如何在调整 inputAccessoryView 大小时解决“API 错误：返回 0 宽度，假设 UIViewNoIntrinsicMetric”？

Question

我将此处的代码示例：https://stackoverflow.com/a/46510833/784637 粘贴到新的单一视图应用程序中，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，一切看起来都很好，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)，但仍然出现此错误。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 required 约束，但最初返回的内部大小为 zero。因此布局系统试图以零大小布置您的视图，无法满足您的约束，因此破坏了文本字段的大小。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required 的值，以便系统可以暂时中断它们。

但是在我们查看代码之前，有一个架构建议怎么样：如果您需要CustomView，为什么不直接在其中创建您的文本字段，而不是您的视图控制器负责将文本字段注入本质上是虚拟视图。

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，在您的视图控制器中，您只需将附件视图声明为：

override var inputAccessoryView = CustomView()

不需要私有存储、隐式解包选项等。