Error while editing in dropdownlist..Object reference not set to an instance of an object.

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

fillgrid();

if (Request.QueryString["id"] != null)
{
Button1.Visible = false;
Button2.Visible = true;
edits();
}
else
{
Button2.Visible = false;
Button1.Visible = true;
}

}

}

public void fillgrid()
{
onlineexam oe = new onlineexam();
//DataTable dt = oe.getcasestudy();
DataTable dt = oe.getlevel();
if (dt.Rows.Count == 0)
{

}
else
{
GridView1.DataSource = dt;
GridView1.DataBind();
}

}
public void edits()
{
onlineexam oe = new onlineexam();
int id = Convert.ToInt32(Request.QueryString["id"].ToString());

DataTable dt = oe.getlevelbyid(id);

string fn= dt.Rows[0]["CategoryId"].ToString();
string sn = dt.Rows[0]["CategoryName"].ToString();
DropDownList1.SelectedItem.Text = fn;
/*error here* Object reference not set to an instance of an object*/ DropDownList2.SelectedItem.Text= sn;

// for (int z = 0; z < DropDownList1.Items.Count; z++)
// {
// if (DropDownList1.Items[z].Text == fn)
// {
// DropDownList1.Items[z].Selected = true;
// }
//}
//for (int x = 0; x < DropDownList2.Items.Count; x++)
//{
// if (DropDownList2.Items[x].Text == sn)
// {
// DropDownList2.Items[x].Selected = true;
// }
//}
TextBox1.Text = dt.Rows[0]["LevelName"].ToString();
}

public void filldropdown()
{
onlineexam oe = new onlineexam();
DataTable dt = oe.getcategoryid();
if (dt.Rows.Count == 0)
{
}
else
{
DropDownList1.DataSource = dt;
DropDownList1.DataTextField = dt.Columns["CategoryName"].ToString();
DropDownList1.DataValueField = dt.Columns["Id"].ToString();
DropDownList1.DataBind();
DropDownList1.Items.Insert(0, "Select");
}
}

protected void Button1_Click(object sender, EventArgs e)
{
string CategoryId = DropDownList1.SelectedItem.Text.ToString();
string CategoryName = DropDownList2.SelectedItem.Text.ToString();
// string CategoryName = DropDownList3.SelectedItem.Text.ToString();
string LevelName = TextBox1.Text;
onlineexam oe = new onlineexam();
oe.addlevel(CategoryId, CategoryName, LevelName);
MessageBox msg = new MessageBox();
msg.Show("Level Added Successfully");
fillgrid();
DropDownList2.Items.Clear();
TextBox1.Text = "";
}
protected void GridView1_RowDeleting(object sender, GridViewDeleteEventArgs e)
{
int id = Convert.ToInt32(GridView1.DataKeys[e.RowIndex].Value);

MessageBox msg = new MessageBox();
onlineexam oe = new onlineexam();
// oe.deletecasestudy(id);
oe.deletelevel(id);

msg.Show("Deleting Successfully");
fillgrid();
DropDownList1.SelectedItem.Text = "Select";
DropDownList2.Items.Clear();
TextBox1.Text = "";
}
protected void Button2_Click(object sender, EventArgs e)
{
int id = Convert.ToInt32(Request.QueryString["id"]);
string CategoryId = DropDownList1.SelectedItem.Text.ToString();
string CategoryName = DropDownList2.SelectedItem.Text.ToString(); ;
//string CategoryName = DropDownList3.SelectedItem.Text.ToString();
string LevelName = TextBox1.Text;
onlineexam oe = new onlineexam();
oe.updatelevel(id, CategoryId, CategoryName, LevelName);
MessageBox msg = new MessageBox();
msg.Show("Level Added Successfully");
}

protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
{
}

public void filldropdown2(int CategoryId)
{
onlineexam oe = new onlineexam();
DataTable dt = oe.getsubcategoryid(CategoryId);
if (dt.Rows.Count == 0)
{

//DropDownList2.Items.Insert(0, "Select");
DropDownList2.Items.Insert(0, "NULL");
}
else
{
DropDownList2.DataSource = dt;
// DropDownList2.DataTextField = dt.Columns["CategoryName"].ToString();
//string d = dt.Columns["CategoryName"].ToString();
//DropDownList2.DataTextField = d;
DropDownList2.DataValueField = dt.Columns["CategoryName"].ToString();
DropDownList2.DataBind();
DropDownList2.Items.Insert(0, "Select");
}
}

protected void DropDownList2_SelectedIndexChanged(object sender, EventArgs e)
{

}
protected void DropDownList1_TextChanged(object sender, EventArgs e)
{
DropDownList2.Items.Clear();
TextBox1.Text = "";
int CategoryId = Convert.ToInt32(DropDownList1.SelectedItem.Value);
filldropdown2(CategoryId);
}
protected void DropDownList2_TextChanged(object sender, EventArgs e)
{

}
protected void DropDownList2_PreRender(object sender, EventArgs e)
{

}
}

4 Replies

Know the answer? Post it — somebody with the same question will find it here.

Neha Rana10y ago
Thanks Bhushan Bhure
Bhushan Bhure14y ago
Amaan,

You are getting object refrence error on this line

DropDownList2.SelectedItem.Text= sn;

because, you don't have any items populated in DropDownlist2 and you are trying to set selectedItem.

Make sure you populate DropDown2 before.

click "accept answer" if this resolves your problem
amaan ahmed14y ago
this is my complete code only...i have three columns in level table categoryId,categoryName,LevelName.in category table i have two columns categoryname and parentid.
Bhushan Bhure14y ago
Amaan,
It will be good, if you post your complete code with question (or attach as zip).

Category Name:	onselectedindexchanged="DropDownList1_SelectedIndexChanged" AutoPostBack="true" Width="146px" ontextchanged="DropDownList1_TextChanged">
SubCategory Name:	AutoPostBack="true" onprerender="DropDownList2_PreRender" onselectedindexchanged="DropDownList2_SelectedIndexChanged" ontextchanged="DropDownList2_TextChanged">
Level Name: /td>