Android Programming

Before programming for Android, you need Downloading and Installing Android Studio. The following list gives the steps of how to program for Android by using Android Studio. Developers may program the following files: Basically, the two examples are used in this page:
  1. Launch the Android Studio.
    2.  Launch the Android Studio by selecting the following Windows options: 
       Start ⇒ All Programs ⇒ Android Studio ⇒ Android Studio

  2. Start a New Android Studio Project.
    3.  Take the following steps:

    1. Fill in options for the new project such as
      • Application name: HelloWorld,
      • Company Domain: wenchen.example.com,
      • Package name: com.example.wenchen.helloworld (given), and
      • Project location: C:\Android-Studio-workspace\HelloWorld.


    2. Select the form factors the app will run on such as
      • Phone and Tablet and
      • Minimum SDK: API 15: Android 4.0.3 (IceCreamSandwich)
        Lower API levels target more devices, but have fewer features available. By targeting API 15 and later, the app will run on approximately 94.0% of the devices that are active on the Google Play Store.


    3. Select an Empty View Activity Blank Activity.


    4. Fill in options such as
      • Activity Name: MainActivity,
      • Layout Name: activity_main,
      • Title: MainActivity, and
      • Menu Resource Name: menu_main.


  3. Start Programming the Android Studio Project.
    4.
      Note that Android is constantly revised and backward compatibility is an issue. This application works on API 15: Android 4.0.3 (IceCreamSandwich) correctly. If a newer version is used and minor compatibility errors show up, you should be able to fix them based on the error messages. One nice resource for Android debugging is Stack Overflow.
    The Android Studio IDE (Integrated Development Environment) is as follows:


  4. Program AndroidManifest.xml.
    5.
    1. Expand the app of the project HelloWorld in the left pane.
    2. Double click the file AndroidManifest.xml and complete it such as:


      C:\Android-Studio-workspace\HelloWorld\app\src\main\AndroidManifest.xml 
       <?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
  package="com.example.wenchen.helloworld" >

 <application
  android:allowBackup="true"
  android:icon="@mipmap/ic_launcher"
  android:label="@string/app_name"
  android:theme="@style/Theme.HelloWorld" >
 <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 =".NextActivity"
           android:label="Next Page" />
 </application>
</manifest>

  5. Program MainActivity.java.
    6.  Double click the file java\com\example\wenchen\helloworld\MainActivity.java and a template will be given as follows:

    C:\Android-Studio-workspace\HelloWorld\app\src\main\java\com\example\wenchen\helloworld\MainActivity.java 
    package com.example.wenchen.helloworld;

import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;

public class MainActivity extends AppCompatActivity {

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

 @Override
 public boolean onCreateOptionsMenu( Menu menu ) {
  // Inflate the menu; this adds items to the action bar if it is present.
  getMenuInflater( ).inflate( R.menu.menu_main, menu );
  return true;
 }

 @Override
 public boolean onOptionsItemSelected( MenuItem item ) {
  // Handle action bar item clicks here. The action bar will
  // automatically handle clicks on the Home/Up button, so long
  // as you specify a parent activity in AndroidManifest.xml.
  int id = item.getItemId( );

  // noinspection SimplifiableIfStatement
  if ( id == R.id.action_settings ) {
   return true;
  }
  return super.onOptionsItemSelected( item );
 }
}

    Complete the Java class MainActivity.java such as


    C:\Android-Studio-workspace\HelloWorld\app\src\main\java\com\example\wenchen\helloworld\MainActivity.java 
    package com.example.wenchen.helloworld;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.view.Menu;
import android.view.MenuItem;

public class MainActivity extends Activity {

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

  final EditText name = (EditText) findViewById( R.id.name );
  final Button button = (Button)   findViewById( R.id.next );
  button.setOnClickListener(
   new View.OnClickListener( ) {
    public void onClick( View v ) {
     /** Here i calls a new screen. **/
     Intent i = new Intent( MainActivity.this, NextActivity.class );
     i.putExtra( "name", name.getText().toString( ) );
     startActivity( i );
    }
   }
  );
 }

 @Override
 public boolean onCreateOptionsMenu( Menu menu ) {
  // Inflate the menu; this adds items to the action bar if it is present.
  getMenuInflater( ).inflate( R.menu.menu_main, menu );
  return true;
 }

 @Override
 public boolean onOptionsItemSelected( MenuItem item ) {
  // Handle action bar item clicks here. The action bar will
  // automatically handle clicks on the Home/Up button, so long
  // as you specify a parent activity in AndroidManifest.xml.
  int id = item.getItemId( );

  // noinspection SimplifiableIfStatement
  if ( id == R.id.action_settings ) {
   return true;
  }
  else if ( id == R.id.next ) {
   Intent i = new Intent( MainActivity.this, NextActivity.class );
   startActivity( i );
  }
  return super.onOptionsItemSelected( item );
 }
}

  6. Program NextActivity.java.
    7.  Using the left pane, add another Java class, NextActivity.java, by right clicking the mouse: 
       com.example.wenchen.helloworld ⇒ New ⇒ Java Class

