SwiftUI 学习记录

@State, @StateObject, @ObservedObject 关键字

@State 定义在使用它的 View 的最外层，当改变时，SwiftUI 刷新依赖它的视图。@State 只对当前视图和子视图可见，属性的初始化在其生命周期内只被赋值一次

@StateObject 配合 ObservableObject 对象的 @Published 属性来检测属性的改变。SwiftUI 会保证 @StateObject 属性在当前视图生命周期内只被改变一次

@ObservedObject
如果视图的输入 (参数)是 ObservableObject 对象（通常是 @StateObject），使用 @ObservedObject 接收它，不要在声明 @ObservedObject 的视图里初始化它。用法如下：
class DataModel: ObservableObject {
    @Published var name = "Some Name"
    @Published var isEnabled = false
}

struct MyView: View {
    @StateObject private var model = DataModel()

    var body: some View {
        Text(model.name)
        MySubView(model: model)
    }
}

struct MySubView: View {
    @ObservedObject var model: DataModel
    init(model: DataModel) {
      self.model = model // 只应该被这样用
      // 不要像以下这样用，和 State，StateObject 表现不一样
      // self.model = DataMoel() // 此时 model 被重新初始化
      // self._model = ObservedObject(wrappedValue: DataModel()) // 此时 model 被重新初始化
    }
    var body: some View {
        Toggle("Enabled", isOn: $model.isEnabled)
    }
}

NavigationView

        NavigationView {
            Text("Row \(number)")
               .frame(height: 50).background(
                   Color.blue
                )
            .navigationBarHidden(false)
            .navigationBarTitle("123", displayMode: .inline)
            .background(Color.red)
            .background(NavigationConfigurator { nc in
                nc.navigationBar.titleTextAttributes = [.foregroundColor: UIColor.blue.withAlphaComponent(calculateOpacity(for: offsetY))]
            })
            .navigationBarItems(
                leading:
                    Button(action: {
                        print("Left button tapped")
                    }) {
                        Image(systemName: "arrow.left")
                    }
                    .buttonStyle(PlainButtonStyle()),

                trailing:
                HStack {
                    Button(action: {
                        print("First button tapped")
                    }) {
                        Image(systemName: "plus")
                    }
                    .buttonStyle(PlainButtonStyle())
                    
                    Spacer()
                    
                    Button(action: {
                        print("Second button tapped")
                    }) {
                        Image(systemName: "plus")
                    }
                    .buttonStyle(PlainButtonStyle())
                }
            )
        }
//设置标题颜色
struct NavigationConfigurator: UIViewControllerRepresentable {
    var configure: (UINavigationController) -> Void

    func makeUIViewController(context: Context) -> UIViewController {
        let viewController = UIViewController()
        DispatchQueue.main.async {
            if let nc = viewController.navigationController {
                self.configure(nc)
            }
        }
        return viewController
    }

    func updateUIViewController(_ uiViewController: UIViewController, context: Context) {}
}

List 自定义高度

            List {
                Text("\(isOn)")
                    .background(Color.clear)
                    .listRowBackground(Color.clear)
                ForEach(0..<5) { number in
                    HStack {
                        
                        Text("Row \(number)")
                            .frame(height: 50).background(
                                Color.blue
                            )
                        Spacer()
                        Text("Row \(number)")
                            .frame(height: 50).background(
                                Color.blue
                            )
                    }
                    .listRowInsets(EdgeInsets(top: 0, leading: 0, bottom: 0, trailing: 0))
                }
                .background(Color.clear)
                .listRowBackground(Color.clear)

            }
            .listRowInsets(EdgeInsets(top: 0, leading: 0, bottom: 0, trailing: 0))
            .listStyle(.plain)
            .navigationBarHidden(false)
            .navigationBarTitle("123", displayMode: .inline)
            .background(Color.red)

Toggle 开关选择器

                Toggle("定位开关", isOn: $isOn).labelsHidden()
                    .tint(Color.blue)
                    .toggleStyle(SwitchToggleStyle(tint: Color.red))
                    .onTapGesture {
                        if !isOn {
                            print("111111111111")
                        } else {
                            print("222222222222222")
                        }
                        
                    }
        //一般不通过 onTapGesture点击来获取事件，一般通过框架combine 监听isOn 来获取事件处理
        self.$isOn.sink { [weak self] isOn in
            guard let self else { return }

        }.store(in: &self.cancellables)

Image 加载图片

// 加载本都图片
Image("iconName")
Image("iconName", bundle: Resources.resourceBundle) // 文件路径

//网络图片
AsyncImage(url: URL(string: "https:pic35.photophoto.cn/20150511/0034034892281415_b.jpg"), content: { image in
                    image.resizable()
                }, placeholder: {
                    Color.red
                })