方法发送到CAEmitterLayer，但转到CALayer

Question

我设置了一个CAEmitterLayer，它工作得很好：

-(void)awakeFromNib
{
    //set ref to the layer
    emitter = (CAEmitterLayer*)self.layer;
    emitter.emitterPosition = CGPointMake(160, 270);

    CAEmitterCell* grassLeft = [self getEmitter];
    CAEmitterCell* grassRight = [self getEmitter];
    grassLeft.emissionLongitude = M_PI*1.20;
    grassRight.emissionLongitude = M_PI*1.80;

    //add the cell to the layer and we're done
    emitter.emitterCells = [NSArray arrayWithObjects:grassLeft,grassRight,nil];


}

但我增加了一行代码：

-(void)awakeFromNib {
    //set ref to the layer
    emitter = (CAEmitterLayer*)self.layer;
    emitter.emitterPosition = CGPointMake(160, 270);
    emitter.backgroundColor = [[UIColor redColor] CGColor];

    CAEmitterCell* grassLeft = [self getEmitter];
    CAEmitterCell* grassRight = [self getEmitter];
    grassLeft.emissionLongitude = M_PI*1.20;
    grassRight.emissionLongitude = M_PI*1.80;

    //add the cell to the layer and we're done
    emitter.emitterCells = [NSArray arrayWithObjects:grassLeft,grassRight,nil];


}

突然间，我得到了Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[CALayer setEmitterPosition:]: unrecognized selector sent to instance 0x7546390'。调试窗口显示该对象是一个CAEmitterLayer，而不仅仅是一个CALayer。当我删除这一行代码时，问题依然存在。

Answer 1

假设此代码位于自定义UIView中，如果是，请确保您已重写：

+ (Class)layerClass

所以应该是：

+ (Class)layerClass
{
    return [CAEmitterLayer class];
}

这将确保在您的UIView中有

emitter = (CAEmitterLayer*)self.layer;

它返回的是一个CAEmitterLayer，而不是默认的普通CALayer。

我猜这就是问题所在，因为错误表明您正在尝试调用一个只存在于普通CAEmitterLayer上的方法。