如何在 SwiftUI 列表中显示 Realm 结果？

Question

我已经能够将数据保存在 Realm 数据库中，但无法在 SwiftUI 中显示结果 List。

我知道我有数据并且在控制台中打印结果没有问题。

有没有办法将 Realm Result 转换成可以在 SwiftUI List 上显示的格式？

import SwiftUI
import RealmSwift
import Combine

class Dog: Object {
    @objc dynamic var name = ""
    @objc dynamic var age = 0

    override static func primaryKey() -> String? {
        return "name"
    }
}

class SaveDog {
    func saveDog(name: String, age: String) {
        let dog = Dog()
        dog.age  = Int(age)!
        dog.name = name

        // Get the default Realm
        let realm = try! Realm()

     print(Realm.Configuration.defaultConfiguration.fileURL!)

        // Persist your data easily
        try! realm.write {
        realm.add(dog)
        }

        print(dog)
    }
}

class RealmResults: BindableObject {
    let didChange = PassthroughSubject<Void, Never>()

    func getRealmResults() -> String{
        let realm = try! Realm()
        var results = realm.objects(Dog.self) { didSet 
 {didChange.send(())}}
        print(results)
        return results.first!.name
    }
}

struct dogRow: View {
    var dog = Dog()
    var body: some View {
        HStack {
            Text(dog.name)
            Text("\(dog.age)")
        }
    }

}

struct ContentView : View {

    @State var dogName: String = ""
    @State var dogAge: String = ""

    let saveDog = SaveDog()
    @ObjectBinding var savedResults = RealmResults()
    let realm = try! Realm()

    let dogs = Dog()

    var body: some View {
        VStack {
            Text("Hello World")
            TextField($dogName)
            TextField($dogAge)
            Button(action: {
                self.saveDog.saveDog(name: self.dogName, 
                age:self.dogAge)
//                self.savedResults.getRealmResults()
            }) {
                Text("Save")
            }
            //insert list here to show realm data

            List(0 ..< 5) { 
             item in
                Text(self.savedResults.getRealmResults())
            } //Displays the same thing 5 times
        }
    }
}

#if DEBUG
struct ContentView_Previews : PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}
#endif

有些代码可能没有意义，因为我尝试了几种方法来查看是否有任何效果。

例如，这一行将在列表视图中显示结果。

return results.first!.name

如果我只是 return 结果，则列表文本视图中不会显示任何内容。

正如我在下面评论的那样，我将在有时间时尝试使用 ForEach 方法。看起来很有希望。

Answer 1

您在 List 或 ForEach 中传递的数据必须符合 Identifiable 协议。

要么在你的 Realm 模型中采用它，要么使用 .identified(by:) 方法。

即便如此，如果数据发生变化，View 也不会重新加载。

您可以包装 Results 并使其成为 BindableObject，这样视图可以检测到更改并自行重新加载：

class BindableResults<Element>: ObservableObject where Element: RealmSwift.RealmCollectionValue {

    var results: Results<Element>
    private var token: NotificationToken!

    init(results: Results<Element>) {
        self.results = results
        lateInit()
    }

    func lateInit() {
        token = results.observe { [weak self] _ in
            self?.objectWillChange.send()
        }
    }

    deinit {
        token.invalidate()
    }
}

并像这样使用它：

struct ContentView : View {

    @ObservedObject var dogs = BindableResults(results: try! Realm().objects(Dog.self))

    var body: some View {
        List(dogs.results.identified(by: \.name)) { dog in
            DogRow(dog: dog)
        }
    }

}

Answer 2

我已经创建了一个通用解决方案来显示和 add/delete 任何 Results<T>。默认情况下，Results<T> 为“实时”。当 @Published 属性 WILL 更新时，SwiftUI 将更改发送到视图。当收到RealmCollectionChange<Results<T>>通知时，Results<T>已经更新；因此，由于索引超出范围，删除时将出现 fatalError。相反，我使用“实时”Results<T> 来跟踪更改，并使用“冻结”Results<T> 与视图一起使用。可以在此处找到完整的工作示例，包括如何将通用 View 与 RealmViewModel<T>（如下所示）一起使用：SwiftUI+Realm。 enum Status 用于在适用时显示 ProgressView、“未找到记录”等，如项目中所示。另请注意，在需要计数或单个对象时使用“frozen”Results<T>。删除时，onDelete 的 IndexSet 将从“冻结”Results<T> return 移动到一个位置，因此它会检查该对象是否仍然存在于“活动”Results<T>.

class RealmViewModel<T: RealmSwift.Object>: ObservableObject, Verbose where T: Identifiable {

typealias Element = T

enum Status {
    // Display ProgressView
    case fetching
    // Display "No records found."
    case empty
    // Display results
    case results
    // Display error
    case error(Swift.Error)
    
    enum _Error: String, Swift.Error {
        case fetchNotCalled = "System Error."
    }
}

init() {
    fetch()
}

deinit {
    token?.invalidate()
}

@Published private(set) var status: Status = .error(Status._Error.fetchNotCalled)

// Frozen results: Used for View

@Published private(set) var results: Results<Element>?

