How to Call Activity in Android | Intent in Android

How to call activiy in Android ?

To call activity in android we use INTENT class.


What is Activity ? 

Activity represents a single screen with a user interface.

Activity is simgle screen in android. 

When we create activity in android studio two files are create one for desing file called xml file and second is Class file that used to write java code.


What is Intent in Andorid ?

Intent is inbuilt class in android studio.

It is used to call activity, pass information from one activity to another, and also used for calling any system components.


There are two types of intent in android

• Explicit  
• Implicit   

Explicit

When we call one activity to another activity it is explicit intent.

Implicit

When we call any system components with Intent class it is Implicit intent like if we call Wifi, Bletooth, Browser etc.. with the help of intent class. 



Example::

activity_main.xml  (inside res/layout folder) 

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#258"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/firstActivity"
        android:layout_width="250dp"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:layout_marginTop="30dp"
        android:text="Open Activity One" />

    <Button
        android:id="@+id/secondActivity"
        android:layout_width="250dp"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:layout_marginTop="30dp"
        android:text="Open Activity Two" />

</LinearLayout>

MainActivity.java 

package com.example.malik.blog;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {

    Button firstActivity, secondActivity;

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

        firstActivity = (Button) findViewById(R.id.firstActivity);
        secondActivity = (Button) findViewById(R.id.secondActivity);

        firstActivity.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(MainActivity.this, FirstActivity.class);
                startActivity(intent);
            }
        });

        secondActivity.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(MainActivity.this, SecondActivity.class);
                startActivity(intent);
            }
        });
    }
}

activity_first.xml  (inside res/layout folder)

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#999"
    android:orientation="vertical"
    tools:context=".FirstActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:padding="15dp"
        android:text="First Activity"
        android:textColor="#f00"
        android:textSize="35sp" />

</LinearLayout>

FirstActivity.java

package com.example.malik.blog;

import android.support.v7.app.AppCompatActivity;

import android.os.Bundle;

public class FirstActivity extends AppCompatActivity {

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_first);

    }

}

activity_second.xml  (inside res/layout folder)

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    xmlns:app="http://schemas.android.com/apk/res-auto"

    xmlns:tools="http://schemas.android.com/tools"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    android:background="#999"

    android:orientation="vertical"

    tools:context=".SecondActivity">

    <TextView

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_gravity="center"

        android:padding="15dp"

        android:text="Second Activity"

        android:textColor="#f00"

        android:textSize="35sp" />

</LinearLayout>

SecondActivity.java

package com.example.malik.blog;

import android.support.v7.app.AppCompatActivity;

import android.os.Bundle;

public class SecondActivity extends AppCompatActivity {

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_second);

    }

}

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>

<manifest xmlns:android="http://schemas.android.com/apk/res/android"

    package="com.example.malik.blog">

    <application

        android:allowBackup="true"

        android:icon="@mipmap/ic_launcher"

        android:label="@string/app_name"

        android:roundIcon="@mipmap/ic_launcher_round"

        android:supportsRtl="true"

        android:theme="@style/AppTheme">

        <activity android:name=".MainActivity">

            <intent-filter>

                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />

            </intent-filter>

        </activity>

        <activity android:name=".FirstActivity"/>

        <activity android:name=".SecondActivity"/>

    </application>

</manifest>

build.gradle file 

apply plugin: 'com.android.application'

android {

    compileSdkVersion 25

    buildToolsVersion "25.0.2"

    defaultConfig {

        applicationId "com.example.malik.blog"

        minSdkVersion 18

        targetSdkVersion 25

        versionCode 1

        versionName "1.0"

        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"

    }

    buildTypes {

        release {

            minifyEnabled false

            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'

        }

    }

}

dependencies {

    compile fileTree(dir: 'libs', include: ['*.jar'])

    androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {

        exclude group: 'com.android.support', module: 'support-annotations'

    })

    compile 'com.android.support:appcompat-v7:25.3.1'

    compile 'com.android.support.constraint:constraint-layout:1.0.2'

    testCompile 'junit:junit:4.12'

}