I'm using Python 3.2.1 in Arch Linux x86_64. This one is really driving me crazy: I just want to have a default, preselected value for a ttk.Combobox
as soon as I grid it. This is my code:
from tkinter import Tk, StringVar, ttk
root = Tk()
def combo(parent):
value = StringVar()
box = ttk.Combobox(parent, textvariable=value, state='readonly')
box['values'] = ('A', 'B', 'C')
box.current(0)
box.grid(column=0, row=0)
combo(root)
root.mainloop()
Which draws an empty Combobox
. What's funny is that if I don't use a function it works perfectly:
from tkinter import Tk, StringVar, ttk
root = Tk()
value = StringVar()
box = ttk.Combobox(root, textvariable=value, state='readonly')
box['values'] = ('A', 'B', 'C')
box.current(0)
box.grid(column=0, row=0)
root.mainloop()
Of course, in the real program I have to use a function, so I need another solution.
The problem is that the instance of StringVar is getting garbage-collected. This is because it's a local variable due to how you wrote your code.
One solution is to use a class so that your StringVar persists:
from tkinter import Tk, StringVar, ttk
class Application:
def __init__(self, parent):
self.parent = parent
self.combo()
def combo(self):
self.box_value = StringVar()
self.box = ttk.Combobox(self.parent, textvariable=self.box_value,
state='readonly')
self.box['values'] = ('A', 'B', 'C')
self.box.current(0)
self.box.grid(column=0, row=0)
if __name__ == '__main__':
root = Tk()
app = Application(root)
root.mainloop()
When your function 'combo' exits, the local variable 'value' is destroyed. You need a persistent variable, such as a global variable or a variable that is a property of a class so that the value isn't garbage-collected while the widget still exists.
The get()
method can be used within your function to rename the StringVar
and save it under another name to avoid losing it altogether via garbage collection.
value = StringVar()
keepvalue = value.get()
then use keepvalue
instead of value:
box = ttk.Combobox(root, textvariable=keepvalue, state='readonly')
This had 'A' showing in the combobox for me.
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