Question

I am passing the following via the request object in codeBehind:

Get the Requested code to be created.

Dim Code As String = Request("code").ToString()

and below is my markup page called barcodes.aspx:

  <form id="Form1" method="post" runat="server">
  <img src="barcodes.aspx?code=XXXXX" alt="barcode" /> 

   <asp:Image id="myBarCode"  runat="server"></asp:Image>
  </form>

Why am I getting the error above?

Answer 1

You need to actually submit the form (POST) or pass the parameters in the URL (GET) to get the request parameters via the Request object. Two easy ways (of many) to do this:

Option 1. Keep just your barcodes.aspx and barcodes.aspx.vb. In barcodes.aspx put:

<form id="Form1" method="post" runat="server">
  <input type="hidden" name="code" value="XXXXX" /> 

  <asp:Image id="myBarCode"  runat="server"></asp:Image>
  <asp:Button runat="server" Text="Submit"></asp:Button>
</form>

In barcodes.aspx.vb put in the Page_Load:

If PostBack Then
  Dim code As String = Request.Form("code")
  If Not String.IsNullOrEmpty(code) Then
    ' Generate your image here, a code has been specified
  End If
End If

Then just hit the submit button on your aspx page.

Option 2. Split it into two aspx pages but basically same as above.

In submitme.aspx put this (for a POST, click the button):

<form id="Form1" method="post" runat="server">
  <input type="hidden" name="code" value="XXXXX" /> 

  <asp:Button runat="server" Text="Submit" PostBackURL="barcodes.aspx"></asp:Button>
</form>

Or this (for a GET, click the link):

<a href="barcodes.aspx?code=XXXXX">Click Me</a>

In barcodes.aspx.vb put this in Page_Load (works for either the GET or POST option):

Dim code As String = Request("code")
If Not String.IsNullOrEmpty(code) Then
  ' Generate your image here, a code has been specified
End If

In barcodes.aspx you would then simply need:

<asp:Image id="myBarCode"  runat="server"></asp:Image>