Activity and Fragment - PowerPoint Presentation

Slide1

Activity and FragmentSlide2

Activity

LifeCycleSlide3

States of an Activity

An activity has essentially four

states:If an activity in the foreground of the screen (at the top of the stack), it is active or running

.

If an activity has lost focus but is still visible it is

paused. A

paused activity is completely alive (it maintains all

state and

member information and remains attached to

the window

manager), but can be killed by the system

in

extreme

low memory situations

.

If an activity is completely obscured by another activity,

it is

stopped. It still retains all state and

member information

, however, it is no longer visible to the user

so its

window is hidden and it will often be killed by

the system

when memory is needed elsewhere

.

If an Activity is completely destroyed.Slide4

Specify Launcher Activity

<activity

android:name=".MainActivity" android:label="@string/app_name

">

<intent-filter>

<

action

android:name

="

android.intent.action.MAIN

" />

<

category

android:name

="

android.intent.category.LAUNCHER

" />

</intent-filter>

</activity

>

For activity to be default specify :

android:name

="

android.intent.category.DEFAULT

" Slide5

On Create

The system creates every new instance of Activity

by calling its onCreate() method

.

You should instantiate your class variables, declare the

UI for

the activity and

congure

the UI elements here.

TextView

mTextView

;

@Override

public void

onCreate

(Bundle

savedInstanceState

) {

super.onCreate

(

savedInstanceState

);

// Set the user interface layout for this Activity

setContentView

(

R.layout.main_activity

);

// Initialize member

TextView

mTextView

= (

TextView

)

findViewById

(

R.id.text_message

);

}Slide6

On Pause

The Activity is paused when the foreground activity

is sometimes obstructed by other visual components.

This

is typically used to commit unsaved changes to persistent data, stop animations and other things that may be consuming CPU, etc.

@Override

public void

onPause

() {

super.onPause

(); // Always call the superclass method first

// Release the Camera because we don't need it when paused

// and other activities might need to use it.

if (

mCamera

!= null) {

mCamera.release

()

mCamera

= null;

}

}Slide7

On Resume

Called when focus comes back to the Activity

Should be used for acquiring back resources which

werereleased

on

onPause

() method and for setting

upanimations

, etc. which make sense when the user is interacting with the Activity

@Override

public void

onResume

() {

super.onResume

();

if (

mCamera

== null) {

// Local method to handle camera

init

initializeCamera

();

}

}Slide8

On Stop

The user opens the Recent Apps window and

switches from your app to another app. The activity in your app that's currently in the foreground is stopped. If the

user returns

to your app from the Home screen launcher icon

or the

Recent Apps window, the activity restarts

.

The user performs an action in your app that starts a

new activity. The current activity is stopped when the

second activity

is created. If the user then presses the

Back button

, the

rst

activity is restarted.

The user receives a phone call while using your app on

his

or

her phone.Slide9

Start/Restart Your Activity

When your activity comes back to the foreground from

the stopped state, it receives a call to onRestart()

The system also calls the

onStart

() method,

whichhappens

every time your activity becomes visible

Tip: Very uncommon for apps to use onRestart

()Slide10

Fragment

A Fragment represents a

behavior or a portion of user interface in an Activity

You can think of a fragment as a modular section of

an activity

, which has its own

lifecycle

Examples of Fragment are :

DialogFragment

,

ListFragment

,

PreferenceFragmentSlide11

3

Fragment

LifeCycleSlide12

Basic Fragment Code

public static class

ExampleFragment extends Fragment {@Overridepublic View onCreateView(LayoutInflater

inflater

,

ViewGroup

container,

Bundle savedInstanceState) { //

Inflate the layout for this fragment

return

inflater.inflate

(

R.layout.example_fragment

,

container

, false);

}

}Slide13

Questions ?