Proximity Sensor: is sensor that can recognize presence of nearby object. we will user this sensor to start voice recognition. So when you take you android device near to your face, proximity sensor will start the voice recognizer.

Voice Recognizer: can convert speech to text. So when you give the voice command, its will return an array of matches and will start TTS.

TTS(Text To Speech): can convert text speech. In this application we will use TTS to listen voice command response.

1. First we will check to see if proximity sensor is available.

SensorManager sensorManager = (SensorManager) getSystemService(Context.SENSOR_SERVICE);
		Sensor proximitySensor = sensorManager
				.getDefaultSensor(Sensor.TYPE_PROXIMITY);

		if (proximitySensor == null) {
			Toast.makeText(this, "No proximity sensor", Toast.LENGTH_SHORT)
					.show();
		} else {
			sensorManager.registerListener(proximitySensorEventListener,
					proximitySensor, SensorManager.SENSOR_DELAY_NORMAL);
		}

2. We will catch proximity event in onSensorChanged callback method in proximitySensorEventListener.

SensorEventListener proximitySensorEventListener = new SensorEventListener() {

		@Override
		public void onAccuracyChanged(Sensor sensor, int accuracy) {
			// TODO Auto-generated method stub

		}

		@Override
		public void onSensorChanged(SensorEvent event) {
			if (event.sensor.getType() == Sensor.TYPE_PROXIMITY) {
				if (event.values[0] < proximitySensor.getMaximumRange()) {
					startSpeechRecognizer();
				}

			}
		}
	};

3. Start speech recognizer, when any object comes near to mobile.

private static final int VOICE_REQUEST_CODE = 101;
private void startSpeechRecognizer() {
		PackageManager pm = getPackageManager();
		List activities = pm.queryIntentActivities(new Intent(
				RecognizerIntent.ACTION_RECOGNIZE_SPEECH), 0);
		if (activities.size() != 0) {
		Intent intent = new Intent(RecognizerIntent.ACTION_RECOGNIZE_SPEECH);
		intent.putExtra(RecognizerIntent.ACTION_RECOGNIZE_SPEECH,
				RecognizerIntent.LANGUAGE_MODEL_FREE_FORM);
		intent.putExtra(RecognizerIntent.EXTRA_PROMPT, "Voice Command");
		startActivityForResult(intent, VOICE_REQUEST_CODE);
		}else{
			Toast.makeText(this, "Speech Recognizer is not present", Toast.LENGTH_SHORT)
			.show();
		}

	}

Explanation of above code:
queryIntentActivities: will return the list of activities that can handle action ACTION_RECOGNIZE_SPEECH.
ACTION_RECOGNIZE_SPEECH: start implicit activity that can handle action ACTION_RECOGNIZE_SPEECH.
EXTRA_PROMPT: It will show custom message "Voice Command" on voice recognizer activity.

4. We will get result of speech recognizer in onActivityResult callback.

protected void onActivityResult(int requestCode, int resultCode, Intent data) {
		if (requestCode == VOICE_REQUEST_CODE && resultCode == RESULT_OK) {
			ArrayList matches = data
					.getStringArrayListExtra(RecognizerIntent.EXTRA_RESULTS);
			for (int i = 0; i < commands.length; i++) {
				if (matches.contains(commands[i])) {
					selectedCommand = i;
				}
			}
			if (isTtsInitialized) {
				if (selectedCommand >= 0) {
					tts.speak("you have selected" + commands[selectedCommand]
							+ " command.", TextToSpeech.QUEUE_FLUSH, null);
				} else {
					tts.speak("I am sorry. could you please repeat that.", TextToSpeech.QUEUE_FLUSH, null);
				}

			}

		}
}

Explanation of above code:

requestCode and resultCode: first we will check requestCode and resultCode to insure that onActivityResult is called by speech recognizer with success response.
getStringArrayListExtra: We will get all matches using getStringArrayListExtra. If matches contains our commands, TTS will say that otherwise it will say "I am sorry. could you please repeat that.".

5. We will check to see if TTS is present. First we need to implement OnInitListener and override onInit method.

@Override
	public void onInit(int status) {
		if (status == TextToSpeech.SUCCESS) {
			int result = tts.setLanguage(Locale.US);
			if (result == TextToSpeech.LANG_MISSING_DATA
					|| result == TextToSpeech.LANG_NOT_SUPPORTED) {
				Toast.makeText(this, "Language is not available",
						Toast.LENGTH_SHORT);
			} else {
				isTtsInitialized = true;
			}
		} else {
			Toast.makeText(this, "Initialization failed", Toast.LENGTH_SHORT);
		}

	}

After completion of TTS engine initialization start the TTs.

