SwiftUI初探

      SwiftUI 虽然出现了好几年(1.0好像2019年出的，还有SPM也是同一年)，现在已经到从1.0到5.0，但受限于对系统的要求(最低iOS13.0,有的要求17.0及以上)，每个版本里面差异也很大，语法和Flutter 的Dart 比较像。空闲之余可以先学习下，给有需要的同学做个参考， 官方也有现成案例，展示效果如图：

地标列表：

import SwiftUI
 
 
/// 列表
struct LandmarkList : View {
    
    @Environment(ModelData.self) var modelData
    
    /// 仅展示收藏
    @State private var showFavoritesOnly = false
    
    /// 数据过滤
    private var filterLandmarks:[Landmark] {
        modelData.landmarkData.filter { $0.isFavorite == true || !showFavoritesOnly }
    }
    
    /// 转场设置
    @State private var selectIndex:Int = 0
    @State private var _index:Int? = nil
    
    var body: some View {
        NavigationView {
            List{
                Toggle(isOn: $showFavoritesOnly, label: {
                    Text("Favorites Only")
                })
                
                if selectIndex == 0 {
                    ForEach(filterLandmarks) { landmark in
                        NavigationLink {
                            LandMarkDetail(landmark: landmark)
                        } label: {
                            LandmarkRow(landmark: landmark)
                        }
                    }
                }
                else{
                    ForEach(filterLandmarks.indices,id:\.self) { index in
                        LandmarkRow(landmark: filterLandmarks[index])
                            .onTapGesture {
                                _index = index
                                debugPrint("onTapGesture:{\(index),\(String(describing: _index))}")
                            }
                    }
                    .sheet(isPresented: .constant(selectIndex > 0 && _index != nil),
                           onDismiss: {
                        _index = nil
                    },
                           content: {
                        if _index != nil && filterLandmarks.count > _index! {
                            LandMarkDetail(landmark: filterLandmarks[_index!])
                        }
                    })
                }
            }
            .navigationBarTitle("Landmarks", displayMode: .large)
            .navigationBarItems(trailing: SegmentButton(selectIndex:$selectIndex))
            .animation(.easeInOut, value: 0.5)
        }
    }
}
 
#Preview {
    let modelData = ModelData()
    return LandmarkList()
        .environment(modelData)
}

详情：

import SwiftUI
 
 
struct LandMarkDetail : View {
    
    @Environment(ModelData.self) var modelData
    var landmark : Landmark
    var landmarkIndex:Int? {
        get{
            modelData.landmarkData.firstIndex { $0.id == landmark.id }
        }
    }
    
    var body: some View {
        @Bindable var modelData = modelData
        
        ScrollView {
            MapView(coordinate: landmark.locationCoordinate).frame(height: 300)
            
            CircleImage(image: landmark.image(forSize: 250))
                .offset(y: -130)
                .padding(.bottom, -130)
            
            VStack(alignment: .leading) {
                HStack{
                    Text(landmark.name)
                        .font(.title)
                    FavoriteButton(isSet: landmarkIndex != nil ? $modelData.landmarkData[landmarkIndex!].isFavorite : .constant(false))
                }
                
                HStack {
                    Text(landmark.park)
                    Spacer()
                    Text(landmark.state)
                }
                .font(.subheadline)
                .foregroundStyle(.secondary)
                
                Divider()
                
                Text("About \(landmark.name)")
                    .font(.title2)
                Text(landmark.description ?? "")
            }
            .padding()
            Spacer()
        }
        .navigationBarTitle(landmark.name, displayMode: .inline)
        .navigationBarItems(trailing: FavoriteButton(isSet: landmarkIndex != nil ? $modelData.landmarkData[landmarkIndex!].isFavorite : .constant(false)))
    }
}
 
#Preview {
    let modelData = ModelData()
    return LandMarkDetail(landmark: modelData.landmarkData[0])
        .environment(modelData)
}

每天学习一小步，进步一大步，Demo示例