Python Tkinter按钮不显示问题求助

问题描述 #

使用Tkinter Designer生成UI后，程序运行无报错，但按钮始终不显示。已尝试调整按钮位置排除遮挡，重新生成UI到新文件可正常运行，但复制到当前文件后按钮仍无法显示。

问题代码 #

from tkinter import *
import new_post
from pathlib import Path
from tkinter import Tk, Canvas, Entry, Text, Button, PhotoImage

def home_page_screen():

    # SETTING UP WINDOW
    top = Toplevel()
    top.resizable(height=False, width=False)
    
    
    # FUNCTIONS
    
    # NEW POST
    def new_post_win():
        new_post.new_post_win()
    
    # ===================================================================================================================
    
    # UI
    # The UI section of the file was generated by the Tkinter Designer by Parth Jadhav
    OUTPUT_PATH = Path(__file__).parent
    ASSETS_PATH = OUTPUT_PATH / Path(r"assets\home_page")
    
    def relative_to_assets(path: str) -> Path:
        return ASSETS_PATH / Path(path)
    
    # WINDOW SETTINGS
    top.geometry("431x728")
    top.configure(bg="#FFFFFF")
    top.resizable(False, False)
    
    # ==========FRAME=====================
    canvas = Canvas(
        top,
        bg="#FFFFFF",
        height=728,
        width=431,
        bd=0,
        highlightthickness=0,
        relief="ridge"
    )
    
    canvas.place(x=0, y=0)
    
    # ========TITLE========
    title_image = PhotoImage(
        file=relative_to_assets("image_1.png"))
    title = canvas.create_image(
        215.0,
        48.0,
        image=title_image
    )
    
    post_holder_image = PhotoImage(
        file=relative_to_assets("image_2.png"))
    post_holder = canvas.create_image(
        215.0,
        364.0,
        image=post_holder_image
    )
    
    # ========POST=LABEL========
    canvas.create_text(
        27.0,
        169.0,
        anchor="nw",
        text="",
        fill="#000000",
        font=("Karantina Regular", 32 * -1),
        width=385
    )
    
    # ========NEW=POST=LABEL========
    new_post_image = PhotoImage(
        file=relative_to_assets("image_3.png"))
    new_post = canvas.create_image(
        107.0,
        134.0,
        image=new_post_image
    )
    
    # ========POST=BUTTON========
    post_btn_image = PhotoImage(
        file=relative_to_assets("button_1.png"))
    post_btn = Button(
        image=post_btn_image,
        borderwidth=0,
        highlightthickness=0,
        command=new_post_win,
        relief="flat"
    )
    post_btn.place(
        x=25.0,
        y=500.0,
        width=194.0,
        height=64.0
    )
    
    # MAIN LOOP
    top.mainloop()

问题原因 #

Tkinter的PhotoImage对象如果没有被持久引用，会被Python的垃圾回收机制自动回收。你的代码中，post_btn_image是函数内的局部变量，当函数执行到末尾时，该变量会被销毁，导致按钮失去图片引用，从而无法显示。

解决方法 #

给所有PhotoImage对象添加持久引用，避免被垃圾回收：

1. 给按钮图片添加引用 #

修改按钮创建部分的代码，将post_btn_image绑定到按钮实例的属性上：

# ========POST=BUTTON========
post_btn_image = PhotoImage(
    file=relative_to_assets("button_1.png"))
post_btn = Button(
    image=post_btn_image,
    borderwidth=0,
    highlightthickness=0,
    command=new_post_win,
    relief="flat"
)
# 添加这行，保持图片引用
post_btn.image = post_btn_image
post_btn.place(
    x=25.0,
    y=500.0,
    width=194.0,
    height=64.0
)

2. 给Canvas中的图片添加引用 #

同样，Canvas中使用的图片也需要添加引用，避免被回收：

# ========TITLE========
title_image = PhotoImage(
    file=relative_to_assets("image_1.png"))
title = canvas.create_image(
    215.0,
    48.0,
    image=title_image
)
# 绑定到canvas的属性上
canvas.title_image = title_image

# ========POST HOLDER========
post_holder_image = PhotoImage(
    file=relative_to_assets("image_2.png"))
post_holder = canvas.create_image(
    215.0,
    364.0,
    image=post_holder_image
)
canvas.post_holder_image = post_holder_image

# ========NEW POST LABEL========
new_post_image = PhotoImage(
    file=relative_to_assets("image_3.png"))
new_post = canvas.create_image(
    107.0,
    134.0,
    image=new_post_image
)
canvas.new_post_image = new_post_image

3. 验证修改 #

修改后重新运行程序，按钮应该能正常显示。如果仍有问题，检查图片路径是否正确，确保assets\home_page目录下存在button_1.png等图片文件。

内容的提问来源于stack exchange，提问作者Coding Master