Intent Class | Android

INTENT CLASS

Hello all,
Today we are going to focus on the intent class in android.

The main purpose of an Intent is to call other activities. i.e., when one activity wants to call another activity Intent class comes into play.

Intents allow the activities to request function from other Android activities.

It allows activities of the same application get interacted with the both the same application or even other applications

Intent class is a data structure generally used for two main purposes

• Calling another activity to perform a particular function.
• Event notifications

Though for a beginner understanding the fields in an intent is a bit difficult, just get to know what the fields are and understand their importance

INTENT FIELDS

Name	Description
Action	This field is used to represent the operation that is to be perform
Data	Data is associated with Intent ;formatted as URI(Uniform Resource Identifier)
Category	Additional information about the component that can handle the intent
Type	Specifies the mime type of the intent’s data
Component	This field is to identify the target activity
Extras	This field stores additional information associated with the intent.
Flags	Specify the information about how the intent should be handled

 

 

How to Start Activities using Intents

One can start an activity using the following methods

• StartActivity(Intent intent,…)
• startActivityForResult(Intent intent, …)

Android uses two ways to find out the target activity when either of the two methods mentioned previously is used

• EXPLICITLY –(To be called)Target activity is explicitly mentioned in the intent’s component
• IMPLICITLY – (If the activity is not mentioned explicitly) Android determines based on the properties of the activities intent that was used for.

Today lets just focus on Explicit calling

Example of an Application that explicitly starts another activity

Consider two activities,

1. MainActivity – This is the first activity called that has a button that directs to HelloAndroidActivity
2. HelloAndroidActivity– This is the target activity which simply displays a text

MainActivity is the first activity which is started. It is a welcome screen has a simple “Welcome” text and a button, which on clicked directs to HelloAndroidActivity activity

And yes, this is done by using Intent in the first Activity, MainActivity. Intent calls the second activity using the following syntax :

STEPS

1. Create a new Android Application Project with a Blank Activity named as MainActivity and layout file named as activity_main.xml.
2. Please find the following java files and respective xml layout files

MainActivity.java : ( src/com/MainActivity.java)

package com.example.androidexample;

import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

public class MainActivity extends Activity {

    Button button1;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        button1=(Button)findViewById(R.id.button1);
    
    button1.setOnClickListener(new OnClickListener(){
    
        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub
            Intent intent=new Intent(MainActivity.this,HelloAndroidActivity.class);
            startActivity(intent);    
        }
    });

    
    }
    
}

3. xml(res/layout/activity_main.xml)

 

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Welcome to First page" />

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_alignParentRight="true"
        android:text="Go to Next Page" />

</LinearLayout>

 

4. HelloAndroidActivity.java(src/com/HelloAndroidActivity.java)

package com.example.androidexample;

import android.app.Activity;
import android.os.Bundle;

public class HelloAndroidActivity extends Activity {

    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.second_activity);
    
    
    }
    
}

5. second_activity.xml (res/layout/second_activity.xml)

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >
    
<TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello Android!!!" />
</LinearLayout>

Last but not the least make sure your AndroidManifest.xml has declared both the activities

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.androidexample"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="21" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <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>
        <activity
            android:name=".HelloAndroidActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.NORMAL" />
            </intent-filter>
        </activity>
    </application>

</manifest>

SCREENSHOT OF THE OUTPUTS

 

Thus we have learned some basics on Intent class and how to explicitly call activities using Intent class.

Will keep posting more. Please feed in your suggestions as  a comment.