CAGradientLayer渐变色的使用

• (void)viewDidLoad {
  [super viewDidLoad];
  // Do any additional setup after loading the view, typically from a nib.
  CAGradientLayer layer = [CAGradientLayer new];
  layer.frame = CGRectMake(20, CGRectGetHeight(self.view.frame)/2, CGRectGetWidth(self.view.frame)-202, 10);
  layer.colors = @[(__bridge id)[UIColor redColor].CGColor,(__bridge id)[UIColor greenColor].CGColor];
  //一下两个属性是核心点，（0，0）是左下角的点，（1，1）是右上角的点
  layer.startPoint = CGPointMake(0, 0);
  layer.endPoint = CGPointMake(1, 0);
  //可以理解成X从0渐变到1，Y不渐变
  //同样，既然Y不渐变，所以它等同于
  //layer.startPoint = CGPointMake(0, 1);
  // layer.endPoint = CGPointMake(1, 1);
  //换句话说，所谓的渐变就必须要有一个直差
  [self.view.layer addSublayer:layer];
  }

效果图