如何在 SwiftUI 中使用 .refreshable 调用 API 并刷新列表

Question

我正在尝试将 .refreshable 添加到我的 SwiftUI openweathermap 应用程序，以便下拉和刷新从 API 返回到应用程序的值。我将我的应用程序设置为允许用户在文本字段中输入城市名称，点击搜索按钮，然后在 sheet 中查看该城市的天气详细信息。关闭 sheet 后，用户可以在列表中看到所有 his/her 之前搜索过的城市作为导航 link，城市名称和温度在每个列表中可见 link .我试图将 .refreshable {} 添加到我的 ContentView 中的列表中。我尝试设置 .refreshable 以在我的 ViewModel 中调用 fetchWeather()，而 ViewModel 又设置为将用户输入的 cityName 作为参数传递到 API URL（也在 ViewModel 中).但是，我现在认为这无法刷新天气数据，因为调用 fetchWeather() 的操作是在工具栏按钮中定义的，而不是在列表中定义的。知道如何设置 .refreshable 来刷新列表中每个搜索城市的天气数据吗？请参阅下面的代码。谢谢！

内容视图

struct ContentView: View {
    // Whenever something in the viewmodel changes, the content view will know to update the UI related elements
    @StateObject var viewModel = WeatherViewModel()
    @State private var cityName = ""
    @State private var showingDetail = false
    
                
    var body: some View {
        NavigationView {
            VStack {
                List {
                    ForEach(viewModel.cityNameList) { city in
                        NavigationLink(destination: DetailView(detail: city), label: {
                            Text(city.name).font(.system(size: 32))
                            Spacer()
                            Text("\(city.main.temp, specifier: "%.0f")&deg;").font(.system(size: 32))
                        })
                    }.onDelete { index in
                        self.viewModel.cityNameList.remove(atOffsets: index)
                    }
                }.refreshable {
                    viewModel.fetchWeather(for: cityName)
                }
            }.navigationTitle("Weather")
            
            .toolbar {
                ToolbarItem(placement: (.bottomBar)) {
                    HStack {
                        TextField("Enter City Name", text: $cityName)
                            .frame(minWidth: 100, idealWidth: 150, maxWidth: 240, minHeight: 30, idealHeight: 40, maxHeight: 50, alignment: .leading)
                        Spacer()
                                                
                        Button(action: {
                            viewModel.fetchWeather(for: cityName)
                            cityName = ""
                            self.showingDetail.toggle()
                        }) {
                            HStack {
                                Image(systemName: "plus")
                                    .font(.title)
                            }
                            .padding(15)
                            .foregroundColor(.white)
                            .background(Color.green)
                            .cornerRadius(40)
                        }.sheet(isPresented: $showingDetail) {
                            ForEach(0..<viewModel.cityNameList.count, id: \.self) { city in
                                if (city == viewModel.cityNameList.count-1) {
                                    DetailView(detail: viewModel.cityNameList[city])
                                }
                            }
                        }
                    }
                }
            }
        }
    }
}
struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

详细视图

struct DetailView: View {
        
    @StateObject var viewModel = WeatherViewModel()
    @State private var cityName = ""
    @State var selection: Int? = nil
    
    var detail: WeatherModel
        
    var body: some View {
        VStack(spacing: 20) {
            Text(detail.name)
                .font(.system(size: 32))
            Text("\(detail.main.temp, specifier: "%.0f")&deg;")
                .font(.system(size: 44))
            Text(detail.firstWeatherInfo())
                .font(.system(size: 24))
        }
    }
}

struct DetailView_Previews: PreviewProvider {
    static var previews: some View {
        DetailView(detail: WeatherModel.init())
    }
}

视图模型

class WeatherViewModel: ObservableObject {
    @Published var cityNameList = [WeatherModel]()

    func fetchWeather(for cityName: String) {
        guard let url = URL(string: "https://api.openweathermap.org/data/2.5/weather?q=\(cityName)&units=imperial&appid=<MyAPIKey>") else { return }

        let task = URLSession.shared.dataTask(with: url) { data, _, error in
            guard let data = data, error == nil else { return }
            do {
                let model = try JSONDecoder().decode(WeatherModel.self, from: data)
                DispatchQueue.main.async {
                    self.cityNameList.append(model)
                }
            }
            catch {
                print(error) // <-- you HAVE TO deal with errors here
            }
        }
        task.resume()
    }
}

型号

struct WeatherModel: Identifiable, Codable {
    let id = UUID()
    var name: String = ""
    var main: CurrentWeather = CurrentWeather()
    var weather: [WeatherInfo] = []
    
    func firstWeatherInfo() -> String {
        return weather.count > 0 ? weather[0].description : ""
    }
}

struct CurrentWeather: Codable {
    var temp: Double = 0.0
}

struct WeatherInfo: Codable {
    var description: String = ""
}

Answer 1

我会做的是这个（或类似的更并发和防错的方法）：

在WeatherViewModel中添加更新所有城市天气信息的功能：

func updateAll() {
    // keep a copy of all the cities names
    let listOfNames = cityNameList.map{[=10=].name}
    // remove all current info
    cityNameList.removeAll()
    // fetch the up-to-date weather info
    for city in listOfNames {
        fetchWeather(for: city)
    }
}

并在 ContentView 中：

.refreshable {
     viewModel.updateAll()
}

注意：DetailView 中不应包含 @StateObject var viewModel = WeatherViewModel()。您应该传入模型（如果需要），并具有 @ObservedObject var viewModel: WeatherViewModel.

