Question

我有一对像这样填充的组合框：

private void PopulateDeptCombox()
{
    try
    {
        ExceptionLoggingService.Instance.WriteLog("Reached FrmInventory.PopulateDeptCombox");
        List<String> depts = hhsdbutils.GetDeptItems();

        foreach (String dept in depts)
        {
            comboBoxsDept.Items.Add(dept);
            comboBoxeDept.Items.Add(dept);
        }

        if (comboBoxsDept.Items.Count > 0)
        {
            comboBoxsDept.SelectedIndex = 0;
        }
        if (comboBoxeDept.Items.Count > 0)
        {
            comboBoxeDept.SelectedIndex = comboBoxeDept.Items.Count - 1;
        }
    }
    catch (Exception ex)
    {
        String msgInnerExAndStackTrace = String.Format(
                "{0}; Inner Ex: {1}; Stack Trace: {2}", ex.Message, ex.InnerException, ex.StackTrace);
        ExceptionLoggingService.Instance.WriteLog(String.Format("From FrmInventory.PopulateDeptCombox(): {0}", msgInnerExAndStackTrace));
    }
}

GetDeptItems（）现在只返回几个项目：

List<string> IHHSDBUtils.GetDeptItems()
{
    ExceptionLoggingService.Instance.WriteLog("Reached SQliteHHSDBUtils.GetDeptItems");
    List<String> depts = new List<String> { "dept 1", "dept 2", "dept 3", "Test dept" };
    // TODO: Replace this test data
    return depts;
}

当我第一次打开它时，此表单崩溃，直到我在try..catch块中包含PopulateDeptCombox（）。它不再立即崩溃，但它仍然在日志文件中记录NRE：

Date: 3/21/2009 1:41:27 AM
Message: Reached FrmInventory.PopulateDeptCombox

Date: 3/21/2009 1:41:27 AM
Message: From FrmInventory.PopulateDeptCombox(): NullReferenceException; Inner Ex: ; Stack Trace:    at 

HHS.FrmInventory.PopulateDeptCombox()
   at HHS.FrmInventory..ctor(String inventoryName, String siteNum, Boolean allowNewItems)
   at HHS.frmNewInventory.buttonOK_Click(Object sender, EventArgs e)
   at System.Windows.Forms.Control.OnClick(EventArgs e)
   at System.Windows.Forms.Button.OnClick(EventArgs e)
   at System.Windows.Forms.ButtonBase.WnProc(WM wm, Int32 wParam, Int32 lParam)
   at System.Windows.Forms.Control._InternalWnProc(WM wm, Int32 wParam, Int32 lParam)
   at Microsoft.AGL.Forms.EVL.EnterModalDialog(IntPtr hwnModal)
   at System.Windows.Forms.Form.ShowDialog()
   at HHS.frmMain.menuItemFILE_NewInventory_Click(Object sender, EventArgs e)
   at System.Windows.Forms.MenuItem.OnClick(EventArgs e)
   at System.Windows.Forms.Menu.ProcessMnuProc(Control ctlThis, WM wm, Int32 wParam, Int32 lParam)
   at System.Windows.Forms.Form.WnProc(WM wm, Int32 wParam, Int32 lParam)
   at System.Windows.Forms.Control._InternalWnProc(WM wm, Int32 wParam, Int32 lParam)
   at Microsoft.AGL.Forms.EVL.EnterMainLoop(IntPtr hwnMain)
   at System.Windows.Forms.Application.Run(Form fm)
   at HHS.Program.Main()

......但是忽略了NRE和士兵（就像它没有注意到NRE一样）。

然而，如果我单击comboBoxsDept来检查它包含哪些项目，它首先是一个“沙漏”，然后它会下降，显示我希望看到的项目 - 但仅限于一个眨眼 - 然后形式崩溃。 “post mortem”（日志文件）显示上面的NRE，加上日志文件末尾的NRE：

Date: 3/21/2009 1:42:08 AM
Message: Reached FrmInventory.BarcodeReader_ReadNotify

Date: 3/21/2009 1:42:08 AM
Message: From application-wide exception handler: System.NullReferenceException: NullReferenceException
   at HHS.FrmInventory.BarcodeReader_ReadNotify(Object sender, EventArgs e)
   at System.Windows.Forms.Control.TASK.Invoke()
   at System.Windows.Forms.Control._InvokeAll()
   at System.Windows.Forms.Control.WnProc(WM wm, Int32 wParam, Int32 lParam)
   at System.Windows.Forms.Control._InternalWnProc(WM wm, Int32 wParam, Int32 lParam)
   at Microsoft.AGL.Forms.EVL.EnterMainLoop(IntPtr hwnMain)
   at System.Windows.Forms.Application.Run(Form fm)
   at HHS.Program.Main()

所以还有另一个与条形码扫描码相关的NRE;由于某种原因，这段代码是疯狂的。我有其他形式与相同的条形码扫描设置代码，但他们不这样做。一切都很好，直到我扫描一个值，然后下拉comboBoxsDept。

填充的组合框如何引出NRE？

更新

如果我首先将某些内容扫描到条形码可扫描文本框中，则会阻止崩溃。如果我直接进入下拉列表，它会崩溃。因此条形码扫描代码显然有些奇怪/可怕。

顺便说一下，这是我今年的最后一个问题;今晚不要喝太多辛辣的V8。

更新2

回答Grant Winney：这是我的重载构造函数（被称为）：

public FrmInventory(string inventoryName, string siteNum, bool allowNewItems)
{
    ExceptionLoggingService.Instance.WriteLog("Reached FrmInventory's overloaded constructor");
    InitializeComponent();

    _siteNum = siteNum;
    _allowNewItems = allowNewItems;
    _invName = inventoryName;
    invFileName = Path.GetFileNameWithoutExtension(HHSUtils.GetGeneratedINVFileName(_siteNum));
    recordDate = HHSUtils.ConvertDateTimeToSQLiteFormat(DateTime.Now);
    comboBoxUPC_PLU.SelectedIndex = 0;
    HookupHandlers();
    PopulateDeptCombox();
    PopulateSubdeptCombox();
    SetRequiredControls();
    textBoxUPC_PLU.Focus();
}

更新3

这最终成了“涵洞”：

private void textBoxUPC_LostFocus(object sender, EventArgs e)
{
    ExceptionLoggingService.Instance.WriteLog("Reached frmVerify.textBoxUPC_LostFocus");
    this.DisposeBarcodeReaderAndData();
}

private void DisposeBarcodeReaderAndData()
{
    ExceptionLoggingService.Instance.WriteLog("Reached 
FrmInventory.DisposeBarcodeReaderAndData");
    // If we have a reader
    if (this.barcodeReader != null)
    {
        // Disable the reader
        this.barcodeReader.Actions.Disable();
        // Free it up
        this.barcodeReader.Dispose();
        // Indicate we no longer have one
        this.barcodeReader = null;
    }

    // If we have a reader data
    if (this.barcodeReaderData != null)
    {
        // Free it up
        this.barcodeReaderData.Dispose();
        // Indicate we no longer have one
        this.barcodeReaderData = null;
    }
}

一旦我注释掉了对 DisposeBarcodeReaderAndData（）的调用 - 让这个方法失效 - 太阳出来了，鸟儿开始唱歌，他们挂起发明作品的混蛋，然后掉线下来不再导致崩溃。

更新4

问题回来了，爸爸爆炸了！我不得不将我的一些构造函数代码移动到表单的Load（）事件中，以使其变直并向右飞行。

为什么要删除填充的组合框会导致表单崩溃？

更新

更新2

更新3

更新4

0 个答案: