在数据网格视图中获取null [英] Getting null on data grid view

问题描述

我遵循本指南，修改了自己的
的一些代码，用于检索datagridview的选择。

这是

这是代码：

  private void LoadDataGrid（）
 {
 con.Open（）; 
 
 cmd = new SqlCommand（@SELECT quotationID，quo_product 
 FROM JobQuotations 
 WHERE quo_custname = @custname，con）; 
 cmd.Parameters.AddWithValue（@ custname，lblLoginName.Text）; 
 da = new SqlDataAdapter（cmd）; 
 dt = new DataTable（）; 
 da.Fill（dt）; 
 GridView1.DataSource = dt; 
 GridView1.DataBind（）; 
 con.Close（）; 
} 
  

这是我选择一行的类：

  private void LoadOrders（）
 {
 con.Open（）; 
 cmd = new SqlCommand（@Select quo_product，quo_address 
 FROM JobQuotations 
 WHERE quotationId = @id 
 AND quo_product = @product，con）; 
 
 cmd.Parameters.AddWithValue（@ id，GridView1.SelectedRow.Cells [1] .Text）; 
 cmd.Parameters.AddWithValue（@ product，GridView1.SelectedRow.Cells [2] .Text）; 
 
 if（rdr.HasRows）
 {
 while（rdr.Read（））
 {
 lblProductName.Text = rdr [quo_product] .ToString（）; 
 lblAddress.Text = rdr [quo_Address]。ToString（）; 
} 
} 
 con.Close（）; 
} 
  

这行代码给我错误：

 `if（rdr.HasRows）`
  

* MejShop.dll中出现类型System.NullReferenceException的异常，但未在用户代码中处理

附加信息：对象引用未设置为一个对象的实例。*

解决方案

尝试添加 rdr = cmd.ExecuteReader（）; while循环。

I followed this guide and modified some of its code for my own for retrieving a selectedrow for datagridview.

This is the guide.It's not that close to my problem thought as it doesn't use any sql query.

I'm using s Select query which needed a value from datagridview so when I triggered the button event,It gives me the value on my label.

here is the datagridview

Here is the code:

 private void LoadDataGrid()
    {
        con.Open();

        cmd = new SqlCommand(@"SELECT quotationID,quo_product
                             FROM JobQuotations
                             WHERE quo_custname = @custname", con);
        cmd.Parameters.AddWithValue("@custname",lblLoginName.Text);
        da = new SqlDataAdapter(cmd);
        dt = new DataTable();
        da.Fill(dt);
        GridView1.DataSource = dt;
        GridView1.DataBind();
        con.Close();
    }

and This is my class for selecting a row:

 private void LoadOrders()
    {
        con.Open();
        cmd = new SqlCommand(@"Select quo_product,quo_address
                            FROM JobQuotations
                            WHERE quotationId = @id
                            AND quo_product = @product",con);

        cmd.Parameters.AddWithValue("@id", GridView1.SelectedRow.Cells[1].Text);
        cmd.Parameters.AddWithValue("@product", GridView1.SelectedRow.Cells[2].Text);

        if(rdr.HasRows)
        {
            while(rdr.Read())
            {
                lblProductName.Text = rdr["quo_product"].ToString();
                lblAddress.Text = rdr["quo_Address"].ToString();
            }
        }
        con.Close();
    }

This line of code that is giving me error:

 `if(rdr.HasRows)`

*An exception of type 'System.NullReferenceException' occurred in MejShop.dll but was not handled in user code

Additional information: Object reference not set to an instance of an object.*

解决方案

Try and add the rdr = cmd.ExecuteReader(); above the while loop.

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