make a label from a Button in kivy ,kv file

Question

ok, look can anyone give an example in kivy .kv file of a button that is set to a command that when you press it,it will make a label beneath the button, I attempted this

python

from kivy.app import App
from kivy.uix.widget import Widget
from kivy.lang import Builder
from kivy.uix.label import Label
Builder.load_file("my.kv")
class MyLayout(Widget,App):
    def __init__(self, **kwargs):
        super(MyLayout, self).__init__(**kwargs)

    def addthelabel(self):
        self.button = Label(text"you have just added me")
        self.add_widget(self.button)
class UiApp(App):
        def build(self):
            return MyLayout()
UiApp().run()

.kv file

<MyLayout>:
    BoxLayout:
        orientation:"horizontal"
        size: root.width, root.height
        Button:
            text:"hello"
            on_press:
            root.addthelabel()

but when I ran it and clicked the button it's not what I expected IMAGE https://i.sstatic.net/ZoOCj.png so I need a fresh example can you guys help.

Answer 1

The reason you are seeing this behaviour is because in addthelabel(), the new Label is being added as a child of the root MyWidget layout, rather than to the BoxLayout that contains the existing button.

To get the behaviour you want you need to add an id to the BoxLayout in the kv file that allows you to access that widget from the Python code. You also need to change the orientation to vertical.

<MyLayout>:
    BoxLayout:
        id: layout
        orientation:"vertical"
        size: root.width, root.height
        Button:
            text:"hello"
            on_press: root.addthelabel()

Then in the Python code, instead of adding the new Label to the root widget, we want to add it to the BoxLayout using its new id

from kivy.app import App
from kivy.uix.widget import Widget
from kivy.lang import Builder
from kivy.uix.label import Label
Builder.load_file("my.kv")
class MyLayout(Widget,App):
    def __init__(self, **kwargs):
        super(MyLayout, self).__init__(**kwargs)

    def addthelabel(self):
        self.button = Label(text="you have just added me")
        self.ids.layout.add_widget(self.button)
class UiApp(App):
        def build(self):
            return MyLayout()
UiApp().run()