以编程方式创建约束时出错答案

【问题标题】：Error when creating constraints programmatically以编程方式创建约束时出错
【发布时间】：2017-04-04 14:14:21
【问题描述】：

我有 2 个视图：aView 和 topView。这两者都具有界面构建器中的所有必要约束。

现在我需要向视图添加一个 WKWebView 实例。所以我创建了一个 webPage 属性。然后我尝试初始化这个东西并像这样添加4个约束：

self.webPage = [[WKWebView alloc] init];

NSLayoutConstraint *topConstraint =[NSLayoutConstraint
                                   constraintWithItem: self.webPage
                                   attribute:NSLayoutAttributeTop
                                   relatedBy:NSLayoutRelationEqual
                                   toItem: self.topBar
                                   attribute:NSLayoutAttributeBottom
                                   multiplier:1.0
                                   constant:0.0];


NSLayoutConstraint *bottomConstraint =[NSLayoutConstraint
                                    constraintWithItem: self.webPage
                                    attribute:NSLayoutAttributeBottom
                                    relatedBy:NSLayoutRelationEqual
                                    toItem: self.aView
                                    attribute:NSLayoutAttributeBottom
                                    multiplier:1.0
                                    constant:50.0];


NSLayoutConstraint *leadingConstraint =[NSLayoutConstraint
                                    constraintWithItem: self.webPage
                                    attribute:NSLayoutAttributeLeading
                                    relatedBy:NSLayoutRelationEqual
                                    toItem: self.aView
                                    attribute:NSLayoutAttributeLeading
                                    multiplier:1.0
                                    constant:0.0];


NSLayoutConstraint *trailingConstraint =[NSLayoutConstraint
                                    constraintWithItem: self.webPage
                                    attribute:NSLayoutAttributeTrailing
                                    relatedBy:NSLayoutRelationEqual
                                    toItem: self.aView
                                    attribute:NSLayoutAttributeTrailing
                                    multiplier:1.0
                                    constant:0.0];

[self.aView addSubview: self.webPage];

[self.aView addConstraints: @[topConstraint, bottomConstraint, leadingConstraint, trailingConstraint]];

所以我的 WKWebView 实例总是在 topView 的正下方，在 aView.bottom 上方 50 pt 并且卡在视图的边缘。

但我得到错误：

[LayoutConstraints] Unable to simultaneously satisfy constraints.
Probably at least one of the constraints in the following list is one you don't want. 
Try this: 
    (1) look at each constraint and try to figure out which you don't expect; 
    (2) find the code that added the unwanted constraint or constraints and fix it.

我不明白我做错了什么。

【问题讨论】：

标签： ios xcode autolayout nslayoutconstraint

【解决方案1】：

您需要将 translatesAutoresizingMaskIntoConstraints 设置为 false

self.webPage.translatesAutoresizingMaskIntoConstraints = false

【讨论】：