iOS UILabel两侧加阴影

 - (void)viewDidLoad
 {
     [super viewDidLoad];
     [self.view setBackgroundColor:[UIColor grayColor]];
     // Do any additional setup after loading the view, typically from a nib.
     MarqueeLabel *label = [[MarqueeLabel alloc]initWithFrame:CGRectMake(, , , )];
     label.backgroundColor = [UIColor clearColor];

     float fadeLength = 15.0f;
     CAGradientLayer* gradientMask = [CAGradientLayer layer];
     gradientMask.bounds = label.layer.bounds;
     gradientMask.position = CGPointMake([label bounds].size.width / , [label bounds].size.height / );
     NSObject *transparent = (NSObject*) [[UIColor clearColor] CGColor];
     NSObject *opaque = (NSObject*) [[UIColor blackColor] CGColor];
     gradientMask.startPoint = CGPointMake(0.0, CGRectGetMidY(label.frame));
     gradientMask.endPoint = CGPointMake(1.0, CGRectGetMidY(label.frame));
     float fadePoint = fadeLength/label.frame.size.width;
     [gradientMask setColors: [NSArray arrayWithObjects: transparent, opaque, opaque, transparent, nil]];
     [gradientMask setLocations: [NSArray arrayWithObjects:
                                  [NSNumber numberWithFloat: 0.0],
                                  [NSNumber numberWithFloat: fadePoint],
                                  [NSNumber numberWithFloat:  - fadePoint],
                                  [NSNumber numberWithFloat: 1.0],
                                  nil]];
     label.layer.mask = gradientMask;

     label.text = @"者是一个测试程序测试长度适用的滚动的是就是";
     [self.view addSubview:label];
 }