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error with listbox selection

Posted on 2008-10-17
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Last Modified: 2013-12-17
I have a listbox on my webform  populated values from the database table. i have a List<string> variable contains some values. i need to get the strings from list<string> variable and select those strings in the Listbox.

Here's the code i tried, but it gives me a error as object reference not set to an instance of the object.

 foreach (string s in Theatres)
                   {
                       TheaterListbox.SelectedItem.Text = s.ToString();   ---Getting Error in this line
                   }


Please help me out in this. Thanks
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Question by:gladstonesheeba
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9 Comments
 
LVL 55

Expert Comment

by:Jaime Olivares
ID: 22744318
is your listbox bound to a datasource? if so, it should be:
TheaterListbox.SelectedValue = s.ToString();  

if not, it should be something like:
TheaterListbox.SelectedItem = s.ToString();  
0
 
LVL 10

Expert Comment

by:jinn_hnnl
ID: 22744412
What type of error do you have.

What you do is like you set the selected item for your listBox which only valid when: your listBox has already contain list of items, and you whan one of them to be selected.
So the code you gave is not quite right.

I think you will have to add them instead of set the selected property


 foreach (string s in Theatres)
  {
        myList.Items.Add(new ListItem(s, s));
}

Hope this helps
0
 
LVL 18

Expert Comment

by:Priest04
ID: 22744416
if its a multiselection then you will need to do this
ListBox1.ClearSelection();
 
foreach (string s in Theatres)
{
    ListItem item = ListBox1.Items.FindByText(s);
    if (item != null) item.Selected = true;
}

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LVL 13

Expert Comment

by:TechTiger007
ID: 22744440
try this code

foreach (string s in Theatres)
                   {
                       TheaterListbox.Items.FindByText(s.ToString()).Selected = true;
                   }
0
 

Author Comment

by:gladstonesheeba
ID: 22744456
I tried what you mentioned Theaterlistbox.selecteditem=s.tostring(); I gave me two errors. please look in to this.

Error      5      Property or indexer 'System.Web.UI.WebControls.ListControl.SelectedItem' cannot be assigned to -- it is read only      

Error      6      Cannot implicitly convert type 'string' to 'System.Web.UI.WebControls.ListItem'      
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LVL 10

Accepted Solution

by:
jinn_hnnl earned 500 total points
ID: 22744490
If you want to select certain value of the list, then

if (myListBox.Items.FindByValue(s) != null)
       myListBox.Items.FindByValue(s).Selected = true;
0
 
LVL 10

Expert Comment

by:jinn_hnnl
ID: 22744514
Have you try my 2nd post, the added solution? Is that you want to add these List<string> values to your ListBox
0
 

Author Closing Comment

by:gladstonesheeba
ID: 31507264
Excellent, Thanks for your help
0
 
LVL 18

Expert Comment

by:Priest04
ID: 22744543
gladstonesheeba, unless you first try the examples we have provided, there is no point to discus further.
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