Android - Android Intent Types
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The document discusses activities and intents in Android programming. It defines an intent as a facility for late runtime binding between components in the same or different applications. Intents can be either explicit, specifying the target component, or implicit, allowing the system to choose the receiver. Key intent components include action, data, category, and extras. The document also covers activity states, saving resources, declaring activities in the manifest, and how the intent resolution process matches intents to potential receiving components.
Android - Android Intent Types
- 2. Programming with Android: Activities and Intents
- 3. Outline 3 Intent with results: Sender side Intent-Resolution process Handling implicit Intents Handling Explicit Intents Intent description What is an intent? Intent with results: Receiver side
- 4. More on Activities: Activity states Active (or running) Foreground of the screen (top of the stack) Paused Lost focus but still visible Can be killed by the system in extreme situations Stopped Completely obscured by another activity Killed if memory is needed somewhere else 4
- 5. More on Activities: Saving resources An activity lifecycle flows between onCreate and onDestroy Create, initialize everything you need in onCreate Destroy everything that is not used anymore, such as background processes, in onDestroy It is fundamental to save the data used by the application inbetween the state-transitions … 5
- 6. Activities and AndroidManifest.xml An Android application can be composed of multiple Activities … Each activity should be declared in the file: AndroidManifest.xml Add a child element to the <application> tag: 6 <application> <activity android:name=".MyActivity" /> <activity android:name=”.SecondActivity" /> </application>
- 7. Activities and AndroidManifest.xml Each activity has its Java class and layout file. 7 public class FirstActivity extends Activity { public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_first); } public class SecondActivity extends Activity { public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_two); }
- 8. Intent Definition Call a component from another component Possible to pass data between components Components: Activities, Services, Broadcast receivers … Something like: “Android, please do that with these data” Reuse already installed applications and components 8 Intent: facility for late run-time binding between components in the same or different applications. Intent: facility for late run-time binding between components in the same or different applications.
- 9. Intent Definition We can think to an “Intent” object as a message containing a bundle of information. Information of interests for the receiver (e.g. name) Information of interests for the Android system (e.g. category). 9 Component NameComponent Name Action NameAction Name DataData CategoryCategory ExtraExtra FlagsFlags Structure of an Intent
- 10. 10 INTENT TYPESINTENT TYPES EXPLICITEXPLICIT IMPLICITIMPLICIT The target receiver is specified through the Component Name Used to launch specific Activities The target receiver is specified by data type/names. The system chooses the receiver that matches the request.
- 11. Intent Components We can think to an “Intent” object as a message containing a bundle of information. Information of interests for the receiver (e.g. data) Information of interests for the Android system (e.g. category). 11 Component NameComponent Name Action NameAction Name DataData CategoryCategory ExtraExtra FlagsFlags Component that should handle the intent (i.e. the receiver). It is optional (implicit intent) void setComponent(ComponentName)
- 12. Intent types: Explicit Intents 12 Explicit Intent: Specify the name of the Activity that will handle the intent. Intent intent=new Intent(this, SecondActivity.class); startActivity(intent); Intent intent=new Intent(); ComponentName component=new ComponentName(this,SecondActivity.class); intent.setComponent(component); startActivity(intent);
- 13. Intent with Results Activities can return results (e.g. data) Sender side: invoke the startActivityForResult() onActivityResult(int requestCode, int resultCode, Intent data) startActivityForResult(Intent intent, int requestCode); 13 Intent intent = new Intent(this, SecondActivity.class); startActivityForResult(intent, CHOOSE_ACTIVITY_CODE); … public void onActivityResult(int requestCode, int resultCode, Intent data) { // Invoked when SecondActivity completes its operations … }
- 14. Intent with Results Activities can return results (e.g. data) Receiver side: invoke the setResult() void setResult(int resultCode, Intent data) 14 Intent intent=new Intent(); setResult(RESULT_OK, intent); intent.putExtra(”result", resultValue); finish(); The result is delivered to the caller component only after invoking the finish() method!
- 15. 15 INTENT TYPESINTENT TYPES EXPLICITEXPLICIT IMPLICITIMPLICIT The target receiver is specified through the Component Name Used to launch specific Activities The target receiver is specified by data type/names. The system chooses the receiver that matches the request.
