Pycon2011 android programming-using_python

Android Development
using Python

+
George Goh
10 June 2011
PyCon APAC
1
Friday, June 10, 2011

HP Labs Singapore

http://www.hpl.hp.com/singapore/

2

Agenda

• Android Programming (Java vs. Python)
• Python Examples / UI Examples
• A More Complex Example

3

Android Rocks!!!

4

Why Python?

5

Programming Android

6

Plus Python

7 http://www.blangy.com/Photos.html

A simple program

8

Simple Program in Java
package com.spodon.pycon;

import android.app.Activity;
import android.app.AlertDialog;
import android.content.DialogInterface;
import android.os.Bundle;
import android.widget.EditText;
import android.widget.Toast;

public class Demo extends Activity {

private EditText mEditText = null;

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);

AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setTitle("Hello!");
builder.setMessage("What is your name?");
mEditText = new EditText(this);
builder.setView(mEditText);

builder.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
Toast.makeText(Demo.this, "Cancelled", Toast.LENGTH_SHORT).show();
}
});

...
9

Simple Program in Python
import android

droid = android.Android()
name = droid.getInput("Hello!", "What is your name?")
droid.makeToast("Hello, %s" % name.result)

• Java program: 35 SLOC
• Equivalent Python program: 4 SLOC
10

Android module
import android


• Exposes android functionality via an
Android() object.
• Talks to a service called SL4A (Scripting
Layer for Android).

11

Invoking functionality
import android


Python Interpreter Android

functionality exposed
via RPC methods

android.py
SL4A

12

Scripting Layer for
Android (SL4A)

Search keyword: android-scripting
13

Scripting Layer for
Android (SL4A)

• Started in 2009 by Damon Kohler
• 20% time project at Google.
• Supports Python, Ruby, Perl, Lua, JavaScript,
BeanShell and more.

14

Users of SL4A

• Rockets
• SmallSat

15 http://www.ﬂickr.com/photos/jurvetson/

Users of SL4A
Cellbots - http://www.cellbots.com

16 http://www.ﬂickr.com/photos/motorbikematt/

SL4A Functionality
• ActivityResult • MediaRecorder
• Android • Phone
• ApplicationManager • Preferences
• BatteryManager • SensorManager
• Camera • Settings
• CommonIntents • Sms
• Contacts • SpeechRecognition
• Event • ToneGenerator
• EyesFree • WakeLock
• Location • Wiﬁ
• MediaPlayer • UI

17

Examples
Speech Recognition
import android

message = droid.recognizeSpeech("What is your command?")
droid.makeToast("You said: %s" % message.result)

18

Examples
Text-to-Speech
import android

droid.vibrate()
droid.ttsSpeak("Hello, this is android speaking!")

19

Examples
Web View

import android

message = droid.webViewShow("http://xkcd.com/353/")

20

Examples
SMS

import android

droid.smsSend(someNumber,"Let’s meet for drinks!")

21

Dealing with UI

22

UI

• WebView Frontend (HTML + Javascript)
• Python Backend
• Frontend talks to Backend using Events

23

Events

• eventPost(name, data)
• eventWaitFor(eventName, timeout)
• eventClearBuffer()
• eventPoll(number_of_events)
• eventWait()
24

example.py
Example
import android

droid.webViewShow("/sdcard/sl4a/scripts/html/example.html")

result = droid.eventWaitFor("EVENT_A").result[“data”]
self.droid.log("Received data from EVENT_A: " + result)

example.html
...
<script language= "javascript" type= "text/javascript">
var droid = new Android();
var date = new Date();

droid.eventPost("EVENT_A", "Page Loaded On " + date);
</script>
...
25

Before we move on...
• What was discussed so far
• Using the android.py module in Python
programs.

• android.py talks to SL4A, which exposes Android
functionality to clients.

• UI can be built using HTML+Javascript, and it
can talk to Python backend using SL4A events.

26

A more complete
example?

27

Control robots!

