How to get reference to an anonymous object 2 levels up

Question

I have code like this:

TextBox txt = new TextBox(){
  public void onLoad(){
    this.addFocusHandler(new FocusHandler(){
      //some codes here
      //if I use "this" keyword, it refers to the handler, but how can I get a reference to the textbox?
    });
  }
};

Question is embedded in the position.

Edit:

In respect to the answers, the creation of a pre-defined reference works for this situation, but this apparently lost (or at least reduce) the benefits of anonymous object/function.

I hope to find a way without creating a new reference. Rather just to get the reference from that scope.

After all the answers, here is a conclusion:

Reflection does not work in GWT. (at least I did not succeed) obj.getClass() works, but others like getMethods() or getEnclosingClass() don't work.
The way to get a reference can either be declaring a reference in the right scope, or get a higher level object reference and reference downwards. I prefer the latter simply because you don't need to create a new variable.

You probably shouldn't extend TextBox in this way just to addFocusHandler. If your concern is _readability_, then use an [anonymous code block](http://stackoverflow.com/questions/1563030/anonymous-code-blocks-in-java) or refactor into a method to construct the TextBox and add a focus handler to it. — Thomas Broyer, Sep 20 '12 at 16:14

Gilberto Torrezan · Answer 1 · 2012-09-20T17:22:24.457

3

TextBox txt = new TextBox(){
    public void onLoad(){
        final TextBox finalThis = this;
        this.addFocusHandler(new FocusHandler(){
             finalThis.doSomething();
        );
    }
};

edited Sep 20 '12 at 17:22

answered Sep 20 '12 at 16:31

Gilberto Torrezan

5,113
4
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1

This looks ok but it is not actually pointing to the right instance. I tried this methods and called a member function, but it cannot find that function. – SwiftMango Sep 20 '12 at 17:10
First one is still not working. It gives error saying no instance of given class is in scope. – SwiftMango Sep 20 '12 at 17:24
1

Yeah I saw some other examples with that method, but it seems like only be working when the outter class is not an anonymous class. I am assuming that if it is anonymous object hierarchy, it would not work. – SwiftMango Sep 20 '12 at 17:29
Looks like this doesn't compile. – John Ericksen Sep 20 '12 at 18:45
@johncart Yeap, FocusHandler needs a method. It is just an example, following the code from the question. – Gilberto Torrezan Sep 20 '12 at 20:51

score 2 · Answer 2 · answered Sep 20 '12 at 16:30

2

The enclosing instance of a non-static inner class (anonymous or named) in Java is available as ClassName.this, i.e.

TextBox txt = new TextBox(){
  public void onLoad(){
    this.addFocusHandler(new FocusHandler(){
      doSomethingCleverWith(TextBox.this);
    });
  }
};

answered Sep 20 '12 at 16:30

Ian Roberts

120,891
16
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183

Doesn't work when that anonymous TextBox subclass is anonymous - that code doesn't compile. – Colin Alworth Sep 20 '12 at 18:14

score 1 · Accepted Answer · edited May 23 '17 at 12:18

1

This has worked for me in the past. It works in client side js too. Here is a reference to more detail What is the difference between Class.this and this in Java

public class FOO {

    TextBox txt = new TextBox(){
          public void onLoad(){
            this.addFocusHandler(new FocusHandler(){

                @Override
                public void onFocus(FocusEvent event) {
                    FOO.this.txt.setHeight("100px");
                }
            });
          }
        };


}

edited May 23 '17 at 12:18

Community

1
1

answered Sep 25 '12 at 22:32

Chris Hinshaw

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Cool this works, but have to use upper level object reference. Anyhow this is the best answer :) – SwiftMango Sep 28 '12 at 13:49

John Ericksen · Answer 4 · 2012-09-20T16:26:57.420

This may work for you:

TextBox txt = new TextBox(){
    public void onLoad(){
        final TextBox ref = this;
        this.addFocusHandler(new FocusHandler(){

            public void doSomething(){ 
                //some codes
                ref.execute();
            }
        });
    }
};

But I prefer to migrate inner classes to named classes:

public class Test {

    public void demo(){
        TextBox txt = new TextBox(){
            public void onLoad(){
                this.addFocusHandler(new DemoFocusHandler(this));
            }
        };
    }
}

External FocusHandler:

public class DemoFocusHandler extends FocusHandler {

    private TextBox textBox;

    public DemoFocusHandler(TextBox textBox){
        this.textBox = textBox;
    }

    public void doSomething(){ 
        //some codes
        textBox.execute();
    }
}

I've added an alternative way that may be considered more elegant. — John Ericksen, Sep 20 '12 at 16:26

score 0 · Answer 5 · answered Sep 28 '12 at 07:18

If gwt supported reflection you could do something along the lines of this:

final TextBox txt = new TextBox() {
   public void onLoad() {

      final Object finalThis  = this;

      this.addFocusHandler(new FocusHandler() {

         @Override
         public void onFocus(FocusEvent event) {
           try {
            Method method= finalThis.getClass().getMethod("getVisibleLength");
            method.invoke(finalThis);
           } catch (Exception e) {
            e.printStackTrace();
           } 
        }
    });
  }
};

Without reflection the existing answers are you best bet. There are two gwt reflection projects gwt reflection and gwt-preprocessor both are in beta and I have not tried them.

How to get reference to an anonymous object 2 levels up

5 Answers5