UILabel字体逐渐变色的方法

-(void)setProgress:(float)progress{  

  _progress = progress;   

 [self setNeedsDisplay];

}

- (void)drawRect:(CGRect)rect{   

 [superdrawRect:rect];    

[[UIColor greenColor]set];    

CGRect fillRect = CGRectMake(0,0,rect.size.width* self.progress,rect.size.height);

//    UIRectFill(fillRect); 

//直接绘图,不会有颜色渐变效果

//用下面混合模式,以渐变.效果为歌词逐字依次变为绿色(基于progress的递增)

UIRectFillUsingBlendMode(fillRect, kCGBlendModeSourceIn);}