Intent checkIntent = new Intent();
		checkIntent.setAction(TextToSpeech.Engine.ACTION_CHECK_TTS_DATA);
		startActivityForResult(checkIntent, TTS_REQUEST_CODE);

6. We will get response in onActivityResult.

@Override
	protected void onActivityResult(int requestCode, int resultCode, Intent data) {

		if (requestCode == TTS_REQUEST_CODE) {
			if (resultCode == TextToSpeech.Engine.CHECK_VOICE_DATA_PASS) {
				// success, create the TTS instance
				tts = new TextToSpeech(this, this);
			} else {
				// missing data, install it
				Intent installIntent = new Intent();
				installIntent
						.setAction(TextToSpeech.Engine.ACTION_INSTALL_TTS_DATA);
				startActivity(installIntent);
			}
		}
		super.onActivityResult(requestCode, resultCode, data);
	}

7. Don't forget to unregister proximity sensor listener.

@Override
	protected void onStop() {
		if (sensorManager != null) {
			sensorManager.unregisterListener(proximitySensorEventListener);
		}
		super.onStop();
	}

Instead of just listening the commands we can do lots of things like opening address book, messages, mails, etc. Here is the complete code.

package com.vimviv;

import java.util.ArrayList;
import java.util.List;
import java.util.Locale;

import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.content.pm.ResolveInfo;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.os.Bundle;
import android.speech.RecognizerIntent;
import android.speech.tts.TextToSpeech;
import android.speech.tts.TextToSpeech.OnInitListener;
import android.widget.Toast;

public class VoiceCommandActivity extends Activity implements OnInitListener {

	private static final int VOICE_REQUEST_CODE = 101;
	private static final int TTS_REQUEST_CODE = 102;
	private static final String[] commands = { "open", "close", "find" };

	private int selectedCommand = -1;
	private String speachMessage = "I am sorry. could you please repeat that.";
	private boolean isTtsInitialized = false;
	TextToSpeech tts;
	SensorManager sensorManager;
	Sensor proximitySensor;

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

		// check proximity sensor
		sensorManager = (SensorManager) getSystemService(Context.SENSOR_SERVICE);
		proximitySensor = sensorManager
				.getDefaultSensor(Sensor.TYPE_PROXIMITY);

		if (proximitySensor == null) {
			Toast.makeText(this, "No proximity sensor", Toast.LENGTH_SHORT)
					.show();
		} else {
			sensorManager.registerListener(proximitySensorEventListener,
					proximitySensor, SensorManager.SENSOR_DELAY_NORMAL);
		}

		//check for TTS data
		Intent checkIntent = new Intent();
		checkIntent.setAction(TextToSpeech.Engine.ACTION_CHECK_TTS_DATA);
		startActivityForResult(checkIntent, TTS_REQUEST_CODE);

	}

	SensorEventListener proximitySensorEventListener = new SensorEventListener() {

		@Override
		public void onAccuracyChanged(Sensor sensor, int accuracy) {
			// TODO Auto-generated method stub

		}

		@Override
		public void onSensorChanged(SensorEvent event) {
			// TODO Auto-generated method stub

			if (event.sensor.getType() == Sensor.TYPE_PROXIMITY) {
				if (event.values[0] < proximitySensor.getMaximumRange()) {
					startSpeachRecognition();
				}

			}
		}
	};

	private void startSpeachRecognition() {
		// Check to see if a recognition activity is present
				PackageManager pm = getPackageManager();
				List activities = pm.queryIntentActivities(new Intent(
						RecognizerIntent.ACTION_RECOGNIZE_SPEECH), 0);
				if (activities.size() != 0) {
					Intent intent = new Intent(RecognizerIntent.ACTION_RECOGNIZE_SPEECH);
					intent.putExtra(RecognizerIntent.ACTION_RECOGNIZE_SPEECH,
							RecognizerIntent.LANGUAGE_MODEL_FREE_FORM);
					intent.putExtra(RecognizerIntent.EXTRA_PROMPT, "Voice Command");
					startActivityForResult(intent, VOICE_REQUEST_CODE);
				} else {
					Toast.makeText(this, "Recognizer not present", Toast.LENGTH_SHORT)
					.show();
				}

	}

	// Initialization response of TTS engine
	@Override
	public void onInit(int status) {
		if (status == TextToSpeech.SUCCESS) {
			int result = tts.setLanguage(Locale.US);
			if (result == TextToSpeech.LANG_MISSING_DATA
					|| result == TextToSpeech.LANG_NOT_SUPPORTED) {
				Toast.makeText(this, "Language is not available",
						Toast.LENGTH_SHORT);
			} else {
				isTtsInitialized = true;
			}
		} else {
			Toast.makeText(this, "Initialization failed", Toast.LENGTH_SHORT);
		}

