这是代码.

- (void)viewDidLoad {
    [super viewDidLoad];

    NSLog(@"view height %f",self.view.frame.size.height); // returns 667 on iPhone 6
    NSLog(@"view width %f",self.view.frame.size.width); // returns 375 on iPhone 6

    NSLog(@"layers count %lu",self.view.layer.sublayers.count); // returns 2

    // Gradient
    UIColor *colorOne = [UIColor blueColor];
    UIColor *colorTwo = [UIColor greenColor];
    NSArray *colorArray = @[colorOne,colorTwo];

    NSNumber *locationOne = [NSNumber numberWithFloat:0.0];
    NSNumber *locationTwo = [NSNumber numberWithFloat:1.0];
    NSArray *locationArray = @[locationOne,locationTwo];

    CAGradientLayer *gradientLayer = [CAGradientLayer layer];
    gradientLayer.frame = self.view.frame;
    gradientLayer.colors = colorArray;
    gradientLayer.locations = locationArray;

    [self.view.layer insertSublayer:gradientLayer atIndex:0];
    //[self.view.layer insertSublayer:gradientLayer above:[self.view.layer.sublayers firstObject]]; // didn't work either

    NSLog(@"layers count %lu",self.view.layer.sublayers.count); //returns 3
}

我尝试将视图的背景颜色设置为clearColor,在viewDidAppear中调用它,但它们都没有工作.我真的不知道自己错过了什么.在任何帮助下谢谢.