编辑 1：

由于 fetching/appending 新的天气信息是异步的，它可能导致 cityNameList.

中的顺序不同

对于少数城市，可以尝试在每个fetchWeather之后对城市进行排序，例如：

func fetchWeather(for cityName: String)
...
                DispatchQueue.main.async {
                    self.cityNameList.append(model)
                    self.cityNameList.sort(by: {[=12=].name < .name}) // <-- here
                }
...

如果要获取大量城市时这变得很麻烦，你将需要一个更健壮和独立的排序机制。

EDIT2：这是一个更强大的排序方案。

从 fetchWeather 中删除 self.cityNameList.sort(by: {[=27=].name < .name})。

在ContentView中对城市进行排序，例如：

ForEach(viewModel.cityNameList.sorted(by: { [=13=].name < .name })) { city in ... }

并使用：

.onDelete { index in
    delete(with: index)
}

与：

private func delete(with indexSet: IndexSet) {
    // must sort the list as in the body
    let sortedList = viewModel.cityNameList.sorted(by: { [=15=].name < .name })
    if let firstNdx = indexSet.first {
        // get the city from the sorted list
        let theCity = sortedList[firstNdx]
        // get the index of the city from the viewModel, and remove it
        if let ndx = viewModel.cityNameList.firstIndex(of: theCity) {
            viewModel.cityNameList.remove(at: ndx)
        }
    }
}

EDIT3：保持原来添加的顺序。

删除 EDIT1 和 EDIT2 的所有模组。

在WeatherViewModel中添加这些函数：

func updateAllWeather() {
    let listOfNames = cityNameList.map{[=16=].name}
    // fetch the up-to-date weather info
    for city in listOfNames {
        fetchWeather(for: city)
    }
}

func addToList( _ city: WeatherModel) {
    // if already have this city, just update
    if let ndx = cityNameList.firstIndex(where: {[=16=].name == city.name}) {
        cityNameList[ndx].main = city.main
        cityNameList[ndx].weather = city.weather
    } else {
        // add a new city
        cityNameList.append(city)
    }
}

在fetchWeather中，使用：

DispatchQueue.main.async {
    self.addToList(model)
}

在ContentView,

.onDelete { index in
     viewModel.cityNameList.remove(atOffsets: index)
} 

.refreshable {
     viewModel.updateAll()
}

请注意，异步函数 fetchWeather 的逻辑存在错误。您应该使用完成处理程序在完成后继续。特别是在 add 按钮中使用时。

最后编辑：

这是我在实验中使用的代码 swift 5.5 async/await:

struct ContentView: View {
    @StateObject var viewModel = WeatherViewModel()
    @State private var cityName = ""
    @State private var showingDetail = false
    
    var body: some View {
        NavigationView {
            VStack {
                List {
                    ForEach(viewModel.cityNameList) { city in
                        NavigationLink(destination: DetailView(detail: city), label: {
                            Text(city.name).font(.system(size: 32))
                            Spacer()
                            Text("\(city.main.temp, specifier: "%.0f")&deg;").font(.system(size: 32))
                        })
                    }.onDelete { index in
                        viewModel.cityNameList.remove(atOffsets: index)
                    }
                }.refreshable {
                    viewModel.updateAllWeather()  // <--- here
                }
            }
            .environmentObject(viewModel)  // <--- here
            .navigationTitle("Weather")
            
            .toolbar {
                ToolbarItem(placement: (.bottomBar)) {
                    HStack {
                        TextField("Enter City Name", text: $cityName)
                            .frame(minWidth: 100, idealWidth: 150, maxWidth: 240, minHeight: 30, idealHeight: 40, maxHeight: 50, alignment: .leading)
                        Spacer()
                        
                        Button(action: {
                            Task {        // <--- here
                                await viewModel.fetchWeather(for: cityName)
                                cityName = ""
                                showingDetail.toggle()
                            }
                        }) {
                            HStack {
                                Image(systemName: "plus").font(.title)
                            }
                            .padding(15)
                            .foregroundColor(.white)
                            .background(Color.green)
                            .cornerRadius(40)
                        }
                        .sheet(isPresented: $showingDetail) {
                            ForEach(0..<viewModel.cityNameList.count, id: \.self) { city in
                                if (city == viewModel.cityNameList.count-1) {
                                    DetailView(detail: viewModel.cityNameList[city])
                                        .environmentObject(viewModel) // <--- here
                                }
                            }
                        }
                    }
                }
            }
        }
    }
}

struct DetailView: View {
    @EnvironmentObject var viewModel: WeatherViewModel // <--- here
    @State private var cityName = ""
    @State var selection: Int? = nil
    
    var detail: WeatherModel
    
    var body: some View {
        VStack(spacing: 20) {
            Text(detail.name)
                .font(.system(size: 32))
            Text("\(detail.main.temp, specifier: "%.0f")&deg;")
                .font(.system(size: 44))
            Text(detail.firstWeatherInfo())
                .font(.system(size: 24))
        }
    }
}

class WeatherViewModel: ObservableObject {
    @Published var cityNameList = [WeatherModel]()
    
