关于Tkinter的command选项疑惑求解

blues177

小甲鱼老师的视频里Button组件里的command选项调用的函数是没有参数的，像这样
b = Button(master, text="确定", command=callback)

但是如果我的command调用的函数是带参数的，例如：

1. from tkinter import *
   
2. 
   
3. master = Tk()
   
4. a = 1
   
5. def callback(a):
   
6.     print(a+1)
   
7. 
   
8. b = Button(master, text="确定", command=callback(a))
   
9. b.pack()
   
10. 
    
11. mainloop()

复制代码

在我点击确定按钮之前，就已经打印出数字 2 了，再点击确定按钮之后就没有反应了。求问这种问题应该怎么解决

wuyaqi45

from tkinter import *

master = Tk()
a = 1
def callback(a):
    print(a+1)

b = Button(master, text="确定", command=lambda: callback(2))
b.pack()

mainloop()

wuyaqi45

from tkinter import *

master = Tk()
a=[0]

def callback(num):
    temp=a[0]
    a[0]=num+temp
    print (a[0])
   

b = Button(master, text="确定", command=lambda: callback(1))
b.pack()

mainloop()

wuyaqi45

Passing Argument to Callbacks

Tkinter’s Button widget doesn’t pass any information to the callback. This makes things a bit complicated if you want to use the same callback for several buttons, like in this example:

def callback():
    print "button", "?"

Button(text="one",   command=callback).pack()
Button(text="two",   command=callback).pack()
Button(text="three", command=callback).pack()
A common beginner’s mistake is to call the callback function when constructing the widget. That is, instead of giving just the function’s name (e.g. “callback”), the programmer adds parentheses and argument values to the function:

def callback(number):
    print "button", number

Button(text="one",   command=callback(1)).pack()
Button(text="two",   command=callback(2)).pack()
Button(text="three", command=callback(3)).pack()
If you do this, Python will call the callback function before creating the widget, and pass the function’s return value to Tkinter. Tkinter then attempts to convert the return value to a string, and tells Tk to call a function with that name when the button is activated. This is probably not what you wanted.

For simple cases like this, you can use a lambda expression as a link between Tkinter and the callback function:

def callback(number):
    print "button", number

Button(text="one",   command=lambda: callback(1)).pack()
Button(text="two",   command=lambda: callback(2)).pack()
Button(text="three", command=lambda: callback(3)).pack()
To be continued.

Scoping rules, binding to variable names or values, creating multiple function objects for the same function, etc.

gopythoner

command=callback(a)换成command=callback就是点击之后才会执行这个函数

payton24

gopythoner 发表于 2017-2-9 14:35
command=callback(a)换成command=callback就是点击之后才会执行这个函数

不传参数会报错哦