如何使用 Autolayout 以编程方式将 UIView 居中在现有 UIView 之上? [英] How can I center a UIView programmatically on top of an existing UIView using Autolayout?

问题描述

如果 Foursquare 签入成功，我的 iPhone 应用会在显示的视图之上添加一个视图.

In case of a successful Foursquare checkin, my iPhone app shows adds a view on top of the view which is shown.

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，但我不确定要输入什么代码才能执行相同的操作，因为稍后会添加此视图以响应应用程序中的成功操作.

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.

我无法让它正常工作，并且 UIView 有一个用 loadNibNamed: 加载的 nib.

I can't get it working properly and the UIView has a nib which it loads with loadNibNamed:.

SuccessView *successfulCheckInView = [[SuccessView alloc] initWithFrame:CGRectZero];
successfulCheckInView.placeNameLabel.text = properVenue.name;
successfulCheckInView.placeAddressLabel.text = properVenue.address;
successfulCheckInView.delegate = self;

[self.ownerVC.view addSubview:successfulCheckInView];

推荐答案

试试这个:

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];

为 Swift 更新:

Updated for Swift:

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

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