这是一段有时会引发异常的代码：
Pendings = ClientCode.PendingOrders.Select(x => new DisplayPending()
{
ItemCode = ClientCode.Items.First(y => y.Id == x.ItemCode).Id,ItemName = ClientCode.Items.First(y => y.Id == x.ItemCode).Name,OrderNo = x.BuyOrderNo == 0 ? x.SellOrderNo : x.BuyOrderNo,OrderType = x.OrderType == OrderType.Buy ? "Buy" : "Sell",PartyCode = x.PartyCode,Price = x.Price,Quantity = x.Quantity
});
这是消息：
System.NullReferenceException: 'Object reference not set to an instance of an object.'
x was null.
PendingOrders是ObservableCollection，它有500多个项目。
编辑
这是我填充扩展ObservableCollection的方式：
public class AsyncObsetion<T> : ObservableCollection<T>
{
SynchronizationContext context = SynchronizationContext.Current;
readonly object _lock = new object();
public AsyncObsetion() { BindingOperations.EnableCollectionSynchronization(this,_lock); }
public AsyncObsetion(IEnumerable<T> list) : base(list) { BindingOperations.EnableCollectionSynchronization(this,_lock); }
void RaiseCollectionChanged(object param) => base.OnCollectionChanged((NotifyCollectionChangedEventArgs)param);
void RaisePropertyChanged(object param) => base.OnPropertyChanged((PropertyChangedEventArgs)param);
protected override void OnCollectionChanged(NotifyCollectionChangedEventArgs e)
{
if (SynchronizationContext.Current == context) RaiseCollectionChanged(e);
else context.Send(RaiseCollectionChanged,e);
}
protected override void OnPropertyChanged(PropertyChangedEventArgs e)
{
if (SynchronizationContext.Current == context) RaisePropertyChanged(e);
else context.Send(RaisePropertyChanged,e);
}
public void InsertRange(IEnumerable<T> items)
{
this.CheckReentrancy();
foreach (var item in items)
this.Items.Add(item);
this.OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedaction.Reset));
}
}
当Client连接到Server时，它将发送6个byte[]，它们被添加到名为AsyncObsetion<T>，Items，{{ 1}}，NewsCollection，Issued，BuyOrders，SellOrders和PendingOrders在客户端。这段代码负责处理客户端从服务器获取的ExecutedOrders：
MyExecutedOrders byte[]是一个事件，当它被触发时，客户端开始从var tasks = new List<Task>();
tasks.Add(Task.Run(() =>
{
for (int i = 0; i < header.ItemSize; i += Constants.itemSize)
{
var item = PacMan<ItemStruct>.Unpack(itemArray.Skip(i).Take(Constants.itemSize).ToArray());
Items.Add(new Item()
{
Id = item.Id,Name = item.Name,Cap = item.Cap,Floor = item.Floor,Mid = item.Floor + ((item.Cap - item.Floor) / 2),Securities = item.Securities,Owners = item.Owners,Govt = item.Govt,Institutions = item.Institutions,Foreign = item.Foreign,Public = item.Public,PerSecurity = PacMan<PerSecurityFinancialsStruct>.ArrayToList<PerSecurityFinancials>(item.PerSecurity),Dividends = PacMan<DividendStruct>.ArrayToList<Dividend>(item.Dividends),InitialSecurity = item.InitialSecurity
});
}
}).ContinueWith(t =>
{
if (header.HasExecuted) GetExOrders(header.ExecutedSize,execArray);
if (header.Hasnews) AddNews(newsArray.ToArray());
}));
tasks.Add(Task.Run(() => { if (header.HasBuy) GetOrders(header.BuySize,buyArray,"buy"); }));
tasks.Add(Task.Run(() => { if (header.HasSell) GetOrders(header.SellSize,sellArray,"sell"); }));
tasks.Add(Task.Run(() => AddIssue(issueArray.ToArray())));
Task.WaitAll(tasks.ToArray());
hasReceivedData = true;
App.Current.Dispatcher.Invoke(() => CommandManager.InvalidateRequerySuggested());
OnConnected();
OrderVM.ItemCode = Items.First().Id;
e.Completed += Receive;
e.SetBuffer(headerBuffer,headerBuffer.Length);
if (!e.acceptsocket.ReceiveAsync(e)) Receive(null,e);
和OnConnected()组成的Pendings中创建PendingOrders的过程。我认为这是问题所在，我相信有时buyArray会在sellArray之前被解雇。如果有人感兴趣，这就是OnConnected()的作用：
Task.WaitAll(tasks.ToArray())这里是GetOrders：
void GetOrders(int size,IEnumerable<byte> array,string type)
{
var orderList = new List<AllOrder>();
var pendingList = new List<AllOrder>();
for (int i = 0; i < size; i += Constants.orderSize)
{
var order = PacMan<AllOrderStruct>.Unpack(array.Skip(i).Take(Constants.orderSize).ToArray());
AddInitNewOrder(order,orderList,pendingList);
}
if (type == "buy") CheckNumberAndAdd(orderList,BuyOrders);
else CheckNumberAndAdd(orderList,SellOrders);
CheckNumberAndAdd(pendingList,PendingOrders);
}
这是AddInitNewOrder：
void AddInitNewOrder(AllOrderStruct order,List<AllOrder> orders,List<AllOrder> pendingOrders)
{
var o = new AllOrder();
o.action = order.action;
o.OrderType = order.OrderType;
o.ItemCode = order.ItemCode;
o.BrokerName = order.BrokerName;
o.PartyCode = order.PartyCode;
o.Price = order.Price;
o.Quantity = order.Quantity;
o.BuyOrderNo = order.BuyOrderNo;
o.SellOrderNo = order.SellOrderNo;
orders.Add(o);
if (o.BrokerName == BrokerName) pendingOrders.Add(o);
}
如果我在CheckNumberAndAdd函数中设置brekpoint，我看到void CheckNumberAndAdd<T>(List<T> normList,AsyncObsetion<T> obsList)
{
var count = normList.Count;
if(count > 50)
{
obsList.InsertRange(normList.Take(count - 50));
var remaining = normList.Skip(count - 50).ToList();
for (int i = 0; i < remaining.Count; i++) obsList.Insert(0,remaining[i]);
}
else for (int i = 0; i < count; i++) obsList.Insert(0,normList[i]);
}
从GetOrders中获得483个项目，而从pendingList中获得494个项目，因此我总共有977个项目。因此，我应该始终在sellArray中获得977个项目，但是如果我在buyArray中删除brekpoint并在PendingOrders方法中设置了断点，则该方法已挂接到该事件GetOrders中，我看到{{ 1}}有时少于977个项目。