Question

I have an Activity with a ListView which I’ve added a listener (setOnItemClickListener).
When I’m inside this method from the listener above mentioned:

    public void onItemClick(AdapterView<?> parent, View view, int pos, long id )

In order to have access to the Activity, I’ve done this:

    MyActivity host = (MyActivity) parent.getContext();

From host variable, I have access to all MyActivity methods and attributes (which aren’t static), but I can’t access to the MyActivity.this reference.

Could someone explain me why? Thanks

Answer 1

MyActivity.this would reference the instance of the “outer” MyActivity class when your code ran in an inner class. — Does it? If so, why would you need the host variable?

Update: It only just occured to me that you may be missing the fact that everything you would access via MyActivity.this from within an inner class, you can access via host in your specific setup.

Update: You seem to have a wrong understanding of the meaning of this. Originally, it stands for this object, i.e. the class in which your code runs.

With the additional notation Class.this, Java enables you to access the instance of the outer class of your code, but only from an inner class.

In the following example, Class.this works:

class A {
    int a;
    class B {
        void process_a_in_A() {
            A.this.a++;
        }
    }
    // however, this does NOT work b/c
    // static inner classes do not have references t oouter classes
    static class C {
        void process_a_in_A() {
            // error -- class A.C is detached from its outer class A
            A.this.a++;
        }
    }
}

Also, in the following example, Class.this does not work. The reason is simply that the system cannot know whether there is an Instance of class A and which one of the possibly many instances of class A you want to refer to.

class A {
    int a;
}

class B {
    void process_a_in_A() {
        // A here is a class name, not an object reference;
        // so A.this is meaningless in this context
        A.this.a++;
    }
}

Once again, please be aware that you asked a question without providing the necessary information to answer it specifically, so it can only be answered in general and it looks like you have a wrong understanding about inner classes and the Class.this notation.