"System.InvalidOperationException: Collection was modified" 在 MvvmCross TableView 绑定中
"System.InvalidOperationException: Collection was modified" in MvvmCross TableView binding
希望有人能帮助我解决以下问题，因为我完全被卡住了。
当我在我的 TableView 上绑定时，我在我的 MvvmCross Xamarin.iOS 应用程序中收到以下异常。这仅在我更改数据源时发生（每次更改日期时，TableView 都需要更新）。
Incident Identifier: 7E7C2B15-7CC4-4AE7-9891-C4FD82358009
CrashReporter Key: 46CC21C0-DDE1-4313-9658-EC79D767939B
Hardware Model: iPhone7,2
Process: UurwerkiOS [4326]
Path: /var/containers/Bundle/Application/75969477-A516-44C3-A5A3-5B24DDDC89C8/UurwerkiOS.app/UurwerkiOS
Identifier: com.route2it.uurwerk
Version: 1.0 (1.0.96)
Code Type: ARM-64
Parent Process: ??? [1]
Date/Time: 2016-07-04T13:16:38Z
Launch Time: 2016-07-04T13:16:31Z
OS Version: iPhone OS 9.3.2 (13F69)
Report Version: 104
Exception Type: SIGABRT
Exception Codes: #0 at 0x1816ac11c
Crashed Thread: 5
Application Specific Information:
*** Terminating app due to uncaught exception 'System.AggregateException', reason: 'System.AggregateException: A Task's exception(s) were not observed either by Waiting on the Task or accessing its Exception property. As a result, the unobserved exception was rethrown by the finalizer thread. ---> System.InvalidOperationException: Collection was modified; enumeration operation may not execute.
at System.ThrowHelper.ThrowInvalidOperationException (ExceptionResource resource) <0x10044bec0 + 0x00024> in <filename unknown>:0
at System.Collections.Generic.List`1+Enumerator[T].MoveNextRare () <0x1003bf900 + 0x0002f> in <filename unknown>:0
at System.Collections.Generic.List`1+Enumerator[T].MoveNext () <0x1003bf830 + 0x0009f> in <filename unknown>:0
at MvvmCross.Binding.BindingContext.MvxTaskBasedBindingContext.<OnDataContextChange>b__20_0 () <0x1007c1990 + 0x0023f> in <filename unknown>:0
at System.Threading.Tasks.Task.InnerInvoke () <0x10043f1f0 + 0x0005f> in <filename unknown>:0
at System.Threading.Tasks.Task.Execute () <0x10043ea20 + 0x00043> in <filename unknown>:0
--- End of inner exception stack trace ---
---> (Inner Exception #0) System.InvalidOperationException: Collection was modified; enumeration operation may not execute.
at System.ThrowHelper.ThrowInvalidOperationException (ExceptionResource resource) <0x10044bec0 + 0x00024> in <filename unknown>:0
at System.Collections.Generic.List`1+Enumerator[T].MoveNextRare () <0x1003bf900 + 0x0002f> in <filename unknown>:0
at System.Collections.Generic.List`1+Enumerator[T].MoveNext () <0x1003bf830 + 0x0009f> in <filename unknown>:0
at MvvmCross.Binding.BindingContext.MvxTaskBasedBindingContext.<OnDataContextChange>b__20_0 () <0x1007c1990 + 0x0023f> in <filename unknown>:0
at System.Threading.Tasks.Task.InnerInvoke () <0x10043f1f0 + 0x0005f> in <filename unknown>:0
at System.Threading.Tasks.Task.Execute () <0x10043ea20 + 0x00043> in <filename unknown>:0
起初我认为它与我的一个 Async 方法有关（可能没有及时完成，而下一个已经 运行）。所以我删除了我所有的异步代码，但异常仍然发生。我还确保自己不会更改可枚举集合。我获取数据（这只是内存数组中的一个）并将其 return 作为新列表添加到 TableView 绑定到的 属性 中。下面是构成绑定的代码片段（信息很多，但我希望尽可能完整）：
日历视图控制器:
public override void ViewDidLoad()
{
base.ViewDidLoad();
if (NavigationController != null)
NavigationController.NavigationBarHidden = false;
InitCalendar();
InitNavigationItem();
InitTableView();
ApplyConstraints();
var shiftForDateTableViewSource = new MvxSimpleTableViewSource(_tableView, CalendarTableViewCell.Key, CalendarTableViewCell.Key);
shiftForDateTableViewSource.DeselectAutomatically = true;
_tableView.RowHeight = 45;
_tableView.Source = shiftForDateTableViewSource;
