dropdownlist错误对象引用未设置为对象的实例[重复]

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I have a DropDownList which is shown below:

我有一个DropDownList,如下所示:

<asp:GridView ID="moduleInfo" runat="server" DataSourceID="currentModules" class="table table-striped table-bordered" AutoGenerateColumns="false"  GridLines="None">
    <Columns>
       <asp:TemplateField HeaderText="module" ItemStyle-Width="30"  >
          <ItemTemplate>
            <asp:DropDownList ID="entryLevel" CssClass="form-control" runat="server">
                <asp:ListItem Text="Level 1" Value="1"></asp:ListItem>
                <asp:ListItem Text="Level 2" Value="2"></asp:ListItem>
                <asp:ListItem Text="Level 3" Value="3"></asp:ListItem>
                <asp:ListItem Text="Level 4" Value="4"></asp:ListItem>
                <asp:ListItem Text="Level 5" Value="5"></asp:ListItem>
          </asp:DropDownList>
        </ItemTemplate>
      </asp:TemplateField>

When I try to reference it in the code behind it was not recognized by typing entryLevel, so i used below code:

当我尝试在后面的代码中引用它时,通过输入entryLevel无法识别,所以我使用下面的代码:

DropDownList ddl = (DropDownList)moduleInfo.FindControl("entryLevel");
string Level = ddl.SelectedValue;

Whenever I run the web-page and select the value, I get the error:

每当我运行网页并选择值时,我都会收到错误:

object reference not set to an instance of an object

你调用的对象是空的

Anyone know why I'm getting this error?

任何人都知道我为什么会收到这个错误?

1 个解决方案

#1

You are missing Rows class of GridView to get the exact DropDownList replace below line:

你缺少GridView的Rows类来获得下面一行的确切DropDownList替换:

DropDownList ddl = (DropDownList)moduleInfo.Rows[rowIndex].FindControl("entryLevel");

And if you are using your code in RowCommand event then you can get rowIndex as like this:

如果您在RowCommand事件中使用您的代码,那么您可以像这样获取rowIndex:

GridViewRow row = (GridViewRow)(((Control)e.CommandSource).NamingContainer);
int rowIndex = row.RowIndex;

#1