- 16. Intent types: Implicit Intents Implicit Intents: do not name a target (component name is left blank) … When an Intent is launched, Android checks out which activies might answer to the Intent … If at least one is found, then that activity is started! Binding does not occur at compile time, nor at install time, but at run-time …(late run-time binding) 16
- 17. Intent Components We can think to an “Intent” object as a message containing a bundle of information. Information of interests for the receiver (e.g. data) Information of interests for the Android system (e.g. category). 17 Component NameComponent Name Action NameAction Name DataData CategoryCategory ExtraExtra FlagsFlags A string naming the action to be performed. Pre-defined, or can be specified by the programmer. void setAction(String)
- 18. Intent Components Predefined actions (http://developer.android.com/reference/android/content/Intent.html) 18 Action Name Description ACTION_EDIT Display data to edit ACTION_MAIN Start as a main entry point, does not expect to receive data. ACTION_PICK Pick an item from the data, returning what was selected. ACTION_VIEW Display the data to the user ACTION_SEARCH Perform a search Defined by the programmer it.example.projectpackage.FILL_DATA (package prefix + name action)
- 19. Intent Components Special actions (http://developer.android.com/reference/android/content/Intent.html) 19 Action Name Description ACTION_IMAGE_CAPTION Open the camera and receive a photo ACTION_VIDEO_CAPTION Open the camera and receive a video ACTION_DIAL Open the phone app and dial a phone number ACTION_SENDTO Send an email (email data contained in the extra) ACTION_SETTINGS Open the system setting ACTION_WIRELESS_SETTINGS Open the system setting of the wireless interfaces ACTION_DISPLAY_SETTINGS Open the system setting of the display
- 20. Intent Components Example of Implicit Intent that initiates a web search. 20 public void doSearch(String query) { Intent intent =new Intent(Intent.ACTION_SEARCH); Intent.putExtra(SearchManager.QUERY,query); if (intent.resolveActivity(getPackageManager()) !=null) startActivity(intent) } Example of Implicit Intent that plays a music file. public void playMedia(Uri file) { Intent intent =new Intent(Intent.ACTION_VIEW); if (intent.resolveActivity(getPackageManager()) !=null) startActivity(intent) }
- 21. Intent Components We can think to an “Intent” object as a message containing a bundle of information. Information of interests for the receiver (e.g. data) Information of interests for the Android system (e.g. category). 21 Component NameComponent Name Action NameAction Name DataData CategoryCategory ExtraExtra FlagsFlags Data passed from the caller to the called Component. Def. of the data (URI) and Type of the data (MIME type) void setData(Uri) void setType(String)
- 22. Intent Components Each data is specified by a name and/or type. name: Uniform Resource Identifier (URI) scheme://host:port/path 22
- 23. Intent Components Each data is specified by a name and/or type. type: MIME (Multipurpose Internet Mail Extensions)-type Composed by two parts: a type and a subtype Image/gif image/jpeg image/png image/tiff text/html text/plain text/javascript text/css video/mp4 video/mpeg4 video/quicktime video/ogg application/vnd.google-earth.kml+xml 23
- 24. Intent Components We can think to an “Intent” object as a message containing a bundle of information. Information of interests for the receiver (e.g. data) Information of interests for the Android system (e.g. category). 24 Component NameComponent Name Action NameAction Name DataData CategoryCategory ExtraExtra FlagsFlags A string containing information about the kind of component that should handle the Intent. > 1 can be specified for an Intent void addCategory(String)
- 25. Intent Components Category: string describing the kind of component that should handle the intent. 25 Category Name Description CATEGORY_HOME The activity displays the HOME screen. CATEGORY_LAUNCHER The activity is listed in the top-level application launcher, and can be displayed. CATEGORY_PREFERENCE The activity is a preference panel. CATEGORY_BROWSABLE The activity can be invoked by the browser to display data referenced by a link.
- 26. Intent Components We can think to an “Intent” object as a message containing a bundle of information. Information of interests for the receiver (e.g. data) Information of interests for the Android system (e.g. category). 26 Component NameComponent Name Action NameAction Name DataData CategoryCategory ExtraExtra FlagsFlags Additional information that should be delivered to the handler(e.g. parameters). Key-value pairs void putExtras() getExtras()
- 27. Intent Components We can think to an “Intent” object as a message containing a bundle of information. Information of interests for the receiver (e.g. data) Information of interests for the Android system (e.g. category). 27 Component NameComponent Name Action NameAction Name DataData CategoryCategory ExtraExtra FlagsFlags Additional information that instructs Android how to launch an activity, and how to treat it after executed.
- 28. Intent types: Implicit Intents Intent i = new Intent(android.content.Intent.ACTION_VIEW, Uri.parse("http://informatica.unibo.it")); startActivity(i); 28 Action to perform Data to perform the action on Implicit intents are very useful to re-use code and to launch external applications … More than a component can match the Intent request … How to define the target component?
- 29. Intent types: Implicit Intents How to declare what intents I'm able to handle? – <intent-filter> tag in AndroidManifest.xml How? <intent-filter> <action android:name=”my.project.ACTION_ECHO” /> </intent-filter> If a component creates an Intent with “my.project.ACTION_ECHO” as action, the corresponding activity will be executed … 29
- 30. Intent types: Intent Resolution The intent resolution process resolves the Intent-Filter that can handle a given Intent. Three tests to be passed: Action field test Category field test Data field test If the Intent-filter passes all the three test, then it is selected to handle the Intent. 30
- 31. Intent types: Intent Resolution (ACTION Test): The action specified in the Intent must match one of the actions listed in the filter. If the filter does not specify any action FAIL An intent that does not specify an action SUCCESS as as long as the filter contains at least one action. 31 <intent-filer … > <action android:name=“com.example.it.ECHO”/> </intent-filter>
- 32. Intent types: Intent Resolution (CATEGORY Test): Every category in the Intent must match a category of the filter. If the category is not specified in the Intent Android assumes it is CATEGORY_DEFAULT, thus the filter must include this category to handle the intent 32 <intent-filer … > <category android:name=“android.intent.category.DEFAULT”/> </intent-filter>
- 33. Intent types: Intent Resolution (DATA Test): The URI of the intent is compared with the parts of the URI mentioned in the filter (this part might be incompleted). 33 <intent-filer … > <data android:mimeType=“audio/* android:scheme=“http”/> <data android:mimeType=“video/mpeg android:scheme=“http”/> </intent-filter> Both URI and MIME-types are compared (4 different sub-cases …)
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