var set = this.CreateBindingSet<CalendarView, CalendarViewModel>();
set.Bind(shiftForDateTableViewSource).To(vm => vm.ShiftsForSelectedDate);
set.Bind(shiftForDateTableViewSource).For(vm => vm.SelectionChangedCommand).To(vm => vm.ShiftSelectedCommand);
set.Apply();
_tableView.ReloadData();
}
private void InitTableView()
{
_tableView = new UITableView();
_tableView.RegisterClassForCellReuse(typeof(UITableViewCell), CalendarTableViewCell.Key);
Add(_tableView);
}
CalendarTableViewCell:
public partial class CalendarTableViewCell : MvxTableViewCell
{
public static readonly NSString Key = new NSString("CalendarTableViewCell");
public static readonly UINib Nib;
static CalendarTableViewCell()
{
Nib = UINib.FromName("CalendarTableViewCell", NSBundle.MainBundle);
}
protected CalendarTableViewCell(IntPtr handle) : base(handle)
{
}
public override void LayoutSubviews()
{
base.LayoutSubviews();
var set = this.CreateBindingSet<CalendarTableViewCell, Shift>();
set.Bind(StartTimeLabel).To(vm => vm.StartDate).WithConversion("StringFormat", "HH:mm");
set.Bind(EndTimeLabel).To(vm => vm.EndDate).WithConversion("StringFormat", "HH:mm");
set.Bind(ColorBarView).For("BackgroundColor").To(vm => vm.Color).WithConversion("RGB");
set.Bind(TitleLabel).To(vm => vm).WithConversion("ConcatenatedEventTitle");
set.Bind(LocationLabel).To(vm => vm.Location);
set.Apply();
}
}
日历视图模型:
public class CalendarViewModel
: MvxViewModel
{
private readonly IShiftService _shiftService;
public CalendarViewModel(IShiftService shiftService)
{
if (shiftService == null)
throw new ArgumentNullException(nameof(shiftService));
_shiftService = shiftService;
}
public override void Start()
{
base.Start();
Shifts = _shiftService.GetShiftsForEmployeeAsync(1);
}
private IEnumerable<Shift> _shifts;
public IEnumerable<Shift> Shifts
{
get { return _shifts; }
set
{
SetProperty(ref _shifts,
value,
nameof(Shifts));
}
}
private IEnumerable<Shift> _shiftsForSelectedDate;
public IEnumerable<Shift> ShiftsForSelectedDate
{
get { return _shiftsForSelectedDate; }
private set
{
if (_shiftsForSelectedDate == value)
return;
SetProperty(ref _shiftsForSelectedDate,
value,
nameof(ShiftsForSelectedDate));
}
}
private DateTime? _selectedDate;
public DateTime? SelectedDate
{
get { return _selectedDate; }
set
{
if (_selectedDate == value)
return;
SetProperty(ref _selectedDate,
value,
nameof(SelectedDate));
if (_selectedDate.HasValue)
FetchShiftsForSelectedDate();
}
}
private void FetchShiftsForSelectedDate()
{
ShiftsForSelectedDate = _shiftService.GetShiftsForSelectedDateAsync(_selectedDate.Value);
}
}
MockShiftService（实现了IShiftService接口）：
public class MockShiftService
: IShiftService
{
private IList<Shift> _shifts;
public MockShiftService()
{
Initialize();
}
public IEnumerable<Shift> GetShiftsForEmployeeAsync(int employeeId)
{
return _shifts;
}
public IEnumerable<Shift> GetShiftsForSelectedDateAsync(DateTime selectedDate)
{
var endDate = selectedDate.Date.Add(new TimeSpan(23, 59, 59));
return _shifts
.Where(s => s.StartDate <= endDate && s.EndDate >= selectedDate)
.ToList();
}
public Shift GetShiftByIdAsync(int shiftId)
{
return _shifts.First((shift) => shift.Id == shiftId);
}
private void Initialize()
{
var shifts = new List<Shift>();
// The in memory array gets populated here which
// is straight forward creating instances of the
// 'Shift' class and assigning it's properties before
// adding it to the 'shifts' collection. I left
// this code out to keep it as short as possible.
