Question

所以我正在创建一个消息传递应用程序，我有4个类属性：

typingView: UIView!
messageTextView: UITextView!
sendButton: UIButton!
typingViewHeight: NSLayoutConstraint?

typingView是主视图的inputAccessoryView，有效！它包含messageTextView和sendButton。但我的问题是......当messageTextView中的文字行数增加时，我希望高度随动画增加（我现在忽略了减少）。通过这样做，我决定改变typingView的高度。

检测到contentSize中的更改完美无缺，我添加了一个观察者添加此行

messageTextView.addObserver(self, forKeyPath: "contentSize", options: .new, context: nil)

并使用此覆盖

override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?)

在这个函数内部，我有（这是一个过度简化和伪代码，只是假设它有效）

UIView.animate(withDuration: keyboardAnimationDuration) {
    self.typingViewHeight?.constaint += (messageTextView.font?.lineHeight)!
}

以下是我自定义inputAccessoryView：

lazy var typingViewContainer: UIView = {
    // Set up typing view
    typingView = UIView(frame: CGRect(x: 0, y: 0, width: self.view.frame.width, height: 55))
    typingView.backgroundColor = UIColor.darkGray
    typingView.translatesAutoresizingMaskIntoConstraints = false

    // Set up animated constraints
    typingViewHeight = typingView.heightAnchor.constraint(equalToConstant: typingView.frame.height)
    typingViewHeight?.isActive = true

    // Set up text view
    messageTextView = UITextView()
    messageTextView.translatesAutoresizingMaskIntoConstraints = false
    messageTextView.font = fakeMessageTextView.font
    messageTextView.keyboardType = fakeMessageTextView.keyboardType
    messageTextView.isScrollEnabled = fakeMessageTextView.isScrollEnabled
    messageTextView.alwaysBounceVertical = fakeMessageTextView.alwaysBounceVertical
    messageTextView.text = fakeMessageTextView.text
    messageTextView.textColor = fakeMessageTextView.textColor
    messageTextView.delegate = self
    typingView.addSubview(messageTextView)

    // Constraints
    messageTextView.bottomAnchor.constraint(equalTo: typingView.bottomAnchor, constant: -fakeMessageTextViewBottom.constant).isActive = true
    messageTextView.topAnchor.constraint(equalTo: typingView.topAnchor, constant: fakeMessageTextViewTop.constant).isActive = true
    messageTextView.leftAnchor.constraint(equalTo: typingView.leftAnchor, constant: fakeMessageTextViewBottom.constant).isActive = true
    messageTextView.widthAnchor.constraint(equalToConstant: fakeMessageTextViewWidth.constant).isActive = true

    // Observers
    NotificationCenter.default.addObserver(self, selector: #selector(keyboardWillShow(_:)), name: NSNotification.Name.UIKeyboardWillShow, object: nil)
    NotificationCenter.default.addObserver(self, selector: #selector(keyboardWillHide(_:)), name: NSNotification.Name.UIKeyboardWillHide, object: nil)  
    messageTextView.addObserver(self, forKeyPath: "contentSize", options: .new, context: nil)

    // Set up send button
    sendButton = UIButton(type: fakeSendButton.buttonType)
    sendButton.translatesAutoresizingMaskIntoConstraints = false
    sendButton.setTitle(fakeSendButton.titleLabel?.text!, for: .normal)
    sendButton.titleLabel?.font = fakeSendButton.titleLabel?.font
    sendButton.titleLabel?.shadowColor = fakeSendButton.titleLabel?.shadowColor
    sendButton.addTarget(self, action: #selector(sendPressed(_:)), for: .touchUpInside)
    typingView.addSubview(sendButton)

    // Constraints
    sendButton.heightAnchor.constraint(equalToConstant: fakeSendButtonHeight.constant).isActive = true
    sendButton.widthAnchor.constraint(equalToConstant: fakeSendButtonWidth.constant).isActive = true
    sendButton.bottomAnchor.constraint(equalTo: typingView.bottomAnchor, constant: -fakeSendButtonBottom.constant).isActive = true
    sendButton.rightAnchor.constraint(equalTo: typingView.rightAnchor, constant: -fakeSendButtonRight.constant).isActive = true

    return typingView
}()

override var inputAccessoryView: UIView? {
    get {
        return typingViewContainer
    }
}

override var canBecomeFirstResponder: Bool {
    get {
        return true
    }
}

但是当我测试它并键入多行时，它会在控制台中打印出来：

2018-04-25 08:52:57.614383-0500 ProxiChat[3351:168967] [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. 
(
"<NSLayoutConstraint:0x608000280a50 UIView:0x7f8528a2cda0.height == 73   (active)>",
"<NSLayoutConstraint:0x6040000993c0 UIView:0x7f8528a2cda0.height == 55   (active)>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x608000280a50 UIView:0x7f8528a2cda0.height == 73   
(active)>

Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful.

为什么有两个限制？我只添加了一个。请帮助，谢谢！

修改

假设我的代码用于更改typingView的高度，因为它在我将视图更改为自定义inputAccessoryView之前有效。我只是想知道为什么它会打印出这个错误，以及如何通过设置两个约束来修复它，即使我只添加了一个？

Answer 1

创建视图时，您将高度设置为55：

typingView = UIView(frame: CGRect(x: 0, y: 0, width: self.view.frame.width, height: 55))

然后你要设置一个高度锚：

typingViewHeight = typingView.heightAnchor.constraint(equalToConstant: typingView.frame.height)
typingViewHeight?.isActive = true

这就是你看到冲突的原因。另一个观察是设置高度锚点时，您可以在创建它的同一行中激活它：

typingViewHeight = typingView.heightAnchor.constraint(equalToConstant: typingView.frame.height).isActive = true

这使您无法每次编写额外的代码行

Answer 2

首先要做的事情

我建议您使用UITextView的委托方法来调整容器和文本视图的高度，而不是观察。该代码也有同样的技巧，但我认为它更简洁干净。

func textViewDidChange(_ textView: UITextView) {
        let sizeToFitIn = CGSize(width: textView.bounds.size.width, height: .greatestFiniteMagnitude)
        let newSize = textView.sizeThatFits(sizeToFitIn)
        var newHeight = newSize.height

        ....

        // That part depends on your approach to placing constraints, it's just my example
        textInputHeightConstraint?.constant = newHeight
        inputContainerHeightConstraint?.constant = newHeight + (interfaceFactory.inputContainerHeight - interfaceFactory.textInputMinimumHeight)
    }

尝试更新您的代码：

typingViewHeight = typingView.heightAnchor.constraint(equalToConstant: typingView.frame.height)
typingViewHeight?.priority = UILayoutPriority(rawValue: 999)
typingViewHeight?.isActive = true

如果没有用，请看一下答案： https://stackoverflow.com/a/27522511/5147552

更改以编程方式创建的自定义inputAccessoryView的高度？迅速4

2 个答案: