Object reference not set to instance of object"

Question

I am inserting values in listbox from database & retrieving text on a button click. but I'm getting the following error

Object reference not set to instance of object

so "selecteditem.text" does not get any value on item selected...

String selectemail = "select email_id from [property].[dbo].[user_membership]";
SqlCommand cmd = new SqlCommand(selectemail, con);
cmd.Connection.Open();

ListBox1.DataSource = cmd.ExecuteReader();
ListBox1.DataTextField = "Email_ID"; 
ListBox1.DataBind();  

//on button click//       
protected void Button1_Click1(object sender, EventArgs e)
{
   ListItem item = new ListItem();
   item.Text = ListBox1.SelectedItem.Text;(error comes here)
   ListBox2.Items.Add(item.Text);
   ListBox1.Items.Remove(item.Text);
   ...
}

Pondidum · Accepted Answer · 2011-03-21 21:32:02Z

3

This will stop the error for you:

//on button click//       
protected void Button1_Click1(object sender, EventArgs e)
{
        if (ListBox1.SelectedItem == null) return;

        ListItem item = new ListItem();
        item.Text = ListBox1.SelectedItem.Text;(error comes here)
        ListBox2.Items.Add(item.Text);
        ListBox1.Items.Remove(item.Text);
}

It looks like it was just a problem of the user not selecting anything in your ListBox1.

EDIT

I threw a test app together to check, and this works fine for me:

    var dt = New DataTable()
    dt.Columns.Add("email_id");

    dt.Rows.Add("first");
    dt.Rows.Add("second");
    dt.Rows.Add("thrid");
    dt.Rows.Add("fourth");

    var lst = New System.Web.UI.WebControls.ListBox;

    lst.DataSource = dt;
    lst.DataTextField = "Email_ID";
    lst.DataBind();

    //lst.SelectedItem is null here
    lst.SelectedIndex = 1;

    //lst.SelectedItem is NOT null here

edited Mar 21, 2011 at 21:32

answered Mar 21, 2011 at 12:09

Pondidum

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4 Comments

user123 Over a year ago

ListBox1.SelectedItem.Text is not getting value if data is inserted from database. but getting value if inserted manually..

marc_s Over a year ago

+1 exactly - just basic "defensive programming" principles - before accessing the properties of an object, check for NOT NULL

user123 Over a year ago

I am checking null as: if (ListBox1.SelectedItem == null) return;

user123 Over a year ago

but how to selecttext from listbox

Chris Dixon · Accepted Answer · 2011-03-21 11:52:54Z

1

Debug the code, but it's more than likely that the object that doesn't exist will be the ListBox1 control, or the ListBox1 control doesn't actually have an item selected when the button has been pressed.

answered Mar 21, 2011 at 11:52

Chris Dixon

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4 Comments

Chris Dixon Over a year ago

When you debug, which is the item that returns null? Place a debug marker and run through your code - is it the ListBox1.SelectedItem?

user123 Over a year ago

item.Text = ListBox1.SelectedItem.Text;

user123 Over a year ago

ListBox1.SelectedItem.Text is not getting if data is inserted from database. but getting value if insertyed manually...

Chris Dixon Over a year ago

Your data binding, is it being performed on every postback? Do you have (!IsPostBack) in your code? If so, remove it and try again - make sure the data is always being bound on postback too.

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