SKSpriteNode失去了它的physicsBody属性

Question

我正在使用SpriteKit创建一个游戏，在这个游戏中，地图底部的对象移动。这些物品是鳄鱼和硬币。

场景使用一个NSTimer来调用这个选择器：

timer  = [NSTimer scheduledTimerWithTimeInterval:0.5 target:self selector:@selector(generateBottomSprite) userInfo:nil repeats:YES];


-(void) generateBottomSprite{

int random = (arc4random() % difficulty+3) + difficulty-3;
if (counter >random){
    SKSpriteNode *bottomSprite;
    if (random>difficulty){
        bottomSprite  = [SKSpriteNode spriteNodeWithImageNamed:@"crocodile"];
        bottomSprite.size = CGSizeMake(70, 120);
        bottomSprite.physicsBody.categoryBitMask = crocMask;

    }else{
        bottomSprite = [SKSpriteNode spriteNodeWithImageNamed:@"coin"];
        bottomSprite.size = CGSizeMake(50, 50);
        bottomSprite.physicsBody.categoryBitMask = coinMask;

    }

    //create a crocodile
    bottomSprite.position = CGPointMake(self.frame.size.width,bottomSprite.frame.size.height/2);
    bottomSprite.name = @"bottomSprite";



    [self addChild: bottomSprite];

    counter = 0;

        [self enumerateChildNodesWithName:@"bottomSprite" usingBlock: ^(SKNode *node, BOOL *stop) {
            node.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:node.frame.size];
            node.physicsBody.affectedByGravity = NO;
            node.physicsBody.mass = 8000.0;
            node.physicsBody.friction = 2.50;
            node.physicsBody.usesPreciseCollisionDetection = YES;

        }];

}

}

问题是:在每次调用选择器时，都会重新初始化physicsWorld的所有属性，为了重新分配它们，我必须遍历场景的子元素。

为什么要重新初始化属性？

Answer 1

在创建skphysicsbody本身之前，您正在设置分类位掩码。

bottomSprite  = [SKSpriteNode spriteNodeWithImageNamed:@"crocodile"];
bottomSprite.size = CGSizeMake(70, 120);
//add the following
bottomSprite.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:bottomSprite.frame.size];
///////////////
bottomSprite.physicsBody.categoryBitMask = crocMask;

将所有物理设置移出枚举，如下所示

if (counter >random){
    SKSpriteNode *bottomSprite;
int currentBitMask;
if (random>difficulty){
    bottomSprite  = [SKSpriteNode spriteNodeWithImageNamed:@"crocodile"];
    bottomSprite.size = CGSizeMake(70, 120);
    currentBitMask = crocMask;
}else{
    bottomSprite = [SKSpriteNode spriteNodeWithImageNamed:@"coin"];
    bottomSprite.size = CGSizeMake(50, 50);
    currentBitMask  = coinMask;

}

**bottomSprite.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:bottomSprite.frame.size];**
bottomSprite.physicsBody.categoryBitMask = currentBitMask ;
bottomSprite.physicsBody.affectedByGravity = NO;
bottomSprite.physicsBody.mass = 8000.0;//way too high
bottomSprite.physicsBody.friction = 2.50;//probably high
bottomSprite.physicsBody.usesPreciseCollisionDetection = YES;//overkill, set only if critical


//create a crocodile
bottomSprite.position = CGPointMake(self.frame.size.width,bottomSprite.frame.size.height/2);
bottomSprite.name = @"bottomSprite";

[self addChild: bottomSprite];

您还可能想要使用最新场景中的update方法和NSTimer来测量时间，直到超过半秒钟，然后调用generateBottomSprite方法，它应该比使用额外的NSTimer更有效。

如果有什么不清楚的地方，请随便问，希望这会有所帮助。