python - Creating a Tkinter class and waiting for a return value

Question

I have a tkinter class:

class DBCreatorWin():
    def closeWindow(self):
        tkMessageBox.showinfo("Ilmiont SQLite Database Manager", "This window cannot be closed.
Enter a database name and press Continue.")

    def returnName(self):
        dbName = self.entry.get()
        self.window.destroy()
        return dbName

    def __init__(self):
        self.window = Toplevel()
        self.window.transient(tkRoot)
        self.window.grab_set()
        self.window.resizable(width=False, height=False)
        self.window.title("Ilmiont SQLite Database Manager")
        self.window.protocol("WM_DELETE_WINDOW", self.closeWindow)

        self.label = Label(self.window, text="Enter the name of the database to be created: ")
        self.entry = Entry(self.window, width=30)
        self.button = Button(self.window, text="Continue", command=self.returnName)
        self.label.grid(row=0, column=0)
        self.entry.grid(row=0, column=1)
        self.button.grid(row=1, column=0, columnspan=2)

I want to create an instance of this class within my main code and wait for the return value. The user types a name into the entry field and presses the Continue button. At that point, the value should be returned to where the class was originally instantiated. How do I go about this? I can't seem to make it work in a normal way and am new to tkinter.

Thanks in advance, Ilmiont

Answer 1

There are a couple of ways to do this. The basic idea is to use a tkinter method to wait for a specific event before returning. Tkinter provides two methods to do just that: wait_window and wait_variable. The most common method is to open a window and then wait for it to be destroyed. Some good examples can be found on the effbot site, on a page titled Dialog Windows.

Here's a simple illustration. It's not production-ready, but illustrates the general idea. At the very least you'll want to add a grab on the dialog so that you can't interact with the main window while the dialog is open, since you said you want the dialog to be modal.

import Tkinter as tk
class MyDialog(object):
    def __init__(self, parent):
        self.toplevel = tk.Toplevel(parent)
        self.var = tk.StringVar()
        label = tk.Label(self.toplevel, text="Pick something:")
        om = tk.OptionMenu(self.toplevel, self.var, "one", "two","three")
        button = tk.Button(self.toplevel, text="OK", command=self.toplevel.destroy)
        label.pack(side="top", fill="x")
        om.pack(side="top", fill="x")
        button.pack()

    def show(self):
        self.toplevel.deiconify()
        self.toplevel.wait_window()
        value = self.var.get()
        return value


class Example(tk.Frame):
    def __init__(self, parent):
        tk.Frame.__init__(self, parent)

        self.button = tk.Button(self, text="Click me!", command=self.on_click)
        self.label = tk.Label(self, width=80)
        self.label.pack(side="top", fill="x")
        self.button.pack(pady=20)

    def on_click(self):
        result = MyDialog(self).show()
        self.label.configure(text="your result: %s" % result)

if __name__ == "__main__":
    root = tk.Tk()
    Example(root).pack(fill="both", expand=True)
    root.mainloop()