我在列表视图布局后更新了ListSource上的ItemsSource。我正在使用对Web服务的异步调用来填充表，如果我在创建包含listview的页面之前等待接收数据，它可以正常工作。当我尝试异步加载listview时，我得到一个空引用异常或一个超出范围异常的参数。
- 如果我将传入的数据添加到新的集合中，然后将其指定为itemsSource，我会得到一个ArgumentOutOfRangeException。
- 如果我尝试将新项直接添加到我的itemsSource，我会在插入第一条记录后得到一个空引用异常。
我已经通过调试器确认没有分配空值，并且看起来异常与过早收集垃圾的对象有关 - 我不确定它指的是什么对象
更新 问题仅发生在iOS实现上。列表视图在Android上完全按预期加载传入数据。
这是我的ListView：
public class TransferListView : ListView
{
public ObservableCollection<TransferCell> transferCells;
public TransferListView()
{
var curData = ESPMobileDS.GetSharedInstance();
transferCells = new ObservableCollection<TransferCell>();
ItemTemplate = TransferListView.GetCellTemplate();
ItemsSource = transferCells;
RowHeight = 75;
HorizontalOptions = LayoutOptions.FillAndExpand;
VerticalOptions = LayoutOptions.FillAndExpand;
BackgroundColor = ESPResources.Color.SoftBackgroundColorLight2;
BindingContext = TransferCell.IdentityProperty;
ItemSelected += async (sender, e) =>
{
curData.SelectedTransfer = e.SelectedItem as TransferCell;
await Navigation.PushAsync(new ItemDetailPage(DetailItemType.Transfer));
};
}
public static DataTemplate GetCellTemplate()
{
var cell = new DataTemplate(typeof(TransferCell));
cell.SetBinding(TransferCell.AccountFromProperty, "AccountFrom");
cell.SetBinding(TransferCell.AccountToProperty, "AccountTo");
cell.SetBinding(TransferCell.DateProperty, "Date");
cell.SetBinding(TransferCell.DescriptionProperty, "Description");
cell.SetBinding(TransferCell.AmountProperty, "Amount");
cell.SetBinding(TransferCell.IdentityProperty, "Identity");
cell.SetBinding(TransferCell.CanDeleteProperty, "CanDelete");
cell.SetBinding(TransferCell.IsPendingProperty, "IsPending");
return cell;
}
public void ParseAndReceiveServerResponse(string data) {
var curData = ESPMobileDS.GetSharedInstance();
var deserializationSettings = new JsonSerializerSettings
{
NullValueHandling = NullValueHandling.Ignore,
MissingMemberHandling = MissingMemberHandling.Ignore
};
Dictionary<string, TransferInfoListResponse> transferDict = JsonConvert.DeserializeObject<Dictionary<string, TransferInfoListResponse>>(data, deserializationSettings);
var transfers = transferDict["d"].Transfers;
if (transfers != null) {
Device.BeginInvokeOnMainThread(() => {
curData.currentPage.RemoveLoadingModal();
for (int i = 0; i < transfers.Count; i++) {
transferCells.Add(new TransferCell
{
AccountFrom = curData.GetNameForAccountNumber(transfers[i].FromAccount).ToUpper(),
AccountTo = curData.GetNameForAccountNumber(transfers[i].ToAccount).ToUpper(),
Description = transfers[i].Description,
Date = transfers[i].Date,
ID = i,
Amount = transfers[i].Amount,
CanDelete = transfers[i].CanDelete,
IsPending = transfers[i].IsPending
});
}
});
}
}
}
以下是其中包含的页面：
public class TransferPage : ESPMobilePage
{
BindableBoolean amountEntryVisible;
CustomEntry amountEntry;
TransferListView transferListView { set; get; }
AbsoluteLayout addTransferModal { set; get; }
Picker fromPicker;
Picker toPicker;
