Kivy: AttributeError: 'NoneType' object has no attribute 'parent' when scroll down and scroll up again in recycle view

问题

My Kivy App Description:

I have 3 types of widgets in MyFirstScreen:

• A RecycleView that has multiple "User"s as its items. (each item is a dictionary)
• Three TextInputs that are related to values of each recycle view item. (if you select any items of RecycleView these TextInputs will loaded with corresponding dictionary values)
• An "Add New User" Button. (if you enter NEW values in TextInputss and press this button, RecycleView will be updated with: previous items + your new item)

Issue:

An error occurs in these two situations:

Situation A:

1. I select an item (for example : "User 1").
2. I scroll DOWN until the selected item hides completely from RecycleView.
3. I scroll UP to show selected item again.

Situation B:

1. I select an item (for example : "User 1").
2. I change the new text values which is loaded in TextInputss.
3. I press the "Add New User" Button.

In both situations when I want to do step 3, this error occurs:

my_text_input= self.parent.parent.parent.parent.parent.system_name_text_input_id

AttributeError: 'NoneType' object has no attribute 'parent'

Does anyone know what am I doing wrong here or how to make this work? Thank you in advance...

My KivyTest.py file:

from kivy.app import App
from kivy.lang import Builder
from kivy.uix.label import Label
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.uix.recycleview import RecycleView
from kivy.uix.recycleview.views import RecycleDataViewBehavior
from kivy.properties import BooleanProperty
from kivy.uix.recycleboxlayout import RecycleBoxLayout
from kivy.uix.behaviors import FocusBehavior
from kivy.uix.recycleview.layout import LayoutSelectionBehavior


class Manager(ScreenManager):

    def __init__(self, **kwargs):
        super().__init__(**kwargs)


class MyFirstScreen(Screen):
    def __init__(self, **kwarg):
        super().__init__(**kwarg)
        print("__init__ of MyFirstScreen is Called")

    def update_recycle_view(self):
        global is_repetitive
        system_name_ti = self.ids.user_name_text_input_id.text
        system_id_ti = self.ids.user_id_text_input_id.text
        current_items_in_recycle_view = self.ids.recycle_view_widget_id.items_of_rv
        new_item = {"color": (0, 0, 0, 1), "font_size": "20", "text": "", "user_id": ""}

        for item_index in range(len(current_items_in_recycle_view)):
            current_item_name = current_items_in_recycle_view[item_index].get("text")
            current_item_id = current_items_in_recycle_view[item_index].get("user_id")
            print(f"current_item_name: {current_item_name}_______current_item_id: {current_item_id}")

            if system_name_ti == current_item_name:
                print("Error: Repetitive User Name")
                is_repetitive = True
                break
            elif system_id_ti == current_item_id:
                print("Error: Repetitive User ID")
                is_repetitive = True
                break
            else:
                is_repetitive = False

        if not is_repetitive:
            print("else situation")
            new_item.update({"text": system_name_ti})
            new_item.update({"user_id": system_id_ti})
            self.ids.recycle_view_widget_id.add_new_item_to_data(new_item)


class RecycleViewWidget(RecycleView):
    def __init__(self, **kwargs):
        super(RecycleViewWidget, self).__init__(**kwargs)
        self.items_of_rv = []
        self.update_my_items()
        self.update_my_data()

    def update_my_items(self):
        for i in range(1, 21):
            self.items_of_rv.append(
                {"color": (0, 0, 0, 1), "font_size": "20", "text": f"Use {i}",
                 "user_id": f"{100 * i}"})

    def update_my_data(self):
        self.data = [item for item in self.items_of_rv]

    def add_new_item_to_data(self, new_item):
        self.data.append(new_item)
        self.refresh_from_data()
        print("add_new_item_to_data called")


class SelectableRecycleBoxLayout(FocusBehavior, LayoutSelectionBehavior, RecycleBoxLayout):
    """ Adds selection and focus behaviour to the view. """


class SelectableLabel(RecycleDataViewBehavior, Label):
    """ Add selection support to the Label """
    index = None
    selected = BooleanProperty(False)
    selectable = BooleanProperty(True)

    def refresh_view_attrs(self, rv, index, data):
        """ Catch and handle the view changes """
        self.index = index
        return super(SelectableLabel, self).refresh_view_attrs(rv, index, data)

    def on_touch_down(self, touch):
        """ Add selection on touch down """
        if super(SelectableLabel, self).on_touch_down(touch):
            return True
        if self.collide_point(*touch.pos) and self.selectable:
            return self.parent.select_with_touch(self.index, touch)

    def apply_selection(self, rv, index, is_selected):
        """ Respond to the selection of items in the view. """

        self.selected = not is_selected
        if is_selected:
            rv.data[index].update({'color': (1, 1, 1, 1)})
            self.refresh_view_attrs(RecycleViewWidget(), index, rv.data[index])
            print("selection changed to {0}".format(rv.data[index]))
            self.update_text_inputs(rv.data[index])
        else:
            print("selection removed from {0}".format(rv.data[index]))
            if rv.data[index].get("color") == (1, 1, 1, 1):
                rv.data[index].update({'color': (0, 0, 0, 1)})
                self.refresh_view_attrs(RecycleViewWidget(), index, rv.data[index])
        self.selected = not self.selected

