CustomTkinter中CTkEntry绑定textvariable后占位符消失问题求助

问题 #

使用CustomTkinter的CTkEntry组件时，同时传入textvariable和placeholder_text参数会导致占位符无法显示。单独传placeholder_text时占位符正常显示但无法绑定变量，单独传textvariable时变量绑定正常但占位符消失。

复现代码：

import tkinter as tk
import customtkinter as ui

ui.set_appearance_mode("dark")
ui.set_default_color_theme("dark-blue")

root = ui.CTk()
root.geometry("500x350")

frame = ui.CTkFrame(master=root)
frame.pack(pady=20, padx=60, fill="both", expand=True)

label = ui.CTkLabel(master=frame, text="Login System", font=("Roboto", 24))
label.pack(pady=12, padx=10)

username = tk.StringVar()
entry1 = ui.CTkEntry(master=frame, textvariable=username, placeholder_text="Username")
entry1.pack(pady=12, padx=10)

password = tk.StringVar()
entry2 = ui.CTkEntry(master=frame, textvariable=password, placeholder_text="Password", show="*")
entry2.pack(pady=12, padx=10)

def login():
    print(username.get())
    print(password.get())

button = ui.CTkButton(master=frame, text="Login", command=login)
button.pack(pady=12, padx=10)

checkbox = ui.CTkCheckBox(master=frame, text="Remember Me")
checkbox.pack(pady=12, padx=10)

root.mainloop()

解决方案 #

问题根源在于textvariable绑定的StringVar初始为空字符串时，CustomTkinter会判定输入框已有内容，进而隐藏占位符。可以通过以下两种方式解决：

方法一：初始化时强制显示占位符 #

给StringVar设置初始空值后，手动调用CTkEntry的_show_placeholder()方法触发占位符显示：

import tkinter as tk
import customtkinter as ui

ui.set_appearance_mode("dark")
ui.set_default_color_theme("dark-blue")

root = ui.CTk()
root.geometry("500x350")

frame = ui.CTkFrame(master=root)
frame.pack(pady=20, padx=60, fill="both", expand=True)

label = ui.CTkLabel(master=frame, text="Login System", font=("Roboto", 24))
label.pack(pady=12, padx=10)

username = tk.StringVar(value="")
entry1 = ui.CTkEntry(master=frame, textvariable=username, placeholder_text="Username")
entry1.pack(pady=12, padx=10)
# 变量为空时强制显示占位符
if username.get() == "":
    entry1._show_placeholder()

password = tk.StringVar(value="")
entry2 = ui.CTkEntry(master=frame, textvariable=password, placeholder_text="Password", show="*")
entry2.pack(pady=12, padx=10)
if password.get() == "":
    entry2._show_placeholder()

def login():
    print(username.get())
    print(password.get())

button = ui.CTkButton(master=frame, text="Login", command=login)
button.pack(pady=12, padx=10)

checkbox = ui.CTkCheckBox(master=frame, text="Remember Me")
checkbox.pack(pady=12, padx=10)

root.mainloop()

方法二：监听变量变化自动切换占位符 #

通过StringVar的追踪功能，在内容为空时显示占位符，有内容时隐藏，更符合交互逻辑：

import tkinter as tk
import customtkinter as ui

ui.set_appearance_mode("dark")
ui.set_default_color_theme("dark-blue")

root = ui.CTk()
root.geometry("500x350")

frame = ui.CTkFrame(master=root)
frame.pack(pady=20, padx=60, fill="both", expand=True)

label = ui.CTkLabel(master=frame, text="Login System", font=("Roboto", 24))
label.pack(pady=12, padx=10)

username = tk.StringVar(value="")
entry1 = ui.CTkEntry(master=frame, textvariable=username, placeholder_text="Username")
entry1.pack(pady=12, padx=10)

# 监听username变量变化
def on_username_change(*args):
    if username.get() == "":
        entry1._show_placeholder()
    else:
        entry1._hide_placeholder()

username.trace_add("write", on_username_change)

password = tk.StringVar(value="")
entry2 = ui.CTkEntry(master=frame, textvariable=password, placeholder_text="Password", show="*")
entry2.pack(pady=12, padx=10)

# 监听password变量变化
def on_password_change(*args):
    if password.get() == "":
        entry2._show_placeholder()
    else:
        entry2._hide_placeholder()

password.trace_add("write", on_password_change)

def login():
    print(username.get())
    print(password.get())

button = ui.CTkButton(master=frame, text="Login", command=login)
button.pack(pady=12, padx=10)

checkbox = ui.CTkCheckBox(master=frame, text="Remember Me")
checkbox.pack(pady=12, padx=10)

# 初始化时触发一次显示逻辑
on_username_change()
on_password_change()

root.mainloop()

这两种方法都能同时实现变量绑定和占位符正常显示的需求。

内容的提问来源于stack exchange，提问作者Coder