方法發送到CAEmitterLayer但去CALayer的

Question

我成立了一個CAEmitterLayer和它完美的作品：

-(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]; 


} 

但是我加了一行代碼：

-(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]; 


} 

突然之間，我得到Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[CALayer setEmitterPosition:]: unrecognized selector sent to instance 0x7546390'。調試窗口說對象是一個CAEmitterLayer，而不僅僅是一個CALayer。當我刪除那行代碼時，問題依然存在。

Answer 1

我假設這個代碼是一個自定義的UIView內，如果是這樣，請確保您已覆蓋：

+ (Class)layerClass 

所以它應該是：

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

這將確保內部你的UIView，你必須

emitter = (CAEmitterLayer*)self.layer; 

它返回一個CAEmitterLayer，而不是一個正常的CAL ayer，它默認使用。

我猜這是問題，因爲錯誤是說你正試圖調用一個方法，只存在於普通CALayer CAEmitterLayer上。