Why is my listbox not showing more than one item?

Question

This seems pretty simple, and I'm not sure why its not working.

I have a button that when clicked adds an item to a list in the class:form.

public partial class Form1 : Form
{
    List<string> photoNames = new List<string>();


    private void button1_Click_1(object sender, EventArgs e)
    {
        //Hunce1947@superrito.com
        photoNames.Add("Ree");
        listBox1.DataSource = photoNames;
    }

However, whenever you click the item only a single item shows up. Why are multiple instances of "Ree" not showing up?

how many elements are there in your list ? Show us more code to determine the problem. — Kaj, Jun 20 '18 at 20:50
@Hunce1947 use the debugger. Check how many items are in `photoNames` every time you click. — maccettura, Jun 20 '18 at 20:55
I think this should help: https://stackoverflow.com/questions/17615069/how-to-refresh-datasource-of-a-listbox-in-c-sharp-winforms — H.Szczepański, Jun 20 '18 at 20:56
Possible duplicate of [How to refresh DataSource of a ListBox in C# WinForms](https://stackoverflow.com/questions/17615069/how-to-refresh-datasource-of-a-listbox-in-c-sharp-winforms) — maccettura, Jun 20 '18 at 21:02

Kaj · Answer 1 · 2018-06-20T21:01:26.863

0

Listbox don't detect the changes in the datasource. So set DataSource to null first, then reassign datasource again. This will work for you.

List<string> photoNames = new List<string>();
private void button1_Click(object sender, EventArgs e)
{
    photoNames.Add("Ree");
    listBox1.DataSource = null;
    listBox1.DataSource = photoNames;                
}

edited Jun 20 '18 at 21:01

answered Jun 20 '18 at 20:56

Kaj

806
6
16

How would this help? OP already sets the DataSource to `photoNames` _after_ they modified `photoNames`... – maccettura Jun 20 '18 at 20:59
@maccettura Well, as I explained, the listbox not catching the changes, you could run the code to see what results you'll get :) – Kaj Jun 20 '18 at 21:00
Setting listBox1.DataSource = null also sets DisplayMember to the empty string (but not ValueMember)... This could be confusing – maccettura Jun 20 '18 at 21:02
@maccettura Why not ValueMember ? would you explain a little ? – Kaj Jun 20 '18 at 21:06
just the way it is. Its better to use a `BindingList` instead of setting the datasource to null – maccettura Jun 20 '18 at 21:07
It'll be useful for sure with `ListChanged` as there is an event for listBox.DataSourceChanged, but I took the shortest way to do that. – Kaj Jun 20 '18 at 21:09

score 0 · Answer 2 · edited Jun 22 '18 at 06:29

0

I do not have enough reputation to comment but I believe photoNames is a dataset, in that case I would say you you create a datatable and add rows.

 DataSet photoNames = new DataSet();

 DataTable dt = new DataTable("photoName");
 dt.Columns.Add(new DataColumn("pname", typeof(string)));

 ds.Tables.Add(dt);

and then instead of doing

photoNames.Add("Ree");

you can add ree as a row in the table of that dataset and bind it to your listbox like this:

 DataRow dr = dt.NewRow();
 dr["photoName"] = "Ree";
 dt.Rows.Add(dr);
 listBox1.DataSource = photoNames;

edited Jun 22 '18 at 06:29

Pang

9,564
146
81
122

answered Jun 20 '18 at 21:04

BlackMarker

139
12

Do you really need DataTable and DataSet to do that ? What a waste of resources. ! – Kaj Jun 20 '18 at 21:07
@Kaj As at when this question was posted, it was not specified that photoNames was a list. I dont have enough reputation to ask in the comment (read my answer) it was sorta safe to assume that it was a dataset as that's not completely out of context – BlackMarker Jun 21 '18 at 14:04

Why is my listbox not showing more than one item?

2 Answers2