Listbox被視爲Nonetype，爲什麼？

Question

self.__tracksListBox = Listbox(self.__master, width=100, height=25).grid(row=0, column=1, 
                      rowspan=4) 

我想顯示一個列表框選擇，但下面的錯誤被拋出：

Exception in Tkinter callback 
Traceback (most recent call last): 
    File "C:\Python33\lib\tkinter\__init__.py", line 1475, in __call__ 
    return self.func(*args) 
    File "C:\Users\aawiesinger5000\Desktop\CS 110 Final Project\layoutGUI.py", line 213, in showTracks 
    self.__tracksListBox.insert(END, titleStr) 
AttributeError: 'NoneType' object has no attribute 'insert' 

當我嘗試使用列表框這樣的：

if tracks: 
      titleStr = "" 
      for track in tracks: 
       titleStr += track + "\n" 
      self.__tracksListBox.insert(END, titleStr) 

有誰知道爲什麼？

謝謝！

Answer 1

grid方法不返回;隱含返回None。

獨立以下語句分爲兩個語句：

self.__tracksListBox = Listbox(self.__master, width=100, height=25).grid(row=0, column=1, 
                      rowspan=4) 

，如：

self.__tracksListBox = Listbox(self.__master, width=100, height=25) 
self.__tracksListBox.grid(row=0, column=1, rowspan=4)