canvas)
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root.mainloop()
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if __name__ == '__main__':
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test()
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