@State 關(guān)聯(lián)View的狀態(tài)，當(dāng)@State修飾的屬性改變時(shí)，對應(yīng)的View會跟著刷新，符合MVVM的設(shè)計(jì)理念

 @State var count: Int = 0
 
 Section(header: Text("@States")) {
                Text("count:\(count)")
                Button("count ++") {
                    self.count = self.count + 1
                }
            }.padding(.bottom, /*@START_MENU_TOKEN@*/10/*@END_MENU_TOKEN@*/)

@Binding swift中值的傳遞是屬于值傳遞類型，使用@Binding修飾后屬性傳遞就變成引用類型,適合用于子節(jié)點(diǎn)關(guān)系中

@State private var showFavorited: Bool = false

Section(header: Text("@Binding")) {
                if showFavorited {
                    Text("收藏")
                } else {
                    Text("不收藏")
                }
                FilterView(showFavorited: $showFavorited)
}.padding(.bottom,10)

struct FilterView: View {
    @Binding var showFavorited: Bool

    var body: some View {
        Toggle(isOn: $showFavorited) {
            Text("改變收藏狀態(tài)")
        }
    }
}

@ObservedObject 這是用來修飾自定義對象的，用@ObservedObject修飾這個(gè)對象時(shí)，這個(gè)對象必須實(shí)現(xiàn) ObservableObject 協(xié)議，然后用 @Published 修飾對象里屬性，表示這個(gè)屬性是可以被 SwiftUI 監(jiān)聽的

import Foundation
final class User: ObservableObject {
    @Published private(set) var name: String = "張三"
    var i: Int = 0
    func change() {
        i = i + 1
        if i % 2 == 0 {
            name = "張三"
        } else {
            name = "李四"
        }
    }
}

@ObservedObject var user: User = User()

Section(header: Text("@ObservedObject")) {
                Text("用戶名:\(user.name)")
                Button("修改名稱") {
                    user.change()
                }
            }.padding(.bottom,10)
            

@EnvironmentObject 用來從當(dāng)前view的環(huán)境變量中獲取ObservableObject值