Organizing Game Objects - Learning C# by Programming Games - page 159

10.5.2 The Reset Method
When the ball object is reset, it needs to be placed at the start position, the shooting
variable should be set to false , and its velocity should be set to zero, and for
completeness, we set the color to blue. We could override the Reset method from
GameObject as follows:
public override void Reset()
{
Color = Color.Blue;
position = new Vector2(65, 390);
velocity = Vector2.Zero;
shooting = false ;
}
However, we are again copying code from the ThreeColorGameObject class and we
argued a few pages ago that copying code is generally a bad idea. The problem here
is that we do not only want to override the Reset method, we want to extend it. What
we actually would like to do is to first call the original Reset method defined in
ThreeColorGameObject , and then set the start position and velocity of the ball and its
shooting status. But how do we call the 'original version' of the Reset method if it is
overridden? Here, the base keyword proves its use again.
10.5.3 base Versus this
The base keyword can be used in a similar way to the this keyword. As you recall,
this refers to the current instance that the method is being called on. Similarly, base
also refers to the current instance, but it refers to the part of that instance that forms
the base class . So in our example, base refers to the ThreeColorGameObject instance
that is a part of the Ball instance. This means that if we want to call the version of the
Reset method that is a part of the ThreeColorGameObject class, we can call it through
the base instance as base .Reset() .The Reset method in the Ball class then becomes
public override void Reset()
{
base .Reset();
position = new Vector2(65, 390);
velocity = Vector2.Zero;
shooting = false ;
}
So, first the part of the instance representing ThreeColorGameObject is reset, and then
we perform the reset operation specific to the ball (setting it at a particular position
and setting the shooting status to false ).