Android Handling Input Events - Learning Day 3

If application inherit a View class and override the methods like onTouchEvent(), application can intercept these events generated by the Android framework. But since this is tedious, another approach is all of these views contains the nested interfaces with callbacks. These interfaces are Event Listeners.

The common listener methods are: 

onClick()  using View.OnClickListener

This is from View.onClickListener. called back on touch down or corresponding action using a jog wheel or track ball etc. 

onLongClick() using View.OnLongClickListener 

Called by the framework on long touch. 

onFocusChange() using View.OnFocusChangeListener 

Called back when one view is getting unfocused due to user moving away. 

onKey() View.OnKeyListener 

Called back when user focused an item and pressed a hardware key. 

onTouch()  using View.OnTouchListener 

When a touch event happens such as press, release, or any movement gesture within the screen 

onCreateContextMenu Using View.onCreateContextMenuListener 

When a context menu being built. 

It is to be noted that some of the callbacks are having Bool return value, while others don't need a return type. The methods which are having BOOL return type assume the listener handled the event if the listener returned back TRUE. 

When creating a custom Views, some of the common callback method used for event handling are the below 

- onKeyDown(int , KeyEvent)

- onKeyUp

- onTrackballEvent 

- onTouchEvent

- onFocusChanged 

There are few events also bit more important which are below. 

Activity.dispatchTouchEvent(MotionEvent) - This allows view to intercept all events before they are passed to the Window

Activity.onInterceptTouchEvent - This allows ViewGroup to watch the events as they are passed to the child views 

ViewParent.requestDisallowInterceptTouchEevnt- This allows to request to disallow the above. 

There is a touch mode for Views. For e.g. Buttons are focusable in non touch mode, i.e. user is interacting with trackball or keys. In this mode, in order to make actions of a button, first it needs to be focused. But if touch in touch mode, the widget action is directly fired instead of first reporting any focus events. 

Focusable components can be specified in the layout XML file like in same below 

 

references:

http://developer.android.com/guide/topics/ui/ui-events.html