我收到此错误 - >对象引用未设置为对象的实例。 [英] I am getting this error->Object reference not set to an instance of an object.

问题描述

我想使用gridview从数据库下载文件



这是我的代码...

I want to download a file from database using gridview

Here is my code...

protected void Page_Load(object sender, EventArgs e)
       {
           if (!IsPostBack)
           {
               BindGrid();
           }
       }
       private void BindGrid()
       {
           string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
           using (SqlConnection con = new SqlConnection(constr))
           {
               using (SqlCommand cmd = new SqlCommand())
               {
                   cmd.CommandText = "select Id, FileName from Career";
                   cmd.Connection = con;
                   con.Open();
                   cmd.ExecuteNonQuery();
                   GridView1.DataBind();
                   con.Close();
               }
           }

       }




       protected void GridView1_RowCommand(object sender, GridViewCommandEventArgs e)
       {
           {
               int id = int.Parse((sender as LinkButton).CommandArgument);
               byte[] bytes;
               string fileName, contentType;
               string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
               using (SqlConnection con = new SqlConnection(constr))
               {
                   using (SqlCommand cmd = new SqlCommand())
                   {
                       cmd.CommandText = "select FileName, Data, contentType from Career where Id=@Id";
                       cmd.Parameters.AddWithValue("@Id", id);
                       cmd.Connection = con;
                       con.Open();
                       using (SqlDataReader sdr = cmd.ExecuteReader())
                       {
                           sdr.Read();
                           bytes = (byte[])sdr["Data"];
                           contentType = sdr["contentType"].ToString();
                           fileName = sdr["FileName"].ToString();
                       }
                       con.Close();
                   }
               }
               Response.Clear();
               Response.Buffer = true;
               Response.Charset = "";
               Response.Cache.SetCacheability(HttpCacheability.NoCache);
               Response.ContentType = contentType;
               Response.AppendHeader("Content-Disposition", "attachment; filename=" + fileName);
               Response.BinaryWrite(bytes);
               Response.Flush();
               Response.End();
           }
       }

   }

请告诉我如何解决这个错误？



更新：此​​行发生错误

Please let me know how to solve this error??

Update: The error occurs on this line

int id = int.Parse((sender as LinkButton).CommandArgument);

推荐答案

你好，

您还没有使用过GridView DataSource属性。像这样修改您的代码

Hello ,
You have not used GridView DataSource property .Modify your code like this way

using (SqlCommand cmd = new SqlCommand())
               {
                   cmd.CommandText = "select Id, FileName from Career";
                   cmd.Connection = con;
                   con.Open();

                //Remove this line
	           //  cmd.ExecuteNonQuery();

	               //Add these lines
         	       DataTable dt = new DataTable();
                   dt.Load(cmd.ExecuteReader());
                
	             GridView1.DataSource=dt;
              
	             GridView1.DataBind();
                 con.Close();
               }

请您检查并更改您的密码如下：

Could you please check and change your code as below:

 protected void GridView1_RowCommand(object sender, GridViewCommandEventArgs e)
  {    
    if (e.CommandName == "YourButtonCommandName")

       {
           int id = Convert.ToInt32(e.CommandArgument.ToString());

           //rest code here

       }
}

希望它有助于：）

Hope it Helps :)

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