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02.14.2008 at 07:17AM PST, ID: 23163126
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7.0
Listbox control question ASP.net C#
Zones: .NET, C# Programming Language, Programming for ASP.NET
Tags: C# asp.net
I'd like to search a listbox bound to a SQL query during load. I have the text box and a search button. First time I enter text and hit search. The selected item changes in listbox. One problem I hit I use the selectedindexchange envent to load another textbox from the selected value in listbox. When I use search button that event doesn't fire. The other problem I'm having is if I enter text again to search I get the null reference errror. Any insight would be appreciated.
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protected void TempSearchTB_TextChanged(object sender, EventArgs e)
    {
        ListBox lst = (ListBox)FormView1.FindControl("ListBox1");
 
        TextBox searchstring = (TextBox)FormView1.Row.FindControl("TempSearchTB");
        
        String searchText = searchstring.Text;
       
        lst.ClearSelection();
        try
        {
            lst.Items.FindByValue(searchText).Selected = true;
            
        }
        catch (Exception ex)
        {
            Response.Write(ex.ToString());
        }
      
    }
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Question Stats
Zone: Programming
Question Asked By: national_fulfillment
Solution Provided By: national_fulfillment
Participating Experts: 2
Solution Grade: A
Views: 287
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02.14.2008 at 07:30AM PST, ID: 20894078

Rank: Master

zkeown:

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02.14.2008 at 07:33AM PST, ID: 20894112

Rank: Wizard

TSmooth:

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02.14.2008 at 08:12AM PST, ID: 20894551
national_fulfillment:

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02.14.2008 at 08:13AM PST, ID: 20894564
national_fulfillment:

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02.14.2008 at 08:20AM PST, ID: 20894617

Rank: Wizard

TSmooth:

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02.19.2008 at 12:57PM PST, ID: 20932504
national_fulfillment:

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02.19.2008 at 01:54PM PST, ID: 20933041

Rank: Wizard

TSmooth:

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02.20.2008 at 05:50AM PST, ID: 20937690
national_fulfillment:

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02.20.2008 at 05:55AM PST, ID: 20937726
national_fulfillment:

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02.21.2008 at 05:49AM PST, ID: 20947634
national_fulfillment:

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02.14.2008 at 07:30AM PST, ID: 20894078

Rank: Master

zkeown:
I had a similar situation, and I wound up using an alternative method, which I'll describe below.  If it won't work for you, can you tell me the line you get the null exception on?

Step 1: Use ListSearch extender from AJAX Control Toolkit to search the listbox.
Step 2: Have a button below the listbox "Load Selection".  AutoPostBack of the ListBox won't work with the ListSearch.

ListSearch: http://www.asp.net/AJAX/AjaxControlToolkit/Samples/ListSearch/ListSearch.aspx
 
02.14.2008 at 07:33AM PST, ID: 20894112

Rank: Wizard

TSmooth:
To answer one of your questions/problems. The SelectedIndexChanged event does not fire whenever you programmatically change the selected item of a list box. In that situation, you would need to call a method that does what you want. You could create the method so that the SelectedIndexChanged event just calls it as well instead of duplicating the code in two different locations.

You didn't specify what line the null reference is occuring on but it appears that the problem will arise if you search for an item that doesn't exist due to the line:

lst.Items.FindByValue(searchText).Selected = true;

In the above line of code, if the list box does not contain the value searched for, it will return Null which would thus make the ".Selected" property invalid and throw the null reference error. Add some code to check to see if the item exists before accessing the Selected property of the item:

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ListBoxItem li = lst.Items.FindByValue(searchText)
if(li)
{
  li.Selected = true;
}
Open in New Window
 
02.14.2008 at 08:12AM PST, ID: 20894551
national_fulfillment:
it's returning a null on the listbox itself. I debugged it and there is a value in the searchtext.
 
02.14.2008 at 08:13AM PST, ID: 20894564
national_fulfillment:
lst.Items.FindByValue(searchText).Selected = true;

this is the line that returns null on the second search.
 
02.14.2008 at 08:20AM PST, ID: 20894617

Rank: Wizard

TSmooth:
Read my solution, it explains why you would get an error on that line and how to work around it.
 
02.19.2008 at 12:57PM PST, ID: 20932504
national_fulfillment:
this does stop the execption but doesn't solve the problem because the item is in the listbox and it's returning a null no matter what.
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ListItem li = lst.Items.FindByValue(searchText);
        if (li!=null)
        {
            lst.Items.FindByValue(searchText).Selected = true;
        }
Open in New Window
 
02.19.2008 at 01:54PM PST, ID: 20933041

Rank: Wizard

TSmooth:
Can you set a break point on line 2 of the above code and take a look at what's in lst.Items using the immediate window or one of the other debug windows?
Assisted Solution
 
02.20.2008 at 05:50AM PST, ID: 20937690
national_fulfillment:
First time I search everything works the way it's suppose to (search value was "test"), but if I try to search again (search value "The State Within") the list is empty. Am I missing some sort of reload function. I assumed ones the listbox was loaded the values stayed am I wrong?

