ios - 跟踪类别的 SKNodes

Question

我有一个函数可以将敌人添加到我的场景中，该函数会按时间间隔调用

我如何跟踪场景中的敌人数量以限制每个关卡中的敌人数量？

**在我的更新函数中**

CFTimeInterval timeSinceLastEnemy = currentTime - self.lastEnemyUpdateTime;
self.lastEnemyUpdateTime = currentTime;
if (timeSinceLastEnemy > 1) { // more than a second since last update
    timeSinceLastEnemy = 1.0 / 60.0;
    self.lastEnemyUpdateTime = currentTime;
}

[self spwanEnemyWithTime:timeSinceLastEnemy];

**定时器和添加敌人的方法**

- (void)spwanEnemyWithTime:(CFTimeInterval)timeSinceLast {

    self.lastEnemySpawn += timeSinceLast;
    if (self.lastEnemySpawn > 0.6) {
        self.lastEnemySpawn = 0;
        [self spawnEnemy];
    }
}

-(void) spawnEnemy {

    SKSpriteNode *enemy = [SKSpriteNode spriteNodeWithImageNamed: enemySprite];

    int minX = 5;
    int maxX = self.frame.size.width;
    int rangeX = maxX - minX;
    int actualX = (arc4random() % rangeX) + minX;

    // Create the enemy slightly off-screen along the upper edge,

    enemy.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:CGSizeMake(enemy.size.height - 10 , enemy.size.width)]; 
    enemy.physicsBody.dynamic = YES;
    enemy.physicsBody.categoryBitMask = enemyCategory; 
    enemy.physicsBody.contactTestBitMask = bulletCategory; 
    enemy.physicsBody.collisionBitMask = 0;     

    // and along a random position along the X axis as calculated above
    enemy.position = CGPointMake(actualX, self.frame.size.height + enemy.size.height);
    [self addChild:enemy];
    enemy.xScale = 0.2;
    enemy.yScale = 0.2;
    enemy.zPosition = 4;

    // Create the actions
    SKAction * actionMove = [SKAction moveToY:(0 - enemy.size.height) duration:4];
    SKAction * actionMoveDone = [SKAction removeFromParent];
    [enemy runAction:[SKAction sequence:@[actionMove, actionMoveDone]]];
}

Answer 1

我承认我无法理解你用双计时器做什么，所以我假设这部分工作如你所愿。对于敌人的数量，这难道不能像在 spawnEnemy 上增加一个计数器并在敌人从场景中移除时减少计数器一样简单吗？

你必须仔细检查我的 Obj-c，我已经有一段时间没有使用它了。

int enemyCount = 0;

-(void) spawnEnemy {

    enemyCount += 1

    ...

    // Create the actions
    SKAction *actionMove = [SKAction moveToY:(0 - enemy.size.height) duration:4];
    SKAction *actionMoveDone = [SKAction removeFromParent];
    SKAction *decrementCount = [SKAction runBlock: ^(void) {
        enemyCount -= 1;                           
    }];

    [enemy runAction:[SKAction sequence:@[actionMove, actionMoveDone, decrementCount]]];
}

仅供引用，您的方法“spwanEnemyWithTime”中有错字