Working on Android

This page gives details on accessing Android APIs and managing other interactions on Android.

Runtime permissions

With API level >= 21, you will need to request runtime permissions to access the SD card, the camera, and other things.

This can be done through the android module which is available per default unless you blacklist it. Use it in your app like this:

from android.permissions import request_permissions, Permission
request_permissions([Permission.WRITE_EXTERNAL_STORAGE])

The available permissions are listed here:

https://developer.android.com/reference/android/Manifest.permission

Other common tasks

Dismissing the splash screen

With the SDL2 bootstrap, the app’s splash screen may be visible longer than necessary (with your app already being loaded) due to a limitation with the way we check if the app has properly started. In this case, the splash screen overlaps the app gui for a short time.

To dismiss the loading screen explicitely in your code, use the android module:

from android import hide_loading_screen
hide_loading_screen()

You can call it e.g. using kivy.clock.Clock.schedule_once to run it in the first active frame of your app, or use the app build method.

Handling the back button

Android phones always have a back button, which users expect to perform an appropriate in-app function. If you do not handle it, Kivy apps will actually shut down and appear to have crashed.

In SDL2 bootstraps, the back button appears as the escape key (keycode 27, codepoint 270). You can handle this key to perform actions when it is pressed.

For instance, in your App class in Kivy:

from kivy.core.window import Window

class YourApp(App):

   def build(self):
      Window.bind(on_keyboard=self.key_input)
      return Widget() # your root widget here as normal

   def key_input(self, window, key, scancode, codepoint, modifier):
      if key == 27:
         return True  # override the default behaviour
      else:           # the key now does nothing
         return False

Pausing the App

When the user leaves an App, it is automatically paused by Android, although it gets a few seconds to store data etc. if necessary. Once paused, there is no guarantee that your app will run again.

With Kivy, add an on_pause method to your App class, which returns True:

def on_pause(self):
    return True

With the webview bootstrap, pausing should work automatically.

Under SDL2, you can handle the appropriate events (see SDL_APP_WILLENTERBACKGROUND etc.).

Advanced Android API use

android for Android API access

As mentioned above, the android Python module provides a simple wrapper around many native Android APIS, and it is included by default unless you blacklist it.

The available functionality of this module is not separately documented. You can read the source on Github.

Also please note you can replicate most functionality without it using pyjnius. (see below)

Plyer - a more comprehensive API wrapper

Plyer provides a more thorough wrapper than android for a much larger area of platform-specific APIs, supporting not only Android but also iOS and desktop operating systems. (Though plyer is a work in progress and not all platforms support all Plyer calls yet)

Plyer does not support all APIs yet, but you can always use Pyjnius to call anything that is currently missing.

You can include Plyer in your APKs by adding the Plyer recipe to your build requirements, e.g. --requirements=plyer.

You should check the Plyer documentation for details of all supported facades (platform APIs), but as an example the following is how you would achieve vibration as described in the Pyjnius section above:

from plyer.vibrator import vibrate
vibrate(10)  # in Plyer, the argument is in seconds

This is obviously much less verbose than with Pyjnius!

Pyjnius - raw lowlevel API access

Pyjnius lets you call the Android API directly from Python Pyjnius is works by dynamically wrapping Java classes, so you don’t have to wait for any particular feature to be pre-supported.

This is particularly useful when android and plyer don’t already provide a convenient access to the API, or you need more control.

You can include Pyjnius in your APKs by adding pyjnius to your build requirements, e.g. --requirements=flask,pyjnius. It is automatically included in any APK containing Kivy, in which case you don’t need to specify it manually.

The basic mechanism of Pyjnius is the autoclass command, which wraps a Java class. For instance, here is the code to vibrate your device:

from jnius import autoclass

# We need a reference to the Java activity running the current
# application, this reference is stored automatically by
# Kivy's PythonActivity bootstrap

# This one works with SDL2
PythonActivity = autoclass('org.kivy.android.PythonActivity')

activity = PythonActivity.mActivity

Context = autoclass('android.content.Context')
vibrator = activity.getSystemService(Context.VIBRATOR_SERVICE)

vibrator.vibrate(10000)  # the argument is in milliseconds

Things to note here are:

  • The class that must be wrapped depends on the bootstrap. This is because Pyjnius is using the bootstrap’s java source code to get a reference to the current activity, which the bootstraps store in the mActivity static variable. This difference isn’t always important, but it’s important to know about.
  • The code closely follows the Java API - this is exactly the same set of function calls that you’d use to achieve the same thing from Java code.
  • This is quite verbose - it’s a lot of lines to achieve a simple vibration!

These emphasise both the advantages and disadvantage of Pyjnius; you can achieve just about any API call with it (though the syntax is sometimes a little more involved, particularly if making Java classes from Python code), but it’s not Pythonic and it’s not short. These are problems that Plyer, explained below, attempts to address.

You can check the Pyjnius documentation for further details.