c# - 如何在 C# 中处理和识别 System.ArgumentOutOfRangeException？

Question

我有一个使用 C# 的基于 Xamarin 的应用程序。我有一个页面 EmployeeProfile。此页面列出了所有员工。有一次提供 10 条记录的 API 调用。当用户向下滚动并且最后一个项目开始出现时，它调用 Loadmore 方法，该方法为另外 10 条记录调用 API。

我使用 AppCenter 来跟踪错误和崩溃。当我检查我的实例时，我没有收到错误。但是，当我查看 AppCenter 崩溃报告时，此页面上有很多崩溃。

Exception: ThrowHelper.ThrowArgumentOutOfRangeException (System.ExceptionArgument argument, System.ExceptionResource resource) System.ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection. Parameter name: index

错误看起来像在 getEmployeeProfile() 方法中。谁能建议我哪一行导致了这个问题，我该如何预防？如果无法预防，我该如何处理？

代码:

publish SearchEmployeeResultsViewModel
{
    public ObservableRangeCollection<EmployeeProfile> SearchEmployee { get; set; }
    public List<EmployeeProfile> ListSearchEmployee { get; set; }
    public bool IsNoDataFound { get; set; }
    public int currentPage { get; set; }
    public int recordCount { get; set; }
    public bool IsBusy { get; set; }

    //constructor
    public SearchEmployeeResultsViewModel()
    {
        currentPage = 0;
        recordCount = 10;
        getEmployeeProfile();
    }

    //Call when user scroll down for more EmployeeProfiles
    //Following method call when last item start to visible(ListView event)
    private async Task LoadMore()
    {
        IsBusy = true;
        await getEmployeeProfile();
        IsBusy = false;
    }

    //Except/Crash raised from here
    private async Task getEmployeeProfile()
    {
        currentPage++;
        //Remove last item if it has no username
        //Purpose: We add blank item at end to manage smooth scrolling while getting next page data
        if (SearchEmployee.Count > 0 && SearchEmployee.Last().UserName == null)
            SearchEmployee.RemoveAt(SearchEmployee.Count() - 1);

        ListSearchEmployee.AddRange((await _profileApiClient.SearchEmployeeCall(currentPage, recordCount)));

        var differenceList = ListSearchEmployee.Except(SearchEmployee).ToList();

        if (differenceList.Count > 0)
        {
            SearchEmployee.AddRange(differenceList);
            //add blank item
            SearchEmployee.Add(new EmployeeProfile());
        }
        IsNoDataFound = (SearchEmployee == null || SearchEmployee.Count() == 0);
    }
}

错误堆栈跟踪:

ThrowHelper.ThrowArgumentOutOfRangeException (System.ExceptionArgument argument, System.ExceptionResource resource)
System.ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection. Parameter name: index

