Event Handling(continued)

Event Listeners Registration

Event Registration is the process by which an Event Handler gets registered with an Event Listener so that the handler is called when the Event Listener fires the event. Though there are several tricky ways to register your event listener for any event, but I'm going to list down only top 3 ways, out of which you can use any of them based on the situation.

• Using an Anonymous Inner Class
• Activity class implements the Listener interface.
• Using Layout file activity_main.xml to specify event handler directly.

Below section will provide you detailed examples on all the three scenarios −

Touch Mode

Users can interact with their devices by using hardware keys or buttons or touching the screen.Touching the screen puts the device into touch mode. The user can then interact with it by touching the on-screen virtual buttons, images, etc.You can check if the device is in touch mode by calling the View class’s isInTouchMode() method.

Focus

A view or widget is usually highlighted or displays a flashing cursor when it’s in focus. This indicates that it’s ready to accept input from the user.

• isFocusable() − it returns true or false
• isFocusableInTouchMode() − checks to see if the view is focusable in touch mode. (A view may be focusable when using a hardware key but not when the device is in touch mode)

android:foucsUp="@=id/button_l"

onTouchEvent()

public boolean onTouchEvent(motionEvent event){
   switch(event.getAction()){
      case TOUCH_DOWN:
      Toast.makeText(this,"you have clicked down Touch button",Toast.LENTH_LONG).show();
      break();
   
      case TOUCH_UP:
      Toast.makeText(this,"you have clicked up touch button",Toast.LENTH_LONG).show();
      break;
   
      case TOUCH_MOVE:
      Toast.makeText(this,"you have clicked move touch button"Toast.LENTH_LONG).show();
      break;
   }
   return super.onTouchEvent(event) ;
}

Event Handling Examples

Event Listeners Registration Using an Anonymous Inner Class

Here you will create an anonymous implementation of the listener and will be useful if each class is applied to a single control only and you have advantage to pass arguments to event handler. In this approach event handler methods can access private data of Activity. No reference is needed to call to Activity.

But if you applied the handler to more than one control, you would have to cut and paste the code for the handler and if the code for the handler is long, it makes the code harder to maintain.

Following are the simple steps to show how we will make use of separate Listener class to register and capture click event. Similar way you can implement your listener for any other required event type.

Step	Description
1	You will use Android studio IDE to create an Android application and name it as myapplication under a package com.example.myapplication as explained in the Hello World Example chapter.
2	Modify src/MainActivity.java file to add click event listeners and handlers for the two buttons defined.
3	Modify the detault content of res/layout/activity_main.xml file to include Android UI controls.
4	No need to declare default string constant android studio takes care of default of the constraints.