ios - 调整 inputAccessoryView 大小时如何解决 "API error: returned 0 width, assuming UIViewNoIntrinsicMetric"？

Question

我从这里粘贴了代码示例:https://stackoverflow.com/a/46510833/784637进入新的单一 View 应用程序以将 inputAccessoryView 固定在屏幕底部:

class ViewController: UIViewController {

    override var canBecomeFirstResponder: Bool { return true }

    var _inputAccessoryView: UIView!

    override var inputAccessoryView: UIView? {

        if _inputAccessoryView == nil {

            _inputAccessoryView = CustomView()
            _inputAccessoryView.backgroundColor = UIColor.groupTableViewBackground

            let textField = UITextField()
            textField.borderStyle = .roundedRect

            _inputAccessoryView.addSubview(textField)

            _inputAccessoryView.autoresizingMask = .flexibleHeight

            textField.translatesAutoresizingMaskIntoConstraints = false

            textField.leadingAnchor.constraint(
                equalTo: _inputAccessoryView.leadingAnchor,
                constant: 8
            ).isActive = true

            textField.trailingAnchor.constraint(
                equalTo: _inputAccessoryView.trailingAnchor,
                constant: -8
            ).isActive = true

            textField.topAnchor.constraint(
                equalTo: _inputAccessoryView.topAnchor,
                constant: 8
            ).isActive = true

            // this is the important part :

            textField.bottomAnchor.constraint(
                equalTo: _inputAccessoryView.layoutMarginsGuide.bottomAnchor,
                constant: -8
            ).isActive = true
        }

        return _inputAccessoryView
    }

    override func loadView() {

        let tableView = UITableView()
        tableView.keyboardDismissMode = .interactive

        view = tableView
    }
}

class CustomView: UIView {

    // this is needed so that the inputAccesoryView is properly sized from the auto layout constraints
    // actual value is not important

    override var intrinsicContentSize: CGSize {
        return CGSize.zero
    }
}

当我运行模拟器时，一切看起来都很棒，但是当我点击 UITextField 时控制台会报告此错误:

API error: <_UIKBCompatInputView: 0x7fc725f20520; frame = (0 0; 0 0); layer = <CALayer: 0x60000232e6c0>> returned 0 width, assuming UIViewNoIntrinsicMetric

我尝试将 intrinsicContentSize 覆盖为非零值，例如 CGSize(width: 50, height: 50) 但仍然收到此错误。我该如何解决这个问题？

Answer 1

发生这种情况是因为您拥有所有必需的约束，但最初返回的内在大小零。因此，布局系统尝试以零大小布局您的 View ，无法满足您的约束，因此会破坏文本字段的大小。解决此问题的最简单(也许是最好的？)方法是将约束的优先级降低到略低于所需，以便系统可以暂时打破它们。

但在我们查看代码之前，我们先来一个架构建议:如果您需要 CustomView，为什么不直接在其中创建文本字段，而不是让 View Controller 负责注入(inject)文本字段本质上是一个虚拟 View 。

class CustomView: UIView {

  private let textField = UITextField(frame: .zero)

  init(frame: CGRect) {
    backgroundColor = .groupTableViewBackground

    // do your textfield setup here
    addSubview(textField)
    textField.translatesAutoresizingMaskIntoConstraints = false
    textField.borderStyle = .roundedRect

    // set up your constraints
    let constraints: [NSLayoutConstraint] = [
      textField.topAnchor.constraint(equalTo: topAnchor, constant: 8),
      textField.bottomAnchor.constraint(equalTo: bottomAnchor, constant: -8),
      textField.leadingAnchor.constraint(equalTo: leadingAnchor, constant: 8),
      textField.trailingAnchor.constraint(equalTo: trailingAnchor, constant: -8),
    ]

    // slightly reduce the priority of all of your constraints
    constraints.forEach { $0.priority = UILayoutPriority(rawValue: 999) }

    // activate them
    NSLayoutConstraint.activate(constraints)
  }
}

现在，在您的 View Controller 中，您只需将附件 View 声明为:

override var inputAccessoryView = CustomView()

不需要私有(private)存储、隐式解包选项等。