	}

	@Override
	protected void onActivityResult(int requestCode, int resultCode, Intent data) {
		if (requestCode == VOICE_REQUEST_CODE && resultCode == RESULT_OK) {
			ArrayList matches = data
					.getStringArrayListExtra(RecognizerIntent.EXTRA_RESULTS);
			for (int i = 0; i < commands.length; i++) {
				if (matches.contains(commands[i])) {
					selectedCommand = i;
				}
			}
			if (isTtsInitialized) {
				if (selectedCommand >= 0) {
					tts.speak("you have selected" + commands[selectedCommand]
							+ " command.", TextToSpeech.QUEUE_FLUSH, null);
					selectedCommand = -1;
				} else {
					tts.speak(speachMessage, TextToSpeech.QUEUE_FLUSH, null);
				}

			}

		}
		if (requestCode == TTS_REQUEST_CODE) {
			if (resultCode == TextToSpeech.Engine.CHECK_VOICE_DATA_PASS) {
				// success, create the TTS instance
				tts = new TextToSpeech(this, this);
			} else {
				// missing data, install it
				Intent installIntent = new Intent();
				installIntent
						.setAction(TextToSpeech.Engine.ACTION_INSTALL_TTS_DATA);
				startActivity(installIntent);
			}
		}
		super.onActivityResult(requestCode, resultCode, data);
	}

	@Override
	protected void onStop() {
		if (sensorManager != null) {
			sensorManager.unregisterListener(proximitySensorEventListener);
		}
		super.onStop();
	}

}

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3. What is intent filter in android?

In this post we will see, how does implicit intent work?
According to google intent filter is “To inform the system which implicit intents they can handle”

e.g. you have more that one activities in your application and you know that there is no “main” method in android application. So how activity launcher will know that which activity to start first.

For that we specify a intent filter.

intent filter with “android.intent.action.MAIN” action and “android.intent.category.LAUNCHER” category tells to launcher to launch HomeActivity.

implicit Intent is luxury provided by android. You just need to know, what do you want to perform. you don’t bother who is going to perform and how that activity is going to perform.(there will be a problem, if no activity is there to perform your task)

When will you specify intent filter?
if you think, any other application can use your activity to perform some task, specify a intent filter for that. You can be a performer using intent filter.

For example, you have created a activity that can display image and you think that other applications also use your activity to view images.

1. specify intent filter like this.

In the above code we can see that intent-filter has following properties.
a. action: type for which this activity will respond for.Like this activity will respond for view action.
b. category: implicit intents are divided in categories.Like this activity is in default category.
c. data: Specify more information about intent-filter. Like this activity will handle file of mimeType “image/*”.

2. Now you need to display image in your activity.

public class MyImageViewerActivity extends Activity {

	TextView textView;
	ImageView imageView;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        Intent intent = getIntent();
        Uri uri = intent.getData();

        textView = (TextView) findViewById(R.id.textView);
        imageView = (ImageView) findViewById(R.id.imageView);

        if(uri != null){
        	imageView.setImageURI(uri);
        	textView.setText(uri.getPath());
        }

    }
}

using getData() we will get the path of the image and we will use that path to display image.

3. When you install this application in your device and click on any image file, you will see a choice dialog that offer you to select between default application and your application. Just select your application to see the image.

4. Just select your app to view image:

When will you call implicit intent?
If you think that any other activity is available in device for handling your application’s specific task, just use the implicit intent to call that activity.

For example, if you want to open a browser to render URI. You can use implicit intent to call browser.

Uri uri = Uri.parse( "http://blog.vimviv.com" );
startActivity(new Intent(Intent.ACTION_VIEW, uri));

In above example we can see that we have a uri and we want to view content of that uri. We don’t need to know that which activity is going to render this uri.

Some more examples of intent filters.
a) intent filter for app launcher

b)intent filter for image view.

c)intent filter for image send:

d) intent filter for custom uri:

e) intent filter for sms:

f)intent filter phone dial:

Some examples for calling implicit intents:
a) start contacts activity:

Intent contacts = new Intent();
              contacts.setAction(android.content.Intent.ACTION_VIEW);
              contacts.setData(People.CONTENT_URI);
              startActivity(contacts);

b) install an app:

Intent intent = new Intent(Intent.ACTION_VIEW);
intent.setDataAndType(Uri.fromFile(new File(Environment.getExternalStorageDirectory() + "app.apk")), "application/vnd.android.package-archive");
startActivity(intent);  

c) uninstall an app:

Uri packageUri = Uri.parse("package:com.vimviv");
            Intent uninstallIntent =
              new Intent(Intent. ACTION_DELETE, packageUri);
            startActivity(uninstallIntent);

d) start sms application:

Intent sendIntent = new Intent(Intent.ACTION_VIEW);        
sendIntent.setData(Uri.parse("sms:"));

We can also search for a matching intent:

final PackageManager packageManager = context.getPackageManager();
    final Intent intent = new Intent(action);
    List list =
            packageManager.queryIntentActivities(intent,
                    PackageManager.MATCH_DEFAULT_ONLY);
    return list.size() > 0;

So help others by creating re-usable activities.

