1 mobile software development framework: android inter- thread, process communications 10/11/2012 y....

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Mobile Software Development Framework:

Android Inter-Thread, Process Communications

10/11/2012

Y. Richard Yang

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Outline

Admin Android

Basic concepts• Activity, View, External Resources, Listener

Inter-thread communications• Handler, ASyncTask

Inter-process communications• Intent, Broadcast, BroadcastReceiver, Service

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Admin.

HW2 Due: Friday @ 11:55 pm

Recap: Mobile GUI App Workflow

App

App lifecycle callbacks/custom-start-pause-…

DisplayComposite

Display

DisplayComposite

Display

Display

DisplayComposite

Display

Display

Data/Model

Data/Model

Event Handler

Event Handler

DisplayComposite

DisplayDisplayComposite

Display Display

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Recap: Android UI App Basic Concepts

Activity

View/ViewGroup External definition of views in XML findViewById() to reduce coupling

Link view events to event handlers set…Listener()

Example: TipCalc

Set listener:

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Example: TipCalc Event HandlerHandler:

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Event Handler Execution

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Event handler executed by the main/UI thread

UI events

systemevents

message

message

message

Looper UI (main) thread

http://www.java2s.com/Open-Source/Android/android-core/platform-frameworks-base/android/os/Looper.java.htm

Event Handler and Responsiveness

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Event handler blocks events in the msg queue from being processed=>slow running handler leads to no UI response

http://developer.android.com/guide/practices/responsiveness.html

UI events

systemevents

message

message

message

Looper UI (main) thread

Responsiveness: Numbers (Nexus One) ~5-25 ms – uncached flash reading a byte ~5-200+(!) ms – uncached flash writing

tiny amount 100-200 ms – human perception of slow

action 108/350/500/800 ms – ping over 3G.

varies! ~1-6+ seconds – TCP setup + HTTP fetch

of 6k over 3G

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Event Handler and ANR

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Android system detects no response Main thread

(“event”/UI) does not respond to input in 5 sec

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Example

play_music

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Discussion

What are some design options if an event may take a while to be processed Time consuming loading process, e.g., slow

onCreate Heavy computation, e.g., voice recognition,

update map display Networking access …

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Typical Design Guidelines

Notify user E.g., progress bar, progress dialog A splash screen

If possible, non-blocking, incremental update UI E.g., gradual add items to map

Whenever possible, release UI thread ASAP Keep event handler simple Post heavy processing off the UI thread

Example: Background Thread

Use a background thread to do the task Background thread behavior controlled by

state State controlled by event handler

See PlayMusic

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Service: Working in Background A basic function of Android Service:

A facility for an application to tell the system about something it wants to be doing in the background (even when the user is not directly interacting with the application).

The system to schedule work for the service, to be run until the service or someone else explicitly stop it.

NO GUI, higher priority than inactive Activities Note

A Service is not a separate process. The Service object itself does not imply it is running in its own process; unless otherwise specified, it runs in the same process as the application it is part of.

A Service is not a thread. It is not a means itself to do work off of the main thread (to avoid Application Not Responding errors).

Background Thread vs UI Thread

Problem: Background thread and UI thread are running

concurrently and may have race conditions if they modify UI simultaneously (e.g., UI switches to a different orientation)

A major sin of programming: concurrency bugs

Example: LoadingScreen

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Example: LoadingScreen

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public class LoadingScreen extends Activity implements Runnable {

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

// start a new thread to load Thread thread = new Thread(this); thread.start(); }

public void run(){ longRunningTask(); setContentView(R.layout.main); }

…}

Solution

Background thread does not directly modify UI: send msg to UI thread, who processes the msg

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Android Handler

Android’s mechanism to send and process Message and Runnable objects associated with a thread's MessageQueue.

Each Handler instance is associated with a single thread and that thread's message queue

A handler is bound to the thread / message queue of the thread that creates it

from that point on, it will deliver messages and runnables to that message queue

That thread processes msgs20

Android Handler

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Using Handler: Examples

There are two main uses for a Handler

to schedule messages and runnables to be executed as some point in the future

• postDelayed(Runnable, delayMillis)

to enqueue an action to be performed on a different thread than your own.