    def update_text_inputs(self, selected_system, *kwarg):
        user_name_text_input = self.parent.parent.parent.parent.parent.user_name_text_input_id
        user_id_text_input = self.parent.parent.parent.parent.parent.user_id_text_input_id

        user_name_text_input.text = selected_system.get("text")
        user_id_text_input.text = selected_system.get("user_id")


main_style = Builder.load_file("test.kv")


class MyApp(App):
    def __init__(self, **kwargs):
        super().__init__(**kwargs)

    def build(self):
        return main_style


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

My test.kv file:

Manager:
    MyFirstScreen:

<SelectableLabel>:
    canvas.before:
        Color:
            rgba: (0, 0, 1, 1) if self.selected else (1, 1, 1, 1)
        Rectangle:
            pos: self.pos
            size: self.size
<RecycleViewWidget>:
    viewclass: 'SelectableLabel'
    SelectableRecycleBoxLayout:
        default_size: None, dp(56)
        default_size_hint: 1, None
        size_hint_y: None
        height: self.minimum_height
        orientation: 'vertical'

<MyFirstScreen>:
    name: 'system_setup_page'
    user_name_text_input_id:user_name_text_input_id
    user_id_text_input_id:user_id_text_input_id
    recycle_view_widget_id:recycle_view_widget_id
    GridLayout:
        cols: 2
        BoxLayout:
            cols: 1
            padding: 20
            RecycleViewWidget:
                id:recycle_view_widget_id
        FloatLayout:
            Label:
                size_hint: None, None
                text: "User Name:"
                font_size: 22
                pos_hint: {'center': (20/100, 90/100)}
            TextInput:
                id: user_name_text_input_id
                size_hint: None, None
                hint_text: "Type Your Name..."
                size: 200, 30
                multiline: False
                pos_hint: {'center': (65/100, 90/100)}
            Label:
                size_hint: None, None
                text: "User ID:"
                font_size: 20
                pos_hint: {'center': (20/100, 70/100)}
            TextInput:
                id: user_id_text_input_id
                size_hint: None, None
                size: 200, 30
                hint_text: "Type Your ID..."
                pos_hint: {'center': (65/100, 70/100)}
            Button:
                text: "Add New User"
                size_hint: None, None
                font_size: 20
                size: 300, 50
                pos_hint: {'center': (50/100, 30/100)}
                on_release: root.update_recycle_view()

回答1:

It seems it removes Label from RecycleViewWidget when it is not visible - and then Label has no parent.

When Label is visible agant then it puts Label in RecycleViewWidget and it has again parent. But first it executes apply_selection - so it runs it before Label has parent again.

Similar when it crates new Label then it first executes apply_selection before it adds Labal to RecycleViewWidget - so it runs it before Label has parent.

---

But in this situation you can use rv (which is instance of RecycleViewWidget) to get access to FirstScreen and to get access to TextInput

Now I sends rv and index instead of rv.data[index] to update_text_inputs so I can use it to get rv.parent.parent.parent and to get rv.data[index]

screen = rv.parent.parent.parent

user_name_text_input = screen.user_name_text_input_id
user_id_text_input   = screen.user_id_text_input_id

---

EDIT: I found you can get it also without using parent and without rv

screen = main_style.screens[0]
# or
#screen = main_style.screens[0].ids

user_name_text_input = screen.user_name_text_input_id
user_id_text_input   = screen.user_id_text_input_id

---

def apply_selection(self, rv, index, is_selected):
    """ Respond to the selection of items in the view. """

    self.selected = is_selected

    if is_selected:
        rv.data[index].update({'color': (1, 1, 1, 1)})

        self.refresh_view_attrs(rv, index, rv.data[index])

        print("selection changed to {0}".format(rv.data[index]))

        self.update_text_inputs(rv, index)
    else:
        rv.data[index].update({'color': (0, 0, 0, 1)})

        self.refresh_view_attrs(rv, index, rv.data[index])

        print("selection removed from {0}".format(rv.data[index]))


def update_text_inputs(self, rv, index, *kwarg):
    screen = rv.parent.parent.parent
    #screen = main_style.screens[0]
    #screen = main_style.screens[0].ids
    print('[DEBUG] screen:', screen)

    user_name_text_input = screen.user_name_text_input_id
    user_id_text_input   = screen.user_id_text_input_id

    user_name_text_input.text = rv.data[index].get("text")
    user_id_text_input.text   = rv.data[index].get("user_id")

---

BTW: I use also rv instead of RecycleViewWidget() in refresh_view_attrs() because it can make the same problem as in previous question - RecycleViewWidget() can creates new instance of RecycleViewWidget and you should work with original first instance of RecycleViewWidget

来源：https://stackoverflow.com/questions/61924388/kivy-attributeerror-nonetype-object-has-no-attribute-parent-when-scroll-do