无法将可打印对象分配给字符串变量

Question

使用以下代码行，我可以打印行的主键：

protected void storyGridView_OnRowDataBound(Object sender, GridViewRowEventArgs e)
{
    System.Diagnostics.Debug.WriteLine(DataBinder.Eval(e.Row.DataItem, "PK_NonScrumStory"));
}

但是我无法将值赋给字符串变量：

和

如何获取分配给变量的值？

编辑：

堆栈追踪：

[NullReferenceException: Object reference not set to an instance of an object.]
   user_nonscrumstories2.storyGridView_OnRowDataBound(Object sender, GridViewRowEventArgs e) in c:\Users\tunnelld2\Documents\Visual Studio 2012\Websites\ZSA_New 21\user\nonscrumstories2.aspx.cs:424
   System.Web.UI.WebControls.GridView.OnRowDataBound(GridViewRowEventArgs e) +111
   System.Web.UI.WebControls.GridView.CreateRow(Int32 rowIndex, Int32 dataSourceIndex, DataControlRowType rowType, DataControlRowState rowState, Boolean dataBind, Object dataItem, DataControlField[] fields, TableRowCollection rows, PagedDataSource pagedDataSource) +181
   System.Web.UI.WebControls.GridView.CreateChildControls(IEnumerable dataSource, Boolean dataBinding) +2188
   System.Web.UI.WebControls.CompositeDataBoundControl.PerformDataBinding(IEnumerable data) +67
   System.Web.UI.WebControls.GridView.PerformDataBinding(IEnumerable data) +14
   System.Web.UI.WebControls.DataBoundControl.OnDataSourceViewSelectCallback(IEnumerable data) +123
   System.Web.UI.DataSourceView.Select(DataSourceSelectArguments arguments, DataSourceViewSelectCallback callback) +33
   System.Web.UI.WebControls.DataBoundControl.PerformSelect() +138
   System.Web.UI.WebControls.BaseDataBoundControl.DataBind() +30
   System.Web.UI.WebControls.GridView.DataBind() +4
   System.Web.UI.WebControls.BaseDataBoundControl.EnsureDataBound() +105
   System.Web.UI.WebControls.CompositeDataBoundControl.CreateChildControls() +75
   System.Web.UI.Control.EnsureChildControls() +83
   System.Web.UI.Control.PreRenderRecursiveInternal() +42
   System.Web.UI.Control.PreRenderRecursiveInternal() +168
   System.Web.UI.Control.PreRenderRecursiveInternal() +168
   System.Web.UI.Control.PreRenderRecursiveInternal() +168
   System.Web.UI.Control.PreRenderRecursiveInternal() +168
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +974

Answer 1

尝试查看此帖子How do I get the value of a gridview Cell?，注意它只会尝试检索类型为DataControlRowType.DataRow的行的值。尝试从标题行中获取不存在的"PF_NonScrumStory"值可能会导致您的空引用异常。

Answer 2

您需要在对象上调用ToString()，但可能会发生NullReferenceException，因为该对象为空。当您调试并在异常中停止时，请查看本地（Debug - ＆gt; Windows - ＆gt; Locals）以查看其实际值。

Answer 3

尝试显式转换为（int）以摆脱“装箱”，然后调用.ToString（）