}
}
更新：
我已经将我的项目直接引用到 MvvmCross 的调试程序集，并发现异常是在 MvxTaskBasedBindingContext class 的第 127 行抛出的，并且总是在第二次迭代时发生。由此我得出结论，集合在第一次迭代期间发生了变化。不幸的是，我不知道为什么或如何。
我注意到 MvxTaskBasedBindingContext 替换了 MvxBindingContext（由 softlion 于 11-5-2016 更改）。当我强制我的应用程序使用 MvxBindingContext class 时，一切正常（虽然有点滞后）。这让我相信问题出在 MvxTaskBasedBindingContext 但我真的不明白为什么，任何帮助将不胜感激。
更新 2：
经过更多的调试和摆弄后，我发现异常与我的 CalendarTableViewCell class 设置的绑定有关（它应该为 tableview 中定义的每个项目提供布局我的 CalendarViewController。当我注释掉 CalendarTableViewCell class 中的绑定时，不会发生异常（请参阅我上面的代码）。不过我仍然不知道哪里出了问题。
您可以在 CalendarTableViewCell 中使用 DelayBind 延迟绑定，直到 DataContext gets set on your BindingContext
public partial class CalendarTableViewCell : MvxTableViewCell
{
...
public override void LayoutSubviews()
{
base.LayoutSubviews();
this.DelayBind(() =>
{
var set = this.CreateBindingSet<CalendarTableViewCell, Shift>();
set.Bind(StartTimeLabel).To(vm => vm.StartDate).WithConversion("StringFormat", "HH:mm");
set.Bind(EndTimeLabel).To(vm => vm.EndDate).WithConversion("StringFormat", "HH:mm");
set.Bind(ColorBarView).For("BackgroundColor").To(vm => vm.Color).WithConversion("RGB");
set.Bind(TitleLabel).To(vm => vm).WithConversion("ConcatenatedEventTitle");
set.Bind(LocationLabel).To(vm => vm.Location);
set.Apply();
});
}
}
延迟绑定无法解决此问题。
问题在于列表是在任务中枚举的，可以在枚举进行时对其进行修改。
Task.Run(() =>
{
foreach (var binding in this._viewBindings)
{
foreach (var bind in binding.Value)
{
bind.Binding.DataContext = this._dataContext;
}
}
foreach (var binding in this._directBindings)
{
binding.Binding.DataContext = this._dataContext;
}
});
枚举之前需要创建集合 ToList() 或 ToArray() 的副本。
此错误已被报告。
Link
希望有人能帮助我解决以下问题，因为我完全被卡住了。
当我在我的 TableView 上绑定时，我在我的 MvvmCross Xamarin.iOS 应用程序中收到以下异常。这仅在我更改数据源时发生（每次更改日期时，TableView 都需要更新）。
Incident Identifier: 7E7C2B15-7CC4-4AE7-9891-C4FD82358009
CrashReporter Key: 46CC21C0-DDE1-4313-9658-EC79D767939B
Hardware Model: iPhone7,2
Process: UurwerkiOS [4326]
Path: /var/containers/Bundle/Application/75969477-A516-44C3-A5A3-5B24DDDC89C8/UurwerkiOS.app/UurwerkiOS
Identifier: com.route2it.uurwerk
Version: 1.0 (1.0.96)
Code Type: ARM-64
Parent Process: ??? [1]
Date/Time: 2016-07-04T13:16:38Z
Launch Time: 2016-07-04T13:16:31Z
OS Version: iPhone OS 9.3.2 (13F69)
Report Version: 104
Exception Type: SIGABRT
Exception Codes: #0 at 0x1816ac11c
Crashed Thread: 5
Application Specific Information:
*** Terminating app due to uncaught exception 'System.AggregateException', reason: 'System.AggregateException: A Task's exception(s) were not observed either by Waiting on the Task or accessing its Exception property. As a result, the unobserved exception was rethrown by the finalizer thread. ---> System.InvalidOperationException: Collection was modified; enumeration operation may not execute.
at System.ThrowHelper.ThrowInvalidOperationException (ExceptionResource resource) <0x10044bec0 + 0x00024> in <filename unknown>:0
at System.Collections.Generic.List`1+Enumerator[T].MoveNextRare () <0x1003bf900 + 0x0002f> in <filename unknown>:0
at System.Collections.Generic.List`1+Enumerator[T].MoveNext () <0x1003bf830 + 0x0009f> in <filename unknown>:0
at MvvmCross.Binding.BindingContext.MvxTaskBasedBindingContext.<OnDataContextChange>b__20_0 () <0x1007c1990 + 0x0023f> in <filename unknown>:0
at System.Threading.Tasks.Task.InnerInvoke () <0x10043f1f0 + 0x0005f> in <filename unknown>:0
at System.Threading.Tasks.Task.Execute () <0x10043ea20 + 0x00043> in <filename unknown>:0
--- End of inner exception stack trace ---
---> (Inner Exception #0) System.InvalidOperationException: Collection was modified; enumeration operation may not execute.
at System.ThrowHelper.ThrowInvalidOperationException (ExceptionResource resource) <0x10044bec0 + 0x00024> in <filename unknown>:0
at System.Collections.Generic.List`1+Enumerator[T].MoveNextRare () <0x1003bf900 + 0x0002f> in <filename unknown>:0
at System.Collections.Generic.List`1+Enumerator[T].MoveNext () <0x1003bf830 + 0x0009f> in <filename unknown>:0
at MvvmCross.Binding.BindingContext.MvxTaskBasedBindingContext.<OnDataContextChange>b__20_0 () <0x1007c1990 + 0x0023f> in <filename unknown>:0
at System.Threading.Tasks.Task.InnerInvoke () <0x10043f1f0 + 0x0005f> in <filename unknown>:0
at System.Threading.Tasks.Task.Execute () <0x10043ea20 + 0x00043> in <filename unknown>:0
起初我认为它与我的一个 Async 方法有关（可能没有及时完成，而下一个已经 运行）。所以我删除了我所有的异步代码，但异常仍然发生。我还确保自己不会更改可枚举集合。我获取数据（这只是内存数组中的一个）并将其 return 作为新列表添加到 TableView 绑定到的 属性 中。下面是构成绑定的代码片段（信息很多，但我希望尽可能完整）：
日历视图控制器:
public override void ViewDidLoad()
{
base.ViewDidLoad();
if (NavigationController != null)
NavigationController.NavigationBarHidden = false;
InitCalendar();
InitNavigationItem();
InitTableView();
ApplyConstraints();
var shiftForDateTableViewSource = new MvxSimpleTableViewSource(_tableView, CalendarTableViewCell.Key, CalendarTableViewCell.Key);
shiftForDateTableViewSource.DeselectAutomatically = true;
_tableView.RowHeight = 45;
_tableView.Source = shiftForDateTableViewSource;
var set = this.CreateBindingSet<CalendarView, CalendarViewModel>();
set.Bind(shiftForDateTableViewSource).To(vm => vm.ShiftsForSelectedDate);
set.Bind(shiftForDateTableViewSource).For(vm => vm.SelectionChangedCommand).To(vm => vm.ShiftSelectedCommand);
set.Apply();
_tableView.ReloadData();
}
private void InitTableView()
{
_tableView = new UITableView();
_tableView.RegisterClassForCellReuse(typeof(UITableViewCell), CalendarTableViewCell.Key);
Add(_tableView);
}
CalendarTableViewCell:
public partial class CalendarTableViewCell : MvxTableViewCell
{
public static readonly NSString Key = new NSString("CalendarTableViewCell");
public static readonly UINib Nib;
static CalendarTableViewCell()
{
Nib = UINib.FromName("CalendarTableViewCell", NSBundle.MainBundle);
}
protected CalendarTableViewCell(IntPtr handle) : base(handle)
{
}
public override void LayoutSubviews()
{
base.LayoutSubviews();
var set = this.CreateBindingSet<CalendarTableViewCell, Shift>();
set.Bind(StartTimeLabel).To(vm => vm.StartDate).WithConversion("StringFormat", "HH:mm");
set.Bind(EndTimeLabel).To(vm => vm.EndDate).WithConversion("StringFormat", "HH:mm");
set.Bind(ColorBarView).For("BackgroundColor").To(vm => vm.Color).WithConversion("RGB");
set.Bind(TitleLabel).To(vm => vm).WithConversion("ConcatenatedEventTitle");
set.Bind(LocationLabel).To(vm => vm.Location);
set.Apply();
}
}
日历视图模型:
public class CalendarViewModel
: MvxViewModel
{
private readonly IShiftService _shiftService;
public CalendarViewModel(IShiftService shiftService)
{
if (shiftService == null)
throw new ArgumentNullException(nameof(shiftService));
_shiftService = shiftService;
}
public override void Start()
{
base.Start();
Shifts = _shiftService.GetShiftsForEmployeeAsync(1);
}
private IEnumerable<Shift> _shifts;
public IEnumerable<Shift> Shifts
{
get { return _shifts; }
set
{
SetProperty(ref _shifts,
