ios 如何使用 Autolayout 以编程方式将 UIView 居中放置在现有 UIView 之上？
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How can I center a UIView programmatically on top of an existing UIView using Autolayout?
提问by Anthony Glyadchenko
In case of a successful Foursquare checkin, my iPhone app shows adds a view on top of the view which is shown.
如果 Foursquare 签入成功，我的 iPhone 应用程序会在显示的视图顶部添加一个视图。
I want the view to be centered on the X and Y and for it to have a definite width and height using autolayout, but I'm not sure which constraints to add programmatically. I know how to do it in Storyboard, but I'm not sure what exactly to type in code to do the same as this view is added later in response to a successful action in the app.
我希望视图以 X 和 Y 为中心，并使用自动布局使其具有确定的宽度和高度，但我不确定要以编程方式添加哪些约束。我知道如何在 Storyboard 中执行此操作，但我不确定在代码中输入什么来执行相同的操作，因为稍后添加此视图以响应应用程序中的成功操作。
I can't get it working properly and the UIView has a nib which it loads with loadNibNamed:.
我无法让它正常工作，UIView 有一个笔尖，它用 loadNibNamed: 加载。
SuccessView *successfulCheckInView = [[SuccessView alloc] initWithFrame:CGRectZero];
successfulCheckInView.placeNameLabel.text = properVenue.name;
successfulCheckInView.placeAddressLabel.text = properVenue.address;
successfulCheckInView.delegate = self;
[self.ownerVC.view addSubview:successfulCheckInView];
回答by Eric
Try this:
尝试这个：
NSLayoutConstraint *xCenterConstraint = [NSLayoutConstraint constraintWithItem:view1 attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:view2 attribute:NSLayoutAttributeCenterX multiplier:1.0 constant:0];
[superview addConstraint:xCenterConstraint];
NSLayoutConstraint *yCenterConstraint = [NSLayoutConstraint constraintWithItem:view1 attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:view2 attribute:NSLayoutAttributeCenterY multiplier:1.0 constant:0];
[superview addConstraint:yCenterConstraint];
Updated for Swift:
为 Swift 更新：
NSLayoutConstraint(item: view1, attribute: .centerX, relatedBy: .equal, toItem: view2, attribute: .centerX, multiplier: 1, constant: 0).isActive = true
NSLayoutConstraint(item: view1, attribute: .centerY, relatedBy: .equal, toItem: view2, attribute: .centerY, multiplier: 1, constant: 0).isActive = true
