Tkinter中Scrollbar无法控制Text文本框滚动问题与原理咨询

• 垂直滚动条使用grid布局时未添加sticky="ns"配置：grid布局默认不会拉伸组件填满分配的单元格，滚动条与Text组件放在同一行单元格时，未指定上下方向拉伸的话，滚动条只会保持默认的极小高度，滑块无法正常显示、拖动。
• 初始状态Text组件为空，内容高度未超出可视区域时，滚动条默认不会显示可拖动滑块，属于组件默认逻辑，填入超过文本框高度的内容后滑块才会出现。

#importing necessary packages
from tkinter import *
from tkinter import font
from tkinter import ttk


#set up main window
root = Tk()

root.title("Notes")
root.geometry("400x650")



#functions

#functions to change all widget button's backgrounds when user hovers over it and leaves it
def enter_button(e):
    e.widget.config(background = "#D4D4D4")
    
#SystemButtonFace is default colour
def leave_button(e):
    e.widget.config(background = "SystemButtonFace")


#clear text in text-box

def clear():
    
    #delete all text from text_box
    text_box.delete(1.0,END)
    
def bold_it():
    
    #create font
    
    try: 
        
        
        bold_font = font.Font(text_box, text_box.cget("font"))
        bold_font.configure(weight = "bold")
    
        #creating tag called "bold" which bolds text upon condition
        text_box.tag_configure("bold", font = bold_font)
    
        #creating a bold tag which highlights first character
        bold_tag = text_box.tag_names("sel.first")
    
        #condition for checking to see if tag is applied or not
        #in the first highlighted character
        #if tag is applied, remove the bold from first-highlighted text
        #- last highlighted text
        #"bold" needs to be matched in the tag
        if "bold" in bold_tag:
        
            text_box.tag_remove("bold","sel.first","sel.last")
        
        else:
        
            text_box.tag_add("bold","sel.first", "sel.last")
        
    except TclError: 
        
        pass

def italics_it():
    
    
    try:
    
        #create a font
        italics_font = font.Font(text_box, text_box.cget("font"))
        italics_font.configure(slant = "italic")
    
        #create a tag called "italic"
        text_box.tag_configure("italics", font = italics_font)
    
        italics_tag = text_box.tag_names("sel.first")
    
        #condition to see whether tag has been applies or not
        if "italics" in italics_tag:
        
            text_box.tag_remove("italics", "sel.first","sel.last")
        
        else: 
        
            text_box.tag_add("italics", "sel.first", "sel.last")
    
    except TclError: 
        
        pass



#frames
top_frame = LabelFrame(root, padx = 30, pady = 10)

button_frame = LabelFrame(root, padx = 30, pady = 10)

text_frame = LabelFrame(root, padx = 10, pady = 10)

bottom_frame = LabelFrame(root, borderwidth = 0, highlightthickness = 5)




top_frame.grid(row = 0 , column = 0)

button_frame.grid(row = 1, column = 0, pady = 10)

text_frame.grid(row = 2, column = 0, pady = 1)

bottom_frame.grid(row = 3, column = 0, pady = 3)


#labels, textboxes, buttons

#top_frame content
Notes_label = Label(top_frame, text = "Notes", fg = "black", font = 1, padx = 141)
Notes_label.grid(row = 0 , column = 0)

save_button = Button(top_frame, text = "save")
#padx increases distance between buttons


#button_frame content

#bold button
bold_button = Button(button_frame, text = "B", padx = 4, pady = 2, command = bold_it)
bold_button.grid(row = 0, column = 0)

#italicsize button
italics_button = Button(button_frame, text = "I", padx = 4, pady = 2, command = italics_it)
italics_button.grid(row = 0, column = 2, padx = 15)

#text_box component
text_box = Text(text_frame, width = 45, height = 27)
text_box.grid(row = 0, column = 0)

#text_box frame scrollbar
main_scrollbar = ttk.Scrollbar(text_frame, orient = "vertical", command = text_box.yview)
# 修复点：添加sticky="ns"让滚动条上下拉伸填满单元格
main_scrollbar.grid(row = 0, column = 1, sticky="ns")

text_box["yscrollcommand"] = main_scrollbar.set


clear_button = Button(bottom_frame, text = "clear", padx = 2, pady = 2, command = clear)
clear_button.grid(row = 0, column = 0, padx = 15, pady = 10)

save_button = Button(bottom_frame, text = "save note", padx = 2, pady = 2)
save_button.grid(row = 0, column =1, padx = 15, pady = 10)


#binding all buttons for changing colours when user hovers over it and leaves it
bold_button.bind("<Enter>", enter_button)
bold_button.bind("<Leave>", leave_button)
italics_button.bind("<Enter>", enter_button)
italics_button.bind("<Leave>", leave_button)
clear_button.bind("<Enter>", enter_button)
clear_button.bind("<Leave>", leave_button)
save_button.bind("<Enter>", enter_button)
save_button.bind("<Leave>", leave_button)


# main program loop
root.mainloop()

修复说明：仅修改了滚动条grid布局的配置行，添加sticky="ns"参数，其余逻辑保持不变。运行后输入超过27行的文本，即可看到滚动条滑块，支持拖动、鼠标滚轮滚动操作。

• yview是可滚动组件（Text、Canvas、Listbox等）内置的视图控制方法：当用户操作滚动条（拖动滑块、点击上下箭头、点击滚动条空白区域跳转）时，滚动条会自动调用绑定的yview方法，传入当前滚动位置对应的比例参数，通知可滚动组件调整内容显示的位置。
• scrollbar.set是滚动条组件内置的滑块位置更新方法：当用户通过其他方式操作可滚动组件（鼠标滚轮滚动、键盘移动光标、代码调用方法调整视图）导致内容显示位置变化时，可滚动组件会自动调用绑定的set方法，传入两个0-1之间的浮点数（分别代表可视区域顶部在总内容中的位置比例、可视区域底部在总内容中的位置比例），通知滚动条更新滑块的位置和长度。
• 双向绑定的必要性：Scrollbar和Text是完全独立的两个组件，没有默认的关联逻辑。如果只配置command=text_box.yview，仅能实现“拖动滚动条时Text内容跟着动”，但用鼠标滚轮滚动Text时，滚动条收不到位置更新通知，滑块会停在原地不动；如果只配置yscrollcommand=main_scrollbar.set，仅能实现“滚动Text时滑块跟着动”，但拖动滚动条时Text收不到滚动指令，内容不会变化。只有两个配置同时写上，才能形成完整的交互闭环。

内容的提问来源于stack exchange，提问作者Safwan Khan