Accessing Android APIs¶
When writing an Android application you may want to access the normal Android APIs, which are available in Java. It is by calling these that you would normally accomplish everything from vibration, to opening other applications, to accessing sensor data, to controlling settings like screen orientation and wakelocks.
These APIs can be accessed from Python to perform all of these tasks and many more. This is made possible by the Pyjnius module, a Python library for automatically wrapping Java and making it callable from Python code. This is fairly simple to use, though not very Pythonic and inherits Java’s verbosity. For this reason the Kivy organisation also created Plyer, which further wraps specific APIs in a Pythonic and cross-platform way - so in fact you can call the same code in Python but have it do the right thing also on platforms other than Android.
These are both independent projects whose documentation is linked above, and you can check this to learn about all the things they can do. The following sections give some simple introductory examples, along with explanation of how to include these modules in your APKs.
Pyjnius lets you call the Android API directly from Python; this let’s you do almost everything you can (and probably would) do in a Java app. Pyjnius is works by dynamically wrapping Java classes, so you don’t have to wait for any particular feature to be pre-supported.
You can include Pyjnius in your APKs by adding the pyjnius or pyjniussdl2 recipes to your build requirements (the former works with Pygame/SDL1, the latter with SDL2, the need to make this choice will be removed later when pyjnius internally supports multiple Android backends). 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 Pygame # PythonActivity = autoclass('org.renpy.android.PythonActivity') # 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 both the Pygame and SDL2
bootstraps store in the
mActivitystatic 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.
Plyer aims to provide a much less verbose, Pythonic wrapper to platform-specific APIs. Android is a supported platform, but it also supports iOS and desktop operating systems, with the idea that the same Plyer code would do the right thing on any of them, though Plyer is a work in progress and not all platforms support all Plyer calls yet. This is the disadvantage of Plyer, it does not support all APIs yet, but you can always Pyjnius to call anything that is currently missing.
You can include Plyer in your APKs by adding the Plyer recipe to your build requirements. It is not included automatically.
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!
At the time of writing, the Plyer recipe is not yet ported, and Plyer doesn’t support SDL2. These issues will be fixed soon.