UIButton 上的 iOS 线性渐变无法正确显示

Question

我正在尝试向自定义 UIButton 添加渐变，但是当我运行它时，该按钮显示为透明，而不是显示所需的渐变。

这是我的代码:

UIButton * button = [UIButton buttonWithType:UIButtonTypeCustom];
button.titleLabel.font = [UIFont fontWithName:@"SFUIDisplay-Medium" size:16];
[button setTitleColor:[UIColor whiteColor]
             forState:UIControlStateNormal];
button.layer.cornerRadius = [UIButton cornerRadius];
button.contentEdgeInsets = UIEdgeInsetsMake(13, 0, 13, 0);

button.frame = CGRectMake(50, 50, 100, 40); //this line is new

CAGradientLayer *gradientLayer = [CAGradientLayer layer];
gradientLayer.frame = button.layer.bounds;
gradientLayer.colors = [NSArray arrayWithObjects:
                        (id)[UIColor lightGrayColor].CGColor,
                        (id)[UIColor blackColor].CGColor,
                        nil];
gradientLayer.locations = [NSArray arrayWithObjects:
                           [NSNumber numberWithFloat:0.0f],
                           [NSNumber numberWithFloat:1.0f],
                           nil];
gradientLayer.cornerRadius = button.layer.cornerRadius;

gradientLayer.startPoint = CGPointMake(0, 0.5); //this line is new
gradientLayer.endPoint = CGPointMake(1, 0.5); //this line is new

[button.layer addSublayer:gradientLayer];
button.translatesAutoresizingMaskIntoConstraints = NO;
[button setTitle:@"Test"
        forState:UIControlStateNormal];
[button constrainHeight:56];
[button addTarget:self
        action:@selector(doAction)
        forControlEvents:UIControlEventTouchUpInside];
[self addSubview:button];

如果我在这一行中添加:

button.backgroundColor = [UIColor colorWithRed:0.2 green:0.2 blue:0.2 alpha:1.0];

然后按钮看起来像这样。

Answer 1

在我分配框架后，您的代码可以正常工作，例如:

button.frame = CGRectMake(50, 50, 100, 40);

并添加到 View Controller 的 View 中，例如:

[self.view addSubview:button];