对RadioButtonList值的引用异常为空

本文关键字：异常 引用 RadioButtonList | 更新日期: 2023-09-27 18:19:21

我有一个数据列表，显示一些帖子与一个RadioButtonList里面，它包含5个选择从1到5，但是，当我试图获得theRadioButtonList的选定值，它抛出空异常，这是我的代码:错误@ string choice = RadioButtonList1.SelectedItem.Value; 

protected void RadioButtonList1_SelectedIndexChanged(object sender, EventArgs e)
        {
            foreach (DataListItem item in DataList2.Items)
            {
                RadioButtonList RadioButtonList1 = (RadioButtonList)DataList2.FindControl("RadioButtonList1");
                string choice = RadioButtonList1.SelectedItem.Value;
                Label post_IDLabel = (Label)item.FindControl("post_IDLabel");
                int post_ID = Convert.ToInt32(post_IDLabel.Text);
                int value = Convert.ToInt32(choice.ToString());
                string connStr = ConfigurationManager.ConnectionStrings["MyDbConn"].ToString();
                SqlConnection conn = new SqlConnection(connStr);
                SqlCommand cmd = new SqlCommand("rate", conn);
                cmd.CommandType = CommandType.StoredProcedure;
                string email = Session["email"].ToString();
                int course_ID = Convert.ToInt32(Request.QueryString["courseID"]);
                cmd.Parameters.Add(new SqlParameter("@course_ID", course_ID));
                cmd.Parameters.Add(new SqlParameter("@postID", post_ID));
                cmd.Parameters.Add(new SqlParameter("@myemail", email));
                cmd.Parameters.Add(new SqlParameter("@rate", value));
                conn.Open();
                cmd.ExecuteNonQuery();
                conn.Close();
                Response.Write(choice);
            }
            DataList2.DataBind();
        }

错误:

Object reference not set to an instance of an object.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 
Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

对RadioButtonList值的引用异常为空

我怀疑你的问题是那些没有选择值的单选按钮。在这种情况下，selecteditem将为null，但您不测试此

这是一个重写，也修复了连接和命令不被处理以及过度打开和关闭连接的潜在问题:

    protected void RadioButtonList1_SelectedIndexChanged(object sender, EventArgs e)
    {
        string connStr = ConfigurationManager.ConnectionStrings["MyDbConn"].ToString();
        using (SqlConnection conn = new SqlConnection(connStr))
        {
            using (SqlCommand cmd = new SqlCommand("rate", conn))
            {
                cmd.CommandType = System.Data.CommandType.StoredProcedure;
                cmd.Parameters.Add("@course_ID", System.Data.SqlDbType.Int);
                cmd.Parameters.Add("@postID", System.Data.SqlDbType.Int);
                cmd.Parameters.Add("@myemail", System.Data.SqlDbType.Int);
                cmd.Parameters.Add("@rate", System.Data.SqlDbType.VarChar);
                conn.Open();
                foreach (DataListItem item in DataList2.Items)
                {
                    RadioButtonList RadioButtonList1 = (RadioButtonList)DataList2.FindControl("RadioButtonList1");
                    if (RadioButtonList1.SelectedItem != null)
                    {
                        string choice = RadioButtonList1.SelectedItem.Value;
                        Label post_IDLabel = (Label)item.FindControl("post_IDLabel");
                        cmd.Parameters["@course_ID"].Value = Convert.ToInt32(Request.QueryString["courseID"]);
                        cmd.Parameters["@postID"].Value = Convert.ToInt32(post_IDLabel.Text);
                        cmd.Parameters["@myemail"].Value = Session["email"] as string;
                        cmd.Parameters["@rate"].Value = Convert.ToInt32(RadioButtonList1.SelectedItem.Value);
                        cmd.ExecuteNonQuery();
                        Response.Write(choice);
                    }
                }
            }
        }
        DataList2.DataBind();
    }

在我看来，你没有找到控件RadioButtonList1

RadioButtonList RadioButtonList1 = (RadioButtonList)DataList2.FindControl("RadioButtonList1"); 
if(RadioButtonList1 == null) throw new Exception("Can't find control RadioButtonList1");
string choice = RadioButtonList1.SelectedItem.Value;
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