tkinter Listbox.bbox方法在滚动列表框后返回None

Question

我正在尝试制作一个列表框，当光标移动到它上面时，它会显示提示，以使我能够创建这样的类：

class CreateToolTip(object):
def __init__(self, widget, text='widget info'):
self.waittime = 300  # miliseconds
self.wraplength = 180  # pixels
self.widget = widget
self.text = text
self.widget.bind("<Enter>", self.enter)
self.widget.bind("<Leave>", self.leave)
self.widget.bind("<ButtonPress>", self.leave)
self.id = None
self.tw = None
self.disp_thread = Thread
def enter(self, event):
self.schedule()
global base_x, base_y
base_x, base_y = event.x_root, event.y_root
t = self.disp_thread(target=self.wait_and_disapr)
t.start()
def wait_and_disapr(self):
sleep(3.5)
self.hidetip()
def leave(self, event=None):
self.unschedule()
self.hidetip()
def schedule(self):
self.unschedule()
self.id = self.widget.after(self.waittime, self.showtip)
def unschedule(self):
id = self.id
self.id = None
if id:
self.widget.after_cancel(id)
def showtip(self, event=None):
x = y = 0
x, y, cx, cy = self.widget.bbox(0)       # exception line
x += base_x
y += base_y
# creates a toplevel window
self.tw = tkinter.Toplevel(self.widget)
# Leaves only the label and removes the app window
self.tw.wm_overrideredirect(True)
self.tw.wm_geometry("+%d+%d" % (x, y))
label = tkinter.Label(self.tw, text=self.text, justify='left',
background="#ffffff", relief='solid', borderwidth=1,
wraplength=self.wraplength)
label.pack(ipadx=1)
def hidetip(self):
tw = self.tw
self.tw = None
if tw:
tw.destroy()

然后我用Listbox对象初始化一个实例：

lstbox = tkinter.Listbox(*args, **kwargs)
lstbox_tip = CreateToolTip(lstbox, text=tip_info)

当列表框没有垂直滚动时，提示会显示在列表框上，但当我向下滚动列表框时，提示没有正常显示，出现了以下异常：

> Traceback (most recent call last):
File "...LocalProgramsPythonPython37-32libtkinter__init__.py", line 1705, in __call__
return self.func(*args)
File "...LocalProgramsPythonPython37-32libtkinter__init__.py", line 749, in callit
func(*args)
File "DYRecorder-ttkVersion4.0-distribution.py", line 617, in showtip
x, y, cx, cy = self.widget.bbox(0)
TypeError: cannot unpack non-iterable NoneType object

似乎Listbox.bbox方法在滚动列表框后返回None。这个问题有什么解决办法吗？

Answer 1

感谢@Bryan Oakley对此链接的评论和解释，我通过修改showtip((方法获得了在搜索列表框时显示的提示，我添加了以下内容：

def showtip(self, event=None):
x = y = 0
index_lst = [0, 4, 8, 12, 16]  # my listbox has 20 elements
for index in index_lst :
if self.widget.bbox(page):
x, y, cx, cy = self.widget.bbox(page)
break
x += base_x
y += base_y
self.tw = tkinter.Toplevel(self.widget)
self.tw.wm_overrideredirect(True)
self.tw.wm_geometry("+%d+%d" % (x, y))
label = tkinter.Label(self.tw, text=self.text, justify='left',
background="#ffffff", relief='solid',
borderwidth=1, wraplength=self.wraplength)