"this" keyword meaning in Android

Question

I am a beginner in Android Development. The this keyword always makes me confused when used in any constructor. Can someone please explain to me what does it mean?

RelativeLayout ob = new RelativeLayout(this);
Button btn = new Button(this);

What does this mean in the previous constructors? What is it referring to?

Solution 1

As shown in the documentation here, the RelativeLayout constructor takes in an instance of Context. I am assuming you are calling that code in an activity, probably in the onStart method. If this is the case, the this keyword refers to the current instance of the activity. In android, Activities extend the ContextWrapper class, making them a subclass of the Context class and therefore passable to the RelativeLayout and Button constructor.

The this keyword refers to the current instance of the class that holds the method containing the constructor that you are calling.

Solution 2

this refers to the instance of class that this is code is in so for example:

public class Foo {
    private string bar = "bar";

    public Foo(string bar)
    {
        this.bar // <-- refers to global bar. Not the bar from constructor.
    }
}

In your case this requires to by of type of the parameter that RelativeLayout requires, so your class probably must be extended by something that RelativeLayout requires.