Picker amountPicker;
protected override async void OnAppearing() {
base.OnAppearing();
var curData = ESPMobileDS.GetSharedInstance();
await curData.PostToServer(curData.GetPostDataForResponseType(ResponseType.TransferInfoResponse), ESPResources.WebService.URL.GetTransferListMethod).ContinueWith((transferListResponse) => {
transferListView.ParseAndReceiveServerResponse(transferListResponse.Result);
});
}
public TransferPage ()
{
Title = " ";
Icon = ESPResources.Image.SystemImage.Empty;
NavigationPage.SetTitleIcon(this, ESPResources.Image.SystemImage.Empty);
var curData = ESPMobileDS.GetSharedInstance();
curData.SetCurrentPage(this);
amountEntryVisible = new BindableBoolean ();
amountEntryVisible.ShouldBeVisible = false;
layout = new AbsoluteLayout () {
HorizontalOptions = LayoutOptions.FillAndExpand,
VerticalOptions = LayoutOptions.FillAndExpand
};
var addTransferTapRecognizer = new TapGestureRecognizer
{
Command = new Command(() => {
OnAddTransfer();
}),
NumberOfTapsRequired = 1
};
var addButton = new CachedImage
{
Source = ESPResources.Image.SystemImage.AddButton,
Aspect = Aspect.Fill
};
addButton.GestureRecognizers.Add(addTransferTapRecognizer);
CustomNavigationBar navigationBar = new CustomNavigationBar(ESPResources.Text.Symbol.MenuSymbol, ESPResources.FontFamily.SymbolFont, LayoutGen.BuildMenuTapHandler());
transferListView = new TransferListView();
var unfinishedLayout = LayoutGen.BuildNewCoreLayout(ESPResources.Text.Title.TransferPage.ToUpper(), transferListView, navigationBar);
var mainLayout = LayoutGen.AddCoreLayoutButton(addButton, unfinishedLayout);
AbsoluteLayout.SetLayoutBounds (unfinishedLayout, new Rectangle(0,0,1,1));
AbsoluteLayout.SetLayoutFlags (unfinishedLayout, AbsoluteLayoutFlags.All);
layout.Children.Add(mainLayout);
Content = layout;
}
这是来自NullReferenceException的堆栈跟踪：
Nov 28 08:26:03 apples-iMac ESPMobileiOS[24684]:
Unhandled Exception:
System.NullReferenceException: Object reference not set to an instance of an object
at (wrapper managed-to-native) UIKit.UIApplication:UIApplicationMain (int,string[],intptr,intptr)
at UIKit.UIApplication.Main (System.String[] args, System.IntPtr principal, System.IntPtr delegate) [0x00005] in /Users/builder/data/lanes/3969/44931ae8/source/xamarin-macios/src/UIKit/UIApplication.cs:79
at UIKit.UIApplication.Main (System.String[] args, System.String principalClassName, System.String delegateClassName) [0x00038] in /Users/builder/data/lanes/3969/44931ae8/source/xamarin-macios/src/UIKit/UIApplication.cs:63
at ESPMobile.iOS.Application.Main (System.String[] args) [0x00008] in /Users/clarkin/Projects/ewu-larkinc/ESPMobile/iOS/Main.cs:13
Nov 28 08:26:03 apples-iMac ESPMobileiOS[24684]: Unhandled managed exception:
Object reference not set to an instance of an object (System.NullReferenceException)
at (wrapper managed-to-native) UIKit.UIApplication:UIApplicationMain (int,string[],intptr,intptr)