value,
nameof(Shifts));
}
}
private IEnumerable<Shift> _shiftsForSelectedDate;
public IEnumerable<Shift> ShiftsForSelectedDate
{
get { return _shiftsForSelectedDate; }
private set
{
if (_shiftsForSelectedDate == value)
return;
SetProperty(ref _shiftsForSelectedDate,
value,
nameof(ShiftsForSelectedDate));
}
}
private DateTime? _selectedDate;
public DateTime? SelectedDate
{
get { return _selectedDate; }
set
{
if (_selectedDate == value)
return;
SetProperty(ref _selectedDate,
value,
nameof(SelectedDate));
if (_selectedDate.HasValue)
FetchShiftsForSelectedDate();
}
}
private void FetchShiftsForSelectedDate()
{
ShiftsForSelectedDate = _shiftService.GetShiftsForSelectedDateAsync(_selectedDate.Value);
}
}
MockShiftService（实现了IShiftService接口）：
public class MockShiftService
: IShiftService
{
private IList<Shift> _shifts;
public MockShiftService()
{
Initialize();
}
public IEnumerable<Shift> GetShiftsForEmployeeAsync(int employeeId)
{
return _shifts;
}
public IEnumerable<Shift> GetShiftsForSelectedDateAsync(DateTime selectedDate)
{
var endDate = selectedDate.Date.Add(new TimeSpan(23, 59, 59));
return _shifts
.Where(s => s.StartDate <= endDate && s.EndDate >= selectedDate)
.ToList();
}
public Shift GetShiftByIdAsync(int shiftId)
{
return _shifts.First((shift) => shift.Id == shiftId);
}
private void Initialize()
{
var shifts = new List<Shift>();
// The in memory array gets populated here which
// is straight forward creating instances of the
// 'Shift' class and assigning it's properties before
// adding it to the 'shifts' collection. I left
// this code out to keep it as short as possible.
}
}
更新：
我已经将我的项目直接引用到 MvvmCross 的调试程序集，并发现异常是在 MvxTaskBasedBindingContext class 的第 127 行抛出的，并且总是在第二次迭代时发生。由此我得出结论，集合在第一次迭代期间发生了变化。不幸的是，我不知道为什么或如何。
我注意到 MvxTaskBasedBindingContext 替换了 MvxBindingContext（由 softlion 于 11-5-2016 更改）。当我强制我的应用程序使用 MvxBindingContext class 时，一切正常（虽然有点滞后）。这让我相信问题出在 MvxTaskBasedBindingContext 但我真的不明白为什么，任何帮助将不胜感激。
更新 2：
经过更多的调试和摆弄后，我发现异常与我的 CalendarTableViewCell class 设置的绑定有关（它应该为 tableview 中定义的每个项目提供布局我的 CalendarViewController。当我注释掉 CalendarTableViewCell class 中的绑定时，不会发生异常（请参阅我上面的代码）。不过我仍然不知道哪里出了问题。
您可以在 CalendarTableViewCell 中使用 DelayBind 延迟绑定，直到 DataContext gets set on your BindingContext
public partial class CalendarTableViewCell : MvxTableViewCell
{
...
public override void LayoutSubviews()
{
base.LayoutSubviews();
this.DelayBind(() =>
{
var set = this.CreateBindingSet<CalendarTableViewCell, Shift>();
set.Bind(StartTimeLabel).To(vm => vm.StartDate).WithConversion("StringFormat", "HH:mm");
set.Bind(EndTimeLabel).To(vm => vm.EndDate).WithConversion("StringFormat", "HH:mm");
set.Bind(ColorBarView).For("BackgroundColor").To(vm => vm.Color).WithConversion("RGB");
set.Bind(TitleLabel).To(vm => vm).WithConversion("ConcatenatedEventTitle");
set.Bind(LocationLabel).To(vm => vm.Location);
set.Apply();
});
}
}
延迟绑定无法解决此问题。 问题在于列表是在任务中枚举的，可以在枚举进行时对其进行修改。
Task.Run(() =>
{
foreach (var binding in this._viewBindings)
{
foreach (var bind in binding.Value)
{
bind.Binding.DataContext = this._dataContext;
}
}
foreach (var binding in this._directBindings)
{
binding.Binding.DataContext = this._dataContext;
}
});
枚举之前需要创建集合 ToList() 或 ToArray() 的副本。
此错误已被报告。 Link