Kivy: Using Popup.open()

Question

I have code with Popup, which containts TextInput. Form code in example is working, but with using TextInputPopup constructor is falling down after using Popup.open() (version with costructor is in the note).

• What must I repair for using constructor?
• Parameter from TextInputPopup is used in function TextInputPopup.next_step(). Can I use this parametr in function SaveAs.on_call_popup(), which call TextInputPopup? How do I it?

Example:

   Builder.load_string('''
    <SaveAs>:
        teinp: teinp
        Button:
            text:'Hi users'
            on_release: root.on_call_popup()
        TextInput:
            id: teinp
            text:'text input'

    <TextInputPopup>:
        answer: answer

        title: root.title
        size_hint: None, None
        size: app.root.width/2, app.root.height/2
        auto_dismis: False

        BoxLayout:
            orientation: 'vertical'
            Label:
                text: root.label
            TextInput:
                id: answer
                text: ''
            BoxLayout:
                Button:
                    text: 'Cancel'
                    on_press: root.dismiss()
                Button:
                    text: 'OK'
                    on_press: root.dismiss()
    ''')

    class TextInputPopup(Popup):
        title = StringProperty()
        label = StringProperty()
        answer = ObjectProperty()
        '''
        def __init__ (self,title, label):
            self.set_description(title, label)
            return
        '''
        def set_description(self,title, label):
            self.title = title
            self.label = label
            return

        def get_answer(self):
            return self.answer.text

    class SaveAs(BoxLayout):
        teinp = ObjectProperty()

        def on_call_popup(self):
            self.poti = TextInputPopup()
    #        self.poti = TextInputPopup('File Manager', 'Name')
            self.poti.open()   
            self.poti.set_description('File Manager', 'Name') 
            self.poti.bind(on_dismiss = self.next_step)
            return

        def next_step(self, obj):
            a = self.poti.get_answer()
            self.teinp.text = self.poti.get_answer()
            return

    class ExplorerApp(App):

        def build(self):
            return SaveAs()

    if __name__ == '__main__':
        ExplorerApp().run()

Answer 1

You must call the initializer of the parent class (__init__), for that use super:

from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.popup import Popup
from kivy.properties import StringProperty, ObjectProperty
from kivy.lang.builder import Builder


Builder.load_string('''
<SaveAs>:
    teinp: teinp
    Button:
        text:'Hi users'
        on_release: root.on_call_popup()
    TextInput:
        id: teinp
        text:'text input'

<TextInputPopup>:
    answer: answer
    title: root.title
    size_hint: None, None
    size: app.root.width/2, app.root.height/2
    auto_dismis: False

    BoxLayout:
        orientation: 'vertical'
        Label:
            text: root.label
        TextInput:
            id: answer
            text: ''
        BoxLayout:
            Button:
                text: 'Cancel'
                on_press: root.dismiss()
            Button:
                text: 'OK'
                on_press: root.dismiss()
 ''')


class TextInputPopup(Popup):
    title = StringProperty()
    label = StringProperty()
    answer = ObjectProperty()

    def __init__(self, title, label, **kwargs):
        super(TextInputPopup, self).__init__(**kwargs)
        self.set_description(title, label)

    def set_description(self, title, label):
        self.title = title
        self.label = label

    def get_answer(self):
        return self.answer.text


class SaveAs(BoxLayout):
    teinp = ObjectProperty()

    def on_call_popup(self):
        poti = TextInputPopup('File Manager', 'Name')
        poti.open()
        poti.bind(on_dismiss=self.next_step)

    def next_step(self, popup):
        self.teinp.text = popup.get_answer()


class ExplorerApp(App):

    def build(self):
        return SaveAs()


if __name__ == '__main__':
    ExplorerApp().run()

If you use __init__ in your class derived, you are re-defining parent constructor, which would normally run the initialization of the base class. super is used to run the parent __init__ without an explicit call to the parent class and allow you to pass parameters to it.

In principle, whenever you overwrite __init__ in a daughter class you should call the __init__ of your parent class with the necessary arguments to be properly initialized.