C＃，WinForms：ListBox.Items.Add生成一個OutOfMemoryException，爲什麼？

首先，我找到了例外的解決方案。我更好奇爲什麼它產生了它所做的特定例外。C＃，WinForms：ListBox.Items.Add生成一個OutOfMemoryException，爲什麼？

我的方案，我加入了POCO到ListBox像這樣：

myListBox.Items.Add(myPOCO);

這是產生OutOfMemoryException。問題是關閉POCO的ToString正在返回null。我添加了一個string.IsNullOrEmpty檢查以返回一個「安全」的值，當null和異常消失時。

爲什麼這會生成OutOfMemoryException而不是別的（比如說NullReferenceException）？

編輯：項目被添加到for循環中。

完整的調用堆棧（刪除公司特定的參考）如下。有一點需要注意 - 當這個被調用時，列表框是空的。

System.OutOfMemoryException was unhandled 
    Message="List box contains too many items." 
    Source="System.Windows.Forms" 
    StackTrace: 
     at System.Windows.Forms.ListBox.NativeAdd(Object item) 
     at System.Windows.Forms.ListBox.ObjectCollection.AddInternal(Object item) 
     at System.Windows.Forms.ListBox.ObjectCollection.Add(Object item) 
     at <FORM>_Load(Object sender, EventArgs e) in <PATH>\<FORM>.cs:line 52 
     at System.Windows.Forms.Form.OnLoad(EventArgs e) 
     at System.Windows.Forms.Form.OnCreateControl() 
     at System.Windows.Forms.Control.CreateControl(Boolean fIgnoreVisible) 
     at System.Windows.Forms.Control.CreateControl() 
     at System.Windows.Forms.Control.WmShowWindow(Message& m) 
     at System.Windows.Forms.Control.WndProc(Message& m) 
     at System.Windows.Forms.ScrollableControl.WndProc(Message& m) 
     at System.Windows.Forms.ContainerControl.WndProc(Message& m) 
     at System.Windows.Forms.Form.WmShowWindow(Message& m) 
     at System.Windows.Forms.Form.WndProc(Message& m) 
     at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m) 
     at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m) 
     at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam) 
     at System.Windows.Forms.SafeNativeMethods.ShowWindow(HandleRef hWnd, Int32 nCmdShow) 
     at System.Windows.Forms.Control.SetVisibleCore(Boolean value) 
     at System.Windows.Forms.Form.SetVisibleCore(Boolean value) 
     at System.Windows.Forms.Control.set_Visible(Boolean value) 
     at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context) 
     at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context) 
     at System.Windows.Forms.Application.RunDialog(Form form) 
     at System.Windows.Forms.Form.ShowDialog(IWin32Window owner) 
     at System.Windows.Forms.Form.ShowDialog() 
     at <APP>.Program.Main() in <PATH>\Program.cs:line 25 
     at System.AppDomain._nExecuteAssembly(Assembly assembly, String[] args) 
     at System.AppDomain.nExecuteAssembly(Assembly assembly, String[] args) 
     at System.Runtime.Hosting.ManifestRunner.Run(Boolean checkAptModel) 
     at System.Runtime.Hosting.ManifestRunner.ExecuteAsAssembly() 
     at System.Runtime.Hosting.ApplicationActivator.CreateInstance(ActivationContext activationContext, String[] activationCustomData) 
     at System.Runtime.Hosting.ApplicationActivator.CreateInstance(ActivationContext activationContext) 
     at System.Activator.CreateInstance(ActivationContext activationContext) 
     at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssemblyDebugInZone() 
     at System.Threading.ThreadHelper.ThreadStart_Context(Object state) 
     at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) 
     at System.Threading.ThreadHelper.ThreadStart()

來源

2009-11-18 Austin Salonen

您是否在循環中添加項目？ – scottm 2009-11-18 17:03:31

在什麼情況下'ToString'返回null？是否當POCO非常大？ – 2009-11-18 17:08:05

出於興趣，你能從異常中發佈完整的堆棧跟蹤嗎？ – 2009-11-18 17:13:19

這是由於的方式System.Windows.Forms.ListBox.NativeAdd方法實現：

private int NativeAdd(object item) 
{ 
    int num = (int) base.SendMessage(0x180, 0, base.GetItemText(item)); 
    switch (num) 
    { 
     case -2: 
      throw new OutOfMemoryException(); 

     case -1: 
      throw new OutOfMemoryException(SR.GetString("ListBoxItemOverflow")); 
    } 
    return num; 
}

的GetItemText方法，它返回null等物體上使用ToString()一個消息與null參數一起發送，反過來返回一個無效的指針，然後輸入引發異常的第二種情況。

來源

2009-11-18 17:49:24

哈，我打算將NativeAdd方法的全部源碼複製到我的答案中，但是決定不這麼做......猜猜我做錯了選擇！ :-) – 2009-11-18 19:04:55

@Justin - 我被撕裂了，但我認爲這樣會更好地幫助解決這個問題的其他人。 – 2009-11-18 19:40:33

沒問題，有點競爭讓我們都變得更聰明！ :-) – 2009-11-18 20:00:52

當底層LB_ADDSTRING的Windows API調用失敗，WinForms的總是返回OutOfMemoryException。在.NET Framework參考源的註釋解釋了原因：

// On some platforms (e.g. Win98), the ListBox control 
// appears to return LB_ERR if there are a large number (>32000) 
// of items. It doesn't appear to set error codes appropriately, 
// so we'll have to assume that LB_ERR corresponds to item 
// overflow. 
// 
throw new OutOfMemoryException(SR.GetString(SR.ListBoxItemOverflow));

來源

2009-11-18 17:38:15

C＃，WinForms：ListBox.Items.Add生成一個OutOfMemoryException，爲什麼？

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