Modules Material App

Material App

KivyMD has the MDApp class that creates all required for KivyMD properties. Before 0.102.1 you had to create the theme_cls property, but with MDApp you don't need to do this.

Minimal app

Example of minimal app using MDApp.

from kivy.lang import Builder

from kivymd.app import MDApp

KV = """
MDScreen:
    md_bg_color: self.theme_cls.backgroundColor

    MDButton:
        pos_hint: {"center_x": .5, "center_y": .5}
        on_release: print("Hi!")

        MDButtonText:
            text: "Click me!"
"""


class MainApp(MDApp):
    def __init__(self, **kwargs):
        self.title = "My Material Application"
        super().__init__(**kwargs)

    def build(self):
        return Builder.load_string(KV)


MainApp().run()

Changing Theme Manager properties

If you want to change theme style, primary colors or other properties of ThemeManager, you can do this in __init__ method.

from kivy.lang import Builder
from kivymd.app import MDApp

root_kv = """
BoxLayout:
    MDRaisedButton:
        text: "Click me!"
        on_release: print("Hi!")
"""


class MainApp(MDApp):
    def __init__(self, **kwargs):
        self.title = "My Material Application"
        self.theme_cls.theme_style = "Dark"
        self.theme_cls.primary_palette = "DeepPurple"
        super().__init__(**kwargs)

    def build(self):
        self.root = Builder.load_string(root_kv)


if __name__ == "__main__":
    MainApp().run()

Accessing app

KivyMD's MDApp is a simple Kivy's App. You can access your app object with App.get_running_app() in Python code and app in KV code.

from kivy.lang import Builder
from kivy.app import App
from kivymd.app import MDApp
from kivymd.uix.chip import MDChip

root_kv = """
BoxLayout:
    MDRaisedButton:
        text: app.title
        on_release: app.title = "Abcd"

    MyWidget:
"""


class MyWidget(MDChip):
    def __init__(self, **kwargs):
        self.label = App.get_running_app().title
        super().__init__(**kwargs)


class MainApp(MDApp):
    def __init__(self, **kwargs):
        self.title = "My Material Application"
        super().__init__(**kwargs)

    def build(self):
        self.root = Builder.load_string(root_kv)


if __name__ == "__main__":
    MainApp().run()

Exceptions

KivyMD: App object should be initialized before loading root widget

Or AttributeError: 'NoneType' object has no attribute 'property' in version 0.102.1

Some of your widgets are created before MainApp().run(). To fix this issue, move Builder.load_... (that loads root widget) to build method of app class and move widget creation to methods that call after app initialization.

Example of incorrect code #1

from kivy.lang import Builder
from kivymd.app import MDApp

Builder.load_string("""
BoxLayout:
    MDLabel:
        text: "Hello World"

    MDRaisedButton:
        text: "Click me!"
""")


class MainApp(MDApp):
    pass


if __name__ == "__main__":
    MainApp().run()

Code above will raise ValueError:

 Traceback (most recent call last):
   File "D:\Py\kivy-venv\lib\site-packages\KivyMD\kivymd\theming.py", line 374, in __init__
     App.get_running_app().property("theme_cls", True),
 AttributeError: 'NoneType' object has no attribute 'property'

 During handling of the above exception, another exception occurred:

 Traceback (most recent call last):
   File "D:\Projects\my_project\main.py", line 11, in <module>
     """)
   File "D:\Py\kivy-venv\lib\site-packages\kivy\lang\builder.py", line 405, in load_string
     rule_children=rule_children)
   File "D:\Py\kivy-venv\lib\site-packages\kivy\lang\builder.py", line 654, in _apply_rule
     child = cls(__no_builder=True)
   File "D:\Py\kivy-venv\lib\site-packages\KivyMD\kivymd\uix\label.py", line 94, in __init__
     super().__init__(**kwargs)
   File "D:\Py\kivy-venv\lib\site-packages\KivyMD\kivymd\theming.py", line 384, in __init__
     "KivyMD: App object should be initialized before loading "
 ValueError: KivyMD: App object should be initialized before loading root widget. See https://github.com/HeaTTheatR/KivyMD/wiki/Modules-Material-App#exceptions

---

Correct code:

from kivy.lang import Builder
from kivymd.app import MDApp

root_kv = """
BoxLayout:
    MDLabel:
        text: "Hello World"

    MDRaisedButton:
        text: "Click me!"
"""


class MainApp(MDApp):
    def build(self):
        self.root = Builder.load_string(root_kv)


if __name__ == "__main__":
    MainApp().run()

Example of incorrect code #2

from kivy.lang import Builder
from kivy.properties import ObjectProperty
from kivy.uix.boxlayout import BoxLayout
from kivymd.app import MDApp
from kivymd.uix.textfield import MDTextField

Builder.load_string("""
<MyRootBoxLayout>:
    MDLabel:
        text: "Hello World"

    MDRaisedButton:
        text: "Click me!"
""")


class MyRootBoxLayout(BoxLayout):
    my_textfield = ObjectProperty(MDTextField())

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

    def add_textfield(self):
        self.add_widget(self.my_textfield)


class MainApp(MDApp):
    def build(self):
        return MyRootBoxLayout()


if __name__ == "__main__":
    MainApp().run()

Code above will raise ValueError:

 Traceback (most recent call last):
   File "D:\Py\kivy-venv\lib\site-packages\KivyMD\kivymd\theming.py", line 374, in __init__
     App.get_running_app().property("theme_cls", True),
 AttributeError: 'NoneType' object has no attribute 'property'

 During handling of the above exception, another exception occurred:

