[Solved] ASP.Net Error: DropDownList has a SelectedValue which is invalid because it does not exist in the list of items

Hi kankon,

You need to check the DropDownList item exists or not before setting the SelectedValue.

Refer below updated code.

 Code

C#

private void SetInitialRow()
{
    DataTable dt = new DataTable();
    DataRow dr = null;
    dt.Columns.Add(new DataColumn("RowNumber", typeof(string)));
    dt.Columns.Add(new DataColumn("Column1", typeof(string)));
    dt.Columns.Add(new DataColumn("Column2", typeof(string)));
    dt.Columns.Add(new DataColumn("Column3", typeof(string)));
    dr = dt.NewRow();
    dr["RowNumber"] = 1;
    dr["Column1"] = string.Empty;
    dr["Column2"] = string.Empty;
    dr["Column3"] = string.Empty;
    dt.Rows.Add(dr);

    //Store the DataTable in ViewState
    ViewState["CurrentTable"] = dt;

    Gridview1.DataSource = dt;
    Gridview1.DataBind();
}
private void AddNewRowToGrid()
{
    int rowIndex = 0;

    if (ViewState["CurrentTable"] != null)
    {
        DataTable dtCurrentTable = (DataTable)ViewState["CurrentTable"];
        DataRow drCurrentRow = null;
        if (dtCurrentTable.Rows.Count < 5)
        {
            for (int i = 1; i <= dtCurrentTable.Rows.Count; i++)
            {
                //extract the TextBox values
                DropDownList ddl1 = (DropDownList)Gridview1.Rows[rowIndex].Cells[1].FindControl("ddl1");
                TextBox box2 = (TextBox)Gridview1.Rows[rowIndex].Cells[2].FindControl("TextBox2");
                TextBox box3 = (TextBox)Gridview1.Rows[rowIndex].Cells[3].FindControl("TextBox3");

                drCurrentRow = dtCurrentTable.NewRow();
                drCurrentRow["RowNumber"] = i + 1;
                if (ddl1.Items.FindByValue(dtCurrentTable.Rows[i - 1]["Column1"].ToString()) != null)
                {
                    dtCurrentTable.Rows[i - 1]["Column1"] = ddl1.SelectedValue;
                }
                dtCurrentTable.Rows[i - 1]["Column2"] = box2.Text;
                dtCurrentTable.Rows[i - 1]["Column3"] = box3.Text;

                rowIndex++;
            }
            dtCurrentTable.Rows.Add(drCurrentRow);
            ViewState["CurrentTable"] = dtCurrentTable;

            Gridview1.DataSource = dtCurrentTable;
            Gridview1.DataBind();
        }
        else
        {
            ClientScript.RegisterClientScriptBlock(this.GetType(), "alert", "alert('Maximum 5 Rows Allow');", true);
        }
    }
    else
    {
        Response.Write("ViewState is null");
    }

    SetPreviousData();
}


private void SetPreviousData()
{
    int rowIndex = 0;
    if (ViewState["CurrentTable"] != null)
    {
        DataTable dt = (DataTable)ViewState["CurrentTable"];
        if (dt.Rows.Count > 0)
        {
            for (int i = 0; i < dt.Rows.Count; i++)
            {
                DropDownList ddl1 = (DropDownList)Gridview1.Rows[rowIndex].Cells[1].FindControl("ddl1");
                TextBox box2 = (TextBox)Gridview1.Rows[rowIndex].Cells[2].FindControl("TextBox2");
                TextBox box3 = (TextBox)Gridview1.Rows[rowIndex].Cells[3].FindControl("TextBox3");

                if (ddl1.Items.FindByValue(dt.Rows[i]["Column1"].ToString()) != null)
                {
                    ddl1.SelectedValue = dt.Rows[i]["Column1"].ToString();
                }
                box2.Text = dt.Rows[i]["Column2"].ToString();
                box3.Text = dt.Rows[i]["Column3"].ToString();

                rowIndex++;
            }
        }
    }
}

protected void OnSelectedIndexChanged(object sender, EventArgs e)
{
    DropDownList ddl1 = Gridview1.FindControl("ddl1") as DropDownList;

}

protected void Page_Load(object sender, EventArgs e)
{
    if (!Page.IsPostBack)
    {
        SetInitialRow();
    }
}

protected void ButtonAdd_Click(object sender, EventArgs e)
{
    AddNewRowToGrid();
}