how to avoid error

maennet · August 3rd, 2004, 04:03 AM

hi all :
i have use the following code and every thing work good .
except when I don't select any radio option,the error
display.
how to avoid this error?
[u]code:</u>

<script language="vb" runat=server>
  sub page_load()
      if page.ispostback then
          select case(destination.selecteditem.value)
          case "Amman":
               message.text= "You select the jordan capital"
          case "Irbed":
               message.text= "You select the best contry city"
          case "Zarqa":
               message.text= "You select my born city"
          case else:
               message.text= "Select city please"

          end select
      end if
  end sub
</script>

<html>
  <head>
    <title>Case</title>
  </head>

  <body>
    <form runat="server">
      Select your choice of destination:
      <br /><br />
      <asp:RadioButtonList ID="destination" Runat=server>
        <asp:ListItem>Amman</asp:ListItem>
        <asp:ListItem>Irbed</asp:ListItem>
        <asp:ListItem>Zarqa</asp:ListItem>
      </asp:RadioButtonList>
      <br /><br />
      <input type=submit value="Submit Chice">
      <br /><br />
      <asp:Label ID="message" Runat=server/>
    </form>
  </body>
</html>

jordan

stu9820 · August 3rd, 2004, 07:34 AM

What is the error?

maennet · August 3rd, 2004, 08:50 AM

[u]this is the error</u>

Server Error in '/b_case' Application.
--------------------------------------------------------------------------------

Object reference not set to an instance of an object.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error:

Line 2: sub page_load()
Line 3: if page.ispostback then
Line 4: select case(destination.selecteditem.value)
Line 5: case "Amman":
Line 6: message.text= "You select the jordan capital"

Source File: c:\inetpub\wwwroot\b_case\case.aspx Line: 4

Stack Trace:

[NullReferenceException: Object reference not set to an instance of an object.]
   ASP.case_aspx.page_load() in c:\inetpub\wwwroot\b_case\case.aspx:4
   System.Web.Util.ArglessEventHandlerDelegateProxy.C allback(Object sender, EventArgs e)
   System.Web.UI.Control.OnLoad(EventArgs e)
   System.Web.UI.Control.LoadRecursive()
   System.Web.UI.Page.ProcessRequestMain()

--------------------------------------------------------------------------------
Version Information: Microsoft .NET Framework Version:1.1.4322.573; ASP.NET Version:1.1.4322.573

jordan

stu9820 · August 3rd, 2004, 09:28 AM

Try adding a Required Field validator to the RadioButtonList.

devanti · August 3rd, 2004, 05:57 PM

Hi Chap,

Another chapter another problem I see! Don't worry I am stuck on chapter 16! but its all fun and games..

I think you just need to move the colon from the else case statement chap, but just incase see below(no pun intended)

Try setting up an If statement that will for instance chack if an option was selected or not,

e.g
<code>

Option 1)

<asp:RadioButtonList ID="destination" Runat=server>
        <asp:ListItem Id="optCapital" Value="Amman"></asp:ListItem>
        <asp:ListItem Id="optBestCity" Value="Irbed"></asp:ListItem>
        <asp:ListItem Id="optMyHome" Value="Zarqa"></asp:ListItem>
      </asp:RadioButtonList>

Option 2)

sub page_load()
      if page.ispostback then
          select case(destination.selecteditem.value)
          case "Amman":
               message.Text= "You select the jordan capital"
          case "Irbed":
               message.Text= "You select the best contry city"
          case "Zarqa":
               message.Text= "You select my born city"
          end select
           else
               message.Text= "Select city please"
      end if

Option 3

Set up a secondary Sub called destinationSelection()
and insert your code into that, then enter the below
into Page_Load Sub.

If Destination.SelectedItem.Value is Nothing then
    Message.Text = "Destination not selected"
        Else
      destinationSelection(Destination)
End If

The.Student

What does my picture not work !

maennet · August 4th, 2004, 01:46 AM

hi United Kingdom
thank you for your help but iam sory to tell you that I try all option but nothing change.
if you could please try a code else and tell me.

jordan

Hal Levy · August 4th, 2004, 08:25 AM

Maennet,

First, is this an example from the book or just a problem your having with some code your writing? If it's from the book please provide a page number.

Second, is there an object, somewhere, called Message?

Hal Levy
Web Developer, PDI Inc.

NOT a Wiley/Wrox Employee