如何制作UIImageView，以編程方式在容器中垂直居中

Question

我想中心的UIImageView（ self.showImageView ）在容器視圖（ self.view ）

我嘗試下面的代碼它不起作用：

NSLayoutConstraint *xCenterConstraint = [NSLayoutConstraint constraintWithItem:self.showImageView attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterX multiplier:1.0 constant:0];
[self.view addConstraint:xCenterConstraint];

NSLayoutConstraint *yCenterConstraint = [NSLayoutConstraint constraintWithItem:self.showImageView attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterY multiplier:1.0 constant:0];
[self.view addConstraint:yCenterConstraint];

Answer 1

試試這個：

- (void)viewDidLoad
{
    [super viewDidLoad];
    UIView *redView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 200, 100)];
    redView.backgroundColor = [UIColor redColor];
    redView.translatesAutoresizingMaskIntoConstraints = NO;
    [self.view addSubview:redView];
    [redView addConstraint:[NSLayoutConstraint constraintWithItem:redView attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:0 multiplier:1 constant:100]];
    [redView addConstraint:[NSLayoutConstraint constraintWithItem:redView attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:nil attribute:0 multiplier:1 constant:200]];

    [self.view addConstraint:[NSLayoutConstraint constraintWithItem:redView attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterY multiplier:1 constant:0]];
    [self.view addConstraint:[NSLayoutConstraint constraintWithItem:redView attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterX multiplier:1 constant:0]];
    [self.view addSubview:redView];
}

Answer 2

嘗試

self.showImageView.center=self.view.center;

這將通過將self.showImageView設置為self.view的中心來完成您的工作。