c# - 错误 : Collection was modified; enumeration operation may not execute

Question

我一直在现场解决这个异常。我不明白如何在迭代时修改集合。我在方法开始时将所有内容复制到局部变量。

  public void Flush() {
            var tempEntities = attachedEntities.Select(item => item).ToList();
            attachedEntities.Clear();

            var tempEntitiesToDelete = entitiesToDelete.Select(item => item).ToList();
            entitiesToDelete.Clear();

            foreach (var attachedEntity in tempEntities) {
                var isTransient = (bool)GetPrivateField(attachedEntity.GetType(), attachedEntity, "isTransient");
                if (isTransient)
                    db.Insert(attachedEntity);
                else
                    db.Update(attachedEntity);
            }

            foreach (var entity in tempEntitiesToDelete)
                db.Delete(entity);
        }

堆栈跟踪

System.InvalidOperationException: Collection was modified; enumeration operation may not execute.
  at System.Collections.Generic.List`1 Enumerator[Compass.Mobile.Core.DataAccess.IEntity].VerifyState () [0x00000] in <filename unknown>:0 
  at System.Collections.Generic.List`1 Enumerator[Compass.Mobile.Core.DataAccess.IEntity].MoveNext () [0x00000] in <filename unknown>:0 
  at System.Linq.Enumerable <CreateSelectIterator>c__Iterator1D`2[Compass.Mobile.Core.DataAccess.IEntity,Compass.Mobile.Core.DataAccess.IEntity].MoveNext () [0x00000] in <filename unknown>:0 
  at System.Collections.Generic.List`1[Compass.Mobile.Core.DataAccess.IEntity].AddEnumerable (IEnumerable`1 enumerable) [0x00000] in <filename unknown>:0 
  at System.Collections.Generic.List`1[Compass.Mobile.Core.DataAccess.IEntity]..ctor (IEnumerable`1 collection) [0x00000] in <filename unknown>:0 
  at System.Linq.Enumerable.ToList[TSource] (IEnumerable`1 source) [0x00000] in <filename unknown>:0 
  at Compass.Mobile.Core.DataAccess.Session.Flush () [0x00000] in <filename unknown>:0 
  at Compass.Mobile.Core.DataAccess.Session.Commit () [0x00000] in <filename unknown>:0 
  at Compass.Mobile.Core.Bootstrap.CommandBus.Flush () [0x00000] in <filename unknown>:0 

Answer 1

替换这个:

foreach (var entity in tempEntitiesToDelete)
     db.Delete(entity);

与:

for (var i = tempEntitiesToDelete.Count - 1; i >= 0; i--)
   db.Delete(tempEntitiesToDelete[i]);

当我尝试在循环中删除时遇到了这个问题；它试图修改项目列表。因此，向后循环为我修复了它。