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@Override
    public String toString() {
    	return super.toString();
    }

In the above example code,
@Override: gives the information that toString() method is overridden from Object class.
In this post we will create custom annotations.

1. First we will create a custom annotation for Database table name.

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
public @interface DatabaseTable {

	String tableName();
}

Explanation of above code:
@interface: We can see in the above code is similar to interface declaration. @Retention(RetentionPolicy.RUNTIME): We need this annotation type at runtime. We are using RetentionPolicy.RUNTIME.
@Target(ElementType.TYPE): Indicates that this annotation type will be used to annotate class declaration

2. Next we will create another annotation for column names.

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface DatabaseField {

	String columnName() default "";
	String columnType();
	boolean canBeNull() default true;

}

Explanation of above code:
@Target(ElementType.FIELD): Indicates that this annotation type will used to annotate fields declarations.
default: is used to assign default value.

3. We will create UserInfo class that we want to save in database.

@DatabaseTable (tableName = "user")
public class UserData {

	@DatabaseField (columnName = "first_name", columnType ="TEXT")
	private String firstName;
	@DatabaseField (columnName = "last_name", columnType ="TEXT")
	private String lastName;
	@DatabaseField (columnName = "age", columnType ="INTEGER")
	private int age;

}

4. Create query for create table.

public String createTableQuery(Class clazz){
		DatabaseTable annot = (DatabaseTable) clazz.getAnnotation(DatabaseTable.class);
		String table = annot.tableName();
		Field[] fields = clazz.getDeclaredFields();
		StringBuilder sb = new StringBuilder("CREATE TABLE ").append(table).append(
						" (_id integer primary key");
				for (Field field : fields) {
					DatabaseField fieldAnnot = (DatabaseField) field.getAnnotation(DatabaseField.class);
					String columnName = fieldAnnot.columnName();
					String columnType = fieldAnnot.columnType();
					sb.append(", ").append(columnName).append(" ").append(columnType);
				}
				sb.append(")");
				return sb.toString();
		}

5. We will call this method like this

String sqlQuery = createTableQuery(UserInfo.Class);

Complete implementation of ORM(object relational mapping) is complex. You can check OrmLite – Lightweight Object Relational Mapping (ORM) Java Package for complete annotation based ORM implementation.

We can also search at run time about annotated classes.

public static List getModels(Context context, String packageName)
			throws IOException, URISyntaxException, ClassNotFoundException,
			NameNotFoundException {

		String apkName = context.getPackageManager().getApplicationInfo(packageName, 0).sourceDir;
		DexFile dexFile = new DexFile(apkName);
		PathClassLoader pathLoader = new PathClassLoader(apkName, Thread.currentThread().getContextClassLoader());
		DexClassLoader classLoader = new DexClassLoader(apkName,
				new ContextWrapper(context).getCacheDir().getAbsolutePath(),
				null, pathLoader);
		List classes = new ArrayList();
		Enumeration entries = dexFile.entries();

		while (entries.hasMoreElements()) {

			String entry = (String) entries.nextElement();

			if (entry.startsWith(packageName)) {
				Class entryClass = classLoader.loadClass(entry);
				if (entryClass != null) {
					Annotation[] annotations = entryClass.getAnnotations();
					for (Annotation annotation : annotations) {
						if (annotation instanceof DatabaseTable) {
							classes.add(entryClass);
						}
					}
				}
			}
		}

		return classes;
	}

This was a small example of custom annotation. We can use custom annotations in a lots of ways like configuration, unit testing, etc.

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 private void checkLocationProviders(){
	    //String provider = Settings.Secure.getString(getContentResolver(),Settings.Secure.LOCATION_PROVIDERS_ALLOWED);
	       if(lm.isProviderEnabled(LocationManager.GPS_PROVIDER)){

	    	   Toast.makeText(EnableLocationActivity.this, "GPS provider Enabled: ",Toast.LENGTH_LONG).show();

	       }else if(lm.isProviderEnabled(LocationManager.NETWORK_PROVIDER)){

	    	   Toast.makeText(EnableLocationActivity.this, "Network provider Enabled: ",Toast.LENGTH_LONG).show();

	       }else{
	    	   AlertDialog.Builder builder = new AlertDialog.Builder(this);
	    	   builder.setMessage("Location providers are not available. Enable GPS or network providers.")
	    	          .setCancelable(false)
	    	          .setPositiveButton("Yes", new DialogInterface.OnClickListener() {
	    	              public void onClick(DialogInterface dialog, int id) {
	    	            	  Intent intent = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS);
	    	   	          startActivityForResult(intent, 1);
	    	              }
	    	          })
	    	          .setNegativeButton("No", new DialogInterface.OnClickListener() {
	    	              public void onClick(DialogInterface dialog, int id) {
	    	            	  EnableLocationActivity.this.finish();
	    	              }
	    	          }).show();

	       }

	   }

	   @Override
	protected void onActivityResult(int requestCode, int resultCode, Intent data) {
		   checkLocationProviders();
	super.onActivityResult(requestCode, resultCode, data);
	}

Explanation of above code.
1. First we need to create LocationManager.
LocationManager lm = (LocationManager) this.getSystemService(Context.LOCATION_SERVICE);

2. using isProviderEnabled Check location providers are already enabled or not.