    // add or update function
    func addToList( _ city: WeatherModel) {
        // if already have this city, just update it
        if let ndx = cityNameList.firstIndex(where: {[=19=].name == city.name}) {
            cityNameList[ndx].main = city.main
            cityNameList[ndx].weather = city.weather
        } else {
            // add a new city to the list
            cityNameList.append(city)
        }
    }
    
    // note the async
    func fetchWeather(for cityName: String) async {
        guard let url = URL(string: "https://api.openweathermap.org/data/2.5/weather?q=\(cityName)&units=imperial&appid=YOURKEY") else { return  }
        do {
            let (data, response) = try await URLSession.shared.data(for: URLRequest(url: url))
            
            guard let httpResponse = response as? HTTPURLResponse, httpResponse.statusCode == 200 else {
                // throw URLError(.badServerResponse)   //  todo
                print(URLError(.badServerResponse))
                return
            }
            let result = try JSONDecoder().decode(WeatherModel.self, from: data)
            DispatchQueue.main.async {
                self.addToList(result)
            }
        }
        catch {
            return //  todo
        }
    }
    
    // fetch all the latest weather info concurrently
    func updateAllWeather() {
        let listOfNames = cityNameList.map{[=19=].name}
        Task {
            await withTaskGroup(of: Void.self) { group in
                for city in listOfNames {
                    group.addTask { await self.fetchWeather(for: city) }
                }
            }
        }
    }
    
}

Answer 2

import UIKit
class VC: UIViewController  {

var arrlabelpass = [String]()
var arrimagepass = [UIImage]()
var arrTable  = ["1","1","1","1","1","1"]
var arrTablelbl  = ["12","14","13","11","16","17"]
let itemcell = "CCell"
let itemcell1 = "TCell"

var refresh : UIRefreshControl {
    let ref = UIRefreshControl()
    ref.addTarget(self, action: #selector(handler(_:)), for: .valueChanged)
    return ref
}

@IBOutlet weak var tableView: UITableView!
@IBOutlet weak var collectionView: UICollectionView!
override func viewDidLoad() {
    super.viewDidLoad()
   
    tableView.delegate = self
    tableView.dataSource = self
    
    collectionView.delegate = self
    collectionView.dataSource = self
    
    let nib = UINib (nibName: itemcell, bundle: nil)
    collectionView.register(nib, forCellWithReuseIdentifier: itemcell)
    
    let nib1 = UINib(nibName: itemcell1, bundle: nil)
    tableView.register(nib1, forCellReuseIdentifier: itemcell1)
    collectionView.addSubview(refresh)
    collectionView.isHidden = true
}

@objc func handler(_ control:UIRefreshControl) {
    
//        collectionView.backgroundColor = self.randomElement()
    control.endRefreshing()
}

}

extension VC : UITableViewDelegate , UITableViewDataSource , UICollectionViewDelegate , UICollectionViewDataSource  {

func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return arrTable.count
}

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let tCell = tableView.dequeueReusableCell(withIdentifier: itemcell1, for: indexPath)as! TCell
    tCell.tIMG.image = UIImage(named: arrTable[indexPath.row])
    tCell.LBL.text = arrTablelbl[indexPath.row]
    return tCell
}

func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
    let lblindex = arrTablelbl[indexPath.row]
    let imageindex = UIImage(named: arrTable[indexPath.row])
    arrlabelpass.append(lblindex)
    arrimagepass.append(imageindex!)
    collectionView.reloadData()
    collectionView.isHidden = false
    arrTablelbl[indexPath.row].removeAll()
    arrTable[indexPath.row].removeAll()
    tableView.reloadData()

}

func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    return arrlabelpass.count
}

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let ccell = collectionView.dequeueReusableCell(withReuseIdentifier: itemcell, for: indexPath)as! CCell
    ccell.cIMG.image = arrimagepass[indexPath.row]
    ccell.cLBL.text = arrlabelpass[indexPath.row]
    return ccell
    
}

func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
    tableView.reloadData()
    arrimagepass.remove(at: indexPath.row)
    arrlabelpass.remove(at: indexPath.row)
    collectionView.reloadData()
}

}

如何在 SwiftUI 中使用 .refreshable 调用 API 并刷新列表

How to use .refreshable in SwiftUI to call API and refresh list

swift

swiftui

swiftui-list

swiftui-navigationlink

swiftui-navigationview