Ios 以编程方式创建约束时出错

我有两个视图：aView和topView。这两者都具有在interface builder中生成的所有必要约束

现在我需要向视图中添加一个WKWebView实例。所以我创建了一个网页属性。然后我尝试初始化该对象，并向其添加4个约束，如下所示：

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]];

因此，我的WKWebView实例始终位于topView的正下方，aView.bottom上方50 pt，并固定在视图的边缘

但我有错误：

[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。

您需要将TranslatesAutoResizengMaskinToConstraints设置为false

self.webPage.translatesAutoresizingMaskIntoConstraints = false