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..

Answer 1

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);