CAGradientLayer 实现背景颜色的渐变

- (void)viewDidLoad {

    [super viewDidLoad];

    

    CAGradientLayer * gradient = [CAGradientLayer layer];

    gradient.frame =  CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height);

    gradient.colors =  [NSArray arrayWithObjects:(id)[UIColor lightGrayColor].CGColor,(id)[UIColor blackColor].CGColor,nil];

    

    [self.view.layer addSublayer:gradient];

 

}