Question

请看下面的代码：

- (void)viewDidLoad {
[super viewDidLoad];

UIView *view = [[UIView alloc] init];

view.translatesAutoresizingMaskIntoConstraints = NO;

NSLayoutConstraint *heightConstraint = [NSLayoutConstraint constraintWithItem:view attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeHeight multiplier:1.0 constant:30];
[view addConstraint:heightConstraint];

NSLog(@"view : %@", view);

}

信息打印出来：

<UIView: 0x7ae4c1b0; frame = (0 0; 0 0); layer = <CALayer: 0x7ae4e790>>

当我使用约束设置时，帧不会更改为30。为什么？如何使它工作？

Answer 1

正如我在评论中所说，您需要先将视图添加到超级视图，然后在该超级视图上调用layoutIfNeeded。我不知道你为什么遇到NSLayoutAttributeNotAnAttribute有问题，它对我来说很好。

- (void)viewDidLoad {
    [super viewDidLoad];
    UIView *view = [[UIView alloc] init];
    view.translatesAutoresizingMaskIntoConstraints = NO;

    NSLayoutConstraint *heightConstraint = [NSLayoutConstraint constraintWithItem:view attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:30];
    [view addConstraint:heightConstraint];
    [self.view addSubview:view];
    [self.view layoutIfNeeded];
    NSLog(@"view : %@", view);
}

当我运行时，日志会给我这个结果，

2014-10-23 22:05:07.701 FrameTest[4293:1869985] view : <UIView: 0x7b724d40; frame = (0 0; 0 30); layer = <CALayer: 0x7b720760>>

添加了布局约束但框架未更改

1 个答案: