Time for action - the enemy manager

  1. Add a new class called EnemyManager to the Robot Rampage project.
  2. Add the following using directives to the top of the class file:
    using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;
  3. Modify the declaration of the class to make it a static class:
    static class EnemyManager
  4. Add declarations to the EnemyManager class:
    #region Declarations
public static List<Enemy> Enemies = new List<Enemy>();
public static Texture2D enemyTexture;
public static Rectangle enemyInitialFrame;
public static int MaxActiveEnemies = 30;
#endregion
  5. Add the Initialize() method to the EnemyManager class:
    #region Initialization
public static void Initialize(
Texture2D texture,
Rectangle initialFrame)
{
enemyTexture = texture;
enemyInitialFrame = initialFrame;
}
#endregion
  6. Add the AddEnemy() method to the EnemyManager class:
    #region Enemy Management
public static void AddEnemy(Vector2 squareLocation)
{
int startX = (int)squareLocation.X;
int startY = (int)squareLocation.Y;
Rectangle squareRect =
TileMap.SquareWorldRectangle(startX, startY);
Enemy newEnemy = new Enemy(
new Vector2(squareRect.X, squareRect.Y),
enemyTexture,
enemyInitialFrame);
newEnemy.currentTargetSquare = squareLocation;
Enemies.Add(newEnemy);
}
#endregion
  7. Add the Update() and Draw() methods to the EnemyManager Class:
    #region Update and Draw
EnemyManager classEnemyManager classupdatingpublic static void Update(GameTime gameTime)
{
for (int x = Enemies.Count - 1; x >= 0; x--)
{
Enemies[x].Update(gameTime);
if (Enemies[x].Destroyed)
{
Enemies.RemoveAt(x);
}
}
}
public static void Draw(SpriteBatch spriteBatch)
{
foreach (Enemy enemy in Enemies)
{
enemy.Draw(spriteBatch);
}
}
#endregion
  8. In the ComputerTerminal class, replace the Update() method with the following:
    public void Update(GameTime gameTime)
{
if (Active)
{
float elapsed = (float)gameTime.ElapsedGameTime. TotalSeconds;
LastSpawnCounter += elapsed;
if (LastSpawnCounter > minSpawnTime)
{
if (Vector2.Distance(activeSprite.WorldCenter,
Player.BaseSprite.WorldCenter) > 128)
{
if (EnemyManager.Enemies.Count <
EnemyManager.MaxActiveEnemies)
{
EnemyManager.AddEnemy(MapLocation);
LastSpawnCounter = 0;
}
}
}
activeSprite.Update(gameTime);
}
else
{
inactiveSprite.Update(gameTime);
}
}
  9. In the LoadContent() method of the Game1 class, initialize the EnemyManager:
    EnemyManager.Initialize(
spriteSheet,
new Rectangle(0, 160, 32, 32));
  10. In the Update() method of the Game1 class, update the EnemyManager right after the GoalManager had been updated:
    EnemyManager.Update(gameTime);
  11. In the Draw() method of the Game1 class, draw the EnemyManager right after the GoalManager has been drawn:
    EnemyManager.Draw(spriteBatch);
  12. Execute Robot Rampage. The computer terminals now spawn robots, which pursue your player tank:
Time for action - the enemy manager

What just happened?

Most of the EnemyManager class is standard for our managers. When an enemy is added via the AddEnemy() method, the enemy's currentTargetSquare member is set to the square that the enemy has been spawned in, meaning that on its first Update() cycle, it will execute PathFinder.FindPath() to determine a path towards the player.

Updating the WeaponManager

It sure would be nice to be able to use our fancy weaponry to destroy those enemy tanks! We have all of the pieces in place to implement this capability, so let's tie them together and allow enemies to be blown to bits.

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