3. If location providers are not enabled, ask user to enable location providers and launch location settings activity.

4. Using onActivityResult check user has changed location settings or not.

5. Dont forget to add user permission to AndroidMenifest.xml file.

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using java code

EditText editText = new EditText(context);

or using XML

Single-line EditText:

Single-line EditText means if you press “enter key” on EditText,focus will go to the next widget. Default behavior of EditText is multi-line.It means if you press “enter key”, a new line will add to the EditText.
using android:singleLine=”true” property you can make single-line EditText. But this property is now deprecated.
So if you add any inputtype property, EditText will become single-line EditText.
e.g. android:inputType=”text”

Multi-line EditText:
There are two properties are available for multi-line Edittext.
a. android:lines:
Using “lines” property you can specify height of edittext in terms of lines.
e.g. android:lines = “3″ means only 3 lines will be visible in EditText and for 4rth line, you have to scroll vertically.

android:lines

android:inputType
Using the inputType property we can restrict use to enter the correct data.
e.g.

b.android:maxLines
In the above example user can enter only numbers in the EditText widget. If you specify a inputType, EditText will become single line.
using maxLines property you can specify the maximum height of the EditText.
e.g.android:maxLines=”3″ means first only single line will be visible and when you press “enter key”, EditText’s height will expend till the maxLines.

android:maxLines

android:maxLine-1

Gravity:

gravity

Read-only EditText:
Sometimes we need to disable EditText. For that we can use “editable” and “enabled” properties of EditText.

disable

Hint(Watermark) in EditText:
If you are using “hint” property of EditText, a small description of field will be visible inside field and if user clicks on EditText, it disappears and user is free to write something in it. So there is no need of label for EditText, if you are using “hint” property.

android:hint

or from java code

editText.setHint("Enter you name");

Error popup in edittext:
Sometimes user entered invalid data in the EditText and you want to notify user that you have entered an invalid data. In this type of case you can use setError() method of EditText. It will show small popup of the error message.

setError

editText.setError("Invalid Input");

Hide soft keyboard:
Sometimes you want to hide soft keyboard on some action. You can do this using this code.

InputMethodManager imm = (InputMethodManager)getSystemService(INPUT_METHOD_SERVICE);
imm.hideSoftInputFromWindow(getWindowToken(), 0);

If in an activity first focus is on EditText, soft keyboard will appear on activity launch. If you don’t want this, you can use this code.

Listen IME key events and enter key:

editText.setOnEditorActionListener(new OnEditorActionListener() {

			@Override
			public boolean onEditorAction(TextView v, int actionId, KeyEvent event) {
				if(event!=null && event.getAction()==KeyEvent.ACTION_DOWN){
					//Handle enter key
					return true;
				}
				if(actionId == EditorInfo.IME_ACTION_NEXT){
					//Handle IME NEXT key
					return true;
				}
				if(actionId == EditorInfo.IME_ACTION_DONE){
					//Handle IME DONE key
					return true;
				}
				return false;
			}
		});

android:layout_weight
using layout_weight we can specify the ratio of the size of the child items in the layout.
e.g.

layout_weight

Drawable:
Best thing about android widgets are, you can easily customize them. And for customization you no need to rush codes in the layout xml. So create a drawable xml in the drawable folder
e.g.

drawable

Selector:
EditText can be in different states like focused, disabled, pressed, etc. You can see in the previous example EditText will look same in all states.So if you want to give different looks to EditText for different states. you need to create selector xml.

I will keep update this article because there are lots of things that we can do with EditText widget. If you want to suggest something to improve this post, your comments are always welcome here.

