Android

Android has a great and extensive API to control devices, your application etc. Some parts of the Android API are directly accessible with Pyjnius but some of them require you to code in Java.

Note

Since Android 8.0 (Oreo) the maximum limit for the local references previously known as “local reference table overflow” after 512 refs has been lifted, therefore PyJNIus can create proper Java applications with a lot of local references. Android JNI tips

Get the DPI

The DisplayMetrics contains multiple fields that can return a lot of information about the device’s screen:

from jnius import autoclass
DisplayMetrics = autoclass('android.util.DisplayMetrics')
metrics = DisplayMetrics()
print('DPI', metrics.getDeviceDensity())

Note

To access nested classes, use $ e.g. autoclass(‘android.provider.MediaStore$Images$Media’).

Recording an audio file

By looking at the Audio Capture guide for Android, you can see the simple steps for recording an audio file. Let’s do it with Pyjnius:

from jnius import autoclass
from time import sleep

# get the needed Java classes
MediaRecorder = autoclass('android.media.MediaRecorder')
AudioSource = autoclass('android.media.MediaRecorder$AudioSource')
OutputFormat = autoclass('android.media.MediaRecorder$OutputFormat')
AudioEncoder = autoclass('android.media.MediaRecorder$AudioEncoder')

# create out recorder
mRecorder = MediaRecorder()
mRecorder.setAudioSource(AudioSource.MIC)
mRecorder.setOutputFormat(OutputFormat.THREE_GPP)
mRecorder.setOutputFile('/sdcard/testrecorder.3gp')
mRecorder.setAudioEncoder(AudioEncoder.AMR_NB)
mRecorder.prepare()

# record 5 seconds
mRecorder.start()
sleep(5)
mRecorder.stop()
mRecorder.release()

And tada, you’ll have a /sdcard/testrecorder.3gp file!

Playing an audio file

Following the previous section on how to record an audio file, you can read it using the Android Media Player too:

from jnius import autoclass
from time import sleep

# get the MediaPlayer java class
MediaPlayer = autoclass('android.media.MediaPlayer')

# create our player
mPlayer = MediaPlayer()
mPlayer.setDataSource('/sdcard/testrecorder.3gp')
mPlayer.prepare()

# play
print('duration:', mPlayer.getDuration())
mPlayer.start()
print('current position:', mPlayer.getCurrentPosition())
sleep(5)

# then after the play:
mPlayer.release()

Accessing the Activity

This example will show how to start a new Intent. Be careful: some Intents require you to setup parts in the AndroidManifest.xml and have some actions performed within your Activity. This is out of the scope of Pyjnius but we’ll show you what the best approach is for playing with it.

Using the Python-for-android project, you can access the default PythonActivity. Let’s look at an example that demonstrates the Intent.ACTION_VIEW:

from jnius import cast
from jnius import autoclass

# import the needed Java class
PythonActivity = autoclass('org.kivy.android.PythonActivity')
Intent = autoclass('android.content.Intent')
Uri = autoclass('android.net.Uri')

# create the intent
intent = Intent()
intent.setAction(Intent.ACTION_VIEW)
intent.setData(Uri.parse('http://kivy.org'))

# PythonActivity.mActivity is the instance of the current Activity
# BUT, startActivity is a method from the Activity class, not from our
# PythonActivity.
# We need to cast our class into an activity and use it
currentActivity = cast('android.app.Activity', PythonActivity.mActivity)
currentActivity.startActivity(intent)

# The website will open.

Accelerometer access

The accelerometer is a good example that shows how to write a little Java code that you can access later with Pyjnius.

The SensorManager lets you access the device’s sensors. To use it, you need to register a SensorEventListener and overload 2 abstract methods: onAccuracyChanged and onSensorChanged.

Open your python-for-android distribution, go in the src directory, and create a file org/myapp/Hardware.java. In this file, you will create everything needed for accessing the accelerometer:

package org.myapp;

import org.kivy.android.PythonActivity;
import android.content.Context;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;

public class Hardware {

    // Contain the last event we got from the listener
    static public SensorEvent lastEvent = null;

    // Define a new listener
    static class AccelListener implements SensorEventListener {
        public void onSensorChanged(SensorEvent ev) {
            lastEvent = ev;
        }
        public void onAccuracyChanged(Sensor sensor , int accuracy) {
        }
    }

    // Create our listener
    static AccelListener accelListener = new AccelListener();

    // Method to activate/deactivate the accelerometer service and listener
    static void accelerometerEnable(boolean enable) {
        Context context = (Context) PythonActivity.mActivity;
        SensorManager sm = (SensorManager) context.getSystemService(Context.SENSOR_SERVICE);
        Sensor accel = sm.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);

        if (accel == null)
            return;

        if (enable)
            sm.registerListener(accelListener, accel, SensorManager.SENSOR_DELAY_GAME);
        else
            sm.unregisterListener(accelListener, accel);
    }
}

So we created one method named accelerometerEnable to activate/deactivate the listener. And we saved the last event received in Hardware.lastEvent. Now you can use it in Pyjnius:

from time import sleep
from jnius import autoclass

Hardware = autoclass('org.myapp.Hardware')

# activate the accelerometer
Hardware.accelerometerEnable(True)

# read it
for i in xrange(20):

    # read the last event
    lastEvent = Hardware.lastEvent

    # we might not get any events.
    if not lastEvent:
        continue

    # show the current values!
    print(lastEvent.values)

    sleep(.1)

# don't forget to deactivate it
Hardware.accelerometerEnable(False)

You’ll obtain something like this:

[-0.0095768067985773087, 9.4235782623291016, 2.2122423648834229]
...

Using TextToSpeech

Same as the audio capture, by looking at the An introduction to Text-To-Speech in Android blog post, it’s easy to do it with Pyjnius:

from jnius import autoclass
Locale = autoclass('java.util.Locale')
PythonActivity = autoclass('org.kivy.android.PythonActivity')
TextToSpeech = autoclass('android.speech.tts.TextToSpeech')
tts = TextToSpeech(PythonActivity.mActivity, None)

# Play something in english
tts.setLanguage(Locale.US)
tts.speak('Hello World.', TextToSpeech.QUEUE_FLUSH, None)

# Queue something in french
tts.setLanguage(Locale.FRANCE)
tts.speak('Bonjour tout le monde.', TextToSpeech.QUEUE_ADD, None)