• post(Runnable)

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Handler

public class MyActivity extends Activity {

    [ . . . ]    // Need handler for callbacks to the UI thread    final Handler mHandler = new Handler();

    // Create runnable task to give to UI thread    final Runnable mUpdateResultsTask = new Runnable() {        public void run() {            updateResultsInUi();        }    };

    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);

        [ . . . ]    }

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Handler

    protected void startLongRunningOperation() {

        // Fire off a thread to do some work that we shouldn't do directly in the UI thread        Thread t = new Thread() {            public void run() {                mResults = doSomethingExpensive();                mHandler.post(mUpdateResultsTask);            }        };        t.start();    }

    private void updateResultsInUi() {

        // Back in the UI thread -- update our UI elements based on the data in mResults        [ . . . ]    }}

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Example: Fixing LoadingScreen

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Example: BackgroundTimer

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Common Pattern

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AsyncTask as Abstraction

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private class DownloadFilesTask extends AsyncTask<URL, Integer, Long> { protected Long doInBackground(URL... urls) { // on some background thread int count = urls.length; long totalSize = 0; for (int i = 0; i < count; i++) { totalSize += Downloader.downloadFile(urls[i]); publishProgress((int) ((i / (float) count) * 100)); } return totalSize; } protected void onProgressUpdate(Integer... progress) { // on UI thread! setProgressPercent(progress[0]); } protected void onPostExecute(Long result) { // on UI thread! showDialog("Downloaded " + result + " bytes"); }}

new DownloadFilesTask().execute(url1, url2, url3); // call from UI thread!

See GoogleSearch

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Outline

Admin Android

Basic concepts• Activity, View, External Resources, Listener

Inter-thread communications• Handler, ASyncTask

Inter-process communications• Intent, Broadcast, BroadcastReceiver, Service

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Inter-Process Communications (IPC)

Inter-thread communications are for one activity

Inter-process communication is designed to promote the development of complex applications, by allowing developers to reuse existing data and services from other applications.

One may also use IPC for intra-app communications (e.g., between Activities of the same app)

Discussion: IPC Use Cases

One component of Android sends messages to another component of Android

An IPC message in Android is called Intent

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Component Component

Target: Activity

startActivity() or startActivityForResult() to launch an activity or get an existing activity to do something new.

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Component Activity

Target: Service

startService() to initiate a service or deliver new instructions to an ongoing service.

bindService() to establish a connection between the calling component and a target service. It can optionally initiate the service if it's not already running.

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Component Service

Target: BroadcastReceiver

broadcastIntent()to send messages to all interested broadcast receivers. Many kinds of broadcasts originate in system code,

e.g., boot, battery low

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Component BroadcastReceiver

Target: Data Provider

startActivityForResult()may target to a data provider (e.g., Contacts)

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Component Data Provider

Example: A SocialApp

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Android Application Component: Gang of Four

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Outline

Admin Android

Basic concepts• Activity, View, External Resources, Listener

Inter-thread communications• Handler, ASyncTask

Inter-process communications• Intent

Application and Component Glues: Intent

Intent An intent is an abstract description of an

operation to be performed.• Indicate operations from your own or others

http://developer.android.com/reference/android/content/Intent.html

Component Component

Intent Data Structure Primary pieces of info in an Intent

Action: The general action to be performed• ACTION_VIEW, ACTION_DIAL, ACTION_EDIT, …• Your own definition of strings

Data: a URI• tel:123• content://contacts/people/1• http://zoo.cs.yale.edu/classes/cs434• hotel://name/Omni_New_Haven

Other attributes Category Type (MIME type) Component (class name) Extras (key-value store)

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scheme

host path

Intent Resolution: Explicit Intent Explicit Intent: specifies the exact class to run

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class name

Context

Explicit Intent and Manifest

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Make sure AndroidManifest.xml announces activities to be started

<application android:icon="@drawable/icon” android:label="@string/app_name" > <activity android:name=".IntentController” android:label="IntentController" > <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity>

<activity android:name=".TipCal android:label="TipCal" > </activity>

Shown in Launcher

Announce class

See IntentController

Explicit Intent

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YelpMapApp

Name: MapActivity

To: MapActivity

Only the specified destination receives this message

Intent Resolution: Implicit Intent

Intent does not specify exact class to run Info in the Intent used by the system to

determine the best component, at run time, to handle the intent

Matching based on Intent Filter Register Activities, Services, and Broadcast

Receivers register Intent Filter to indicate as being capable of performing an action on a particular kind of data