at UIKit.UIApplication.Main (System.String[] args, System.IntPtr principal, System.IntPtr delegate) [0x00005] in /Users/builder/data/lanes/3969/44931ae8/source/xamarin-macios/src/UIKit/UIApplication.cs:79
at UIKit.UIApplication.Main (System.String[] args, System.String principalClassName, System.String delegateClassName) [0x00038] in /Users/builder/data/lanes/3969/44931ae8/source/xamarin-macios/src/UIKit/UIApplication.cs:63
at ESPMobile.iOS.Application.Main (System.String[] args) [0x00008] in /Users/clarkin/Projects/ewu-larkinc/ESPMobile/iOS/Main.cs:13
Nov 28 08:26:03 apples-iMac ESPMobileiOS[24684]: critical: Stacktrace:
Nov 28 08:26:03 apples-iMac ESPMobileiOS[24684]: critical:
Native stacktrace:
Nov 28 08:26:03 apples-iMac ESPMobileiOS[24684]: critical: 0 ESPMobileiOS 0x000000010b21f6bd mono_handle_native_sigsegv + 253
Nov 28 08:26:03 apples-iMac ESPMobileiOS[24684]: critical: 1 libsystem_platform.dylib 0x00000001119a3bba _sigtramp + 26
Nov 28 08:26:03 apples-iMac ESPMobileiOS[24684]: critical: 2 ??? 0x000000010b61f99b 0x0 + 4485937563
Nov 28 08:26:03 apples-iMac ESPMobileiOS[24684]: critical: 3 libsystem_c.dylib 0x00000001116fafd7 abort + 129
Nov 28 08:26:03 apples-iMac ESPMobileiOS[24684]: critical: 4 ESPMobileiOS 0x000000010b3c4f0f xamarin_unhandled_exception_handler + 47
Nov 28 08:26:03 apples-iMac ESPMobileiOS[24684]: critical: 5 ESPMobileiOS 0x000000010b21ff8c mono_invoke_unhandled_exception_hook + 92
Nov 28 08:26:03 apples-iMac ESPMobileiOS[24684]: critical: 6 ESPMobileiOS 0x000000010b21ef0f mono_handle_exception_internal + 5119
Nov 28 08:26:03 apples-iMac ESPMobileiOS[24684]: critical: 7 ESPMobileiOS 0x000000010b21db08 mono_handle_exception + 24
Nov 28 08:26:03 apples-iMac ESPMobileiOS[24684]: critical: 8 ESPMobileiOS 0x000000010b19867f mono_amd64_throw_exception + 143
Nov 28 08:26:03 apples-iMac ESPMobileiOS[24684]: critical: 9 ??? 0x000000011dcaa9e7 0x0 + 4794788327
Nov 28 08:26:03 apples-iMac ESPMobileiOS[24684]: critical: 10 ESPMobileiOS 0x000000010b3ca845 xamarin_invoke_trampoline + 7541
Nov 28 08:26:03 apples-iMac ESPMobileiOS[24684]: critical: 11 ESPMobileiOS 0x000000010b3d1cdd xamarin_arch_trampoline + 189
Nov 28 08:26:03 apples-iMac ESPMobileiOS[24684]: critical: 12 ESPMobileiOS 0x000000010b3d3021 xamarin_x86_64_common_trampoline + 110
Nov 28 08:26:03 apples-iMac ESPMobileiOS[24684]: critical: 13 UIKit 0x000000010b80f7b5 -[UITableView _createPreparedCellForGlobalRow:withIndexPath:willDisplay:] + 757
Nov 28 08:26:03 apples-iMac ESPMobileiOS[24684]: critical: 14 UIKit 0x000000010b80fa13 -[UITableView _createPreparedCellForGlobalRow:willDisplay:] + 74
Nov 28 08:26:03 apples-iMac ESPMobileiOS[24684]: critical: 15 UIKit 0x000000010b7e347d -[UITableView _updateVisibleCellsNow:isRecursive:] + 3295
Nov 28 08:26:03 apples-iMac ESPMobileiOS[24684]: critical: 16 UIKit 0x000000010b818d95 -[UITableView _performWithCachedTraitCollection:] + 110
Nov 28 08:26:03 apples-iMac ESPMobileiOS[24684]: critical: 17 UIKit 0x000000010b7ff5ef -[UITableView layoutSubviews] + 222
