C# exception ==0 SQL

Question

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I would like to apply the following exception to my script..

VB.NET

ListBoxKlanten.Items.Count == 0

The idea is that when the listbox "ListBoxKlanten.Items.Count == 0" that the "listBoxKlantenContact" is made blank. (it is possible that there ready records in "listBoxKlantenContact") How do I apply this exception and what code can I best use for this option

C#

private void KlantenContactBOX()
{

    string queryKLantID = "SELECT IDKlantContactpersonen, FK_ID_Klant, Naam From Klantencontact WHERE FK_ID_Klant = @SELKlantID";

    using (connection = new SqlConnection(connectionstring))
    using (SqlCommand command = new SqlCommand(queryKLantID, connection))
    using (SqlDataAdapter adapter = new SqlDataAdapter(command))

    {
        command.Parameters.AddWithValue("@SELKlantID", ListBoxKlanten.SelectedValue);

        DataTable KlantenContactlijst = new DataTable();
        adapter.Fill(KlantenContactlijst);

            listBoxKlantenContact.DisplayMember = "Naam";
            listBoxKlantenContact.ValueMember = "IDKlantContactpersonen";
            listBoxKlantenContact.DataSource = KlantenContactlijst;
   }
}

Posted 22-Nov-15 22:44pm

MaikelO1

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Comments

phil.o 23-Nov-15 5:19am

There is no such thing as 'applying an exception'. Why don't you just test for the Count property, and act accordingly to the result?

MaikelO1 23-Nov-15 6:03am

Okay, :( I came upon this solution because the two list boxes are linked.

I use the list as parameter ListBoxKlanten.SelectedValue, but the problem is that the SelectedValue hold the last known value. When someone mistyped in the filter of the and there are not results the ListBoxKlanten.SelectedValue hold the last known result. But actually he should not run this query.

How do I fix than this??

phil.o 23-Nov-15 6:10am

That is the perfect job for a debugging session: this way you will be able to check the value of your variables, and react accordingly.

Sinisa Hajnal 23-Nov-15 6:15am

React to https://msdn.microsoft.com/en-us/library/system.windows.forms.listbox.selectedindexchanged(v=vs.110).aspx
selected index changed. That way, if the item is not changed, nothing will change the original.

By your description, the system works as intended, if the user didn't select anything, old value stands.

Sinisa Hajnal 23-Nov-15 6:09am

Please rephrase your question. It is incomprehensible. If you just want to check if you list is empty, use the code from the start of your question, just add "if" in front of it

MaikelO1 23-Nov-15 6:22am

I have tried. But that works with a message box but when I use the code below, I get an error during the debugging.

listBoxKlantenContact.Items.Clear();

CHill60 23-Nov-15 6:50am

And the error is...?

1 solution

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MaikelO1 · Answer 1 · 2015-11-23T02:08:00

Problem solved, Thank you for your help!!

if (ListBoxKlanten.Items.Count == 0)
               {
                   command.Parameters.AddWithValue(&quot;@SELKlantcontactinfoID&quot;, DBNull.Value);
               }
               else
               {
                   command.Parameters.AddWithValue(&quot;@SELKlantcontactinfoID&quot;, listBoxKlantenContact.SelectedValue);
               }