1 - (void)viewDidLoad 2 { 3     [super viewDidLoad]; 4     [self.view setBackgroundColor:[UIColor grayColor]]; 5     // Do any additional setup after loading the view, typically from a nib. 6     MarqueeLabel *label = [[MarqueeLabel alloc]initWithFrame:CGRectMake(0, 0, 100, 20)]; 7     label.backgroundColor = [UIColor clearColor]; 8      9     float fadeLength = 15.0f;10     CAGradientLayer* gradientMask = [CAGradientLayer layer];11     gradientMask.bounds = label.layer.bounds;12     gradientMask.position = CGPointMake([label bounds].size.width / 2, [label bounds].size.height / 2);13     NSObject *transparent = (NSObject*) [[UIColor clearColor] CGColor];14     NSObject *opaque = (NSObject*) [[UIColor blackColor] CGColor];15     gradientMask.startPoint = CGPointMake(0.0, CGRectGetMidY(label.frame));16     gradientMask.endPoint = CGPointMake(1.0, CGRectGetMidY(label.frame));17     float fadePoint = fadeLength/label.frame.size.width;18     [gradientMask setColors: [NSArray arrayWithObjects: transparent, opaque, opaque, transparent, nil]];19     [gradientMask setLocations: [NSArray arrayWithObjects:20                                  [NSNumber numberWithFloat: 0.0],21                                  [NSNumber numberWithFloat: fadePoint],22                                  [NSNumber numberWithFloat: 1 - fadePoint],23                                  [NSNumber numberWithFloat: 1.0],24                                  nil]];25     label.layer.mask = gradientMask;26     27     label.text = @"者是一个测试程序测试长度适用的滚动的是就是";28     [self.view addSubview:label];29 }