Why should I use anonymous classes in Android instead of class redefinition?

Question

I'm new in Android dev. I read some books about it. And all authors strongly recommend to use anonymous classes instead of class redefinition.

They say that

TextView txtTitle;
...
txtTitle.setOnClickListener(new OnClickListener() {
   @Override
   public void onClick(View v) {

   }
});

better than

   txtTitle.setOnClickListener(new MyOnClickListener(position));
   ...

private class MyOnClickListener implements OnClickListener{
...
}

Can anybody explain me why?

Ofc, if I will use redefinition class for many different object this will be the problem for modification.

But if I use my own class only for specific object, so logic of my class will not strongly change, can I use it? Or should I use anonymous class?

No reason in particular, except that it avoids multiplying classes, and the scope of the anonymous class gives you access to the content of the including class. — njzk2, Oct 09 '13 at 07:26
@njzk2 quite the contrary, when you use new OnClickListener you de facto create a new class, try to do it 5 times in some class and see 5 inner classes in the comipler out folder — pskink, Oct 09 '13 at 07:43
@pskink : my formulation is incorrect. I mean that it avoids multiplying java files, which can be bad for organisation, in particular if they are very specialized. Of course, when applicable, I'm all for factorization. — njzk2, Oct 09 '13 at 07:55

kamituel · Accepted Answer · 2013-10-09T07:40:08.570

11

Anonymous class will have access to the final outer variables, so it might be more convienient to use this. For instance:

 final String x = "123";
 Button button = (Button) findViewById(R.id.button);
 button.setOnClickListener(new View.OnClickListener() {
        public void onClick(View v) {
                 // You can acces "x" here.
        }
 });

In addition, it's the question of the coding style. Using anonymous can lead to the code which is more verbose but, at the same time, a little bit easier to follow.

Also, non-anonymous class can be instantiated in multiple places.

edited Oct 09 '13 at 07:40

answered Oct 09 '13 at 07:28

kamituel

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But in this example i can send x to my class in constructor. private class MyOnClickListener implements OnClickListener{ ... public MyOnClickListener(Strin x){} } But ok, i understand that it's question of the coding style, Tnx (: – Suvitruf - Andrei Apanasik Oct 09 '13 at 07:36
@Suvitruf - yes, you can, but then you'll need a private class member to hold it an use it in `onClick()`. It's just not that convienient. – kamituel Oct 09 '13 at 07:38
@Suvitruf - what do you mean? - it is final – kamituel Oct 09 '13 at 07:42
yeh. But what should I do if i need to use not final variable? – Suvitruf - Andrei Apanasik Oct 09 '13 at 07:44
@Suvitruf - unfortunately, you can't. Are you sure you can't just make it final? – kamituel Oct 09 '13 at 07:50
or you can make it an instance member. – njzk2 Oct 09 '13 at 07:53
What is the correct way to access the `Context` of my Class in this case? Say I want to create a `Toast` where I need to add the Context of my Class. In the Anonymous class I can not access it. – Adrian Jandl Oct 09 '13 at 08:06
1

@AdrianJandl - you can just use `MyActivity.this` to access `this` of the outer class - assuming your outer class is called `MyActivity`. – kamituel Oct 09 '13 at 08:10

score 3 · Answer 2 · answered Oct 09 '13 at 08:00

3

why not to implement OnClickListener in your Activity class?

class MyActivity extends Activity implements OnClickListener

answered Oct 09 '13 at 08:00

pskink

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I need it in my Adapter: class public class WorkshopListAdapter extends BaseAdapter{...} to hang listener on List items – Suvitruf - Andrei Apanasik Oct 09 '13 at 08:06
1

so let WorkshopListAdapter implements OnClickListener – pskink Oct 09 '13 at 08:11
but if I want, for example, use onClickListener only on 1 element inside ListItem. Is it correct to use listener on Adapter in this situation? – Suvitruf - Andrei Apanasik Oct 09 '13 at 08:13
Than onClickListener on Adapter will listen all events on List items. Hmmm, I thought it is redundant. – Suvitruf - Andrei Apanasik Oct 09 '13 at 08:20

Why should I use anonymous classes in Android instead of class redefinition?

2 Answers2