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