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Intent intent = new Intent(FirstActivity.this,SecondActivity.class);
startActivity(intent);

Implicit Intents: Instead of giving name of the intent you tell the system what you want to perform and system will find suitable activity for your task.
e.g.

intent = new Intent(Intent.ACTION_VIEW,
Uri.parse("http://www.vimviv.com"));
startActivity(intent);

Some example of explicit intents:
1. Start Activity:

Intent intent = new Intent(FirstActivity.this, SecondActivity.class);
startActivity(intent);

2. Get result from activity:

a. FirstActivity.java

public class FirstActivity extends Activity {

	Button button;
	private static final int REQUEST_CODE = 10;
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        LinearLayout ll = new LinearLayout(this);
        button = new Button(this);
        ll.addView(button);
        setContentView(ll);
        button.setText("Call Second Activity");
        button.setOnClickListener(new OnClickListener() {

			@Override
			public void onClick(View v) {
				Intent i = new Intent(FirstActivity.this, SecondActivity.class);
				i.putExtra("data", "Hi from First Activity");
				// Set the request code to any code you like, you can identify the
				// callback via this code
				startActivityForResult(i, REQUEST_CODE);

			}
		});
    }
    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    	if (resultCode == RESULT_OK && requestCode == REQUEST_CODE) {
			if (data.hasExtra("result")) {
				String message = data.getExtras().getString("result");
				Toast.makeText(FirstActivity.this, message, Toast.LENGTH_SHORT).show();
			}
		}
    }
}

Explanation of above code is as below:
setContentView: we have added button to linear layout and after that linear layout to activity.
putExtra: using startActivity we are launching SecondActivity and with putExtra method we are sending data also.
onActivityResult: When Second Activity will finish it will call the onActivityResult method of FirstActivity.

b. SecondActivity.java

public class SecondActivity extends Activity{

	Button button;
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		LinearLayout ll = new LinearLayout(this);
		button = new Button(this);
		ll.addView(button);
		setContentView(ll);
		button.setText("back");
		String message = getIntent().getExtras().getString("data");
		Toast.makeText(this, message, Toast.LENGTH_SHORT).show();
		button.setOnClickListener(new OnClickListener() {

			@Override
			public void onClick(View v) {
				finish();

			}
		});
	}

	@Override
	public void finish() {
		Intent data = new Intent();
		data.putExtra("result", "Hi from second activity");
		setResult(RESULT_OK, data);
		super.finish();
	}
}

Explanation of above code is as below:
getExtras: Using the getExtras method we are fetching of data sent by FirstActivity.
finish() :finish method will remove SecondActivity from the display stack and send data to the FirstActivity.

3. Start Service:

Intent intent=new Intent("com.vimviv.service.serviceClass");
startService(intent);

implicit intents examples:

1. make a call:

Intent callIntent = new Intent(Intent.ACTION_CALL, Uri.parse(“1234567890”));
startActivity(callIntent);

2. Launch google map

intent = new Intent(Intent.ACTION_VIEW,
Uri.parse("geo:37.423156,-122.084917?z=19"));
startActivity(intent);

3. email client:

final Intent emailIntent = new Intent(android.content.Intent.ACTION_SEND);

emailIntent .setType("plain/text");
emailIntent .putExtra(android.content.Intent.EXTRA_EMAIL, newString[]{"yourmail@website.com"});
emailIntent .putExtra(android.content.Intent.EXTRA_SUBJECT, mySubject);

emailIntent .putExtra(android.content.Intent.EXTRA_TEXT, myBodyText);

startActivity(Intent.createChooser(intent, "Send mail));

4. start SMS app:

Intent sendIntent = new Intent(Intent.ACTION_VIEW);
sendIntent.setData(Uri.parse("sms:"));
sendIntent.putExtra("sms_body", x);

5. To start a search in the Internet:

Intent intent = new Intent(Intent.ACTION_WEB_SEARCH );
intent.putExtra(SearchManager.QUERY, "Android");
startActivity(intent);

For implicit intents read my next post What is intent filter in android?

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Environment setup: “http://developer.android.com/sdk/installing.html” provides updated and complete step by step process to setup android Environment setup with troubleshooting.

In this post we will create “AddTwoNumbers” application In which we will learn.
1. How to create simple screens in android?
2. How to add simple UI components on the screens in android?
3. How to listen button click event?
4. How to switch between screens?
5. How to send data from one screen to another?

Step 1: Create new android project in eclipse. In “New Android Project” wizard you have to fill some information about your project.

Project name: AddTwoNumbers
Build Target: Android 2.2
Application name: AddTwoNumbers
Package name: com.vimviv
Create Activity: HomeActivity
Min SDK Version: 8

When you click on “finish” button it will automatically generate different folder structures, HomeActivity.java file and other files that are useful for your project.

Step 2: The thing which I like most in android is that UI development part is completely separate from your logical java code. In Android you can do UI designing in 3 different ways.
1. using drag and drop interface.
2. using XML UI file structure.
3. In you java code also you can do UI designing.

I usually prefer XML interface for UI designing. So go to res -> layout -> main.xml
For this particular application I am using two TextViews as a label, two EditTexts for numbers input and one “Add” button.

