python-2.7 - 对 Tkinter bind_class 感到困惑

Question

我定义了 GCanvas，它是 Canvas 的扩展。我的意图是在类级别绑定(bind)到 GCanvas。它不起作用。

我还尝试绑定(bind)到 tk.Canvas，但它也不起作用。绑定(bind)到 root 或 GCanvas 实例工作正常。 (这两种选择对我都没有用，但我只是尝试了它们以查看发生了什么。)。运行 OS X，El Capitan。

import Tkinter as tk

class GCanvas(tk.Canvas, object):

    def __init__(self, master, **kwargs):
        tk.Canvas.__init__(self, master, kwargs)

    @staticmethod
    def enter(e):
        print "enter", e.widget, e.x, e.y

    @staticmethod
    def leave(e):
        print "leave", e.widget

    @staticmethod
    def motion(e):
        print "motion", e.widget, e.x, e.y

approach = "bindinstance"

root = tk.Tk()
gc = GCanvas(root, width=400, height=300)
print "root is", root, "gc is", gc
gc.pack()

if approach == "bindGCanvas":
    print "binding to GCanvas"
    root.bind_class(GCanvas, '<Enter>', GCanvas.enter)
    root.bind_class(GCanvas, '<Leave>', GCanvas.leave)
    #root.bind_class(GCanvas, '<Motion>', GCanvas.motion)
elif approach == "bindCanvas":
    print "binding to Canvas"
    root.bind_class(tk.Canvas, '<Enter>', GCanvas.enter)
    root.bind_class(tk.Canvas, '<Leave>', GCanvas.leave)
    #root.bind_class(tk.Canvas, '<Motion>', GCanvas.motion)
elif approach == "bindinstance":
    print "binding to instance"
    gc.bind('<Enter>', GCanvas.enter)
    gc.bind('<Leave>', GCanvas.leave)
    #gc.bind('<Motion>', GCanvas.motion)
else:
    print "binding to root"
    root.bind('<Enter>', GCanvas.enter)
    root.bind('<Leave>', GCanvas.leave)
    #root.bind('<Motion>', GCanvas.motion)

root.mainloop()

Answer 1

bind_class中的“类”是指tk库使用的内部类名，不是python类名。更准确地说，在这种情况下，它指的是一个 bind 标签，它恰好与 tk 类同名，它也恰好与核心 Tkinter 类之一同名(例如: Toplevel、Canvas 等)。

要在类级别绑定(bind)到 GCanvas，最简单的方法是将名为 GCanvas 的绑定(bind)标签添加到您的 Canvas ，如下例所示:

class GCanvas(tk.Canvas, object):
    def __init__(self, master, **kwargs):
        ...
        # get the current bind tags
        bindtags = list(self.bindtags())

        # add our custom bind tag before the Canvas bind tag
        index = bindtags.index("Canvas")
        bindtags.insert(index, "GCanvas")

        # save the bind tags back to the widget
        self.bindtags(tuple(bindtags))

然后您可以像这样使用 bind_class:

root.bind_class("GCanvas", "<Enter>", GCanvas.enter)
root.bind_class("GCanvas", "<Leave>", GCanvas.leave)

有关绑定(bind)标签的更多信息，请参阅这些对其他一些 tkinter 问题的回答:

• https://stackoverflow.com/a/11542200/7432
• https://stackoverflow.com/a/3513906/7432