GWT Note 2

Event and Event handler

有四種方式來實作UI介面與事件觸發處理的關係
1.handler獨立成一個class，這樣會多很多class file不好review code和維護。

public class GwtEvents implements EntryPoint {
   ...
   public void onModuleLoad() {
     textfield = new TextBox();
     textfield.addKeyUpHandler(new MyHandler(this));
     ...
   }//end onModuleLoad
}//end class

public class MyHandler implements KeyUpHandler {
   ...
   public void onKeyUp(KeyUpEvent event) {
   ...
   }
}//end class

2.直接實作handler

public class GwtEvents implements EntryPoint, KeyUpHandler {
   ...
   public void onModuleLoad() {
     textfield = new TextBox();
     textfield.addKeyUpHandler(this);
     ...
    }

   public void onKeyUp(KeyUpEvent event) {
   ...
   }

}//end class

3. (Named)Inner class

public class GwtEvents implements EntryPoint { 
   public void onModuleLoad() { 
      textfield = new TextBox(); 
      textfield.addKeyUpHandler(new MyHandler()); 

   private class MyHandler implements KeyUpHandler { 
     public void onKeyUp(KeyUpEvent event) { 
     ... 
    } 

   }//end onModuleLoad 
}//end class 

4.Anonymous inner classes

public class GwtEvents implements EntryPoint { 
   ... 
   public void onModuleLoad() { 
     textfield = new TextBox(); 
     textfield.addKeyUpHandler(new KeyUpHandler() { 
     @Override 
     public void onKeyUp(KeyUpEvent event) { 
      ... 
     } 
    }); 
   }//end onModuleLoad 
}//end class 

請依情況選擇2、3的作法，避免用方法4。