Explanation of above XML is as below:

LinearLayout: Androids provides different layouts for arranging UI components on the screen. In this example I have used LinearLayout. As the name suggest using LinearLayout you can arrange UI components in horizontally or vertically. Default orientation of LinearLayout is horizontal. But in this example I want to arrange UI components vertically so I have given orientation “vertical”.

android:layout_width & android:layout_height: We can specify width and height of the layout but for good portability on different screen sizes, we should give general values like “fill_parent”(take all available space) and “wrap_content” (takes the space that will be enaugh to show the content).

android:id : We have to provide some unique id to the UI component that will be helpful to UI component from java code.

Now in the layout folder create a new layout “result.xml” for result screen and add this code.

Explanation of above XML is as below:

android:gravity : Using gravity property we give alignment to the TextView’s text. In this example I have given “center_vertical|center_horizontal” alignment.

Step 3: Open the HomeActivity.java and add this code.

package com.vimviv;

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

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

        final EditText numberText1 = (EditText) findViewById(R.id.number1_text);
        final EditText numberText2 = (EditText) findViewById(R.id.number2_text);
        Button addButton = (Button) findViewById(R.id.add_button);

        addButton.setOnClickListener(new OnClickListener() {

			public void onClick(View arg0) {
				int num1 = Integer.parseInt(numberText1.getText().toString());
				int num2 = Integer.parseInt(numberText2.getText().toString());
				int result = num1+num2;
				Intent intent = new Intent(HomeActivity.this,ResultActivity.class);
				intent.putExtra("result","Result: "+result);
				startActivity(intent);
			}
		});

    }
}

Explanation of the above code is as below:

Activity: For creating an activity you have extend the Activity class.

onCreate: When activity is first created onCreate method is called. In this method first line should be super.onCreate(savedInstanceState) . setContentView method will set the content view to main.xml that we have created as our first screen.

findViewById: Using findViewById method we can access xml defined UI components in java code.

Listener: In android listener pattern is simple, if you want to listen for any event call the method setOnListener, pass the OnListener object and you will catch the event in on method.

In this example we are adding the click event listener so just replace with click.

Intent: Using intents we can launch an activity and using putExtra method of intent we can send data to the other activity.

Now create new Activity ResultActivity.java and add this code.

package com.vimviv;

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

public class ResultActivity extends Activity {

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.result);
		String result = getIntent().getStringExtra("result");

		TextView resultView = (TextView) findViewById(R.id.result_view);
		resultView.setText(result);
	}
}

Step 4: Whenever you create a new activity don’t forget to add its information in AndroidManifest.xml

The application is ready now. Go to windows->Android SDK and AVD manager and create new virtual device and run this application in that device.

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I will use these methods in my simple application.

1. We are creating a Ui application. So first we will create a class that will extend UiApplication class.

public class App extends UiApplication{

	public static void main(String[] args) {

		new App().enterEventDispatcher();
	}

	public App() {
		pushScreen(new FirstScreen());
	}

}

In the above code.
“main” method is the entry point for the application. enterEventDispatcher() method will make this thread to event dispatcher thread. pushScreen(new FirstScreen()) method will push “FirstScreen” to the display stack.

2. We need to create our FirstScreen. For that create a class with name FirstScreen and extend MainScreen.

class FirstScreen extends MainScreen{

	public FirstScreen() {
		final BasicEditField number1 = new BasicEditField("Number 1:","",10,EditField.NO_NEWLINE|EditField.FILTER_NUMERIC);
		final BasicEditField number2 = new BasicEditField("Number 2:","",10,EditField.NO_NEWLINE|EditField.FILTER_NUMERIC);
		ButtonField addButton = new ButtonField("Add",ButtonField.CONSUME_CLICK);
		addButton.setChangeListener(new FieldChangeListener() {

			public void fieldChanged(Field field, int context) {
				int num1 = Integer.parseInt(number1.getText());
				int num2 = Integer.parseInt(number2.getText());
				int result = num1 + num2;
				UiApplication ui = UiApplication.getUiApplication();
				//ui.popScreen(FirstScreen.this);
				ui.pushScreen(new ResultScreen(result));

			}
		});
		add(number1);
		add(new SeparatorField());
		add(number2);
		add(new SeparatorField());
		add(addButton);
	}

}

In above code:
I have created 2 fields for taking number inputs from user and 1 “ADD” button for calculating addition of two numbers and switch to the result screen.
UiApplication class has the pushScreen and popScreen methods but we are in the MainScreen class. So we need the UiApplication object for calling these two methods.

In this example i have commented out popScreen method because if you don’t pop current screen, user can use blackberry device’s “ESC” button as a back button. So on the ResultScreen if user presses “ESC” button, blackberry application manager will automatically pop the current screen and send user to the
FirstScreen.But if you pop the current screen, only one screen is there in the display stack so “ESC” button will exit the application.

