Working on Android¶
This page gives details on accessing Android APIs and managing other interactions on Android.
If you want to store and retrieve data, you shouldn’t just save to the current directory, and not hardcode /sdcard/ or some other path either - it might differ per device.
Instead, the android module which you can add to your –requirements allows you to query the most commonly required paths:
from android.storage import app_storage_path settings_path = app_storage_path() from android.storage import primary_external_storage_path primary_ext_storage = primary_external_storage_path() from android.storage import secondary_external_storage_path secondary_ext_storage = secondary_external_storage_path()
app_storage_path() gives you Android’s so-called “internal storage” which is specific to your app and cannot seen by others or the user. It compares best to the AppData directory on Windows.
primary_external_storage_path() returns Android’s so-called “primary external storage”, often found at /sdcard/ and potentially accessible to any other app. It compares best to the Documents directory on Windows. Requires Permission.WRITE_EXTERNAL_STORAGE to read and write to.
secondary_external_storage_path() returns Android’s so-called “secondary external storage”, often found at /storage/External_SD/. It compares best to an external disk plugged to a Desktop PC, and can after a device restart become inaccessible if removed. Requires Permission.WRITE_EXTERNAL_STORAGE to read and write to.
Even if secondary_external_storage_path returns a path the external sd card may still not be present. Only non-empty contents or a successful write indicate that it is.
Read more on all the different storage types and what to use them for in the Android documentation:
A note on permissions¶
Only the internal storage is always accessible with no additional permissions. For both primary and secondary external storage, you need to obtain Permission.WRITE_EXTERNAL_STORAGE and the user may deny it. Also, if you get it, both forms of external storage may only allow your app to write to the common pre-existing folders like “Music”, “Documents”, and so on. (see the Android Docs linked above for details)
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:
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 explicitly in your code, use the android module:
from android import loadingscreen loadingscreen.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.
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.
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=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
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.