Android Development - A Kick Start for beginners .

Tools Required for android 

• Java Development Kit(JDK)
• Android Studio
• Genymotion

Activity 

In Android, an activity is represent a single screen. Most applications have multiple activities to represent different screens, for example, one activity to display a list of the application settings, another activity to display the application status.

Create following two XML layout files in “res/layout/” folder :

1. res/layout/main.xml – Represent screen 1
2. res/layout/main2.xml – Represent screen 2

File : res/layout/main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/linearLayout1"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="I'm screen 1 (main.xml)"
        android:textAppearance="?android:attr/textAppearanceLarge" />

    <Button
        android:id="@+id/button1"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="Click me to another screen" />

</LinearLayout>

File : res/layout/main2.xml

Markup

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/linearLayout1"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" >

    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="I'm screen 2 (main2.xml)"
        android:textAppearance="?android:attr/textAppearanceLarge" />

</LinearLayout>

2. Activities

Create two activity classes :

AppActivity.java –> main.xml
App2Activity.java –> main2.xml


To navigate from one screen to another screen, use following code :


Java

    Intent intent = new Intent(context, anotherActivity.class);
    startActivity(intent); 


File : AppActivity.java


Java

package com.mkyong.android;

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

public class AppActivity extends Activity {

 Button button;

 @Override
 public void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.main);
  addListenerOnButton();
 }

 public void addListenerOnButton() {

  final Context context = this;

  button = (Button) findViewById(R.id.button1);

  button.setOnClickListener(new OnClickListener() {

   @Override
   public void onClick(View arg0) {

       Intent intent = new Intent(context, App2Activity.class);
                            startActivity(intent);   

   }

  });

 }

}


File : App2Activity.java


Java

package com.mkyong.android;

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

public class App2Activity extends Activity {

 Button button;

 @Override
 public void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.main2);
 }

}

3. AndroidManifest.xml

Declares above two activity classes in AndroidManifest.xml.

File : AndroidManifest.xml


Markup

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.mkyong.android"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk android:minSdkVersion="10" />

    <application
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name" >
        <activity
            android:label="@string/app_name"
            android:name=".AppActivity" >
            <intent-filter >
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:label="@string/app_name"
            android:name=".App2Activity" >
        </activity>
    </application>

</manifest>


Now try running application and see what happens :)