With these 3, OS will understand the input given by us and perform the action to the corresponding input.
 
Example : when we press key 2 in the keyboard... event sequence will be like the below

In ubuntu,  (I wrote a c program to read the input even from device and the output is below)
Event: type 4 (Misc), code 4 (ScanCode), value 458783   [Conveying the event is scancode]
Event: type 1 (Key), code 3 (2), value 1                             [key 2 pressed]
Event: type 0 (Sync), code 0 (Sync), value 0                      [sync event]
Event: type 4 (Misc), code 4 (ScanCode), value 458783    [conveying the event is scancode]
Event: type 1 (Key), code 3 (2), value 0                             [key 2 release]
Event: type 0 (Sync), code 0 (Sync), value 0                      [sync event]

In andriod,
Event: type 1 (Key), code 3 (2), value 1                             [key 2 pressed]
Event: type 0 (Sync), code 0 (Sync), value 0                      [sync event]
Event: type 1 (Key), code 3 (2), value 0                             [key 2 release]
Event: type 0 (Sync), code 0 (Sync), value 0                      [sync event]

This is for pressing the key 2 once... This will be written into the device, OS will read it and perform the actions.

ok now...

getevent : will print the event written into the device.
syntax    : getevent device
example : getevent /dev/input/event0
output    :  In android, it didn't say the scancode... but all the inputs are handled as scancodes. output is,
0001 0003 00000001
0000 0000 00000000
0001 0003 00000000
0000 0000 00000000

sendevent : will allow us to give the input in the terminal.
syntax       : sendevent device type code value.
example    : for writing key 2 into the device.
shell@android:/ # sendevent dev/input/event0 0000 0000 00000000
shell@android:/ # sendevent dev/input/event0 0001 0003 00000001
shell@android:/ # sendevent dev/input/event0 0000 0000 00000000
shell@android:/ # sendevent dev/input/event0 0000 0000 00000000


P.S. : Remember the two points below,

1.  Run it in the android shell.
2.  Should have root permission.

Hi friend,

Today, I was working in creating the Notification. I have to notify, when back button is pressed from my android app. As usual I went through the android developer site and studied how to do notify in the notification bar. But I had a small problem in it, which you can also get, when you work in Android Notification. So I planned to share it here.

Android Notification ++

Creating Notification is very simple. Just read it in android developer portal, probably you have to end with the following lines of code to create notification.

/Overriding the Back Button press event /
@Override
    public void onBackPressed() {
    // do something on back.

/* Get a reference to the NotificationManager */
    NotificationManager notificationManager = (NotificationManager)
                getSystemService(NOTIFICATION_SERVICE);

/* Instantiate the Notification */
    Notification notification = new Notification(R.drawable.icon,
            "A new notification", System.currentTimeMillis());

/* Hide the notification after its selected */
    notification.flags |= Notification.FLAG_AUTO_CANCEL;


/*  Creating the intent to an activity, which has to be called and setting it to notification */
    Intent intent = new Intent(this, ActivityName.class);
    intent.addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP);
    PendingIntent activity = PendingIntent.getActivity(this, 0, intent, 0);
    notification.setLatestEventInfo(this, "This is the title",
            "This is the text", activity);

/*Pass the Notification to the NotificationManager */   
    notification.number += 1;
    notificationManager.notify(0, notification);
    }

Sending the activity to background

But above lines of code will not send the activity to the background. So you will see the notification but the activity will be open. So you have to add the following line to send the activity to the background.

moveTaskToBack (true);

Bringing the activity to front


Once the notification is clicked, the intent will be created newly (note that the activity will be created newly). Older activity will be running in the back of the newly created activity. But most of the case we don't need it. We will need to open the activity that we sent to the background. The following line will do that magic for us.

intent.addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP);

NOW

Creating the notification and sending the task to the back and on clicking the notification bringing the same old activity (or task) to the front is done by the following lines of code.

 @Override
    public void onBackPressed() {
        // do something on back.
        moveTaskToBack (true);
        NotificationManager notificationManager = (NotificationManager)
                getSystemService(NOTIFICATION_SERVICE);
    Notification notification = new Notification(R.drawable.ic_launcher,
            "A new notification", System.currentTimeMillis());
    // Hide the notification after its selected
    notification.flags |= Notification.FLAG_AUTO_CANCEL;

    Intent intent = new Intent(this, Test.class);
    intent.addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP);
    PendingIntent activity = PendingIntent.getActivity(this, 0, intent, 0);
    notification.setLatestEventInfo(this, "This is the title",
            "This is the text", activity);
    notification.number += 1;
    notificationManager.notify(0, notification);
    }

 Thats All!!! enjoy!!!