python - 为什么 Tkinter 画布要求 4 个额外像素的宽度和高度？

Question

>>> import Tkinter
>>> c = Tkinter.Canvas(width=100, height=100)
>>> c.winfo_reqwidth()
104
>>> c.winfo_reqheight()
104

如果我将边框宽度设置为零，结果是相同的。我找不到解释或控制这 4 个额外像素的设置或属性。

Answer 1

知道了！

c = Tkinter.Canvas(width=100, height=100, highlightthickness=0)
>>> c.winfo_reqwidth()
100

我调试问题的方式也可能对其他有需要的人有用：

import pprint
pprint.pprint(c.configure())
{'background': ('background',
                'background',
                'Background',
                'SystemButtonFace',
                'SystemButtonFace'),
 'bd': ('bd', 'borderWidth'),
 'bg': ('bg', 'background'),
 'borderwidth': ('borderwidth', 'borderWidth', 'BorderWidth', '0', '0'),
 'closeenough': ('closeenough', 'closeEnough', 'CloseEnough', '1', '1.0'),
 'confine': ('confine', 'confine', 'Confine', '1', '1'),
 'cursor': ('cursor', 'cursor', 'Cursor', '', ''),
 'height': ('height', 'height', 'Height', '7c', '100'),
 'highlightbackground': ('highlightbackground',
                         'highlightBackground',
                         'HighlightBackground',
                         'SystemButtonFace',
                         'SystemButtonFace'),
 'highlightcolor': ('highlightcolor',
                    'highlightColor',
                    'HighlightColor',
                    'SystemWindowFrame',
                    'SystemWindowFrame'),
 'highlightthickness': ('highlightthickness',
                        'highlightThickness',
                        'HighlightThickness',
                        '2',
                        '0'),
 'insertbackground': ('insertbackground',
                      'insertBackground',
                      'Foreground',
                      'SystemButtonText',
                      'SystemButtonText'),
 'insertborderwidth': ('insertborderwidth',
                       'insertBorderWidth',
                       'BorderWidth',
                       '0',
                       '0'),
 'insertofftime': ('insertofftime', 'insertOffTime', 'OffTime', '300', '300'),
 'insertontime': ('insertontime', 'insertOnTime', 'OnTime', '600', '600'),
 'insertwidth': ('insertwidth', 'insertWidth', 'InsertWidth', '2', '2'),
 'offset': ('offset', 'offset', 'Offset', '0,0', '0,0'),
 'relief': ('relief', 'relief', 'Relief', 'flat', 'flat'),
 'scrollregion': ('scrollregion', 'scrollRegion', 'ScrollRegion', '', ''),
 'selectbackground': ('selectbackground',
                      'selectBackground',
                      'Foreground',
                      'SystemHighlight',
                      'SystemHighlight'),
 'selectborderwidth': ('selectborderwidth',
                       'selectBorderWidth',
                       'BorderWidth',
                       '1',
                       '1'),
 'selectforeground': ('selectforeground',
                      'selectForeground',
                      'Background',
                      'SystemHighlightText',
                      'SystemHighlightText'),
 'state': ('state', 'state', 'State', 'normal', 'normal'),
 'takefocus': ('takefocus', 'takeFocus', 'TakeFocus', '', ''),
 'width': ('width', 'width', 'Width', '10c', '100'),
 'xscrollcommand': ('xscrollcommand',
                    'xScrollCommand',
                    'ScrollCommand',
                    '',
                    ''),
 'xscrollincrement': ('xscrollincrement',
                      'xScrollIncrement',
                      'ScrollIncrement',
                      '0',
                      '0'),
 'yscrollcommand': ('yscrollcommand',
                    'yScrollCommand',
                    'ScrollCommand',
                    '',
                    ''),
 'yscrollincrement': ('yscrollincrement',
                      'yScrollIncrement',
                      'ScrollIncrement',
                      '0',
                      '0')}

因此，在查看了全套配置之后，我猜它要么是 highlight 要么是 closeenough 参数。

Answer 2

Because that winfo_reqwith() and winfo_reqheight() methods doesn't return actual width and height of a widget. This is what documentation says:

winfo_reqheight(), winfo_reqwidth().

Return the "natural" height (width) for self. The natural size is the minimal size needed to display the widget's contents, including padding, borders, etc. This size is calculated by the widget itself, based on the given options. The actual widget size is then determined by the widget's geometry manager, based on this value, the size of the widget's master, and the options given to the geometry manager.