    Complete the Java class NextActivity.java such as

    C:\Android-Studio-workspace\HelloWorld\app\src\main\java\com\example\wenchen\helloworld\NextActivity.java 
    package com.example.wenchen.helloworld;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class NextActivity extends Activity {
 /** Called when the activity is first created. */
 @Override
 public void onCreate( Bundle savedInstanceState ) {
  super.onCreate( savedInstanceState );
  setContentView( R.layout.activity_next );

  final TextView tvView = (TextView) findViewById( R.id.tvView );
  Intent intent = getIntent( );
  String name = intent.getStringExtra( "name" );
  tvView.setText( "Welcome, " + name );
  final Button button = (Button) findViewById( R.id.home );
  button.setOnClickListener(
   new View.OnClickListener( ) {
    public void onClick( View v ) {
     Intent i = new Intent( NextActivity.this, MainActivity.class );
     startActivity( i );
    }
   }
  );
 }

 @Override
 public boolean onCreateOptionsMenu( Menu menu ) {
  // Inflate the menu; this adds items to the action bar if it is present.
  getMenuInflater( ).inflate( R.menu.menu_next, menu );
  return true;
 }

 @Override
 public boolean onOptionsItemSelected( MenuItem item ) {
  // Handle action bar item clicks here. The action bar will
  // automatically handle clicks on the Home/Up button, so long
  // as you specify a parent activity in AndroidManifest.xml.
  int id = item.getItemId( );

  // noinspection SimplifiableIfStatement
  if ( id == R.id.action_settings ) {
   return true;
  }
  else if ( id == R.id.home ) {
   Intent i = new Intent( NextActivity.this, MainActivity.class );
   startActivity( i );
  }
  return super.onOptionsItemSelected( item );
 }
}

  7. Program activity_main.xml.
    8.  Double click the file activity_main.xml and complete it such as:


    Android Studio is a WYSIWYG (What You See Is What You Get) IDE. You may use the palette to draw the user interface and the Android Studio will convert it into XML:


    C:\Android-Studio-workspace\HelloWorld\app\src\main\res\activity_main.xml 
    <LinearLayout
 xmlns:android         = "http://schemas.android.com/apk/res/android"
 android:orientation   = "vertical"
 android:layout_width  = "match_parent"
 android:layout_height = "match_parent"
 android:weightSum     = "1"
 android:gravity       = "center_vertical|center_horizontal">

 <TextView
  android:layout_width   = "wrap_content"
  android:layout_height  = "wrap_content"
  android:textAppearance = "?android:attr/textAppearanceLarge"
  android:text           = "Hello, your name:"
  android:layout_weight  = "0.07"
  android:textStyle      = "bold" />

 <EditText
  android:layout_width  = "216dp"
  android:layout_height = "wrap_content"
  android:id            = "@+id/name" />

 <Button
  android:layout_width  = "wrap_content"
  android:layout_height = "wrap_content"
  android:text          = "Next Page"
  android:id            = "@+id/next" />

</LinearLayout>

  8. Program activity_next.xml.
    9.  Using the left pane, add another layout XML file, activity_next.xml, by selecting the following options:

      Right clicking the “layout ⇒ New ⇒ XML ⇒ layout XML file”


    C:\Android-Studio-workspace\HelloWorld\app\src\main\res\activity_next.xml 
    <LinearLayout
 xmlns:android         = "http://schemas.android.com/apk/res/android"
 android:layout_width  = "match_parent"
 android:layout_height = "match_parent"
 android:orientation   = "vertical"
 android:weightSum     = "1"
 android:gravity       = "center_vertical|center_horizontal">

 <TextView
  android:layout_width   = "287dp"
  android:layout_height  = "wrap_content"
  android:textAppearance = "?android:attr/textAppearanceLarge"
  android:id             = "@+id/tvView"
  android:textStyle      = "bold"
  android:layout_weight  = "0.10"
  android:gravity        = "center_horizontal" />

 <Button
  android:layout_width  = "wrap_content"
  android:layout_height = "40dp"
  android:text          = "Home Page"
  android:id            = "@+id/home" />

</LinearLayout>

  9. Program menu_main.xml.
    10.  Double click the file menu_main.xml and complete it such as:


    You may use the Android Studio to view the result:



    C:\Android-Studio-workspace\HelloWorld\app\src\main\res\menu_main.xml 
    <menu
 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"
 tools:context=".MainActivity">

 <item android:id="@+id/action_settings"
  android:title="@string/action_settings"
  android:orderInCategory="100"
  app:showAsAction="never" />

 <item android:id="@+id/next"
  android:title="Next Page"
  android:orderInCategory="100"
  app:showAsAction="never" />
</menu>

  10. Program menu_next.xml.
    11.
    C:\Android-Studio-workspace\HelloWorld\app\src\main\res\menu_next.xml 
    <menu
 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"
 tools:context=".NextActivity">

 <item android:id="@+id/action_settings"
  android:title="@string/action_settings"
  android:orderInCategory="100"
  app:showAsAction="never" />
 
 <item android:id="@+id/home"
  android:title="Home Page"
  android:orderInCategory="100"
  app:showAsAction="never" />
</menu>

  11. Program strings.xml.
    12.  The file defines some string variables such as

    C:\Android-Studio-workspace\HelloWorld\app\src\main\res\values\strings.xml 
    <resources>
 <string name="app_name">HelloWorld</string>
 <string name="hello_world">Hello world!</string>
 <string name="action_settings">Settings</string>
</resources>

  12. Build the App.
    13.  Build the project by selecting the following options: 
       Build ⇒ Rebuild Project

  13. Run the App.
    14.  Before running the project, you may pick a running device by selecting the following options: 
       Tools ⇒ Android ⇒ AVD Manager
    ⇓
    ⇓

    If the device does not start the project, run the project by selecting the following options: 
       Run ⇒ Run 'app'
    ⇓
    ⇓   ⇑