28 http://www.ﬂickr.com/photos/motorbikematt/

The Design
direction
control Arduino
Bluetooth
FWD
module Cellbots
LEFT STOP RIGHT ﬁrmware
BACK

analog
motor
control

29

The Design
Arduino
Bluetooth
module
Arduino
Cellbots
• Cellbots project for firmware
firmware • PDE files on Cellbots site

Android
•
FWD

LEFT STOP RIGHT HTML + Javascript for frontend UI

•
BACK

Python for backend, Cellbot control

• Bluetooth module required (Py4A project)

30

Cellbot Controller

• Looks for Cellbot devices via Bluetooth.
• Connects to a selected device and controls
its movement.
• Invokes WebView to display UI.
• Interacts with UI using SL4A events.
Code available at https://github.com/georgegoh/cellbot-controller
31

Connecting to the Device
cellbot.py
1. Display scan view
Start scan.html
2. even t(scanBluetooth) User clicks “Scan”
Scan for list of
nearby devices 3. event(bluetoothDevicesFound)
and post
UI shows devices list

luetoothDevice)
Connect to selected 4. event(connectB User selects device
device

32

Bluetooth scanning
def scan_bluetooth(self, arg):
""" Discover nearby Bluetooth devices and trigger an SL4A
event "bluetoothDevicesFound" with the list of devices
found.
"""
self.droid.log("Scanning bluetooth devices")
self.discovered_devices =
bluetooth.discover_devices(lookup_names=True)
self.droid.log("Devices found: " +
str(self.discovered_devices))
self.droid.eventPost("bluetoothDevicesFound",
json.dumps(self.discovered_devices))

33

Bluetooth connection

def connect_bluetooth_device(self, bd_addr):
""" Connect to a Bluetooth device specified by the bd_addr
address and display the control view for the device.
"""
service = bluetooth.find_service(uuid=CELLBOT_UUID,
address=bd_addr)[0]
self.socket = bluetooth.BluetoothSocket(bluetooth.RFCOMM)
self.socket.connect((service["host"], service["port"]))
self.droid.webViewShow(CONTROL_VIEW)

34

Controlling the Device
cellbot.py
1. Display control view
Start control.html
2. event(move) User clicks a
direction
Send direction
to connected
cellbot

35

Motion Control
def move(self, direction):
""" Move a connected Cellbot in one of the following directions:
f - Forward
b - Back
l - Left
r - Right
s - Stop
"""
if self.socket:
self.socket.send(direction + "n")

36

Frontend HTML/JS Control 1
<head>
  <title>Robot demo</title>
  <script type="text/javascript" src="./js/mootools.js"></script>
  <script language="javascript" type="text/javascript">
    var droid=new Android();

    function postToPython(data) {
      droid.eventPost("PYTHON", JSON.stringify(data));
    }

    function move(direction) {
      postToPython({action: "move", data: direction});
    }

    window.addEvent("domready", function() {
      $('bFwd').addEvent('click', function() { move("f"); });
      $('bLeft').addEvent('click', function() { move("l"); });
      $('bStop').addEvent('click', function() { move("s"); });
      $('bRight').addEvent('click', function() { move("r"); });
      $('bBack').addEvent('click', function() { move("b"); });
      $('bExit').addEvent('click', function() { postToPython
({action:"EXIT", data:""}); });
    });
  </script>
</head> 37

Frontend HTML/JS Control 2

<body>
  <table align=center>
    <tr>
      <td />
      <td align=center><button id="bFwd">FWD</button></td>
      <td />
    </tr>
    <tr>
      <td align=center><button id="bLeft">LEFT</button></td>
      <td align=center><button id="bStop">STOP</button></td>
      <td align=center><button id="bRight">RIGHT</button></td>
    </tr>
    <tr>
      <td />
      <td align=center><button id="bBack">BACK</button></td>
      <td />
    </tr>
  </table>
  <button id="bExit">EXIT</button>
</body>
38

Python for
Android (Py4A)

• Additional python modules added:
- Bluez, Twisted, Zope, pyEphem
• Current maintainers:
- Naranjo Manuel Francisco
- Robbie Matthews

39

References
• Scripting Layer for Android
http://code.google.com/p/android-scripting

• Python for Android
http://code.google.com/p/python-for-android

• In Love with a Droid
http://android-scripting.blogspot.com/

• Cellbots
http://www.cellbots.com

40

Acknowledgements

• Damon Kohler
• Robbie Matthews
• Colleagues @ HP Labs Singapore

41

?

