Ch 6: Intents and Broadcast Receivers

Question 1

Definition:

Intent

Answer 1

Intent

A message passing mechanism that can be used within an application, between applications, between the system and an application.

Intents are a fundamental part of the Android OS and are unique to Android.

Question 2

Common Uses for Intents

Answer 2

• Explicitly start a particular Service, Broadcast Receiver, Activity or sub-Activity using its class name
• Start an Activity, sub-Activity or Service to perform an action with(or on) a particular piece of data
• Return information from a sub-Activity
• Broadcast that an event has occurred

Question 3

Starting Activities

Explicitly

vs

Implicitly

Answer 3

• An Activity is started Explicitly using an Intent that specifies the name of the Activity class
  
  • The Activity class must be within the calling application
• An Activity is started Implicitly when an Intent requests that a specific action be performed on a piece of data
  
  • Android will dynamically choose an Activity or Service through the process of “Intent Resolution”

Question 4

Explicitly Starting New Activities:

Steps

Answer 4

1. Construct an Intent, specifying the current activity as context and the class of the Activity to be started
   
   • Intent intent = new Intent( MyActivity.this, MyOtherActivity.class)​
   • 2. Use the “startActivity()” method, with the Intent as a parameter, to submit a request to create, start and resume the Activity
   • startActivity( intent )

Question 5

Explicitly Starting New Activities:

How the Activity is Managed on the Activity Stack

Answer 5

• After “startActivity()” is called, the new Activity is created, started and resumed
  
  • It is placed on top of the Activity stack
• Calling “finish()” on the new Activity, or pressing the hardware back button will close the Activity and remove it from the stack
• It may also navigate to other Activities using “startActivity()”
• Each call to “startActivity()” will create a new Instance of the Activity and add it to the stack
• If an Activity is closed without a call to finish, it might remain in the Activity Stack
• Multiple instances of the same Activity can exist in the Activity stack

Question 6

Implicit Intent:

Definition

Answer 6

Implicit Intent

Used to ask the system to find and start an Activity that can perform a particular action, without you knowing exactly which application, or Activity, will be started.

Question 7

Implicit Intent:

Constructing the Intent

Answer 7

• Uses an different constructor for Intent
  
  • new Intent( Action , URI )
• Specify an Action
  
  • There are several predefined Actions in the Intent class, ( Intent.ACTION_* )
• Specify the URI of the data on which the action should be performed
• After construction, may add additional primitive values to the Intent, called “Extras”
  
  • Use the “putExtra()” method
  • intent.putExtra(“STRING_EXTRA”, “My String”);

Question 8

What is

“intent resolution” ?

Answer 8

When an Intent specifies a particular action to perform, rather than an Activity,

the run time will dynamically choose an Activity that is able to perform that action.

• This allows an app to use Activities from other applications, such as the dialer
• Some Activities have “Intent Filters” that help determine the Intent Resolution

Question 9

How to recieve feedback/results

from launching a sub-activity

Answer 9

• Start the activity by passing the Intent to “startActivityForResult()” instead of “startActivity()”
• StartActivity does not provide any feedback

Question 10

What are Broadcast Intents?

Answer 10

Intents that are used to broadcast messages across the system.

Applications can register Broadcast Receivers to listen for, and react to, the broadcast intents.

This enables event-driven applications.

The Android system uses Broadcast Intents to announce system events, such as changes in Internet Connectivity or Battery Level

Question 11

Implicit Intents:

Extras

Answer 11

Extras

• A mechanism used to attach primitive values to an Intent
• Can use the overloaded “putExtra()” method on any Intent to attach a name-value pair
• Extras are stored within the Intent as Bundle objects
• Extract values from the bundle using the get[type]extra( name ) method

Question 12

How to check at run time

if an Intent will be resolved?

