How can I verify that my textfield is empty?

Question

    def check_full_name(self):
        toast("You have to enter your full name to use the app correctly ! ")

    MDTextFieldRound:
        id:user_app
        hint_text: "Full Name"
        size_hint_x:  None
        size_hint_y: 0.08
        width: 247
        font_size: 18
        pos_hint: {'center_x':0.5, 'center_y':0.62}
        on_release: app.check_full_name() if user_app.text == '' else app.root.current = "accueil"

I don't know why it doesn't work, I want that when a field is empty calls my check_full_name function.Thanks for answering

Answer 1

According to your question, this should fix your problem:

.py file

from kivymd.app import MDApp
from kivymd.toast import toast

class PyApp(MDApp):
    def on_start(self):
        if self.root.ids.user_app.text == '':
            self.check_full_name() 
        else: 
            self.root.ids.user_app.current = "accueil"
    def check_full_name(self):
        toast("You have to enter your full name to use the app correctly ! ")

PyApp().run()

.kv file

FloatLayout:
    MDTextFieldRound:
        id:user_app
        hint_text: "Full Name"
        size_hint_x:  None
        size_hint_y: 0.08
        width: 247
        font_size: 18
        pos_hint: {'center_x':0.5, 'center_y':0.62}
        on_text_validate: app.on_start()
        

Answer 2

class SplashScreenApp(MDApp):
    dialog = None
    def build(self):
        dialog = None
        self.title = "ReviewinApp"
        global sm 
        sm = ScreenManager()
        sm.add_widget(Builder.load_file("splash.kv"))
        sm.add_widget(Builder.load_file("accueil.kv"))
        sm.add_widget(Builder.load_file('conditions.kv'))
        sm.add_widget(Builder.load_file("register.kv"))
        sm.add_widget(Builder.load_file("faq.kv"))
        sm.add_widget(Builder.load_file("login.kv"))
        sm.add_widget(Builder.load_file("User2.kv"))
        self.theme_cls.theme_style = "Light"
        return sm
    def on_start(self):
        if self.root.ids.user_app.text == ' ':
           toast("Please register correctly")
        else:
            toast("It's okay")
    ```
        MDFillRoundFlatButton:
            text: "Finish !"
            font_size: "20sp"
            font_name: "OpenSans"
            pos_hint: {'center_x':0.5, 'center_y':0.07}
            halign: 'center'
            theme_text_color:'Custom'
            text_color: 255/255, 255/255, 255/255, 1
            size_hint: (0.58, 0.06)
            md_bg_color: 62/255, 216/255, 133/255, 1
            background_normal:''
            on_press: app.on_start()
    ```
    The python file and the kivy files are on different pages. One with extension .kv and one with .py