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C#,WinForms:ListBox.Items.Add生成OutOfMemoryException,为什么?

winforms c#

Austin Salonen gmlacrosse · 技术社区 · 15 年前

首先,我找到了异常的解决方案。我更好奇它生成了它所做的特定异常。

在我的场景中,我添加了一个 POCO 对于这样的列表框:

myListBox.Items.Add(myPOCO);

OutOfMemoryException . 问题是 ToString 波科回来了 null string.IsNullOrEmpty 检查以在null和异常消失时返回“安全”值。

为什么这会产生一个 OutOfMemoryException 而不是别的(比如 NullReferenceException

编辑

完整的调用堆栈(特定于公司的引用已删除)如下所示。需要注意的一点是,调用此函数时,列表框为空。

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()

2 回复 | 直到 15 年前

Darin Dimitrov 15 年前

这是因为方式 System.Windows.Forms.ListBox.NativeAdd

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;
}

这个 GetItemText 方法使用 ToString() 在返回的对象上 null 因此,会发送一条消息 无效的

Justin Grant 15 年前

当潜在的 LB_ADDSTRING Windows API调用失败,WinForms始终返回 OutOfMemoryException . .NET Framework参考源中的注释解释了原因:

// 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));

helvete user3408541 4 年前

listbox.Items.Add 或 listbox.DataSource = xxxxx Object 类型已添加或绑定到列表框中,列表框中必须返回非Null ToString() 方法。默认情况下,如果不重写,则.net将返回类型名称 ToString() 方法。

如果您已经实现了自己版本的 (使用override关键字)然后确保该方法具有fail-safe以返回非空字符串。请参阅下面的示例,了解如何添加额外的两行,以避免许多人会发现完全误导的这种奇怪错误。

//listbox.Items.Add(new MyItem());
//--or--
//listbox.DataSource= new List<MyItem>(){ new MyItem() };

public class MyItem
{
    public string Name { get; set; }
    public string Label { get; set; }

    public override string ToString()
    {
        //Not adding below 2 lines might throw OutOfMemoryException in listbox.Items.Add or listbox.DataSOurce = somelist
        if (string.IsNullOrEmpty(Label)) //Added this check to avoid 
            return this.GetType().Name; //Return string.Empty or something other than null else you will get OutOfMemoryException error when you add or bind this object to listbox

        return Label;
    }
}