GWT Event listeners

What is GWT Event Listeners?
Answer : GWT defines the event listeners that you can attach to a widget to monitor browser
 events. Event Listeners are just interfaces ,that you can implement on your widget.

Question : How to trap mouse click events?
Answer :  your widget must implement clickListener Interface and defines the method
 onClick(widget sender)  the code inside this method will triggered whenever user clicks on that
widget.

Question : How to Implement clickListener Interface ?
Answer : Can be implemented anonymously  like below :
          button.addClickListener(new ClickListener() {

     public void onClick(Widget sender) {
     processData(sender.getText());
     reportData(sender.getText());
      logResults();
     }
   });

Note: The button widget add methods addClickListener and attaches object

ClickListener to it.

Question : What are the disadvantages of above anonymous implementation?

Answer : code should b repeat on each object. 

Question : What are the other way of implementing listener?

answer  : Put the listener implementation in the class.

Example : Public class MainPanel extends composite implements

           ClickListener {

               private Button mybutton = new Button("Click");

               MainPanel(){

              ......

               mybutton.addClickListener(this);

               }

             public void onClick(Widget sender){

              if(sender == button){

               //Do implementation for button;

             }

           }

NOTE: Implement the listeners in container widget to handle the events of

       Contained widget.

Question : What can i do if i want add clicklistener in another link.

Answer : Simple ,

link.addClickListener(this);

if(sender == link || sender == button)

{ Do somethng this } 

Note: all Event Listener are available to all Widgets.

Question : What is composite ?

Answer : Combination of two widgets.

Question : How will you implement the keyUpActionListener in textField?

Answer : public class KeyListener 

{

TextField tf = new TextField();

tf.addKeyUpHandler(new keyUp(this));

}

--------------------------------------------------------

public class keyUp implements KeyUpHandler {

private KeyListener app ;

keyUp(KeyListener app)

{ this.app = app}

public void onKeyUp(KeyUpEvent event){

...................

}