42

Thank you
@georgegoh
https://github.com/georgegoh/
http://www.linkedin.com/in/georgegoh

43

ﬁn

44

Bonus/Misc Slides

45

Event loop
while action != "EXIT":
self.droid.log("Python: Waiting for event.")
event_data = self.droid.eventWaitFor("PYTHON").result["data"]
self.droid.log("Python: Event received. Processing...")

# unpack the event data and perform action(if available).
properties = json.loads(event_data)
self.droid.log("Result: " + str(properties))
action = properties["action"]
if action in self.handlers:
self.handlers[action](properties["data"])

46

Packaging your app
• Download the template project archive
• http://android-scripting.googlecode.com/hg/android/
script_for_android_template.zip

• Modify the following according to your project
• Import into Eclipse

• Refactor package name from com.dummy.fooforandroid to
your package name.

• Modify or put your script into the res/raw directory.

• http://code.google.com/p/android-scripting/wiki/SharingScripts

47

How SL4A works

• Android functionality is abstracted into
methods.
• These methods are grouped in subsystems
called ‘Facades’.
• A JSON-RPC server exposes the methods
contained in these Facades.

48

SL4A Architecture

Facade 0

.
Client functionality exposed
via RPC methods
FacadeManager .
.
JsonRpcServer
Facade N

49

Facades
• A facade represents a
collection of functionality RPCReceiver

• @Rpc annotation <<implements>>

exposes methods XYZFacade

• @RpcParameter, <<Rpc>> + doIt()

@RpcDefault,
@RpcOptional describe
method arguments.

50

Facades
public void dialogCreateInput(final String title, final String message, final String text)
throws InterruptedException {
dialogDismiss();
mDialogTask = new AlertDialogTask(title, message);
((AlertDialogTask) mDialogTask).setTextInput(text);
}

Common/src/com/googlecode/android_scripting/facade/ui/UIFacade.java
public class UiFacade extends RpcReceiver {
RpcReceiver is the abstract
[...] parent of all Facade classes

@Rpc(description = "Create a text input dialog.") @Rpc annotation to indicate
public void dialogCreateInput( method is exposed via RPC
@RpcParameter(name = "title", description = "title of the input box") @RpcDefault("Value") final String title,
@RpcParameter(name = "message", description = "message to display above the input box") @RpcDefault("Please
enter value:") final String message,
@RpcParameter(name = "defaultText", description = "text to insert into the input box") @RpcOptional final
String text)
throws InterruptedException { used in
@RpcParameter
dialogDismiss(); generating user-readable Default values can be
descriptions
mDialogTask = new AlertDialogTask(title, message); speciﬁed using the
((AlertDialogTask) mDialogTask).setTextInput(text); @RpcDefault annotation
}

[...]
}

51

Code details
For details, see:
• AndroidProxy
• FacadeManagerFactory
• FacadeManager
• FacadeConﬁguration
52

Facades

http://code.google.com/p/android-scripting/wiki/ApiReference

53

Remote Control

• Write programs using your computer keyboard and
monitor and control an Android device remotely.
• Start a SL4A server on your Android, export some
environment variables and import the “android.py”
module.
• http://bit.ly/startpy4a

54 http://xkcd.com/722/

SL4A Architecture

Language Interpreter Facade 0

.
functionality exposed
via RPC methods
FacadeManager .
Language .
speciﬁc
library JsonRpcServer
Facade N

55

What you need
• On your dev machine
• Android SDK
• Python 2.6
• On your Android
• Barcode Scanner

56

If you don’t have a
barcode scanner
1. Start the Android Market App.
2. Search for pub: “ZXing Team”
3. Install “Barcode Scanner”

57

So I’ve installed
SL4A and Py4A.

What’s next?

58

Install more...
• Py4A is not the Python environment.
• It is the manager for the Python
interpreter, extras, and scripts.
• Extras => libraries
• Scripts => sample python scripts to get you
started.

59

Install the env

• Start “Python for
Android”

• Click “Install”

60

Pycon2011 android programming-using_python

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