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Updating a simple ListBox from the DataSource

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Alex Maghen (VIP)

I have a simple ListBox "LB" and an ArrayList "TheList". I load the ArrayList
with a few items and then do

LB.DataSource = TheList;
LB.DisplayMember = "XXX";
LB.ValueMember = "YYY"; // or whatever.

Everything works fine and my values are displayed.

BUT, if I then add more items to my ArrayList, they are not reflected in the
ListBox. Is there a setting to have the ListBox do this automatically? If
not, how do I force it to re-load itself?

Thanks. Alex

Reply to this message...

Rami Saad (VIP)

Hello Alex,

In an ArrayList, the 'plumbing' is not available to support two-way binding
as with a dataset. So, you have to handle the synchronization yourself. One
way to do this is to set the listBox1.DataSource to null and then reset it
to your ArrayList. Another way is to use the CurrencyManager as shown in
the code below.

private System.Windows.Forms.ListBox listBox1;

private System.Windows.Forms.Button button1;

private ArrayList myArrayList;

public Form1()

{

//

// Required for Windows Form Designer support

//

InitializeComponent();

myArrayList = new ArrayList();

myArrayList.Add("orange");

myArrayList.Add("green");

myArrayList.Add("blue");

myArrayList.Add("red");

listBox1.DataSource = myArrayList;

}

......

//change the arraylist

private void button1_Click(object sender, System.EventArgs e)

{

myArrayList[1] = "pink";

myArrayList.Add("lavendar");

//use currency manger to sync up the listbox

BindingManagerBase bm =
this.listBox1.BindingContext[myArrayList];

CurrencyManager cm = (CurrencyManager) bm;

if (cm != null)

cm.Refresh();

//Or, you can just reset the datasource

//listBox1.DataSource = null;

//listBox1.DataSource = myArrayList;

}

Hope this helps.

Regards,
Rami Saad
MEA Developer Support Center
ITworx on behalf of Microsoft EMEA GTSC

Reply to this message...

Alex Maghen (VIP)

Thanks for this. When I use the approach of setting the DataSource to NULL
and then back again, their's a strange delay of up to a second and a half or
more. Any idea why this might be? There are only three entries!

Thanks.

Alex

""Rami Saad"" wrote:

[Original message clipped]

Reply to this message...

	System.Collections.ArrayList
	System.EventArgs
	System.Web.UI.WebControls.ListBox
	System.Windows.Forms.BindingManagerBase
	System.Windows.Forms.Button
	System.Windows.Forms.CurrencyManager
	System.Windows.Forms.ListBox

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