Mobile ComputingIntents, Intent-Filters

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Lecture#06

Lecture Contents

IntentsIntent-FiltersLinkifyInent-ResolutionResponding to Intents

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Intents

Message passing mechanism used within application or among applications:

Majorly used for1. Declare your intention to start an

activity / service with some piece of data2. Broadcast that an event has occurred3. Explicitly start an activity / service

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Full Device as Interconnected System

Enhance interaction among applications on a device One application can register for any global

event e.g. incoming call, sms received, sms sent, internet connection status changed etc

Any application registered for a global event can respond to event without caring ‘where’ that event occurred within the system

Intents can broadcast message among system’s applications (event driven system can be created)

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Start ActivityIntent open = new Intent(MyActivity.this,

OtherActivity.class);startActivity(open);

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1. No connection among newly opened activity and current activity

2. For feedback from newly opened activity one should use startActivityForResult(Inent) method instead

Implicit IntentAn activity can announce that some event has

occurred and some component should respond to this event (mentioning some data for said purpose)

No need to explicitly mention which component (activity/service) should respond to this event

Examples:a) Call to given number

i. Intent intent = new Intent(Intent.ACTION_DIAL, Uri.parse("tel:555-2368"));

b) Open given URL in web browseri. Intent viewIntent = new

Intent("android.intent.action.VIEW", Uri.parse("http://www.google.com"));

c) Send SMS to provided number

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Sub Activity & ResultsUri uri = Uri.parse("content://contacts/people");Intent intent = new Intent(Intent.ACTION_PICK, uri);startActivityForResult(intent, PICK_CONTACT_SUBACTIVITY);

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Bundle stats = new Bundle();stats.putString(“channel",“Banking"");stats.putString(“level”, “high");stats.putString(“code", “success");setResult(0, Activity.RESULT_OK, stats);finish();

Start Implicit for ResultUri uri = Uri.parse("content://contacts/people");//Uri for phone contacts

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startActivityForResult(intent, PICK_CONTACT_SUBACTIVITY);

//Starting activity and waiting for result

Intent intent = new Intent(Intent.ACTION_PICK, uri);//Intent just mentioning the action

Native Android ActionsACTION_ANSWER

Handles incoming call

ACTION_CALL Calls through default dialer

ACTION_DELETE Lets you delete the content

ACTION_DIAL Opens default dialer with number

ACTION_EDIT Let you edit the data

ACTION_PICKLets you pick the item

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LinkifyAutomatic linking of special data with applicationsTextView textView = …….;Linkify.addLinks(textView, Linkify.WEB_URLS);

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Other data types:::1. Linkify.EMAIL_ADDRESSES2. Linkify.WEB_URLS3. Linkify.MAP_ADDRESSES4. Linkify.PHONE_NUMBERS5. Linkify.ALL

Linkify & XML<TextViewAndroid:layout_width=“fill_parent”Android:layout_height=“fill_parent”Android:text=“@string/linkify_string”Android:autoLink=“phone|email”/>

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Intent FilterAn intent is an expression of interest for an

action to be performed (a request for something to be happened)

Intent-Filter is an expression of interest for response against some event or to handle some data-type

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Intent-Filter

Using intent-filter an application tells android that it can serve against particular applications coming from

1. Same application2. Native phone applications3. Third party applications

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Manifest/intent-filter<intent-filter><action android:name="android.intent.action.MAIN" /><category

android:name="android.intent.category.LAUNCHER" /></intent-filter>

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Action::::1. Describes what action needs to be served. 2. android:name to describe name of action3. Preferably use java package naming conventionsCategory::::4. Describes under what circumstances action should be

served5. Each intent-filter can describe multiple category tags6. One can specify his own category values7. Using predefined category values is also possible

Manifest/intent-filter

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Data:::::One can specify type of data your application can handle toMultiple data types for one application is also possibleList of supported data types

1. android:host (valid host name e.g. com.google)2. android:mimetype (<type

android:value=“vnd.android.Cursor.dir/*”/>)3. android:path (valid path)4. android:port (valid port for specified host)5. android:scheme (requires particular scheme http:// or

content://)

Intent-Filter

<activity><intent-filter>

      <action />                <category />                <data />       </intent-filter>       <meta-data />

</activity>

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Broader PictureRelationship among terms (Intent, Intent-

Filter, Broadcast ReceiverIntent is a wish that a job is to be done,

Intent-Filter is registration of an Activity for a particular data type or even for some global event (A class registering for contacts handling, A class responding to sms received).

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Intent-Resolution

Process of deciding which action to performed against some event is called intent resolution. In case of implicit intents it is very important to understand how android resolves intents…..

Rules for intent resolution1. All intent-filters from installed packages are

kept together2. Intnet-filters with non-match action/category

for intent to be resolved are removed from list3. Each part of intent’s data uri is matched with

intent-filter’s data tag

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Intent-Resolution

4. If more than one intent-filters are matched then highest priority value intent-filter serves the task

5. If still conflict exists then user may be given option to choose the application to be served for that task

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Response for Intent-Filter Match

When application/activity starts through an implicit intent, it needs to find out action (what to do) and data upon which action is to be appliedpublic void onCreate(Bundle bundle){super.onCreate(bundle);setContentView(R.layout.main);Intent intent = getIntent();String action = intent.getAction();Uri data = intent.getData();…….. //// Action to be done}

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Passing on Responsibilitypublic void onCreate(Bundle bundle){

super.onCreate(bundle);setContentView(R.layout.main);Intent intent = getIntent();if(TODAY IS SATURDAY OR SUNDAY){startNextMatchingActivity(intent);}

}

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