tkinter 单选按钮不更新变量

Question

--UPDATE: I changed

variable=self.optionVal.get()

to

variable=self.optionVal

But nothing changed.Also I wonder why it automatically call self.selected while compiling?

----Original:

I'm trying to get familiar with radiobutton, but I don't think I understand how radiobutton works. Here's a brief code for demonstration:

     self.optionVal = StringVar()
     for text, val in OPTIONS:
         print(text,val)
         radioButton = Radiobutton(self,
                                   text=text,
                                   value=val,
                                   variable=self.optionVal.get(),
                                   command = self.selected())
        radioButton.pack(anchor=W) 

     def selected(self):
        print("this option is :"+self.optionVal.get())

In my opinion this should work like once I choose certain button, and it prints out "this option is *the value*", however now what it does is once compiled, it prints out everything, and the self.optionVal.get() is blankspace, as if value wasn't set to that variable.

I wonder what happens to my code,
Many thanks in advance. 

Answer 1

AHA! I beleive I've figured it out. I had the exact same issue. make sure you are assigning a master to the IntVar like self.rbv=tk.IntVar(master) #or 'root' or whatever you are using) :

import Tkinter as tk
import ttk

class My_GUI:

    def __init__(self,master):
        self.master=master
        master.title("TestRadio")

        self.rbv=tk.IntVar(master)#<--- HERE! notice I specify 'master'
        self.rb1=tk.Radiobutton(master,text="Radio1",variable=self.rbv,value=0,indicatoron=False,command=self.onRadioChange)
        self.rb1.pack(side='left')
        self.rb2=tk.Radiobutton(master,text="Radio2",variable=self.rbv,value=1,indicatoron=False,command=self.onRadioChange)
        self.rb2.pack(side='left')
        self.rb3=tk.Radiobutton(master,text="Radio3",variable=self.rbv,value=2,indicatoron=False,command=self.onRadioChange)
        self.rb3.pack(side='left')

    def onRadioChange(self,event=None):
        print self.rbv.get()

root=tk.Tk()
gui=My_GUI(root)
root.mainloop()

try running that, click the different buttons (they are radiobuttons but with indicatoron=False) and you will see it prints correctly changed values!

Answer 2

You're very close. Just take out the .get() from self.optionVal.get() . The Radiobutton constructor is expecting a traced variable, you're giving it the result of evaluating that variable instead.

Answer 3

You need to:

1. Remove the .get() from the variable=self.optionVal argument in the constructor the button. You want to pass the variable, not the evaluated value of the variable; and
2. Remove the parenthesis from command=self.selected() and use command=self.selected instead. The parenthesis says "call this function now and use the return value as the callback". Instead, you want to use the function itself as the callback. To better understand this, you need to study closures: a function can return a function (and, if that was the case, that would be used as your callback).

EDIT: A quick reminder, also: Python is not compiled, but interpreted. Your callback is being called while the script is being interpreted .

Answer 4

def view(interface):
    choice = interface.v.get()
    if choice == 0:
        output = "0"
    elif choice == 1:
        output = "1"
    elif choice == 2:
        output = "2"
    elif choice == 3:
        output = "3"
    else:
        output = "Invalid selection"

    return tk.messagebox.showinfo('PythonGuides', f'You Selected {output}.')    


class Start:
    
        def __init__(self):
            self.root = tk.Tk()
            self.root.geometry('500x500')
            self.root.resizable(False, False)
            self.root.title('find out the degree of severity')
            self.v = tk.IntVar()
            dolori_ossa = {"nessun dolore": 0,
                              "dolori articolari": 1,
                              "frattura composta": 2,
                              "frattura scomposta": 3}
            for (txt, val) in dolori_ossa.items():
                    tk.Radiobutton(self.root,
                                   text=txt,
                                   variable=self.v,
                                   value=val,
                                   command=lambda:view(self)
                                   
                                   ).pack()