以编程方式添加某些约束时出现NSGenericException

Question

简单这是我的代码

func showMessageView(){
    let leftConstraint = messageView.leftAnchor.constraintEqualToAnchor(self.view.leftAnchor)
    let bottomConstraint = messageView.bottomAnchor.constraintGreaterThanOrEqualToAnchor(self.view.bottomAnchor)
    let highConstratin = messageView.heightAnchor.constraintEqualToConstant(44.0)
    let widthConstraint = messageView.widthAnchor.constraintGreaterThanOrEqualToAnchor(self.view.widthAnchor)
    NSLayoutConstraint.activateConstraints([leftConstraint, bottomConstraint, highConstratin, widthConstraint])
    self.view.translatesAutoresizingMaskIntoConstraints = false
    self.view.addSubview(messageView)
}

我收到了这个例外：

  

由于未捕获的异常'NSGenericException'而终止应用程序，原因：'无法激活带有项目的约束＆lt; UIView：0x7fe62e00be70; frame =（0 0; 240 128）; autoresize = RM + BM; layer =＆lt; CALayer：0x7fe62e06c8f0＆gt;＆gt;和＆lt; UITableView：0x7fe62c80be00; frame =（0 0; 375 667）; clipsToBounds = YES; autoresize = W + H; gestureRecognizers =＆lt; NSArray：0x7fe62b6a54f0＆gt ;; layer =＆lt; CALayer：0x7fe62b53aba0＆gt ;; contentOffset：{0，-64}; contentSize：{375,658}＆gt;因为他们没有共同的祖先。约束是否引用不同视图层次结构中的项目？这是非法的。'

Answer 1

我通过首先将messageView添加到视图中解决了我的问题：

func showMessageView(){
        self.view.addSubview(messageView)
        let leftConstraint = messageView.leftAnchor.constraintEqualToAnchor(self.view.leftAnchor)
        let bottomConstraint = messageView.bottomAnchor.constraintGreaterThanOrEqualToAnchor(self.view.bottomAnchor)
        let highConstratin = messageView.heightAnchor.constraintEqualToConstant(44.0)
        let widthConstraint = messageView.widthAnchor.constraintGreaterThanOrEqualToAnchor(self.view.widthAnchor)
        NSLayoutConstraint.activateConstraints([leftConstraint, bottomConstraint, highConstratin, widthConstraint])
        self.view.translatesAutoresizingMaskIntoConstraints = false
}