Intents New

7/31/2019 Intents New

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Introduction

To

Intents

(Our Intent is to make you

fundamentally clear onIntents )


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Intents:2

Intents are the most important and uniqueconcept in android.

Androids innovative navigation and triggering

mechanism is achieved by intents.i.e. intents are used for message passingbetween the different android components aswell as for starting other android components

( Activities, Services and Broadcast receivers)


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Understanding intents and

intentFilters3

An Intent is a declaration of need.

An Intent-Filter is a declaration of capabilityand interest in offering assistance to those in

need.

An Intent is made up a number of pieces ofinformation describing the desired action or

service. An intent-Filter may be generic or specific with

respect to which intents it offers to service.


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Understanding intents and

intentFilters4

New City

Feelshungry

Xerox Shop(10 Digital

xeroxmachines)

Indoor

stadiumRestaurantTea stall

Intent

Manifest file

Intent filterResolution


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Intents:

School of Computer Engineering & InnoVAdors Lab

one of the most common use of intents is tostart an activity.

Methods required to start an activity

startActivity(Intent intent);

startActivityForResult(Intent intent,int RequestCode);


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Intents:


Types

Implicit

Explicit

In explicit intent there is a short circuit to thetarget activity.

In implicit intent the actual activity to start is

decided at runtime by looking into the intentfilter.


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Intents: (Explicit)


import staements

public class x extends Activity {

/** Called when the activity is first created. */

class clicking implements Button.OnClickListener

{

public void onClick(View v)

{

Intent in=new Intent(x.this,y.class);

startActivity(in);

}

}

Button bt;

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.main);

bt=(Button)findViewById(R.id.Button01);

bt.setOnClickListener(new clicking());

}

}


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Intents: (Explicit)


package x.first;

import android.app.Activity;

import android.os.Bundle;

public class y extends Activity{

public void onCreate(Bundle a)

{

super.onCreate(a);

setContentView(R.layout.y);}

}

Intent Y


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Intents: (Explicit)


Manifest file


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Intents: (Explicit)


Intent in=new Intent(x.this,y.class);startActivity(in );

Activity X Activity Y


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Intents: (Explicit)


Values can be sent between activities in bothdirections if the required method is :

startActivityForResult(Intent intent,int requestcode);

To send values to the target activity, it is required to

put values in the intent using the method :

putExtra(name,value) ;


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Intents: (Explicit)


Intent in=new Intent(x.this,y.class);In.putExtra(name1,10);In.putExtra(name2,20);

startActivityForResult(in );

Activity X Activity Y

name1,10name2,20


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Intent


To retrieve the values from the intent first theintent is caught using the getIntent() method.

The values are then retrieved using the

getIntExtra() , getFloatExtra().etc methods.


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Intents: (Explicit)




Activity X

Intent i=getIntent();int num1=i.getIntextra(name1,999);

Activity Y

Name1,10Name2,20


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Intent


To return values from the target activity back to thecaller activity the

setResult(int resultcode,intent) method is used

The return values can be put in the intent using the

usual methods.(putExtra()) The result code can be ant integer value(Android

system defines a set of integer values likeRESULT_OK,RESULT_CANCELED etc.)

As the control will always go to the calling activitythe intent can be created in the simplest form like:

Intent res=new Intent();


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Intents: (Explicit)




Activity X

Intent i=getIntent();int num1=i.getIntextra(name1,999);

Intent res=new Intent();Res.putExtra(ret1,30);

setResult(RESULT_OK,res);

Activity Y

name1,10name2,20

ret1,30


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Intent


To retrieve the return values from the finishedactivity the

onActivityResult(int requestcode,int resultcode,Intent intent)

method has to be overridden in the calling

activity.

The returned values can be retrieved from the

intent by using the usual methods.(getIntExtra(),getFloatExtra().etc)


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Intents: (Explicit)


onCreate( Bundle b){Intent in=new Intent(x.this,y.class);

In.putExtra(name1,10);

In.putExtra(name2,20);startActivityForResult(in,req );

}

onActivityResult(int requestcode,intresultcode,Intent in)

{r.onActivityResult(requestcode,resultcode

,in);int p=in.getIntExtra(ret1,998);

}

Activity X

onCreate( ){

Intent i=getIntent();int

num1=i.getIntextra(name1,999);Intent res=new Intent();Res.putExtra(ret1,30);

setResult(RESULT_OK,res);}

Activity Y

name1,10name2,20

ret1,30


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Attributes of Intent

Primary Attributes

Action

Data

Secondary Attributes

Category

Type

Component

Extras


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Attributes of Intent

Category Gives additional information about theaction to execute.

Example : CATEGORY_HOME

CATEGORY_LAUNCHER CATEGORY_PREFERENCE

CATEGORY_LAUNCHER means it shouldappear in the Launcher as a top-levelapplication.

I Fil


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Intent Filters

The core components of an application (its activities,

services, and broadcast receivers) are activatedby intents. An intent is a bundle of information describinga desired action including the data to be acted upon,the category of component that should perform theaction. Android locates an appropriate component to

respond to the intent, launches a new instance of thecomponent if one is needed, and passes it the Intentobject.

Components advertise their capabilities the kinds ofintents they can respond to through intent filters. TheAndroid system must learn which intents a componentcan handle before it launches the component. Intent

filters are specified in the manifest as


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Intent Filters

Intents New

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