Question

我正在将excel文件导入DataGridView，我必须获得某些列的平均值。当我在大约300行的示例excel文件上尝试它时，一切正常。但是当我尝试使用41000行的实际excel文件时，我得到错误＆＃34;指定的强制转换无效＆＃34;当我点击按钮来计算平均值时。我真的不知道什么是错的，不知道如何解决它。这是我用来获得平均值的代码，错误在我分组的列上。

private void Ave_Click(object sender, EventArgs e)
{
    BindingSource bindingSource1 = new BindingSource();
    bindingSource1.DataSource = (from r in dt.AsEnumerable()
                                 group r by new
                                 {
                                     RNCID = r.Field<Double?>("RNCID"),
                                     Date = r.Field<DateTime>("Date"),
                                     WBTSNAME = r.Field<String>("WBTSNAME")

                                 } into g

                                 select new
                                 {
                                     g.Key.Date,
                                     g.Key.RNCID,
                                     g.Key.WBTSNAME,
                                     VSLCDLMeanLicenseGroupShare = g.Average(r => r.Field<Double>("VS LC DLMean LicenseGroup Share")),
                                     VSLCDLCreditAvailableShared = g.Average(r => r.Field<Double>("VS LC DLCreditAvailable Shared")),
                                     VSLCULMeanLicenseGroupShare = g.Average(r => r.Field<Double>("VS LC ULMean LicenseGroup Share")),
                                     VSLCULCreditAvailableShared = g.Average(r => r.Field<Double>("VS LC ULCreditAvailable Shared")),
                                     UtilDL = g.Average(r => r.Field<Double?>("Util DL")),
                                     UtilUL = g.Average(r => r.Field<Double?>("Util UL")),

                                 });

    dataGridView1.DataSource = bindingSource1;
}

这是我得到的堆栈跟踪

System.InvalidCastException was unhandled

消息=＆＃34;指定的演员表无效。＆＃34; 源=＆＃34; System.Data.DataSetExtensions＆＃34; 堆栈跟踪： at System.Data.DataRowExtensions.UnboxT 1.NullableField[TElem](Object value) at System.Data.DataRowExtensions.Field[T](DataRow row, String columnName) at CE_Fin.Form1.<Ave_Click>b__0(DataRow r) in C:\Users\Administrator\Documents\Visual Studio 2008\Projects\Final\CE_Fin\Form1.cs:line 215 at System.Linq.Lookup 2.Create [TSource]（IEnumerable 1 source, Func 2 keySelector，Func 2 elementSelector, IEqualityComparer 1 comparer）在System.Linq.GroupedEnumerable 3.GetEnumerator() at System.Linq.Enumerable.WhereSelectEnumerableIterator 2.MoveNext（）在System.Windows.Forms.BindingSource.GetListFromEnumerable（IEnumerable enumerable）在System.Windows.Forms.BindingSource.ResetList（）在System.Windows.Forms.BindingSource.set_DataSource（对象值） at CE_Fin.Form1.Ave_Click（Object sender，EventArgs e）位于C：\ Users \ Administrator \ Documents \ Visual Studio 2008 \ Projects \ Final \ CE_Fin \ Form1.cs：第214行在System.Windows.Forms.Control.OnClick（EventArgs e）在System.Windows.Forms.Button.OnClick（EventArgs e）在System.Windows.Forms.Button.OnMouseUp（MouseEventArgs mevent）在System.Windows.Forms.Control.WmMouseUp（消息＆amp; m，MouseButtons按钮，Int32点击）在System.Windows.Forms.Control.WndProc（消息＆amp; m）在System.Windows.Forms.ButtonBase.WndProc（消息＆amp; m）在System.Windows.Forms.Button.WndProc（消息＆amp; m）在System.Windows.Forms.Control.ControlNativeWindow.OnMessage（Message＆amp; m）在System.Windows.Forms.Control.ControlNativeWindow.WndProc（Message＆amp; m）在System.Windows.Forms.NativeWindow.DebuggableCallback（IntPtr hWnd，Int32 msg，IntPtr wparam，IntPtr lparam）在System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW（MSG＆amp; msg）在System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop（Int32 dwComponentID，Int32 reason，Int32 pvLoopData）在System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner（Int32 reason，ApplicationContext context）在System.Windows.Forms.Application.ThreadContext.RunMessageLoop（Int32 reason，ApplicationContext context）在System.Windows.Forms.Application.Run（Form mainForm）在C：\ Users \ Administrator \ Documents \ Visual Studio 2008 \ Projects \ Final \ CE_Fin \ Program.cs中的CE_Fin.Program.Main（）：第18行在System.AppDomain._nExecuteAssembly（Assembly assembly，String [] args）在System.AppDomain.ExecuteAssembly（String assemblyFile，Evidence assemblySecurity，String [] args）在Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly（）在System.Threading.ThreadHelper.ThreadStart_Context（对象状态）在System.Threading.ExecutionContext.Run（ExecutionContext executionContext，ContextCallback回调，对象状态）在System.Threading.ThreadHelper.ThreadStart（） InnerException：

Answer 1

可能的原因是其中一个字段具有空值：

r.Field<Double>("VS LC DLMean LicenseGroup Share")
r.Field<Double>("VS LC DLCreditAvailable Shared")
r.Field<Double>("VS LC ULMean LicenseGroup Share")
r.Field<Double>("VS LC ULCreditAvailable Shared")

让它们成为可空<double?>（正如您对"Util DL"和"Util UL"所做的那样）

指定的强制转换在linq上无效

1 个答案: