Tkinter Entry always returning empty string

问题

I'm trying to create a GUI application using Tkinter. This interface is made of the following widgets: a button, an entry and a text. The image below shows it.

The idea behind this app is: the user enters a word on the entry and on hit the Meaning button it's meaning is showed in the text widget.

My code is splitted in two classes: one for GUI and another for the app itself.

GUI (removed the imaged showed before to reduce coding):

 class Gui:
    def __init__(self, master=None):
        if master is None:
            return
        else:
            self.word = StringVar()
            self.word_meaning = None
            self.app_frame = Frame(master)
            self.app_frame.grid()
            self.create_app_frame()
            self.entry_widget = Entry(self.app_frame, textvariable=self.word)
            self.button_widget = Button(self.app_frame, text='Meaning', command=self.__handler_entry)
            self.text_widget = Text(self.app_frame, height=10, width=30)
            self.crete_app_frame()

    def crete_app_frame(self):    
        self.entry_widget.grid(row=0, column=0)
        self.button_widget.grid(row=0, column=1)
        self.text_widget.grid(row=1, column=0, columnspan=2)

    def get_word(self):
        return self.word.get()

    def set_word_meaning(self, meaning):
        self.word_meaning = meaning

    def __handler_entry(self):
        self.text_widget.delete(0., END)
        self.text_widget.insert(END, self.word_meaning)

Application:

class InteractiveDictionary:
    def __init__(self, filename):
        with open(filename, 'r') as file:
            self.data = json.load(file)

    def get_meaning(self, term):
        print('-------------------')
        print(f"world is:{term}")
        print('-------------------')
        term = str(term)
        term = term.lower()
        if term in self.data:
            return self.data[term]
        else:
            return "The world you\'re looking for doesn\'t exist."

Main:

if __name__ == '__main__':
    window = Tk()
    window.title('Interactive Dictionary')
    dictionary = InteractiveDictionary('words.json')
    app = Gui(master=window)
    word = app.get_word()
    word_meaning = dictionary.get_meaning(word)
    if type(word_meaning) == list:
        for i in word_meaning:
            app.set_word_meaning(i)
    else:
        app.set_word_meaning(word_meaning)
    window.mainloop()

The application works fine when results are shown on console. However, when I try to show on the GUI, the word captured by get_word() method is not correctly passed to dictionaries get_meaning() method. An empty is passed.

My suspect that it is related to the way I call Tkinter on main. I would like to keep Gui and the app isolated. So, remove code in the main to __handler_entry() is not an option. Someone knows how can I fix it and made my app run properly?

回答1:

It seems you don't know how GUIs works - all starts with mainloop(), it displays window, gets mouse/keyboard events from system, sends events to widgets, (re)draws widgets.

Everything before mainloop() is executed before you see window - so word = app.get_word() is executed before you see window. You have to use it in __handler_entry which is executed when you press button.

More precisly in __handler_event` you will have to use all of this

def __handler_entry(self):

    word = self.get_word()

    word_meaning = dictionary.get_meaning(word)

    if isinstance(word_meaning, list):
        for i in word_meaning:
            self.set_word_meaning(i)
    else:
        self.set_word_meaning(word_meaning)

    self.text_widget.delete(0., END)
    self.text_widget.insert(END, self.word_meaning)

来源：https://stackoverflow.com/questions/55773536/tkinter-entry-always-returning-empty-string