在运行时填充下拉列表时出现错误

问题描述

当我尝试在GridView中填充下拉列表时，出现以下错误:

对象引用未设置为对象的实例.

该代码受

I am getting the following error when i am trying to fill a Dropdown inside the GridView:

Object reference not set to an instance of an object.

the code is

protected void ProjectOnFormGrid_RowDataBound(object sender, GridViewRowEventArgs e)
        {
            try
            {
                string selectcommand;
                DataSet dsrow;
                if (e.Row.RowType == DataControlRowType.DataRow)
                {
                    selectcommand = "select QuantityDescId,QuantityDescName from QuantityDescriptions";
                    DropDownList EditddQuantDesc = (DropDownList)e.Row.FindControl("EditddQuantDesc");
                    if (EditddQuantDesc == null)
                    {
                        da = new SqlDataAdapter(selectcommand, con);
                        dsrow = new DataSet();
                       da.Fill(dsrow, "QuantityDescriptions");
                       EditddQuantDesc.DataSource = dsrow.Tables["QuantityDescriptions"];
                       EditddQuantDesc.DataValueField = dsrow.Tables[0].Columns[0].ToString();
                       EditddQuantDesc.DataTextField = dsrow.Tables[0].Columns[1].ToString();

                    }
                }
                if (e.Row.RowType == DataControlRowType.Footer)
                {
                    selectcommand = "select QuantityDescId,QuantityDescName from QuantityDescriptions";
                    DropDownList FooterddQuantDesc = (DropDownList)e.Row.FindControl("FooterddQuantDesc");
                    if (FooterddQuantDesc != null)
                    {
                        da = new SqlDataAdapter(selectcommand, con);
                        dsrow = new DataSet();
                        da.Fill(dsrow, "QuantityDescriptions");
                        FooterddQuantDesc.DataSource = dsrow;
                        FooterddQuantDesc.DataValueField = dsrow.Tables[0].Columns[0].ToString();
                        FooterddQuantDesc.DataTextField = dsrow.Tables[0].Columns[1].ToString();
                    }
                }
            }
            catch (Exception ce)
            {
                lblError.Text = ce.Message;
                lblError.Visible = true;
            }
        }

我在此行遇到错误:

EditddQuantDesc.DataSource = dsrow.Tables["QuantityDescriptions"];

推荐答案

if (EditddQuantDesc == null)
{
      da = new SqlDataAdapter(selectcommand, con);
      dsrow = new DataSet();
   da.Fill(dsrow, "QuantityDescriptions");
   EditddQuantDesc.DataSource = dsrow.Tables["QuantityDescriptions"];
   EditddQuantDesc.DataValueField = dsrow.Tables[0].Columns[0].ToString();
   EditddQuantDesc.DataTextField = dsrow.Tables[0].Columns[1].ToString();
}

您检查EditddQuantDesc是否为null并以任何方式使用它，并且因为您知道该错误，所以未将其设置为对象的引用.

祝你好运！

You check if EditddQuantDesc null and work with it anyway and as the error let''s you know, it isn''t set to a reference of an object.

Good luck!

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