ios - SwiftUI 可观察对象不更新 UI

Question

我有一个可观察对象，它从 View 上的 onAppear 操作加载银行列表。进行更改后，我退出 View ，然后返回调用 loadBankMembers 的 View ，但这些更新未反射(reflect)在 UI 中。如果我退出并返回，则会反射(reflect)更新。

import SwiftUI

struct BankMembersView: View {
    @EnvironmentObject var userData: UserData

    var body: some View {
        ZStack {
            if userData.showPlaidModal {
                PlaidView()
            }

            List {
                ForEach(userData.bankMembers) { bankMember in
                    BankMemberRowView(bankMember: bankMember)
                }
            }
        }
        .onAppear(perform: { self.userData.loadBankMembers() })
        .navigationBarTitle("Bank Accounts")
        .navigationBarItems(trailing:
            Button(action: { self.userData.showPlaidModal = true }) {
                Text("Add")
            }
        )
    }
}

import SwiftUI
import Combine

final class UserData: ObservableObject  {
    let objectWillChange = ObservableObjectPublisher()

    let apollo = Apollo()

    var bankMembers: [BankMember] = [] {
        willSet { self.objectWillChange.send() }
    }

    func loadBankMembers() {
        apollo.client.fetch(query: ListBankMembersQuery(), cachePolicy: .fetchIgnoringCacheCompletely) { result in
            guard let data = try? result.get().data else { return }
            var bankMembers: [BankMember] = []

            for bankMemberData in data.bankMembers ?? [] {
                var bankAccounts: [BankAccount] = []

                for bankAccountData in bankMemberData?.bankAccounts ?? [] {
                    if let bankAccountid = bankAccountData?.id {
                        let bankAccount = BankAccount(id: bankAccountid, name: bankAccountData?.name ?? "", sync: bankAccountData?.sync ?? false)
                        bankAccounts.append(bankAccount)
                    }
                }

                if let id = bankMemberData?.id {
                    let bankMember = BankMember(id: id, name: bankMemberData?.name ?? "", status: bankMemberData?.status, bankAccounts: bankAccounts)
                    bankMembers.append(bankMember)
                }
            }

            self.bankMembers = bankMembers
        }
    }
}

我尝试在加载开始时设置 UserData.banksMembers = [] 但随后出现崩溃并出现此错误:

2019-11-07 20:51:58.191689-0700 Spendable[5839:255244] [TableView] Warning once only: UITableView was told to layout its visible cells and other contents without being in the view hierarchy (the table view or one of its superviews has not been added to a window). This may cause bugs by forcing views inside the table view to load and perform layout without accurate information (e.g. table view bounds, trait collection, layout margins, safe area insets, etc), and will also cause unnecessary performance overhead due to extra layout passes. Make a symbolic breakpoint at UITableViewAlertForLayoutOutsideViewHierarchy to catch this in the debugger and see what caused this to occur, so you can avoid this action altogether if possible, or defer it until the table view has been added to a window. Table view: <_TtC7SwiftUIP33_BFB370BA5F1BADDC9D83021565761A4925UpdateCoalescingTableView: 0x7fe05689fa00; baseClass = UITableView; frame = (0 0; 0 0); clipsToBounds = YES; gestureRecognizers = <NSArray: 0x600000813990>; layer = <CALayer: 0x60000064be20>; contentOffset: {0, 0}; contentSize: {0, 0}; adjustedContentInset: {0, 0, 0, 0}; dataSource: <_TtGC7SwiftUIP13$7fff2c6b223419ListCoreCoordinatorGVS_20SystemListDataSourceOs5Never_GOS_19SelectionManagerBoxS2___: 0x7fe0564235c0>>
2019-11-07 20:51:58.191948-0700 Spendable[5839:255244] *** Assertion failure in -[_TtC7SwiftUIP33_BFB370BA5F1BADDC9D83021565761A4925UpdateCoalescingTableView _endCellAnimationsWithContext:], /BuildRoot/Library/Caches/com.apple.xbs/Sources/UIKitCore_Sim/UIKit-3900.12.15/UITableView.m:2039
2019-11-07 20:51:58.198956-0700 Spendable[5839:255244] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'attempt to delete section 0, but there are only 0 sections before the update'

Answer 1

您错过了 var bankMembers 的 @Published。让我展示一个简单的例子(不能使用你的代码，所以写了类似的东西):

final class UserData: ObservableObject  {

    @Published var bankMembers: [String] = []

    func loadBankMembers() {
        bankMembers.append("Steve")
        bankMembers.append("Bob")
    }

    func updateBankMembers() {
        bankMembers.append("John")
        bankMembers.append("Ann")
    }
}

struct BankMembersView: View {
    @EnvironmentObject var userData: UserData

    var body: some View {

        NavigationView {
            List {
                ForEach(userData.bankMembers, id: \.self) { bankMember in
                    Text(bankMember)
                }
            }
            .onAppear(perform: { self.userData.loadBankMembers() })
            .navigationBarTitle("Bank Accounts")
            .navigationBarItems(trailing:
                Button(action: { self.userData.updateBankMembers() }) {
                    Text("Add")
                }
            )
        }
    }
}

一开始你会得到:

按下“添加”按钮后:

P.S.找好article针对您的情况了解更多信息