 Traceback (most recent call last):
   File "D:\Projects\my_project\main.py", line 17, in <module>
     class MyRootBoxLayout(BoxLayout):
   File "D:\Projects\my_project\main.py", line 18, in MyRootBoxLayout
     my_textfield = ObjectProperty(MDTextField())
   File "D:\Py\kivy-venv\lib\site-packages\KivyMD\kivymd\uix\textfield.py", line 573, in __init__
     field=self,
   File "D:\Py\kivy-venv\lib\site-packages\KivyMD\kivymd\uix\textfield.py", line 526, in __init__
     super().__init__(**kwargs)
   File "D:\Py\kivy-venv\lib\site-packages\KivyMD\kivymd\theming.py", line 384, in __init__
     "KivyMD: App object should be initialized before loading "
 ValueError: KivyMD: App object should be initialized before loading root widget. See https://github.com/HeaTTheatR/KivyMD/wiki/Modules-Material-App#exceptions

---

Correct code:

from kivy.lang import Builder
from kivy.properties import ObjectProperty
from kivy.uix.boxlayout import BoxLayout
from kivymd.app import MDApp
from kivymd.uix.textfield import MDTextField

Builder.load_string("""
<MyRootBoxLayout>:
    MDLabel:
        text: "Hello World"

    MDRaisedButton:
        text: "Click me!"
""")


class MyRootBoxLayout(BoxLayout):
    my_textfield = ObjectProperty()

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

    def add_textfield(self):
        if not self.my_textfield:
            self.my_textfield = MDTextField()
        self.add_widget(self.my_textfield)


class MainApp(MDApp):
    def build(self):
        return MyRootBoxLayout()


if __name__ == "__main__":
    MainApp().run()

ValueError: KivyMD: App object should be inherited from kivymd.app.MDApp

Use the template at Material App page.

Example of incorrect code #1

from kivy.lang import Builder
from kivy.app import App
from kivymd.theming import ThemeManager

root_kv = """
BoxLayout:
    MDLabel:
        text: "Hello World"

    MDRaisedButton:
        text: "Click me!"
"""


class MainApp(App):
    def build(self):
        self.root = Builder.load_string(root_kv)


if __name__ == "__main__":
    MainApp().run()

Code above will raise ValueError:

 Traceback (most recent call last):
   File "D:\Projects\my_project\main.py", line 21, in <module>
     MainApp().run()
   File "D:\Py\kivy-venv\lib\site-packages\kivy\app.py", line 829, in run
     root = self.build()
   File "D:\Projects\my_project\main.py", line 17, in build
     self.root = Builder.load_string(root_kv)
   File "D:\Py\kivy-venv\lib\site-packages\kivy\lang\builder.py", line 405, in load_string
     rule_children=rule_children)
   File "D:\Py\kivy-venv\lib\site-packages\kivy\lang\builder.py", line 654, in _apply_rule
     child = cls(__no_builder=True)
   File "D:\Py\kivy-venv\lib\site-packages\KivyMD\kivymd\uix\label.py", line 94, in __init__
     super().__init__(**kwargs)
   File "D:\Py\kivy-venv\lib\site-packages\KivyMD\kivymd\theming.py", line 378, in __init__
     "KivyMD: App object should be inherited from "
 ValueError: KivyMD: App object should be inherited from `kivymd.app.MDApp`. See https://github.com/HeaTTheatR/KivyMD/blob/master/README.md#api-breaking-changes

---

Correct code:

from kivy.lang import Builder
from kivymd.app import MDApp

root_kv = """
BoxLayout:
    MDLabel:
        text: "Hello World"

    MDRaisedButton:
        text: "Click me!"
"""


class MainApp(MDApp):
    def build(self):
        self.root = Builder.load_string(root_kv)


if __name__ == "__main__":
    MainApp().run()

Example of incorrect code #2

from kivy.lang import Builder
from kivy.app import App
from kivymd.theming import ThemeManager

root_kv = """
BoxLayout:
    MDLabel:
        text: "Hello World"

    MDRaisedButton:
        text: "Click me!"
"""


class MainApp(App):
    theme_cls = ThemeManager()

    def build(self):
        self.root = Builder.load_string(root_kv)


if __name__ == "__main__":
    MainApp().run()

Code above will raise ValueError:

 Traceback (most recent call last):
   File "D:\Projects\my_project\main.py", line 23, in <module>
     MainApp().run()
   File "D:\Py\kivy-venv\lib\site-packages\kivy\app.py", line 829, in run
     root = self.build()
   File "D:\Projects\my_project\main.py", line 17, in build
     self.root = Builder.load_string(root_kv)
   File "D:\Py\kivy-venv\lib\site-packages\kivy\lang\builder.py", line 405, in load_string
     rule_children=rule_children)
   File "D:\Py\kivy-venv\lib\site-packages\kivy\lang\builder.py", line 654, in _apply_rule
     child = cls(__no_builder=True)
   File "D:\Py\kivy-venv\lib\site-packages\KivyMD\kivymd\uix\label.py", line 94, in __init__
     super().__init__(**kwargs)
   File "D:\Py\kivy-venv\lib\site-packages\KivyMD\kivymd\theming.py", line 378, in __init__
     "KivyMD: App object should be inherited from "
 ValueError: KivyMD: App object should be inherited from `kivymd.app.MDApp`. See https://github.com/HeaTTheatR/KivyMD/blob/master/README.md#api-breaking-changes

---

Correct code:

from kivy.lang import Builder
from kivymd.app import MDApp

root_kv = """
BoxLayout:
    MDLabel:
        text: "Hello World"

    MDRaisedButton:
        text: "Click me!"
"""


class MainApp(MDApp):
    def build(self):
        self.root = Builder.load_string(root_kv)


if __name__ == "__main__":
    MainApp().run()