响应更改 - SwiftUI

在此页面上

观察对象

观察查询结果
对观察结果排序
观察分节结果
观察应用程序状态

Atlas Device SDK 已弃用。有关详细信息，请参阅弃用页面。

观察对象

Swift SDK提供了 @ObservedRealmObject属性包装器，该包装器可在观察到的对象发生更改时使视图失效。您可以使用此属性包装器创建一个视图，该视图在观察到的对象发生更改时自动更新。

struct DogDetailView: View {
    @ObservedRealmObject var dog: Dog
    
    var body: some View {
        VStack {
            Text(dog.name)
                .font(.title2)
            Text("\(dog.name) is a \(dog.breed)")
            AsyncImage(url: dog.profileImageUrl) { image in
                            image.resizable()
                        } placeholder: {
                            ProgressView()
                        }
                        .aspectRatio(contentMode: .fit)
                        .frame(width: 150, height: 150)
            Text("Favorite toy: \(dog.favoriteToy)")
        }
    }
}

观察查询结果

Swift SDK 提供了@ObservedResults属性包装器，可让您观察查询结果的集合。您可以对 ObservedResults 集合执行快速写入，并且当观察到的查询发生更改时，视图会自动更新。例如，您可以使用 onDelete从观察到的狗列表中删除一条狗。

注意

@ObservedResults 属性包装器用于“SwiftUI 视图”。如果您想观察视图模型中的结果，请注册更改监听器。

struct DogsView: View {
    @ObservedResults(Dog.self) var dogs
    /// The button to be displayed on the top left.
    var leadingBarButton: AnyView?
    var body: some View {
        NavigationView {
            VStack {
                // The list shows the dogs in the realm.
                // The ``@ObservedResults`` above implicitly opens a realm and retrieves
                // all the Dog objects. We can then pass those objects to views further down the
                // hierarchy.
                List {
                    ForEach(dogs) { dog in
                        DogRow(dog: dog)
                    }.onDelete(perform: $dogs.remove)
                }.listStyle(GroupedListStyle())
                    .navigationBarTitle("Dogs", displayMode: .large)
                    .navigationBarBackButtonHidden(true)
                    .navigationBarItems(
                        leading: self.leadingBarButton,
                        // Edit button on the right to enable rearranging items
                        trailing: EditButton())
            }.padding()
        }
    }
}

提示

另请参阅：

有关 Realm 支持的查询语法和查询类型的更多信息，请参阅：读取 - Swift SDK和筛选数据 - Swift SDK。

对观察结果排序

@ObservedResults属性包装器可以采用SortDescriptor参数对查询结果进行排序。

struct SortedDogsView: View {
    @ObservedResults(Dog.self,
                     sortDescriptor: SortDescriptor(keyPath: "name",
                        ascending: true)) var dogs
    
    var body: some View {
        NavigationView {
            // The list shows the dogs in the realm, sorted by name
            List(dogs) { dog in
                DogRow(dog: dog)
            }
        }
    }
}

提示

您不能将计算属性用作 @ObservedResults 的 SortDescriptor。

观察分节结果

10.29.0 版中的新增功能。

您可以观察结果集，该结果集通过从对象属性生成的键划分为多个部分。我们在模型中添加了一个计算变量，但这个变量并不持久存在；我们只是用它来对结果集进行分区。

var firstLetter: String {
    guard let char = name.first else {
        return ""
    }
    return String(char)
}

然后我们可以使用 @ObservedSectionedResults 属性包装器来观察根据计算变量键划分的结果集。

@ObservedSectionedResults(Dog.self,
                          sectionKeyPath: \.firstLetter) var dogs

您可以使用这些观察到的分节结果来填充按节划分的“列表”视图：

struct SectionedDogsView: View {
    @ObservedSectionedResults(Dog.self,
                              sectionKeyPath: \.firstLetter) var dogs
    /// The button to be displayed on the top left.
    var leadingBarButton: AnyView?
    var body: some View {
        NavigationView {
            VStack {
                // The list shows the dogs in the realm, split into sections according to the keypath.
                List {
                    ForEach(dogs) { section in
                        Section(header: Text(section.key)) {
                            ForEach(section) { dog in
                                DogRow(dog: dog)
                            }
                        }
                    }
                }
                .listStyle(GroupedListStyle())
                    .navigationBarTitle("Dogs", displayMode: .large)
                    .navigationBarBackButtonHidden(true)
                    .navigationBarItems(
                        leading: self.leadingBarButton,
                        // Edit button on the right to enable rearranging items
                        trailing: EditButton())
            }.padding()
        }
    }
}

观察应用程序状态

如果您的应用使用Atlas Device Sync ，您可以观察应用程序对象对登录状态更改的React 。这样，您的应用就能在有app.currentUser的情况下执行操作，或者在没有app.currentUser的情况下引导用户登录。

由于 Realm 会在设备上缓存用户凭据，因此应用可以在具有 app.currentUser 的情况下离线运行。

/// This view observes the Realm app object.
/// Either direct the user to login, or open a realm
/// with a logged-in user.
struct FlexibleSyncContentView: View {
    // Observe the Realm app object in order to react to login state changes.
    @ObservedObject var app: RealmSwift.App
    var body: some View {
        if let user = app.currentUser {
            // Create a `flexibleSyncConfiguration` with `initialSubscriptions`.
            // We'll inject this configuration as an environment value to use when opening the realm
            // in the next view, and the realm will open with these initial subscriptions.
            let config = user.flexibleSyncConfiguration(initialSubscriptions: { subs in
                let peopleSubscriptionExists = subs.first(named: "people")
                let dogSubscriptionExists = subs.first(named: "dogs")
                // Check whether the subscription already exists. Adding it more
                // than once causes an error.
                if (peopleSubscriptionExists != nil) && (dogSubscriptionExists != nil) {
                    // Existing subscriptions found - do nothing
                    return
                } else {
                    // Add queries for any objects you want to use in the app
                    // Linked objects do not automatically get queried, so you
                    // must explicitly query for all linked objects you want to include.
                    subs.append(QuerySubscription<Person>(name: "people"))
                    subs.append(QuerySubscription<Dog>(name: "dogs"))
                }
            })
            OpenFlexibleSyncRealmView()
                .environment(\.realmConfiguration, config)
        } else {
            // If there is no user logged in, show the login view.
            LoginView()
        }
    }
}

后退

配置并打开 Realm

来年

在各视图之间传递 Realm 数据