致命错误：在特定视图上刷新数据时索引超出范围

Posted 2023-02-24

【中文标题】致命错误：在特定视图上刷新数据时索引超出范围

【英文标题】：Fatal error: Index out of range when refreshing data on specific view

【发布时间】：2020-07-30 12:24:08

【问题描述】：

我有以下代码：

import SwiftUI
import SwiftUIRefresh // added via SwiftPM: https://github.com/timbersoftware/SwiftUIRefresh.git

struct AView: View 
    
    @State private var aObjects = [A]()
    @State private var refreshing = false
    
    var body: some View 
        NavigationView 
            VStack 
                if(aObjects.isEmpty) 
                    Text("loading")
                 else 
                    List(aObjects.indices, id: \.self)  idx in
                        NavigationLink(destination: BView(parentA: self.$aObjects[idx])) 
                            Text(self.aObjects[idx].name)
                        
                    .pullToRefresh(isShowing: self.$refreshing) 
                        API.getAs()  newAObjects in
                            self.aObjects = newAObjects
                            self.refreshing = false
                        
                    
                
            .navigationBarTitle("All", displayMode: .large)
            
        .onAppear() 
            if(self.aObjects.isEmpty) 
                API.getAs()  newAObjects in
                    self.aObjects = newAObjects
                
            
        
    


struct BView: View 
    
    @Binding var parentA : A
    
    @State private var refreshing = false
    
    var body: some View 
        VStack 
            if(parentA.bs.isEmpty) 
                Text("loading")
             else 
                List(parentA.bs.indices, id: \.self)  idx in
                    NavigationLink(destination: CView(parentA: self.$parentA, parentB: self.$parentA.bs[idx])) 
                        Text(self.parentA.bs[idx].name)
                    
                .pullToRefresh(isShowing: self.$refreshing) 
                    API.getBs(forA: self.parentA)  newBObjects in
                        self.parentA.bs = newBObjects
                        self.refreshing = false
                    
                
            
        
        .navigationBarTitle(Text(parentA.name), displayMode: .inline)
        .onAppear() 
            if(self.parentA.bs.isEmpty) 
                API.getBs(forA: self.parentA)  newBObjects in
                    self.parentA.bs = newBObjects
                
            
        
    


struct CView: View 
    
    @Binding var parentA : A
    @Binding var parentB : B
    
    @State private var refreshing = false
    
    var body: some View 
            VStack 
                if(parentB.cs.isEmpty) 
                    Text("loading")
                 else 
                    List(parentB.cs.indices, id: \.self)  idx in
                        Text(self.parentB.cs[idx].name + self.parentB.cs[idx].description)
                    .pullToRefresh(isShowing: self.$refreshing) 
                        API.getCs(forB: self.parentB, inA: self.parentA)  newCObjects in
                            self.parentB.cs = newCObjects
                            self.refreshing = false
                        
                    
                
            
            .navigationBarTitle(Text(parentB.name), displayMode: .inline)
            .onAppear() 
                if(self.parentB.cs.isEmpty) 
                    API.getCs(forB: self.parentB, inA: self.parentA)  newCObjects in
                        self.parentB.cs = newCObjects
                    
                
            
    



class API 
    
    static func getAs(complete : @escaping ([A]) -> Void) 
        // normaly download from server
        let aobjects = [A(id: 1, name: "1"), A(id: 2, name: "2"), A(id: 3, name: "3")]
        complete(aobjects)
    
    
    static func getBs(forA : A, complete: @escaping ([B]) -> Void) 
        // normaly download all bs for a provided A from server
        let bObjects = [B(id: 4, name: "4"), B(id: 5, name: "5")]
        complete(bObjects)
    
    
    static func getCs(forB : B, inA: A, complete: @escaping ([C]) -> Void) 
        // normaly download all cs for a provided B in parent A from server
        let cObjects = [C(id: 6, name: "name", description: "desc")]
        complete(cObjects)
    


struct A 
    public let id : Int
    public let name : String
    public var bs = [B]()
    
    init(id: Int, name: String) 
        self.id = id
        self.name = name
    


struct B 
    public let id : Int
    public let name : String
    public var cs = [C]()
    
    init(id: Int, name: String) 
        self.id = id
        self.name = name
    


struct C 
    public let id : Int
    public let name : String
    public let description : String
    
    init(id: Int, name: String, description : String) 
        self.id = id
        self.name = name
        self.description = description
    

到目前为止，这有效。用户可以从 AView 导航到 BView 再到 CView。如果用户执行以下操作，则会出现标题中的问题和错误：从 AView 开始，转到 BView，转到 CView，返回 BView，返回 AView，通过下拉手势刷新。在其他情况下，它不会发生，例如。从 AView 开始，转到 BView，转到 CView，返回 BView，返回 AView，转到另一个 BView，返回 AView， 通过下拉手势刷新，这样可以。知道如何防止异常吗？

提前致谢

编辑：完整的错误消息

致命错误：索引超出范围：文件 /Library/Caches/com.apple.xbs/Sources/swiftlang/swiftlang-1103.2.25.8/swift/stdlib/public/core/ContiguousArrayBuffer.swift，第 444 行 2020-07-30 14:16:37.652919+0200 TestForArray[11908:625819] 致命错误：索引超出范围：文件 /Library/Caches/com.apple.xbs/Sources/swiftlang/swiftlang-1103.2.25.8/swift/ stdlib/public/core/ContiguousArrayBuffer.swift，第 444 行

【问题讨论】：

它是在“正常”条件下（新数据到达时）失败，还是在固定刷新数据时也失败，就像问题中一样

【参考方案1】：

您试图从超出数组范围的索引中获取数据。您可以使用此扩展程序。它将帮助您安全地获取对象。 https://github.com/MahmoudMMB/MahmoudMMB-Fetching_an_item_from_array_safely/blob/main/SafeFetching.swift

【讨论】：

不允许仅链接答案。链接会随着时间而中断。如果链接中有相关代码，请将代码贴在答案中

您应该观看 WWDC21 中的 Demystify SwiftUI，因此 Apple 认为这种特定做法是不安全的，应该避免

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