Q: benefit of dynamic binding?45http://developer.android.com/guide/topics/intents/intents-filters.html

Implicit Intents

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Yelp

ClockApp

MapApp

Handles Action: VIEW

Handles Action: DISPLAYTIME

Implicit IntentAction: VIEW

Implicit Intents

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Yelp

BrowserApp

MapApp

Handles Action: VIEW

Handles Action: VIEW

Implicit IntentAction: VIEW

Intent Filter

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action

category

data

Intent Resolution: Implicit Intent

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data

action

See IntentController

Implicit Intent and Manifest

AndroidManifest.xml file for com.android.browser

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String action = "android.intent.action.VIEW";Uri data = Uri.parse("http://www.google.com");Intent myIntent = new Intent(action, data);startActivity(myIntent);

<intent-filter>    <action android:name="android.intent.action.VIEW" />    <category android:name="android.intent.category.DEFAULT" />    <scheme android:name="http" />    <scheme android:name="https" />    <scheme android:name="file" /></intent-filter>

A Design Template: Invoker

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String action = “com.hotelapp.ACTION_BOOK";String hotel = “hotel://name/“ + selectedHotel;Uri data = Uri.parse(hotel);Intent bookingIntent = new Intent(action, data);startActivityForResults(bookingIntent, requestCode);

A Design Template: Provider

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<activity android:name=".Booking" android:label=“Booking"> <intent-filter> <action android:name=“com.hotelapp.ACTION_BOOK" /> <data android:scheme=“hotel" android:host=“name”/> </intent-filter></activity>

A Design Template: Provider

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

Intent intent = getIntent(); // why am I called String action = intent.getAction(); Uri data = intent.getdata();

String hotelName = data.getPath(); // do the booking

setResult(RESULT_OK); finish();}

Intent and Broadcast: Sender

String action = "edu.yale.cs434.RUN";

Intent cs434BroadcastIntent = new Intent(action);

cs434BroadcastIntent.putExtra("message", "Wake up.");

sendBroadcast(cs434BroadcastIntent);

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Example: IntentLaunch

Intent and Broadcast: Receiver

<receiver android:name=".CS434BroadcastReceiver" android:enabled="true">

<intent-filter>

<action android:name="edu.yale.cs434.RUN" />

</intent-filter>

</receiver>

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Intent, Broadcast, Receiver, Notificationpublic class CS434BroadcastReceiver extends BroadcastReceiver {

public static final String CUSTOM_INTENT = "edu.yale.cs434.RUN";

// Display an alert that we've received a message.

@Override

public void onReceive(Context context, Intent intent) {

if (intent.getAction().equals(CUSTOM_INTENT)) {

String message = (String)intent.getExtras().get("message");

CharSequence text = "Got intent " + CUSTOM_INTENT + " with " + message;

int duration = Toast.LENGTH_SHORT;

Toast mToast = Toast.makeText(context, text, duration);

mToast.show();

} // end of if

} // end of onReceive

}

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Android: Content Provider

Each provider can expose its data as a simple table on a database model

Each content provider exposes a public URI that uniquely identifies its data set:

android.provider.Contacts.Phones.CONTENT_URI android.provider.Contacts.Photos.CONTENT_URI android.provider.CallLog.Calls.CONTENT_URI android.provider.Calendar.CONTENT_URI

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Intent and Content Provider private void pickContact() {

    // Create an intent to "pick" a contact, as defined by the content provider URI    Intent intent = new Intent(Intent.ACTION_PICK, Contacts.CONTENT_URI);    startActivityForResult(intent, PICK_CONTACT_REQUEST);}

@Overrideprotected void onActivityResult(int requestCode, int resultCode, Intent data) {    // If the request went well (OK) and the request was PICK_CONTACT_REQUEST    if (resultCode == Activity.RESULT_OK && requestCode == PICK_CONTACT_REQUEST) {        // Perform a query to the contact's content provider for the contact's name        Cursor cursor = getContentResolver().query(data.getData(),        new String[] {Contacts.DISPLAY_NAME}, null, null, null);        if (cursor.moveToFirst()) { // True if the cursor is not empty            int columnIndex = cursor.getColumnIndex(Contacts.DISPLAY_NAME);            String name = cursor.getString(columnIndex);            // Do something with the selected contact's name...        }    }}

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