未将对象引用设置为对象的实例（NullreferenceException 未由用户代码处理）
我怎样才能解决这个异常？
Dim imagepathlit As Literal = DownloadsRepeater.FindControl("imagepathlit")
imagepathlit.Text = imagepath
这是中继器：
<asp:Repeater ID="DownloadsRepeater" runat="server">
<HeaderTemplate>
<table width="70%">
<tr>
<td colspan="3"><h2>Files you can download</h2></td>
</tr>
</HeaderTemplate>
<ItemTemplate>
<tr>
<td width="5%">
<asp:Literal ID="imagepathlit" runat="server"></asp:Literal></td>
<td width="5%"></td>
<td> </td>
</tr>
</table>
</ItemTemplate>
</asp:Repeater>
这是获取中继器数据的代码：
c.Open()
r = x.ExecuteReader
While r.Read()
If r("filename") Is DBNull.Value Then
imagepath = String.Empty
Else
imagepath = "<img src=images/" & getimage(r("filename")) & " border=0 align=absmiddle>"
End If
End While
c.Close()
r.Close()
How can I get around this exception?
Dim imagepathlit As Literal = DownloadsRepeater.FindControl("imagepathlit")
imagepathlit.Text = imagepath
Here is the repeater:
<asp:Repeater ID="DownloadsRepeater" runat="server">
<HeaderTemplate>
<table width="70%">
<tr>
<td colspan="3"><h2>Files you can download</h2></td>
</tr>
</HeaderTemplate>
<ItemTemplate>
<tr>
<td width="5%">
<asp:Literal ID="imagepathlit" runat="server"></asp:Literal></td>
<td width="5%"></td>
<td> </td>
</tr>
</table>
</ItemTemplate>
</asp:Repeater>
Here is the code that gets the data for the repeater:
c.Open()
r = x.ExecuteReader
While r.Read()
If r("filename") Is DBNull.Value Then
imagepath = String.Empty
Else
imagepath = "<img src=images/" & getimage(r("filename")) & " border=0 align=absmiddle>"
End If
End While
c.Close()
r.Close()
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评论（3）
我的猜测是，在
DownloadsRepeater控件中找不到名为imagepathlit的控件，因此imagepathlit控件在调用后为 null。请记住，
Control.FindControl()根据ID查找控件，而不是控件的名称。因此，要在集合中找到控件...您必须在应用程序的早期部分具有类似的内容：更新
由于您使用的是转发器，因此子控件的布局略有不同。
Repeater中的每个Item都会有一个Literal实例。因此，要获取控件的每个实例，您必须循环遍历Repeater中的Items并在每个上调用FindControl()>项目：My guess is that there is no control found in the
DownloadsRepeatercontrol calledimagepathlit, therefore theimagepathlitcontrol is null after the call.Remember that
Control.FindControl()looks up the control based onID, not the name of the control. Therefore, to find the control in the collection...you would have to had something like this earlier in the application:UPDATE
Since you're using a repeater, the child controls get layed out a bit differently. You're going to have an instance of the
Literalfor eachItemin theRepeater. Therefore, to get each instance of the control, you have to loop through theItemsin theRepeaterand callFindControl()on eachItem:假设您发布的代码确实引发了异常，我会说
DownloadRepeater中没有 ID 为imagepathlit的控件。检查您的
aspx。Assuming the code you posted is where the exception is indeed thrown, I would say that the
DownloadRepeaterdoes not have a control in it that has an ID ofimagepathlit.Check your
aspx.因为该控件位于 ItemTemplate 内，所以不能使用 Repeater.findcontrol；您必须循环遍历转发器的项目才能查找控件，因为项目模板是可重复的。因此，您必须循环遍历每个控件来查找控件，如下所示：
使用该语法。
Because the control is within the ItemTemplate, you cannot use repeater.findcontrol; you have to loop through the items of the repeater to look for the control, as the itemtemplate is repeatable. So you have to loop through each one to look for the control as in:
Use that syntax.