Aswin Balaji

Aswin Balaji

186 Sadasivam Nagar,Madipakkam,Chennai, TN 600091
Aswin Balaji

Android – Event Handling

July 29, 2015, by Aswin Balaji, category ANDROID

Events are a useful way to collect data about a user’s interaction with interactive components of Applications. Like button presses or screen touch etc. The Android framework maintains an event queue as first-in, first-out (FIFO) basis. You can capture these events in your program and take appropriate action as per requirements.

There are following three concepts related to Android Event Management −

  • Event Listeners − An event listener is an interface in the View class that contains a single callback method. These methods will be called by the Android framework when the View to which the listener has been registered is triggered by user interaction with the item in the UI.
  • 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.
  • Event Handlers − When an event happens and we have registered and event listener for the event, the event listener calls the Event Handlers, which is the method that actually handles the event.

Event Listeners & Event Handlers

Event Handler Event Listener & Description
onClick() OnClickListener()
This is called when the user either clicks or touches or focuses upon any widget like button, text, image etc. You will use onClick() event handler to handle such event.
onLongClick() OnLongClickListener()
This is called when the user either clicks or touches or focuses upon any widget like button, text, image etc. for one or more seconds. You will use onLongClick() event handler to handle such event.
onFocusChange() OnFocusChangeListener()
This is called when the widget looses its focus i.e. user goes away from the view item. You will use onFocusChange() event handler to handle such event.
onKey() OnFocusChangeListener()
This is called when the user is focused on the item and presses or releases a hardware key on the device. You will use onKey() event handler to handle such event.
onTouch() OnTouchListener()
This is called when the user presses the key, releases the key, or any movement gesture on the screen. You will use onTouch() event handler to handle such event.
onMenuItemClick() OnMenuItemClickListener()
This is called when the user selects a menu item. You will use onMenuItemClick() event handler to handle such event.
onCreateContextMenu() onCreateContextMenuItemListener()
This is called when the context menu is being built(as the result of a sustained “long click)

There are many more event listeners available as a part of View class like OnHoverListener, OnDragListener etc which may be needed for your application. So I recommend to refer official documentation for Android application development in case you are going to develop a sophisticated apps.

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 classes is in TouchMode() method.
Event

Touch Event

Focus

A view or widget is usually highlighted or displays a flashing cursor when it is in focus. This indicates 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"