    ThrowHelper.ThrowArgumentOutOfRangeException (System.ExceptionArgument argument, System.ExceptionResource resource)
    ThrowHelper.ThrowArgumentOutOfRangeException ()
    List`1[T].get_Item (System.Int32 index)
    Collection`1[T].get_Item (System.Int32 index)
    ReadOnlyCollection`1[T].get_Item (System.Int32 index)
    RendererPool.UpdateRenderers (Xamarin.Forms.Element newElement)
    RendererPool.UpdateNewElement (Xamarin.Forms.VisualElement newElement)
    VisualElementPackager.SetElement (Xamarin.Forms.VisualElement oldElement, Xamarin.Forms.VisualElement newElement)
    VisualElementPackager.OnRendererElementChanged (System.Object sender, Xamarin.Forms.Platform.iOS.VisualElementChangedEventArgs args)
    VisualElementRenderer`1[TElement].OnElementChanged (Xamarin.Forms.Platform.iOS.ElementChangedEventArgs`1[TElement] e)
    VisualElementRenderer`1[TElement].SetElement (TElement element)
    IVisualElementRenderer.SetElement (Xamarin.Forms.VisualElement element)
    RendererPool.UpdateRenderers (Xamarin.Forms.Element newElement)
    RendererPool.UpdateNewElement (Xamarin.Forms.VisualElement newElement)
    VisualElementPackager.SetElement (Xamarin.Forms.VisualElement oldElement, Xamarin.Forms.VisualElement newElement)
    VisualElementPackager.OnRendererElementChanged (System.Object sender, Xamarin.Forms.Platform.iOS.VisualElementChangedEventArgs args)
    VisualElementRenderer`1[TElement].OnElementChanged (Xamarin.Forms.Platform.iOS.ElementChangedEventArgs`1[TElement] e)
    VisualElementRenderer`1[TElement].SetElement (TElement element)
    IVisualElementRenderer.SetElement (Xamarin.Forms.VisualElement element)
    RendererPool.UpdateRenderers (Xamarin.Forms.Element newElement)
    RendererPool.UpdateNewElement (Xamarin.Forms.VisualElement newElement)
    VisualElementPackager.SetElement (Xamarin.Forms.VisualElement oldElement, Xamarin.Forms.VisualElement newElement)
    VisualElementPackager.OnRendererElementChanged (System.Object sender, Xamarin.Forms.Platform.iOS.VisualElementChangedEventArgs args)
    VisualElementRenderer`1[TElement].OnElementChanged (Xamarin.Forms.Platform.iOS.ElementChangedEventArgs`1[TElement] e)
    VisualElementRenderer`1[TElement].SetElement (TElement element)
    IVisualElementRenderer.SetElement (Xamarin.Forms.VisualElement element)
    RendererPool.UpdateRenderers (Xamarin.Forms.Element newElement)
    RendererPool.UpdateNewElement (Xamarin.Forms.VisualElement newElement)
    VisualElementPackager.SetElement (Xamarin.Forms.VisualElement oldElement, Xamarin.Forms.VisualElement newElement)
    VisualElementPackager.OnRendererElementChanged (System.Object sender, Xamarin.Forms.Platform.iOS.VisualElementChangedEventArgs args)
    VisualElementRenderer`1[TElement].OnElementChanged (Xamarin.Forms.Platform.iOS.ElementChangedEventArgs`1[TElement] e)
    VisualElementRenderer`1[TElement].SetElement (TElement element)
    IVisualElementRenderer.SetElement (Xamarin.Forms.VisualElement element)
    ViewCellRenderer+ViewTableCell.UpdateCell (Xamarin.Forms.ViewCell cell)
    ViewCellRenderer+ViewTableCell.set_ViewCell (Xamarin.Forms.ViewCell value)
    ViewCellRenderer.GetCell (Xamarin.Forms.Cell item, UIKit.UITableViewCell reusableCell, UIKit.UITableView tv)
    CustomViewCellRenderer.GetCell (Xamarin.Forms.Cell item, UIKit.UITableViewCell reusableCell, UIKit.UITableView tv)
    CellTableViewCell.GetNativeCell (UIKit.UITableView tableView, Xamarin.Forms.Cell cell, System.Boolean recycleCells, System.String templateId)
    ListViewRenderer+ListViewDataSource.GetCell (UIKit.UITableView tableView, Foundation.NSIndexPath indexPath)
    (wrapper managed-to-native) ObjCRuntime.Messaging:objc_msgSend (intptr,intptr)
    UITableView.EndUpdates ()
    ListViewRenderer.UpdateItems (System.Collections.Specialized.NotifyCollectionChangedEventArgs e, System.Int32 section, System.Boolean resetWhenGrouped)
    ListViewRenderer.OnCollectionChanged (System.Object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
    TemplatedItemsList`2[TView,TItem].OnCollectionChanged (System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
    TemplatedItemsList`2[TView,TItem].OnProxyCollectionChanged (System.Object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e, System.Boolean fixWindows)
    TemplatedItemsList`2[TView,TItem].OnProxyCollectionChanged (System.Object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
    ListProxy.OnCollectionChanged (System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
    ListProxy+<>c__DisplayClass33_0.<OnCollectionChanged>b__0 ()
    ListProxy.OnCollectionChanged (System.Object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
    ListProxy+WeakNotifyProxy.OnCollectionChanged (System.Object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
    ObservableCollection`1[T].OnCollectionChanged (System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
    ObservableRangeCollection`1[T].OnCollectionChanged (System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
    ObservableCollection`1[T].OnCollectionChanged (System.Collections.Specialized.NotifyCollectionChangedAction action, System.Object item, System.Int32 index)
    ObservableCollection`1[T].InsertItem (System.Int32 index, T item)
    Collection`1[T].Add (T item)
    SearchEmployeeResultsViewModel+<getEmployeeProfile>d__76.MoveNext ()
    ExceptionDispatchInfo.Throw ()
    TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task)
    TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task)
    TaskAwaiter.ValidateEnd (System.Threading.Tasks.Task task)
    TaskAwaiter.GetResult ()
    SearchEmployeeResultsViewModel+<LoadMore>d__75.MoveNext ()
    ExceptionDispatchInfo.Throw ()
    AsyncMethodBuilderCore+<>c.<ThrowAsync>b__6_0 (System.Object state)
    UIKitSynchronizationContext+<Post>c__AnonStorey0.<>m__0 ()
    NSAsyncActionDispatcher.Apply ()
    (wrapper managed-to-native) UIKit.UIApplication:UIApplicationMain (int,string[],intptr,intptr)
    UIApplication.Main (System.String[] args, System.IntPtr principal, System.IntPtr delegate)
    UIApplication.Main (System.String[] args, System.String principalClassName, System.String delegateClassName)
    Application.Main (System.String[] args)

Answer 1

Error looks like in getEmployeeProfile() method. Can anybody please suggest me which line cause this issue....

根据您的堆栈跟踪，此行发生错误:

SearchEmployee.Add(new EmployeeProfile());

... how can I prevent it?

原因 似乎是绑定(bind)的 UI 控件试图遍历已更改的列表。如需更多帮助，您必须包括设计代码或绑定(bind)到此属性的代码。这是基于您发布的堆栈跟踪中的前 5 行。

---

On the UI side, there is a ListView. ListView binds to SearchEmployee. Is there any way to prevent it or handle it

看起来像是一个已报告的错误，请参阅 Bug 59974 - ArgumentOutOfRangeException in listview with ObservableCollection async Updates .