Answer 12

• Use PackageManager to query which, if any, Activity would be launched:
• Get the Package Manager:
  
  • PackageManager pm = getPackageManager();
• Pass it to the “resolveActivity()” method of the Intent Instance, which will return a ComponentName object
  
  • ComponentName cn = intent.resolveActivity(pm)
• It will return null if no Activity is found
• This should be checked before passing the Intent to StartActivity()

Question 13

Using a Sub-Activity:

Steps

Answer 13

• Launch:
  
  • startActivityForResult( Intent , RequestCode)
• Preparing to Return:
  
  • call setResult( ResultCode, ResultData)
  • Call finish() to indicate that the sub-activity has completed
• Handle Results:
  
  • onActivityResult() handler is triggered, with parameters:
  • Request Code, Result Code, Data

Question 14

Sub-Activities:

Important Methods and Parameters

Answer 14

Methods

• startActivityForResult()
• setResult()
• finish()
• onActivityResult() - event handler
• intent.resolveActivity()

Parameters/Values

• Request Code
• Result Code
• Data

Question 15

Platform-Native Actions:

What are they?

Answer 15

A set of common Actions on the Android platform.

The Intent class has a set of static string constants used to represent the actions, these can be used when creating Implicit Intents to start Activities and sub-Activities.

• Example: ACTION_DIAL brings up the phone dialer Activity

Question 16

Platform-Native Actions:

List of Common Action strings

defined in the Intent class

(10)

Answer 16

*Note: this is NOT comprehensive

• ACTION_DELETE
• ACTION_EDIT
• ACTION_INSERT
• ACTION_DIAL
• ACTION_PICK
• ACTION_SEARCH
• ACTION_SENDTO
• ACTION_SEND
• ACTION_VIEW
• ACTION_WEB_SEARCH

Question 17

Platform-Native Actions:

ACTION_DELETE

Answer 17

Starts an Activity that lets you delete the data specified at the Intent’s data URI

Question 18

Platform-Native Actions:

ACTION_DIAL

Answer 18

Brings up a dialer application.

With the number to dial pre-populated from the Intent’s data URI.

• By default this is handled by the native Android phone dialer

Question 19

Platform-Native Actions:

ACTION_EDIT

Answer 19

Requests an Activity that can edit the data at the Intent’s data URI

Question 20

Platform-Native Actions:

ACTION_INSERT

Answer 20

Opens an Activity capable of inserting new items into the Cursor specified in the Intent’s data URI

When called as a sub-Activity, it should return a URI to the newly inserted item.

Question 21

Platform-Native Actions:

ACTION_PICK

Answer 21

Launches a sub-Activity that lets you pick an item from the Content Provider specified by the Intent’s data URI.

When closed, it should return a URI to the item that was picked.

The Activity launched depends on the data being picked.

Ex:

content://contacts/people will invoke the native contacts list

Question 22

Platform-Native Actions:

ACTION_SEARCH

Answer 22

Typically used to launch a specific search Activity.

When it’s fired without a specific Activity, the user will be prompted to select from all applications that support search.

Supply the search term as a string in the Intent’s extras, using “SearchManager.QUERY” as the key.

Question 23

Platform-Native Actions:

ACTION_SENDTO

Answer 23

Launches an Activity to send data to the contact specified by the Intent’s data URI.

Question 24

Platform-Native Actions:

ACTION_SEND

Answer 24

Launches an Activity that sends the data specified by the Intent.

• The recipient contact needs to be selected by the resolved Activity.
• Use only to send data to a remote recipient ( not to another app on the device)
• Use “setType” to set the MIME type of the transmitted data
• The data itself should be stored as an extra by means of the key “EXTRA_TEXT” or “EXTRA_STREAM”, depending on the type
• In the case of email, the native Android applications will also accept extras via several other keys

Question 25

Platform-Native Actions: ACTION\_VIEW

Answer 25

* Asks that the data supplied in the Intent's data URI be viewed in the most reasonable manner * This is the most common generic action * Different applications will handle view requests depending on the URI schema of the data supplied: * **"http:"** addresses open in the browser * **"tel:"** addresses will open the dialer to call the number * **"geo:"** addresses will be displayed in Google Maps * **"contact"** content will be displayed in Contact Manager

