AN4430 datasheet(12/42 Pages) STMICROELECTRONICS

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Android Application Overview

AN4430

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DocID025722 Rev 1

Intent filters

Intent filters are xml structured definition stored with the component declaration in the

android manifest file (detailed later on in this application note). This structure is attached to a

component definition and declares the intent(s) the component is able to receive to perform

action. By this way, user makes possible for other application to start an activity component

with a defined intent. Likewise, if component activity declaration doesn’t have an intent filter

declaration the activity is only start from its application owner.

Activities

Activity is a component belonging to an application and described in the android manifest of

the application it belongs to. The activity may provide a (partial) screen with which the user

can interact with. Application is usually composed by several activities that are loosely

bound to each other. One activity is declared as the main activity which launched on the

application start. This main property is declared in the application manifest.xml file.

Each activity from the started application can start other activity, which present a new screen

to the user. Every time a new activity is started it is put in a stack and the previous one put in

stopped state while the Android system keeps the activity in a stack abiding to the basic

“last in, first out” stack mechanism also called back stack. When the current activity is

finished (action ended, back button pressed) it is popped from the back stack and destroy,

the activity on the top of the back stack is then resumed.

Activities life cycle

Activity life cycle is handled with callback methods that the system calls when the activity

transition between various states. Each activity developer implements must inherit for

Activity class (or an existing subclass of it).

Figure 3. Activity Java skeleton

public class ExampleActivity extends Activity {

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

// The activity is being created.

}

@Override

protected void onStart() {

super.onStart();

// The activity is about to become visible.

}

@Override

protected void onResume() {

super.onResume();

// The activity has become visible (it is now "resumed").

}

@Override

protected void onPause() {

super.onPause();

// Another activity is taking focus (this activity is about to be

"paused").

}

@Override

protected void onStop() {

super.onStop();

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

}

@Override

protected void onDestroy() {

super.onDestroy();

// The activity is about to be destroyed.

}

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