一、@State
二攘宙、@State和@Binding
三屯耸、@StateObject和@Published
四、@Environment
五蹭劈、@EnvironmentObject

SwiftUI屬性包裝器.png

一疗绣、@State

State是修飾狀態(tài)屬性的，狀態(tài)屬性改變時會自動刷新視圖铺韧。狀態(tài)屬性聲明為私有屬性多矮，以防止其它視圖訪問它們。從任何線程突變狀態(tài)屬性都是安全的。

struct ContentView: View {
   @State private var showState: String = "默認顯示State"
   var body: some View {
       VStack{
           Text(showState).padding()
           Text("點擊更改State"  ) .onTapGesture {
                   showState = "State已經(jīng)被更改了"
            }
       }
   }
}

二塔逃、@State和@Binding

@State和@Binding結(jié)合使用實現(xiàn)了MVVM模式讯壶。視圖傳@State修飾的參數(shù)時，須使用@Binding修飾的屬性接收參數(shù)湾盗，從而實現(xiàn)雙向綁定伏蚊，保證數(shù)據(jù)實時更新。

struct BindingView: View {
   @State private var paramState: String = "State傳參"
   var body: some View {
       VStack{
           ParamView(paramState: $paramState)
           Text("點擊State傳參"  ).onTapGesture {
               paramState = "State傳參成功格粪！"
            }
       }
   }
   struct ParamView:View {
       @Binding var paramState:String
       var body:some View{
           Text(paramState).padding()
           Text("內(nèi)部改變參數(shù)").padding().onTapGesture {
               paramState = "State在內(nèi)部修改成功躏吊！"
            }
       }
   }
}

三、@StateObject和@Published

@StateObject是修飾class實例的狀態(tài)屬性帐萎，該實例的狀態(tài)屬性改變時會自動刷新視圖比伏。該實例須實現(xiàn)ObservableObject協(xié)議，該實例的屬性用@Published修飾疆导。

struct StateObjectView: View {
   @StateObject var model = StateModel(name: "默認名字",age: 18)
   var body: some View {
       VStack{
           Text(model.name).padding()
           Text("點擊更改StateObject"  ).onTapGesture {
               model.name = "星星編程"
            }
       }
   }
   class  StateModel:ObservableObject {
       @Published var name: String
       @Published var age: Int
       init(name: String, age: Int) {
           self.name = name
           self.age = age
      }
   }
}

四赁项、@Environment

@Environment是獲取系統(tǒng)環(huán)境變量的。例如isEnabled澈段，editMode悠菜，presentationMode，horizontalSizeClass均蜜，verticalSizeClass等李剖。

struct EnvironmentView: View {
   @Environment(\.editMode) var mode
   var body: some View {
       VStack{
           EditButton()
           if  mode?.wrappedValue == .active{
             Text("完成編輯").padding()
           } else {
              Text("開始編輯").padding()
           }
       }
   }
}

五、@EnvironmentObject

@EnvironmentObject是自定義的環(huán)境對象囤耳，須實現(xiàn)ObservableObject協(xié)議篙顺，該對象的屬性用@Published修飾，可以跨視圖傳參充择、反向傳參德玫，保證數(shù)據(jù)實時更新。

創(chuàng)建EnvironmentModel環(huán)境對象椎麦。

class EnvironmentModel:ObservableObject {
   @Published var id: Int
   @Published var name: String
  
   init(id: Int,name: String) {
       self.id = id
       self.name = name
  }
}

創(chuàng)建EnvironmentObjectView視圖宰僧。

struct EnvironmentObjectView: View {
   @EnvironmentObject var model: EnvironmentModel
   var body: some View {
        
       Text(model.name)
        
   }
}

給EnvironmentObjectView傳值。

 EnvironmentObjectView().environmentObject(EnvironmentModel(id:888,name: "星星編程"))