Question 26

Platform-Native Actions: ACTION\_WEB\_SEARCH

Answer 26

Opens the Browser to perform a web search based on the query supplied using the **SearchManager.QUERY** key

Question 27

Intent Filter: Basic Idea

Answer 27

An Intent Filter is a declaration that a particular Activity is capable of performing an action on a type of data. They are also used by **Broadcast Recievers** to indicate the broadcast actions that will be recieved

Question 28

Intent Filters: Defining an Intent Filter

Answer 28

* Must add an tag to the desired Activity's manifest node * The tag must included the following tags: * (at least one) * (can be multiple) * (can be multiple)

Question 29

Intent Filters: action tag

Answer 29

Uses the **android:name** attribute to specify the name of the action to be performed. * Each Intent Filter must have at least one action tag * Actions should be unique strings that are self describing. * You can define your own actions, or use one of the system actions

Question 30

Intent Filters: category tag

Answer 30

* Uses the android:name attribute to specify under which circumstances the action can be performed. * Each Intent Filter tag can include multiple category tags. * You can specify your own categories or use one of the standard values provided by Android

Question 31

Intent Filters: data tag

Answer 31

* Enables you to specify which data types your component can act on * You can include several data tags as appropriate * You can use any combination of the following attributes to specify the data the component supports: * android:host * android:mimetype * android:path * android:port * android:scheme

Question 32

Intent Filters: data tag attributes: android:host

Answer 32

android:host Specifies a valid hostname for example: google.com

Question 33

Intent Filters: data tag attributes: android:mimetype

Answer 33

**_android:mimetype_** Specifies the type of data your component is capable of handling. For example: vnd.android.cursor.dir/\* would match any Android Cursor

Question 34

Intent Filters: data tag attributes: **_android:path_**

Answer 34

**_android:path_** Specifies valid path values for the URI For example: /transport/boats/

Question 35

Intent Filters: data tag attributes: **_android:port_**

Answer 35

**_android:port_** Specifies valid ports for the specified host

Question 36

Intent Filters: data tag attributes: **_android:scheme_**

Answer 36

**_android:scheme_** Requires a particular scheme (for example "content" or "http")

Question 37

Intent Resolution: Basic steps Android uses to resolve Intents using Intent Filters

Answer 37

1. List all available Intent Filters 2. Remove Intent Filters that do not match the Action or Category associated with the Intent being resolved 3. Compares the Intent's data URI to the Intent Filter's data tag. Mismatches are removed from list 4. If the list contains more than one viable component, all matching possibilities are presented to the user to decide

Question 38

Intent Resolution: Action Matching criteria

Answer 38

Action matches are made only if the Intent Filter includes the action specified by the Intent. An Intent Filter will fail the action match check if NONE of its actions matches.

Question 39

Intent Resolution: Category Matching criteria

Answer 39

For a category match, Intent filters must include ALL of the categories defined in the resolving Intent. The Intent Filter can include additional categories that are not included in the Intent. An Intent Filter with no categories specified matches only Intents with no categories

Question 40

Intent Resolution: Data match criteria

Answer 40

Each part of the Intent's data URI is compared to the Intent Filter's data tag. * If the Intent Filter specifies a scheme, host/authority, path, or MIME type, these values are compared to the Intent's URI * Any mismatch removes the Intent Filter from the list * Specifying no data values in an Intent Filter will result in a match with ALL Intent data values

Question 41

Intent Resolution: Parts of an Intent's URI Data tag

Answer 41

* MIME type of the data to be matched * Wildcards can be used for matching * Scheme * the "protocol" part of the URI * ex: "http:", "mailto:", "tel:" * Hostname or Data Authority * Section between the scheme and the path * ex: developer.android.com * Path * The data path, comes after the authority * A path can match only if the scheme and hostname parts of the data tag

Question 42

How an Activity can access the Intent that started it

Answer 42

Intent intent = **getIntent**() This returns the Intent that started the Activity * Use intent.**getAction**() * to find the Action the Activity should perform * Use intent.**getData**() * to get a URI data object from the Intent * Use intent.**getExtra** methods * to get any extra data stored in the extras bundle

Question 43

Code snippet: Updating an Activity's Intent

Answer 43

Use **setIntent(** newIntent **)** in the handler responding to a new Intent

Question 44

Using Intent Filters for Plug-Ins and Extensibility: To advertise an Activity's available Actions, what tag and value on the Intent Filters is required?

