尝试添加子项时出现“ NSInvalidArgumentException”

Question

运行代码时出现错误。 错误是;

由于未捕获的异常'NSInvalidArgumentException'而终止应用程序，原因：'试图添加已经具有父级的SKNode：名称：'（null）'纹理：['topObstacle1'

我搜索了问题，但找不到任何解决方案。 我知道发生错误的行。 [self addChild：topObstacles [y]]是问题的根源。 这是我的代码；

- (void)createObstacles
{
    // Calculate how many obstacles we need, the less the better
    nbObstacles = ceil(WIDTH(self)/(OBSTACLE_INTERVAL_SPACE));

    CGFloat lastBlockPos = 0;
    bottomObstacles = @[].mutableCopy;
    topObstacles = @[].mutableCopy;

    SKSpriteNode * topObstacle1 = [SKSpriteNode   spriteNodeWithImageNamed:@"topObstacle1"];
[topObstacles addObject:topObstacle1];

SKSpriteNode * topObstacle2 = [SKSpriteNode spriteNodeWithImageNamed:@"topObstacle2"];
[topObstacles addObject:topObstacle2];

SKSpriteNode * bottomObstacle1 = [SKSpriteNode spriteNodeWithImageNamed:@"bottomObstacle1"];
[bottomObstacles addObject:bottomObstacle1];

SKSpriteNode * bottomObstacle2 = [SKSpriteNode spriteNodeWithImageNamed:@"bottomObstacle2"];
[bottomObstacles addObject:bottomObstacle2];


for (int i=0;i<nbObstacles;i++) {

    int y = arc4random() % 2;
    [topObstacles[y] setAnchorPoint:CGPointZero];

    [self addChild:topObstacles[y]];

    int z = arc4random() % 2;
    [bottomObstacles[z] setAnchorPoint:CGPointZero];

    [self addChild:bottomObstacles[z]];

    }

那么，您对此有何看法？

Answer 1

您可以在for循环中选择一个随机数组索引，在该循环中可以再次随机选择相同的索引（y），从而将相同的对象（例如索引1中的对象）添加两次：

// 1st iteration, y is 1:
int y = arc4random() % 2;
[self addChild:topObstacles[y]];

// 2nd iteration, y is randomly chosen to be 1 again:
int y = arc4random() % 2;
[self addChild:topObstacles[y]]; // BAM! This node has already been added...

要解决此问题，如果topObstacles[y].parent不为零，则选择另一个随机数；或者使用[topObstacles removeObjectAtIndex:y]从数组中删除添加的节点-这要求topObstacles是NSMutableArray。