如果满足某些条件，如何配置Tkinter小部件？

Question

Normally, this isn't hard. I can usually do it without much trouble. For example:

b = Button(main, text="Button", command=function)
x = 3
def function():
    x -=1
if x == 0:
    b.configure(state=DISABLED)

This would disable my button after pushing it three times. However, my issue is slightly more complicated. I want a button that can switch back and forth based on a variable, not just go from one to the other one time. In my real thing, all variables are IntVar or StringVar .

addB = Button(main, text="Add", command=add)
subtractB = Button(main, text="Subtract", command=subtract)

x = IntVar()
x.set(0)

def add():
    x.set(x.get() + 1)

def subtract():
    x.set(x.get() - 5)

At this point, I'm looking for something that'll disable the subtract button ( subtractB.configure(state=DISABLED) ) unless x is at least five. If x is more than five before the button is pressed and then x becomes less than five again, the button should disable itself again. How is this done?

Answer 1

You can trace an IntVar , which means you call a function every time the variable is changed. This way you can check the value of x every time it is changed, and set the state of the button accordingly:

def add():
    x.set(x.get() + 1)

def subtract():
    x.set(x.get() - 5)

def trace_var(*args):
    if x.get() < 5:
        subtractB.configure(state=DISABLED)
    else:
        subtractB.configure(state=NORMAL)


main = Tk()

addB = Button(main, text="Add", command=add)
addB.pack()
subtractB = Button(main, text="Subtract", command=subtract)
subtractB.pack()

x = IntVar()
x.trace('w', trace_var)
x.set(0)
Label(main, textvariable=x).pack()

main.mainloop()