// Live results: Used for NotificationToken

private var __results: Results<Element>?

private var token: NotificationToken?

private func notification(_ change: RealmCollectionChange<Results<Element>>) {
    switch change {
        case .error(let error):
            verbose(error)
            self.__results = nil
            self.results = nil
            self.token = nil
            self.status = .error(error)
        case .initial(let results):
            verbose("count:", results.count)
            //self.results = results.freeze()
            //self.status = results.count == 0 ? .empty : .results
        case .update(let results, let deletes, let inserts, let updates):
            verbose("results:", results.count, "deletes:", deletes, "inserts:", inserts, "updates:", updates)
            self.results = results.freeze()
            self.status = results.count == 0 ? .empty : .results
    }
}

var count: Int { results?.count ?? 0 }

subscript(_ i: Int) -> Element? { results?[i] }

func fetch() {
    
    status = .fetching
    
    //Realm.asyncOpen(callback: asyncOpen(_:_:))
    
    do {
        let realm = try Realm()
        let results = realm.objects(Element.self).sorted(byKeyPath: "id")
        self.__results = results
        self.results = results.freeze()
        self.token = self.__results?.observe(notification)
        
        status = results.count == 0 ? .empty : .results
        
    } catch {
        verbose(error)
        
        self.__results = nil
        self.results = nil
        self.token = nil
        
        status = .error(error)
    }
}

func insert(_ data: Element) throws {
    let realm = try Realm()
    try realm.write({
        realm.add(data)
    })
}

func delete(at offsets: IndexSet) throws {
    let realm = try Realm()
    try realm.write({
        
        offsets.forEach { (i) in
            guard let id = results?[i].id else { return }
            guard let data = __results?.first(where: { [=10=].id == id }) else { return }
            realm.delete(data)
        }
    })
}

}

Answer 3

这是另一个使用新的 Realm frozen() 集合的选项。虽然这是早期 UI 会在 'assets' 添加到数据库时自动更新。在此示例中，它们是从 NSOperation 线程添加的，该线程应该是后台线程。

在此示例中，侧边栏根据数据库中的不同值列出了不同的属性组 - 请注意，您可能希望以更稳健的方式实现它 - 但作为快速 POC，它工作正常。见下图。

struct CategoryBrowserView: View {
    @ObservedObject var assets: RealmSwift.List<Asset> = FileController.shared.assets
    @ObservedObject var model = ModelController.shared
    
    @State private var searchTerm: String = ""
    @State var isEventsShowing: Bool = false
    @State var isProjectsShowing: Bool = false
    @State var isLocationsShowing: Bool = false
    
    var projects: Results<Asset> {
        return assets.sorted(byKeyPath: "project").distinct(by: ["project"])
    }
    var events: Results<Asset> {
        return assets.sorted(byKeyPath: "event").distinct(by: ["event"])
    }
    var locations: Results<Asset> {
        return assets.sorted(byKeyPath: "location").distinct(by: ["location"])
    }
    @State var status: Bool = false
    
    var body: some View {
        VStack(alignment: .leading) {
        ScrollView {
            VStack(alignment: .leading) {
                
                // Projects
                DisclosureGroup(isExpanded: $isProjectsShowing) {
                    
                    VStack(alignment:.trailing, spacing: 4) {
                        
                        ForEach(filteredProjectsCollection().freeze()) { asset in
                            HStack {
                                    Text(asset.project)
                                    Spacer()
                                Image(systemName: self.model.selectedProjects.contains(asset.project) ? "checkmark.square" : "square")
                                        .resizable()
                                        .frame(width: 17, height: 17)
                                    .onTapGesture { self.model.addProject(project: asset.project) }
                            }
                        }
                    }.frame(maxWidth:.infinity)
                    .padding(.leading, 20)
                    
                } label: {
                    HStack(alignment:.center) {
                        Image(systemName: "person.2")
                        Text("Projects").font(.system(.title3))
                        Spacer()
                    }.padding([.top, .bottom], 8).foregroundColor(.secondary)
                }
                
