存在记录时，对象引用未设置为对象的实例 [英] Object reference not set to an instance of an object when records exist

问题描述

大家好，



我知道上面的错误显示没有找到记录。但在下面的例子中，他们在数据表中有15条记录。



我试图在gridview中的每一行的列中显示一个下拉列表。以下是vb中的代码：

Hi All,

I know that the above error shows when there are no records found. But in the following case their are 15 records in datatable.

I am trying to show a dropdown list in a column for each row in a gridview. the following is the code in vb:

If dtPersons.Rows.Count > 0 Then
           Dim ddlJuniors As DropDownList = DirectCast(e.Row.FindControl("ddlJuniors"), DropDownList)
           **ddlJuniors.DataSource = dtPersons
           ddlJuniors.DataTextField = "USERN"
           ddlJuniors.DataValueField = "USERID"
           ddlJuniors.DataBind()
       End If

dtPersons表在调试中确认了15条记录。



以下是html中的列：

dtPersons table has 15 records as confirmed in debugging.

Following is column in html:

<asp:TemplateField HeaderText="Delegate" HeaderStyle-HorizontalAlign="Left" ControlStyle-Width="100">
                  <ItemTemplate>
                        <asp:DropDownList ID="ddlJuniors" runat="server" DataTextField="USERN" DataValueField="USERID" CssClass="ddl"> </asp:DropDownList>
                </ItemTemplate>
            </asp:TemplateField>

请建议。

谢谢

Atul

Please suggest.
Thanks
Atul

推荐答案

它没有说数据表是什么都没有

您的ddlJuniors可能没什么，访问ddlJuniors.DataSource失败。

It doesn't say that datatable is nothing
Your ddlJuniors is probably nothing and accessing ddlJuniors.DataSource fails.

If dtPersons.Rows.Count > 0 Then
If (e.Row.RowType = DataControlRowType.DataRow) Then
           Dim ddlTemp As DropDownList = DirectCast(e.Row.FindControl("ddlJuniors"), DropDownList)
           ddlTemp.DataTextField = "USERN"
           ddlTemp.DataValueField = "USERID"
           ddlTemp.DataSource = dtPersons

           ddlTemp.DataBind()
       End If
End If

不是这个代码工作如下：

- 在名为ddlJuniors的网格控件中查找

- 将找到的控件分配给本地名称ddlTemp< - 这可以是任何你可以称之为dasfalksadfj的东西并且它仍然可以工作

- 使用< u>完全< / u>通过函数引用



你不能分配ddlTmp然后尝试在函数中使用ddlJuniors。

Not this code works as follows:
- find in the grid control named ddlJuniors
- assign the found control to local name ddlTemp <-- this can be anything you could call it dasfalksadfj and it would still work
- work with <u>that exact</u> reference through the function

You cannot assign ddlTmp and then try to use ddlJuniors later in the function.

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