Answer 44

For each action, the Intent Filter must have a tag with a value of either ALTERNATIVE or SELECTED\_ALTERNATIVE ex:

Question 45

Using Intent Filters for Plug-Ins and Extensibility: Difference between the category values ALTERNATIVE and SELECTED\_ALTERNATIVE

Answer 45

ALTERNATIVE Used to indicate that the action is an alternative to what the user may currently be viewing. Displayed in a set of Alternative Actions, usually as part of an Options menu SELECTED\_ALTERNATIVE Similar, but indicates an action that is typically performed on a selected item displayed within a list

Question 46

Using Intent Filters for Plug-Ins and Extensibility: Basic Steps of Discovering Available Actions

Answer 46

1. Create an Intent to search for actions * Use **addCategory()** to give the Intent a Category of action it will accept, either * Intent.CATEGORY\_ALTERNATIVE or * Intent.CATEGORY\_SELECTED\_ALTERNATIVE 2. Query the PackageManager by passing the Intent and a Flags value to **PackageManager.queryIntentActivityOptions()**​ 1. It will return a list of "**ResolveInfo**" items representing the matching available actions

Question 47

Linkify: Basic Overview

Answer 47

Linkify * A helper class * Creates hyperlinks within Text View classes through RegEx pattern matching * Text matching a specific pattern will be turned into a clickable hyperlink with the matched text as it's URI * Has preset string patterns that can match: * web URLs * email addresses * map addresses * phone numbers

Question 48

Linkify: How matching text is turned into a link

Answer 48

1. A text View instance is passed to LInkfiy using the static "**addLinks()**" method: * Linkify.**addLinks(** textView , Linkify.WEB\_URLS | Linkify.EMAIL\_ADDRESSES**)** * Can include several patterns OR'd together 2. Linkify generates a URI from the matching pattern 3. A click handler is added to the Link , * Fires: **startActivity**(new **Intent**( Intent.ACTION\_VIEW, uri) )

Question 49

Linkify: Create Custom Link Strings

Answer 49

* Create a RegEx pattern * Do this with the **Pattern** class * Linkify the target Text View by calling **Linkify.addLinks()** * Pass in your pattern * May also pass in a prefix that will be prepended to the target URI * May also pass in filters

Question 50

Linkify: What are Filters?

Answer 50

Filters offer additional control over: * the target URI structure * and the definition of matching string Filters * Defined as interfaces that must be implemented by you * **Match Filters** apply extra criteria for matches * **Transform Filters** make changes to the uri

Question 51

Broadcast Intents: Overview

Answer 51

* Intents are a system-level message passing mechanism * Can cross process boundaries * Implement **Broadcast Receivers** to listen for, and respond to, **Broadcast Intents** * Can respond to **Broadcast Intents** from your own App, from other apps, or from the system itself * Android broadcasts events extensively using Intents

Question 52

How to Broadcast an Intent

Answer 52

* Construct your Intent * Same as a normal Intent * If Implicit, specify an **action** string to identify the type of intent being broadcast * Add data and extras * Broadcast using * **sendBroadcast(**myIntent**)**

Question 53

Broadcasting an Intent: What is the Action string?

Answer 53

The Action string is used to identify the type of event being broadcast. Used to help resolve implicit Intents by matching a particular action that should be performed. By Convention, Action strings are constructed with the same form as Java package names: "com.mycompany.derp.action.MY\_ACTION"

Question 54

Broadcast Intents: Broadcast Receivers Overview

Answer 54

* A class that is able to listen and respond to broadcast Intents * commonly just called "Receivers" * Extend the **BroadcastReceiver** class * Must be registered to receive broadcasts * Either in code or in the application manifest * Override the **onReceive()** event handler

Question 55

Broadcast Intents: Handling the Broadcast Intent with a Receiver

Answer 55

* The Receiver class should extend BroadcastReceiver * Override the onReceive method: * Will be executed on the main application Thread * All processing in the Broadcast Receiver must finish within 10 seconds to avoid an ANR event * Any non-trivial work should be performed asynchronously: * Schedule a background job * Launch a bound Service * call **goAsync()**

Question 56

Broadcast Intents: Registering Broadcast Receivers: in Code

Answer 56

Typically done for responding to broadcasts sent from your own application. Best Practice: Register within the onStart() handler, unregister during onStop() * Register with the **registerReceiver()** method * May pass an IntentFilter as well * Unregister with the **unregisterReceiver()** method

Question 57

Broadcast Intents: Registering a Broadcast Receiver: In Application Manifest

Answer 57

BRs registered statically in the Application Manifest are always active. They receive Broadcast Intents even when app is not active. Application will be started automatically when a matching Intent is broadcast. * Add a tag to the application node in the Manifest

• Specify the class name of the receiver

* Limited number of supported actions

Question 58

Broadcast Intents: How to Manage Manifest Receivers at Run Time

Answer 58

Can Enable/Disable any of your app's manifest Receivers at run time through the Package Manager * Use the **setComponentEnabledSetting()** method, parameters: * Component Name(Receiver) * State to set it in * Option to kill app * Enabled/Disabled states are defined in Package Manager: * PackageManager.COMPONENT\_ENABLED\_STATE\_**ENABLED** * PackageManager.COMPONENT\_ENABLED\_STATE\_**DISABLED**

Question 59

Broadcast Intents: Common System Service Broadcast Events

Answer 59

* Completion of device booting * Time-Zone changes * Changes to Dock state * Battery Status

Question 60

Broadcast Intents: Dock Change event

Answer 60

Intent.ACTION\_DOCK\_EVENT

Question 61

Broadcast Intents: Battery Status Event and Associated Action strings

Answer 61

Intent.ACTION\_BATTERY\_CHANGED Action Strings (Appended to android.intent.action.): * ACTION\_BATTERY\_LOW * ACTION\_BATTERY\_OKAY * ACTION\_POWER\_CONNECTED * ACTION\_POWER\_DISCONNECTED

Question 62

Broadcast Intents: Event for changes in Network Connectivity

Answer 62

ConnectivityManager.CONNECTIVITY\_ACTION * Note: Apps targeting Android 7.0+ will not receive this broadcast if they declare Receiver in the Manifest

Question 63

Local Broadcast Manager: Overview

Answer 63

* Simplifies the process of registering for, sending and receiving Intents broadcast only within the application * More efficient than sending a global Broadcast * More secure * Part of the Android Support Library

Question 64

Local Broadcast Manager: Getting an Instance of the Local Broadcast Manager

Answer 64

Use the static getInstance() method: LocalBroadcastManager lbm = LocalBroadcastManager.**getInstance(**this**)**

Question 65

Local Broadcast Manager: Register/Unregister Broadcast Receivers

Answer 65

* First, get an instance of the LocalBroadcastManager * Register: * Just like a global receiver, use the **registerReceiver**() method, passing in a Broadcast Receiver and Intent Filter * lbm.**registerReceiver( receiver, filter)** * Unregister: * lbm.**unregisterReceiver(receiver)**

Question 66

Pending Intents: Overview

Answer 66

* Class: PendingIntent * Provides a mechanism for creating Intents that can be fired later * Fired by the system, or another application, at a later time * Commonly used to package Intents that will be fired in response to a future event, like touching a notification * Provides static methods to "package" a normal intent

Question 67

Pending Intents: Common constructing methods in the PendingIntent class

Answer 67

* _Start an Activity_ * PendingIntent.getActivity() * _Start a Service_ * PendingIntent.getService() * _Start a Foreground Service_ * PendingIntent.getForegroundService() * _Broadcast an Intent to explicit Receiver_ * PendingIntent.getBroadcast() * _Broadcast an implicit Intent_ * also PendingIntent.getBroadcast() * Just pass an implicit Intent