                // Events
                DisclosureGroup(isExpanded: $isEventsShowing) {
                    
                    VStack(alignment:.trailing, spacing: 4) {
                        
                        ForEach(filteredEventsCollection().freeze()) { asset in
                            HStack {
                             Text(asset.event)
                                Spacer()
                            Image(systemName: self.model.selectedEvents.contains(asset.event) ? "checkmark.square" : "square")
                                    .resizable()
                                    .frame(width: 17, height: 17)
                                .onTapGesture { self.model.addEvent(event: asset.event) }
                            }
                        }
                    }.frame(maxWidth:.infinity)
                    .padding(.leading, 20)
                    
                } label: {
                    HStack(alignment:.center) {
                        Image(systemName: "calendar")
                        Text("Events").font(.system(.title3))
                        Spacer()
                    }.padding([.top, .bottom], 8).foregroundColor(.secondary)
                }
                
                // Locations
                DisclosureGroup(isExpanded: $isLocationsShowing) {
                    
                    VStack(alignment:.trailing, spacing: 4) {
                        
                        ForEach(filteredLocationCollection().freeze()) { asset in
                            HStack {
                             Text(asset.location)
                                Spacer()
                            Image(systemName: self.model.selectedLocations.contains(asset.location) ? "checkmark.square" : "square")
                                    .resizable()
                                    .frame(width: 17, height: 17)
                                .onTapGesture { self.model.addLocation(location: asset.location) }
                            }
                        }
                    }.frame(maxWidth:.infinity)
                    .padding(.leading, 20)
                    
                } label: {
                    HStack(alignment:.center) {
                        Image(systemName: "flag")
                        Text("Locations").font(.system(.title3))
                        Spacer()
                    }.padding([.top, .bottom], 8).foregroundColor(.secondary)
                }
                
            }.padding(.all, 10)
            .background(Color(NSColor.controlBackgroundColor))
        }
            SearchBar(text: self.$searchTerm)
                .frame(height: 30, alignment: .leading)
        }
    }
    
    func filteredProjectsCollection() -> AnyRealmCollection<Asset> {
        if self.searchTerm.isEmpty {
            return AnyRealmCollection(self.projects)
        } else {
            return AnyRealmCollection(self.projects.filter("project CONTAINS[c] %@ || event CONTAINS[c] %@ || location CONTAINS[c] %@ || tags CONTAINS[c] %@", searchTerm, searchTerm, searchTerm, searchTerm))
        }
    }
    func filteredEventsCollection() -> AnyRealmCollection<Asset> {
        if self.searchTerm.isEmpty {
            return AnyRealmCollection(self.events)
        } else {
            return AnyRealmCollection(self.events.filter("project CONTAINS[c] %@ || event CONTAINS[c] %@ || location CONTAINS[c] %@ || tags CONTAINS[c] %@", searchTerm, searchTerm, searchTerm, searchTerm))
        }
    }
    func filteredLocationCollection() -> AnyRealmCollection<Asset> {
        if self.searchTerm.isEmpty {
            return AnyRealmCollection(self.locations)
        } else {
            return AnyRealmCollection(self.locations.filter("project CONTAINS[c] %@ || event CONTAINS[c] %@ || location CONTAINS[c] %@ || tags CONTAINS[c] %@", searchTerm, searchTerm, searchTerm, searchTerm))
        }
    }
    func filteredCollection() -> AnyRealmCollection<Asset> {
        if self.searchTerm.isEmpty {
            return AnyRealmCollection(self.assets)
        } else {
            return AnyRealmCollection(self.assets.filter("project CONTAINS[c] %@ || event CONTAINS[c] %@ || location CONTAINS[c] %@ || tags CONTAINS[c] %@", searchTerm, searchTerm, searchTerm, searchTerm))
        }
    }
    func delete(at offsets: IndexSet) {
        if let realm = assets.realm {
            try! realm.write {
                realm.delete(assets[offsets.first!])
            }
        } else {
            assets.remove(at: offsets.first!)
        }
    }
    
}

struct CategoryBrowserView_Previews: PreviewProvider {
    static var previews: some View {
        CategoryBrowserView()
    }
}

struct CheckboxToggleStyle: ToggleStyle {
    func makeBody(configuration: Configuration) -> some View {
        return HStack {
            configuration.label
            Spacer()
            Image(systemName: configuration.isOn ? "checkmark.square" : "square")
                .resizable()
                .frame(width: 22, height: 22)
                .onTapGesture { configuration.isOn.toggle() }
        }
    }
}

Answer 4

这是最直接的方法：

struct ContentView: View {
    @State private var dog: Results<Dog> = try! Realm(configuration: Realm.Configuration(schemaVersion: 1)).objects(Dog.self)

    var body: some View {
        ForEach(dog, id: \.name) { i in
        Text(String((i.name)!))
        }
    }
}

...就是这样，而且有效！

如何在 SwiftUI 列表中显示 Realm 结果？

How to display Realm Results in SwiftUI List?

realm

swift

swiftui