Thanks for your advice/help so far.
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************************Debug FIRST TIME:**********************
-		li	{test}	System.Web.UI.WebControls.ListItem
-		Attributes	{System.Web.UI.AttributeCollection}	System.Web.UI.AttributeCollection
		Count	0	int
+		CssStyle	{System.Web.UI.CssStyleCollection}	System.Web.UI.CssStyleCollection
+		Keys	{System.Collections.Specialized.ListDictionary.NodeKeyValueCollection}	System.Collections.ICollection {System.Collections.Specialized.ListDictionary.NodeKeyValueCollection}
+		Non-Public members		
		Enabled	true	bool
		Selected	false	bool
		Text	"test"	string
		Value	"test"	string
+		Non-Public members		
-		lst.Items	{System.Web.UI.WebControls.ListItemCollection}	System.Web.UI.WebControls.ListItemCollection
		Capacity	128	int
		Count	126	int
		IsReadOnly	false	bool
		IsSynchronized	false	bool
+		SyncRoot	{System.Web.UI.WebControls.ListItemCollection}	object {System.Web.UI.WebControls.ListItemCollection}
+		Non-Public members		
		searchText	"test"	string
-		this	{ASP.vremail_aspx}	VREmail {ASP.vremail_aspx}
+		[ASP.vremail_aspx]	{ASP.vremail_aspx}	ASP.vremail_aspx
+		base	{ASP.vremail_aspx}	System.Web.UI.Page {ASP.vremail_aspx}
+		ApplicationInstance	{ASP.global_asax}	ASP.global_asax
+		form1	{System.Web.UI.HtmlControls.HtmlForm}	System.Web.UI.HtmlControls.HtmlForm
+		FormView1	{System.Web.UI.WebControls.FormView}	System.Web.UI.WebControls.FormView
+		HyperLink1	{Text = "BBC America Scheduling"}	System.Web.UI.WebControls.HyperLink
+		Image1	{System.Web.UI.WebControls.Image}	System.Web.UI.WebControls.Image
+		Label2	{Text = "Viewer Relations Response Page"}	System.Web.UI.WebControls.Label
+		LinkButton1	{Text = "Records"}	System.Web.UI.WebControls.LinkButton
+		LinkButton2	{Text = "Home"}	System.Web.UI.WebControls.LinkButton
+		Profile	{System.Web.Profile.DefaultProfile}	System.Web.Profile.DefaultProfile
 
 
***********************Debug of Second Search**************
		li	null	System.Web.UI.WebControls.ListItem
-		lst.Items	{System.Web.UI.WebControls.ListItemCollection}	System.Web.UI.WebControls.ListItemCollection
		Capacity	128	int
		Count	126	int
		IsReadOnly	false	bool
		IsSynchronized	false	bool
+		SyncRoot	{System.Web.UI.WebControls.ListItemCollection}	object {System.Web.UI.WebControls.ListItemCollection}
+		Non-Public members		
		searchText	"The State Within"	string
-		this	{ASP.vremail_aspx}	VREmail {ASP.vremail_aspx}
+		[ASP.vremail_aspx]	{ASP.vremail_aspx}	ASP.vremail_aspx
+		base	{ASP.vremail_aspx}	System.Web.UI.Page {ASP.vremail_aspx}
+		ApplicationInstance	{ASP.global_asax}	ASP.global_asax
+		form1	{System.Web.UI.HtmlControls.HtmlForm}	System.Web.UI.HtmlControls.HtmlForm
+		FormView1	{System.Web.UI.WebControls.FormView}	System.Web.UI.WebControls.FormView
+		HyperLink1	{Text = "BBC America Scheduling"}	System.Web.UI.WebControls.HyperLink
+		Image1	{System.Web.UI.WebControls.Image}	System.Web.UI.WebControls.Image
+		Label2	{Text = "Viewer Relations Response Page"}	System.Web.UI.WebControls.Label
+		LinkButton1	{Text = "Records"}	System.Web.UI.WebControls.LinkButton
+		LinkButton2	{Text = "Home"}	System.Web.UI.WebControls.LinkButton
+		Profile	{System.Web.Profile.DefaultProfile}	System.Web.Profile.DefaultProfile
Open in New Window
 
02.20.2008 at 05:55AM PST, ID: 20937726
national_fulfillment:
The values I'm searching for are definately part of the listbox; and just to mention if i search again with the orginal value ("test") all works the way it's suppose to.
 
02.21.2008 at 05:49AM PST, ID: 20947634
national_fulfillment:
I figured it out. My listbox displays one column but the value points to a different column. So I have to switch to using
ListItem li = lst.Items.FindByText(searchText);
all is well now; it worked for my "test" value because that's what I had as it's value "test".  
Anyway thanks for the help; while I'm on the subject does anyone happen to know how to make the search ignore case when looking at the list items?
Accepted Solution
 
 
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