2. similar to FirstScreen i will create ResultScreen by extending MainScreen. In the ResultScreen instead of default constructor i will use parametrized constructor

that will take the result from the previous screen.

class ResultScreen extends MainScreen{

	public ResultScreen(int result) {
		LabelField resultLabel = new LabelField("Result: "+result);
		add(resultLabel);
	}
}

So in this example we have seen that how we can switch between screens and how we send data to the another screen.

Some more scenarios you can face while switching screens.

You can push or pop screens only if you are in event thread. So suppose you are not in event thread or you don’t know that your are in event thread or not or you don’t have the object of current screen. how you can switch screen.
I have created a simple method for that.

public void switchScreen(final Screen nextScreen) {
		final UiApplication ui = UiApplication.getUiApplication();
		final Screen currentScreen = ui.getActiveScreen();

		if (UiApplication.isEventDispatchThread()) {
			ui.popScreen(currentScreen);
			ui.pushScreen(nextScreen);
		} else {
			ui.invokeLater(new Runnable() {
				public void run() {
					ui.popScreen(currentScreen);
					ui.pushScreen(nextScreen);
				}
			});
		}
	}

In the above code.
UiApplication.isEventDispatchThread() method will check that you are in event thread or not.
ui.getActiveScreen() method will get the object of current active screen.
one more method getScreenCount() is also useful for checking that how many screens are present in the display stack.

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In this screen shot you can see a list with some options. So if you want to select “About” option without hotkeys, you have to scroll down to the “About” and press.

But using hotkey only you have to press single key ‘A’ for “About” option.

There are two steps to create hotkeys in blackberry application.

1. Underline hotkey character: If you want the ‘N’ as hotkey in “New Game”, insert the Unicode of underscore(u0332) after ‘N’.

String[] listItems = { "Nu0332ew Game", "Lu0332evel", "Hu0332elp",
				"Au0332bout" };
		ObjectListField listField = new ObjectListField();
		listField.set(listItems);
		add(listField);

2. Key press event: Now we have handle key press event of hotkey.

protected boolean keyChar(char c, int status, int time) {
		if(c == 'N' || c == 'n'){
			Dialog.inform("New Game");
		}
		if(c == 'L' || c == 'l'){
			Dialog.inform("Level");
		}
		if(c == 'H' || c == 'h'){
			Dialog.inform("Help");
		}
		if(c == 'A' || c == 'a'){
			Dialog.inform("About");
		}

		return super.keyChar(c, status, time);
	}

We can also create HotKey for application launching.

1. create resource file in your project.
2. in resource file add key as “App” and values as “HotKu0332ey”(Your application name).
3. in BlackBerry_App_Descriptor.xml file check the option “Internationalized resource bundle available”.
4. select the Resource bundle and select the TitleID as App.

Note:
a. For sample application HotKey i have used the shortcut key as ‘k’. because ‘h’, ‘o’ and ‘t’ are already register for “Help”, “options” and “task” applications respectively. So you have to avoid collisions with other applications.

b. make sure to disable “Dial from home screen” option (Options –>Phone Options –> General options –> Dial from home screen)in phone setting.

Now if you press ‘k’ key in home screen, blackberry will launch HotKey application.

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Pros of native apps:

1. You can take advantage of hardware features of devices.

2. You can sell your application on app stores.

3. User can download and install your app.

Cons of native apps:

1. You have to use different platforms, SDK’s, languages for different mobile platforms.

2. You have to pay to become iphone or android or blackberry developer.

3. You have to maintan different builds for different mobile platforms so maintenance, debugging will be slow.

Web Apps: web apps reside on sever and there is no need to install or download the apps. It just a web page optimized for mobile devices. Web Apps can be written in HTML, CSS and javascript. You can simply bookmark the apps for future use.

Pros of web apps:

1. You can use simple HTML, CSS and JS for most of the mobile platforms.

2. You can maintain and fix bugs in real time.

Cons of web apps:

1. You cannot access all hardware functions of mobile devices.

2. You cannot sell your app.

3. For selling from your app you have implement your own checkout system.

Hybrid apps: Hybrid apps are just web apps with native wrapper. Hybrid apps run in web view not in native browser. So you can download and install hybrid apps.

There are many mobile development frameworks are available using them you can create hybrid apps.

1. PhoneGap: is an open-source mobile development framework. Using PhoneGap you can create apps in HTML, CSS and javascript.  PhoneGap also gives access to the native features from javascript.

Supporting platforms:

iOS, android, blackberry, palm webos, symbian, windows mobile

2. Appcelerator Titanium: Another powerfull mobile development framework is Titanium. Its similar to phonegap with greater native support.

Supporting platforms:

iOS, android

You can see other mobile development frameworks on wikipedia.

Multiple phone web-based application framework

I can’t say that web apps will end the native apps but I can say that web apps are great development platform and every mobile developer should consider.

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