Question

I have seen a convention in android programming, that when forexample calling another activity from some activity:

Intent i=new Intent(Caller.this,Called.class);
startActivity(i);

My question is why we write Caller.this instead of just writing this?

Answer 1

You only need Caller.this if you are inside an inner class.

For example:

button.setOnClickListener(new View.OnClickListener() {
  public void onClick(View v) {
    Intent i=new Intent(Caller.this, Called.class);
    startActivity(i);
  }
};

Here, this is not an instance of Caller, but rather an instance of an anonymous inner class inheriting from View.OnClickListener. To get to the “outer” this, you prefix it with the outer class name (i.e., Caller.this).