C# InvalidOperationException

Question

Hello, i have this code:

Nodo N;  
        foreach (string S in listBox_nodos.Items)  
        {  
            N = graph.getNodoName(S);  
            string comp = (string) listBox_nodos.SelectedItem;  
            if (comp == S)  
               System.Console.WriteLine(N.NAME);  
        }  

I get InvalidOperationException and the application crashes.
Cant get why. Any help? thanks

EDIT: The 'N.NAME' prints! And then goes the crash.
EDIT2: I've tried to catch the Exception, the application crashes anyway

Answer 1

At which line do you get the exception? Without knowing what datatype listBox_nodos has, my first guess w2ould be that Items does not contain a lot of strings, but rather ListBoxItems

foreach (var item in listBox_nodos.Items)  
{  
    N = graph.getNodoName(item.Value); // or .SomethingElse

Answer 2

Perhaps the SelectedItem property isn't a string. Try using ToString() on it instead of casting and see if that solves your problem (or cast to the actual type and compare).

Answer 3

• as mentioned before, the full exception would be nice to see (if in the VS debugger, you can get it from the exception helper dialog or the $exception entry in Debug -> Windows -> Locals). Worst-case you should be able to try { .. } catch (Exception ex) { System.Console.WriteLine(ex); (Exception's ToString includes the stack trace)

  • if you're not sure of the types involved, could get the Items/SelectedItem as IEnumerable/object and then gettype() on them and display that.

• when trying to display things, may also want to try MessageBox.Show just in case the exception is coming from the use of Console for some reason.

• unrelated to the exception, but it looks like you're interating over the listbox items to find the selected item - if that's true, why not just use the selected item directly?