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You learned how to design, create, and use a simple Sprite class in an earlier module. You also learned to use a generic List object to store references to objects of the Sprite class.
I will explain improvements made to the Sprite class and will show you how to write a Game1 class that takes advantage of those improvements.
Figure 1 shows a reduced screen shot of the program while it is running.
Figure 1 . Screen shot of the running program.
When this screen shot was taken, the program had 24 space rocks, 12 red power pills and six UFOs all navigating in the game window.
As usual, I will discuss and explain the program code in fragments. A complete listing of the Sprite class is provided in Listing 19 and a complete listing of the Game1 class is provided in Listing 20 .
The Sprite class begins in Listing 1 with the declaration of several instance variables.
Listing 1 . Beginning of the Sprite class.
namespace XNA0128Proj {
class Sprite {private Texture2D image;
private Vector2 position = new Vector2(0,0);private Vector2 direction = new Vector2(0,0);
private Point windowSize;private Random random;
double elapsedTime;//in milliseconds//The following value is the inverse of speed in
// moves/msec expressed in msec/move.double elapsedTimeTarget; The purpose of these instance variables will become clear later in the discussion.
This class has the following properties:
In addition, the class has the following instance variables that are set either by the constructor or by a method:
The first three property accessor methods are shown in Listing 2 .
Listing 2 . The first three property accessor methods.
//Position property accessor
public Vector2 Position {get {
return position;}
set {position = value;
}//end set}//end Position property accessor
//-------------------------------------------------////WindowSize property accessor
public Point WindowSize {set {
windowSize = value;}//end set
}//end WindowSize property accessor//-------------------------------------------------//
//Direction property accessorpublic Vector2 Direction {
get {return direction;
}set {
direction = value;}//end set
}//end Direction property accessor 
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