Nov 28 08:26:03 apples-iMac ESPMobileiOS[24684]: critical: 18 UIKit 0x000000010b766f50 -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 1237
Nov 28 08:26:03 apples-iMac ESPMobileiOS[24684]: critical: 19 QuartzCore 0x000000010d5bbcc4 -[CALayer layoutSublayers] + 146
Nov 28 08:26:03 apples-iMac ESPMobileiOS[24684]: critical: 20 QuartzCore 0x000000010d5af788 _ZN2CA5Layer16layout_if_neededEPNS_11TransactionE + 366
Nov 28 08:26:03 apples-iMac ESPMobileiOS[24684]: critical: 21 QuartzCore 0x000000010d5af606 _ZN2CA5Layer28layout_and_display_if_neededEPNS_11TransactionE + 24
Nov 28 08:26:03 apples-iMac ESPMobileiOS[24684]: critical: 22 QuartzCore 0x000000010d53d680 _ZN2CA7Context18commit_transactionEPNS_11TransactionE + 280
Nov 28 08:26:03 apples-iMac ESPMobileiOS[24684]: critical: 23 QuartzCore 0x000000010d56a767 _ZN2CA11Transaction6commitEv + 475
Nov 28 08:26:03 apples-iMac ESPMobileiOS[24684]: critical: 24 QuartzCore 0x000000010d56b0d7 _ZN2CA11Transaction17observer_callbackEP19__CFRunLoopObservermPv + 113
Nov 28 08:26:03 apples-iMac ESPMobileiOS[24684]: critical: 25 CoreFoundation 0x000000010ef88e17 __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 23
Nov 28 08:26:03 apples-iMac ESPMobileiOS[24684]: critical: 26 CoreFoundation 0x000000010ef88d87 __CFRunLoopDoObservers + 391
Nov 28 08:26:03 apples-iMac ESPMobileiOS[24684]: critical: 27 CoreFoundation 0x000000010ef6db9e __CFRunLoopRun + 1198
Nov 28 08:26:03 apples-iMac ESPMobileiOS[24684]: critical: 28 CoreFoundation 0x000000010ef6d494 CFRunLoopRunSpecific + 420
Nov 28 08:26:03 apples-iMac ESPMobileiOS[24684]: critical: 29 GraphicsServices 0x00000001106f5a6f GSEventRunModal + 161
Nov 28 08:26:03 apples-iMac ESPMobileiOS[24684]: critical: 30 UIKit 0x000000010b6a2964 UIApplicationMain + 159
Nov 28 08:26:03 apples-iMac ESPMobileiOS[24684]: critical: 31 ??? 0x000000011f656ca2 0x0 + 4821707938
Nov 28 08:26:03 apples-iMac ESPMobileiOS[24684]: critical: 32 ??? 0x000000011f656b30 0x0 + 4821707568
Nov 28 08:26:03 apples-iMac ESPMobileiOS[24684]: critical:
=================================================================
Got a SIGABRT while executing native code. This usually indicates
a fatal error in the mono runtime or one of the native libraries
used by your application.
答案 0 :(得分：0)
我似乎记得在iOS上更新ObservableCollections存在问题。尝试替换整个事物。例如，在ParseAndReceiveServerResponse方法的底部试试这个：
var tempList = new List<TransferCell>();
for (int i = 0; i < transfers.Count; i++)
{
tempList.Add(new TransferCell
{
AccountFrom = curData.GetNameForAccountNumber(transfers[i].FromAccount).ToUpper(),
AccountTo = curData.GetNameForAccountNumber(transfers[i].ToAccount).ToUpper(),
Description = transfers[i].Description,
Date = transfers[i].Date,
ID = i,
Amount = transfers[i].Amount,
CanDelete = transfers[i].CanDelete,
IsPending = transfers[i].IsPending
});
}
ItemsSource = new ObservableCollection<TransferCell>(tempList);