View.OnClickListener() a function or Interface

Question

Is View.OnClickListener() a function or interface? When we try to set a onclicklistener() method in android, we use new View.OnClickListener() and it bugs me there cuz as far as I know,

we don't need to initialize an object of class containing static method inorder to use those methods. Why we do this?
When we use implements inorder to implement an interface, we don't call the static methods of the interface.

So can some one tell me why do we do:

new View.OnClickListener(), for using onclick() method?
Why do we use () with View.OnClickListener if it is an interface?

Thanks for your reply..

score 19 · Accepted Answer · answered Aug 05 '12 at 09:01

I'm not sure I understand what you are writing about static methods. View.OnClickListener is an interface: http://developer.android.com/reference/android/view/View.OnClickListener.html

To set a click listener on a view, you pass an instance implementing the OnClickListerner interface: http://developer.android.com/reference/android/view/View.html#setOnClickListener(android.view.View.OnClickListener)

The most common way to do this in android is to define an anonymous inner class (http://docs.oracle.com/javase/tutorial/java/javaOO/innerclasses.html) that implements OnClickListener like

myView.setOnClickListener(new View.OnClickListener() {
    @Override           
    public void onClick(View v) {
        // Handle view click here           
    }
});

The code above both defines an anonymous inner class and creates an instance of it. It is equivalent to first defining a class implementing View.OnClickListener (if defined in the same class)

class MyOnClickListener implements View.OnClickListener {
    @Override           
    public void onClick(View v) {
        // Handle view click here           
    }
}

And later using this

MyOnClickListener listener = new MyOnClickListener();
myView.setOnClickListener(listener);

One thing that I didn't understand is why do we use () when using IMPLEMENTS for using the interface. — Alfred James, Aug 05 '12 at 09:43
() is the call to the constructor of the anonymous inner class, i.e., where the object implementing OnClickListener is created. Google for "anonymous inner class" or have a look here http://stackoverflow.com/questions/355167/how-are-anonymous-inner-classes-used-in-java or here http://viralpatel.net/blogs/inner-classes-in-java/ — toucan, Aug 05 '12 at 10:00

score 3 · Answer 2 · answered Sep 08 '17 at 10:34

Sample Code,

Internally it works something like this,

public class MyView{

public stinterface MyInterface{
        public void myOnClick(View view);
    }

}

 public class MyButton{
        View view;

        public void setOnClicker(MyInterface onClicker) {
            onClicker.myOnClick(view);
        }
    }


public class MyExample{

    public void method(){
        MyButton myButton = new MyButton();
        myButton.setOnClicker(new MyInterface() {
            @Override
            public void myOnClick(View view) {

            }
        });
    }
}

View.OnClickListener() a function or Interface

2 Answers2

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