MobAppDev

Activity Lifecycle Management, Intent Resolution, Implicit Intents,

Data Transfer with Intents

Vladimir Kulyukin

www.vkedco.blogspot.com

Outline● Activity Lifecycle Management● Explicit & Implicit Intents● Intent Resolution● Data Transfer with Intents

Activity Lifecycle Management

Review: Lifecycle Callback Methodspublic class MyActivity {

// The activity is created

public void onCreate(Bundle savedInstanceState) { }

// The activity is about to become visible

protected void onStart() { }

//The activity is visible (it is resumed)

protected void onResume() { }

// Another activity is taking focus (it is paused)

protected void onPause() { }

// The activity is no longer visible (it is stopped)

protected void onStop() { }

// The activity is about to be destroyed

protected void onDestroy() { }

}

Source: http://developer.android.com/guide/components/activities.html#Lifecycle

Review: Activity's Lifecycle Diagram

Source:http://developer.android.com/training/basics/activity-lifecycle/starting.html

Review: Activity's Lifecycle Diagram

Review: Activity's Three Basic States● Running/Resumed – this activity is in the foreground of the screen and receives

user focus● Paused – This activity is partially obscured by another activity that gets into the

foreground and receives user focus Paused activity objects are 1) in memory, 2) attached to Window Manager,

3) killable only in extremely low memory conditions● Stopped – This activity is completely obscured by another activity

Stopped activity objects are 1) in memory, 2) detached from Window Manag-er, 3) killable when memory is needed somewhere else

Activity Lifecycle Management: Example

● Develop an app that has two Activities: the first activity allows the user to sign in with the user name and password

● If the user name and password are correct, the second activity is launched that displays the list of friends of the user who signed in

● The activity overrides all lifecycle management methods and logs appropriate messages in LogCat

● Source code is here

Application Screenshots

Explicit Intents

● If Android OS resolves an explicit intent via its Java class identifier & the component specified by the class identifier is accessible, the component will likely be launched

● Explicit intents are typically used within one application when the developers have control over the Java class identifiers of the components

Data Transfer with Intents

Data Transfer with Intents

● Intents can bundle and transfer data to other components via Android

● An intent sender creates an intent, puts a few key-value pairs into its bundle and sends it to Android

● An intent receiver receives an intent, checks it for the presence/absence of specific keys and then does some action

● Keys are always Strings

Putting Data into Explicit Intents

@Override

public void onClick(View v) {

Intent i=new Intent(getApplicationContext(),ListOfUserFriends.class);

// you would have to encrypt user name and password here

i.putExtra("username", mEdTxtUsername.getText().toString());

i.putExtra("password", mEdTxtPwd.getText().toString());

startActivity(i);

}

Extracting Data from Explicit Intents

@Override

protected void onCreate(Bundle savedInstanceState) {

Intent profile = getIntent();

final String userName = profile.getStringExtra("username");

final String password = profile.getStringExtra("password");

…

}

Implicit Intents

Implicit Intents● Implicit intents provide a mechanism for anonymous (no

explicit activity specification) requests ● An activity asks Android OS to do an action by specifying

high-level requirements but without knowing which activity or application will actually perform the action

● The requesting action can specify a URI to the data which the performing activity must process or add that data to the implicit intent

Native Android Actions● Android OS defines many actions that can be satisfied by native or 3-rd

party components and are launched via implicit intents● Here are some examples:

ACTION_ANSWER – open an activity that handles incoming calls ACTION_CALL – open an activity with a phone dialer ACTION_PICK – launch an activity to pick an item from a list of

items ACTION_WEB_SEARCH – launch an activity to perform a web

search ACTION_VIEW – launch an activity that can view the specified data

in a reasonable manner

Implicit Intents

● Implicit intents provide a mechanism for anonymous requests

● An implicit intent is launched with startActivity(Intent i)● Activities and applications use intent filters to tell Android

ecosystem about the actions they respond to and/or which data types they work with

● An component that has an intent filter is called an intent filter

Intent Filter's Structure● Action

Name of the action being serviced Name should be a unique string Best practice is to use the Java package naming conven-

tion ● Category

When the action should be serviced● Data

Data types that the action can work with

Intent Resolution● Intent resolution starts when an activity calls

startActivity() or startActivityForResult() with some intent Intnt

● Android OS gets the list of all intent filters available from the installed packages

● Intent filters that do not match Intnt's requested action or category are removed from the list

Intent Resolution● An action match occurs when Intnt's action and the

filter's action are the same or no action is specified● A category match occurs when Intnt's categories

and the filter's categories are the same● A data match occurs when Intnt's data types are the

same as the filter's data types

Intent Resolution● Native Android components are part of the Intent resolution

process● Native components are no different from 3rd-part components● Native components do not have higher-priorities and can be

completely replaced with 3rd-party components with the user's consent

● Android ecosystem does not give anyone a priori advantages to any components

Implicit Intent Example● Develop an app that uses an implicit intent to request Android

ecosystem to find a component that can display the wiki entry about Kurt Gödel

● This implicit intent must contain two components: Intent.ACTION_VIEW and the URI (e.g., URL of a web page)

● The default native component that responds to this intent is the web browser

● Source code is here

Sample Screenshot

Code Fragments

Wiki Constant in /res/values/strings.xml

<resources>

...

<string name=”kurt_godel_wiki_url”>

http://en.wikipedia.org/wiki/Kurt_Godel

</string>

...

</resources>

Launching Intent for Viewing URL

public class GodelWikiPageBrowserAct extends Activity {

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.godel_wiki_page_browser_act_layout);

Intent myIntent = new Intent(Intent.ACTION_VIEW,

Uri.parse(getResources().getString(R.string.kurt_godel_wiki_url)));

this.startActivity(myIntent);

}

…

}