swiftui - 如何避免“无法同时满足约束”错误？

Question

我正在尝试将代码应用到this 问题的已接受答案中，以了解如何使 SwiftUI TextField 成为第一响应者。这是从该答案复制的代码，我尝试在 xcode 中使用：

struct CustomTextField: UIViewRepresentable {

    class Coordinator: NSObject, UITextFieldDelegate {

        @Binding var text: String
        var didBecomeFirstResponder = false

        init(text: Binding<String>) {
            _text = text
        }

        func textFieldDidChangeSelection(_ textField: UITextField) {
            text = textField.text ?? ""
        }

    }

    @Binding var text: String
    var isFirstResponder: Bool = false

    func makeUIView(context: UIViewRepresentableContext<CustomTextField>) -> UITextField {
        let textField = UITextField(frame: .zero)
        textField.delegate = context.coordinator
        return textField
    }

    func makeCoordinator() -> CustomTextField.Coordinator {
        return Coordinator(text: $text)
    }

    func updateUIView(_ uiView: UITextField, context: UIViewRepresentableContext<CustomTextField>) {
        uiView.text = text
        if isFirstResponder && !context.coordinator.didBecomeFirstResponder  {
            uiView.becomeFirstResponder()
            context.coordinator.didBecomeFirstResponder = true
        }
    }
}

但是，运行该代码会给我一个运行时错误，提示“无法同时满足约束条件”。错误如下所示。

在makeUIView中

在 onEditingChanged 中的 updateUIView 2020-08-14 16:02:48.445045-0600 OpenRussian[2965:122005] [LayoutConstraints] 无法同时 满足约束。可能至少有一个约束条件 以下列表是您不想要的。试试这个：（1）看每个 约束并尝试找出您不期望的； (2) 找到 添加不需要的约束或约束的代码并修复它。 ( "<0x600002580d20 tuisysteminputassistantview:0x7fde585064a0.height="="><0x600002591b30 tuisysteminputassistantview:0x7fde585064a0.bottom="=" _uikbcompatinputview:0x7fde51b78c50.top><0x600002591ae0 v:><0x600002591720 v:>

<0x600002591b30 tuisysteminputassistantview:0x7fde585064a0.bottom="=" _uikbcompatinputview:0x7fde51b78c50.top>

Answer 1

让我们一一来看看：

<NSLayoutConstraint:0x600002580d20 'assistantHeight' TUISystemInputAssistantView:0x7fde585064a0.height == 44 (active)>

这表示视图 0x7fde585064a0 处于活动状态，高度为 44 点

<NSLayoutConstraint:0x600002591ae0 'assistantView.top' V:|-(0)-[TUISystemInputAssistantView:0x7fde585064a0] (active, names: '|':UIInputSetHostView:0x7fde58518070 )>

这就是说 0x7fde585064a0 的上边缘必须与其父视图 0x7fde58518070 的顶部有 0 个点的差距

<NSLayoutConstraint:0x600002591b30 'assistantView.bottom' TUISystemInputAssistantView:0x7fde585064a0.bottom == _UIKBCompatInputView:0x7fde51b78c50.top (active)>

这是说视图 0x7fde51b78c50 和 0x7fde585064a0 是冲突的。这四件事不可能都是真的。还有约束 0x600002591b30 的问题。找出问题所在并设置真正的约束。

我认为了解基础知识并了解 Apple / Xcode 试图通过日志告诉您的内容很有用：

H = Horizontal constraint(for leading and Trailing)
V = Vertical constraint(top and bottom edge)
h = height
w = width

TopEdge    -> V:|-(points)-[VIEW:memoryAddress] 
BottomEdge -> V:[VIEW:memoryAddress]-(points)-|
Leading    -> H:|-(points)-[VIEW:memoryAddress] 
Trailing   -> H:[VIEW:memoryAddress] -(points)-|
height     -> h= --& v=--& V:[VIEW:memoryAddress((points)] 
width      -> VIEW:memoryAddress.width == points 
between    -> H:[VIEW 1]-(51)-[VIEW 2]

Answer 2

尝试下面提供的稍微更正的变体（带有测试视图）。使用 Xcode 12 / iOS 14 测试 - 未观察到控制台警告。

struct CustomTextField: UIViewRepresentable {

    class Coordinator: NSObject, UITextFieldDelegate {

        @Binding var text: String
        var didBecomeFirstResponder = false

        init(text: Binding<String>) {
            _text = text
        }

        func textFieldDidChangeSelection(_ textField: UITextField) {
            DispatchQueue.main.async {
                self.text = textField.text ?? ""
            }
        }

    }

    @Binding var text: String
    var isFirstResponder: Bool = false

    func makeUIView(context: UIViewRepresentableContext<CustomTextField>) -> UITextField {
        let textField = UITextField(frame: .zero)
        textField.delegate = context.coordinator
        textField.setContentHuggingPriority(.defaultHigh, for: .vertical)
        textField.setContentCompressionResistancePriority(.defaultLow, for: .horizontal)

        DispatchQueue.main.async {
            textField.becomeFirstResponder()
        }
        return textField
    }

    func makeCoordinator() -> CustomTextField.Coordinator {
        return Coordinator(text: $text)
    }

    func updateUIView(_ uiView: UITextField, context: UIViewRepresentableContext<CustomTextField>) {
        uiView.text = text
    }
}

struct TestConstraintsError: View {
    @State private var text = ""
    var body: some View {
        VStack {
            Text("Input: " + text)
            CustomTextField(text: $text, isFirstResponder: true)
                .padding()
                .border(Color.red)
        }
    }
}