CODEWITHSUNDEEP
c#listbox
user1016020
user1016020

Reputation: 11

deselecting the listbox value

I'm selecting items from one ListBox and adding them to second ListBox on button click. The problem is that when I want to deselect the selected items from listbox2, it gives "Object reference not set to an instance of an object" error. Below is the code I added behind SELECT button. I have used the same code for deselecting with listbox1 replaced by listbox2 and vice versa.

NOTE: Items in listbbox1 are being retrieved from database and items that got selected in listbox2 will be saved to database

List<int> rowIndexes = new List<int>();

foreach (int index in listBox1.SelectedIndices)
{
    DataRowView view = listBox1.Items[index] as DataRowView;
    string id = view["Course_Id"].ToString();
    string name = view["Course_Name"].ToString();
    listBox2.Items.Add(name);
    rowIndexes.Add(index);
}

try
{
    for (int i = rowIndexes.Count; i > 0; i--)
    {
        dt.Rows.RemoveAt(rowIndexes[i - 1]);
        dt.AcceptChanges();
    }
}

catch (Exception er)
{
    MessageBox.Show(er.Message);
}

Upvotes: 1

Views: 458

Answers (2)

sq33G
sq33G

Reputation: 3360

This is a guess, at best, because the claim that it fails on the first line makes no sense.

My psychic powers tell me that this actually failing at

string id = view["Course_Id"].ToString();

because view is null. The problem is that

DataRowView view = listBox1.Items[index] as DataRowView;

is trying to cast the items from a ListBox to DataRowView. This will always return null, unless for some (odd) reason you populated your ListBox.Items with a collection of DataRowView.

EDIT

You may be filling listBox1 with DataRowView, but you're filling listBox2 with System.String:

string name = view["Course_Name"].ToString();
listBox2.Items.Add(name);

Try changing that to

//string id = view["Course_Id"].ToString();
//string name = view["Course_Name"].ToString();
listBox2.Items.Add(view);

Upvotes: 6

ChrisBD
ChrisBD

Reputation: 9209

Assuming that this is copied exactly from your code. This line is incorrect:

List<int> row Indexes = new List<int>();

its should be:

List<int> rowIndexes = new List<int>();

Also what is dt?

edit

If it really is failing on:

List<int> rowIndexes = new List<int>();

The perhaps you're not:

using System.Collections.Generic;

Or have a reference to System in your project references.

Upvotes: 0

Related Questions