Python Tkinter Scrollbar：如何设置箭头按钮单次滚动像素偏移量？

问题描述 #

我使用ScrollbarFrame(tk.Frame)类展示表格，希望点击滚动条的向上/向下箭头时，表格刚好滚动1行（每行高度为21像素），但目前单次点击箭头会滚动约28像素。发现点击箭头是滚动1个单位，但找不到设置单位或修改滚动长度的配置，需要解决这个问题。

原代码如下：

import tkinter as tk

class ScrollbarFrame(tk.Frame):
    """
    Extends class tk.Frame to support a scrollable Frame 
    This class is independent from the widgets to be scrolled and 
    can be used to replace a standard tk.Frame
    """
    def __init__(self, parent, width=0, height=0, **kwargs):
        tk.Frame.__init__(self, parent, **kwargs)

        # The Scrollbar, layout to the right
        vsb = tk.Scrollbar(self, orient="vertical")
        vsb.pack(side="right", fill="y")

        # The Canvas which supports the Scrollbar Interface, layout to the left
        self.canvas = tk.Canvas(self, borderwidth=0, background="#ffffff")
        self.canvas.configure(width=width, height=height)

        self.canvas.pack(side="left", fill="both", expand=True)

        # Bind the Scrollbar to the self.canvas Scrollbar Interface
        self.canvas.configure(yscrollcommand=vsb.set)
        vsb.configure(command=self.canvas.yview)

        # The Frame to be scrolled, layout into the canvas
        # All widgets to be scrolled have to use this Frame as parent
        self.scrolled_frame = tk.Frame(self.canvas, background=self.canvas.cget('bg'))
        
        self.canvas.create_window((0, 0), window=self.scrolled_frame, anchor="nw")

        # Configures the scrollregion of the Canvas dynamically
        self.scrolled_frame.bind("<Configure>", self.on_configure)

    def on_configure(self, event):
        """Set the scroll region to encompass the scrolled frame"""
        self.canvas.configure(scrollregion=self.canvas.bbox("all"))

解决方案 #

方法一：设置Canvas滚动增量（推荐） #

直接给Canvas设置yscrollincrement参数，指定每次滚动1单位对应的像素值为21，这样点击滚动条箭头时就会精确滚动单行高度。

修改Canvas初始化代码：

self.canvas = tk.Canvas(self, borderwidth=0, background="#ffffff", yscrollincrement=21)

方法二：自定义滚动回调（精准控制） #

如果方法一不生效，可自定义滚动条的回调方法，手动控制每次滚动的像素量：

1. 在ScrollbarFrame类中添加自定义滚动方法：

def _on_scroll(self, action, delta, type=None):
    if action == "scroll":
        # delta=1向下滚动，delta=-1向上滚动，每次滚动21像素
        self.canvas.yview_scroll(delta, "units")
    elif action == "moveto":
        # 处理拖动滚动条滑块的情况
        self.canvas.yview_moveto(delta)

2. 修改Scrollbar的command绑定，替换为自定义方法：

vsb.configure(command=self._on_scroll)

修改后的完整代码 #

import tkinter as tk

class ScrollbarFrame(tk.Frame):
    """
    Extends class tk.Frame to support a scrollable Frame 
    This class is independent from the widgets to be scrolled and 
    can be used to replace a standard tk.Frame
    """
    def __init__(self, parent, width=0, height=0, row_height=21, **kwargs):
        tk.Frame.__init__(self, parent, **kwargs)
        self.row_height = row_height

        # The Scrollbar, layout to the right
        vsb = tk.Scrollbar(self, orient="vertical")
        vsb.pack(side="right", fill="y")

        # The Canvas which supports the Scrollbar Interface, layout to the left
        self.canvas = tk.Canvas(self, borderwidth=0, background="#ffffff", yscrollincrement=self.row_height)
        self.canvas.configure(width=width, height=height)

        self.canvas.pack(side="left", fill="both", expand=True)

        # Bind the Scrollbar to the self.canvas Scrollbar Interface
        self.canvas.configure(yscrollcommand=vsb.set)
        # 若方法一不生效，替换为下面一行注释的代码，使用自定义滚动回调
        # vsb.configure(command=self._on_scroll)
        vsb.configure(command=self.canvas.yview)

        # The Frame to be scrolled, layout into the canvas
        # All widgets to be scrolled have to use this Frame as parent
        self.scrolled_frame = tk.Frame(self.canvas, background=self.canvas.cget('bg'))
        
        self.canvas.create_window((0, 0), window=self.scrolled_frame, anchor="nw")

        # Configures the scrollregion of the Canvas dynamically
        self.scrolled_frame.bind("<Configure>", self.on_configure)

    def on_configure(self, event):
        """Set the scroll region to encompass the scrolled frame"""
        self.canvas.configure(scrollregion=self.canvas.bbox("all"))
    
    def _on_scroll(self, action, delta, type=None):
        if action == "scroll":
            self.canvas.yview_scroll(delta, "units")
        elif action == "moveto":
            self.canvas.yview_moveto(delta)

内容的提问来源于stack exchange，提问作者KNUT