Android Event handling gives you an overview of different types of Event handlers and Event Listeners. An Event is a response to an user’s interaction with input controls, such as press of a button or touch of the screen. Android framework places each occurring Event in a queue based on FIFO (first-in first-out) logic.
When an Event triggers, the Event Listener that is involved with the View object should be registered. Then, the registered Event Listener should implement a corresponding callback method (Event Handler) in order to handle the Event.
There are different ways to register an Event Listener.
• onClick() – onClickListener(): The system calls this method when a user clicks a View component.
Ex:
[java]
Button click=(Button)findViewById(R.id.click);
click.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
// TODO Auto-generated method stub
}
});
[/java]
• onLongClick() – onLongClickListener(): This method is called when a user clicks or holds a View component for more than one second.
Ex:
[java]
Button click=(Button)findViewById(R.id.click);
click.setOnLongClickListener(new View.OnLongClickListener() {
@Override
public boolean onLongClick(View arg0) {
// TODO Auto-generated method stub
return false;
}
});
[/java]
• onTouch() – onTouchListener(): This method is called when a user performs actions like pressing the key, releasing the key or any movement gesture on the screen.
Ex:
[java]
ImageView touch=( ImageView)findViewById(R.id.touch);
touch.setOnTouchListener(new View.OnTouchListener() {
@Override
public boolean onTouch(View arg0, MotionEvent arg1) {
int action = arg1.getAction();
switch (action) {
case MotionEvent.ACTION_DOWN:
break;
case MotionEvent.ACTION_MOVE:
break;
case MotionEvent.ACTION_UP:
break;
case MotionEvent.ACTION_CANCEL:
break;
default:
break;
}
return true;
}
});
[/java]
• OnKey() – onKeyListener(): This method is called when a hardware key is pressed or released on the device.
Ex:
[java]
EditText ed=(EditText)findViewById(R.id.editText1);
ed.setOnKeyListener(new View.OnKeyListener() {
@Override
public boolean onKey(View arg0, int arg1, KeyEvent arg2) {
// TODO Auto-generated method stub
return false;
}
});
[/java]
• onFocusChange() – onFocusChangeListener(): This method is called when a user navigates towards or away from an item.
Ex:
[java]
EditText ed=(EditText)findViewById(R.id.editText1);
ed.setOnFocusChangeListener(new OnFocusChangeListener() {
@Override
public void onFocusChange(View v, boolean hasFocus) {
}
}
});
[/java]
• Implement the Event Listener interface into the Activity class.
• Use an anonymous inner Event Listener class.
• Use a separate Event Listener class.
• Declare it into the layout XML file.
Some of the most common Event Handlers with the respective Event Listeners are as follows: