Changes from Classic ASP
When moving from classic ASP and VBScript to ASP.NET and VB.NET, developers will often run into syntactical errors or other problems due to the migration. The following sections describe these errors and their solutions.
Problems with VBScript
Error:
Wend is no longer supported; use End While instead.
Description:
You've tried to close a
while
statement with the keyword
wend
.
Solution:
In VB.NET, the
wend
keyword is not supported. Simply use
End While
instead.
Error:
The syntax <lower bound> To <upper bound> is no longer supported for specifying array bounds.
Description:
Your array is trying to declare a fixed
size
.
Solution:
In VBScript, you are able to use
dim MyArray(0 to 5)
to declare a
fixed-size
array. This is not supported in VB.NET.
Error:
The
name
'
myArray
' is not declared.
where
myArray
is an array variable.
Description:
You haven't yet declared the array variable.
Solution:
You are trying to declare an array using the
ReDim
keyword. In VB.NET, you must declare an array using the
Dim
keyword
before
using
ReDim
, unlike VBScript.
Error:
A value of type '
type
' cannot be converted to '
object
'.
Description:
This typically means that you are trying to assign a property to an object without specifying the property name.
Solution:
In VBScript, objects supported default properties. In other words, you weren't required to specify the name of a property to set it. For example, given a
Label
control, the following would be possible in VBScript:
dim Label as Label
Label = "Hello World"
This would set the
Text
property to the string
"Hello World"
. In VB.NET, default properties are no longer supported unless they take parameters. You must instead use the following:
Label.Text = "Hello World"
Problem:
Let and Set are no longer supported on assignment statements.
Description:
You are using the
Let
or
Set
keyword to assign something to an object.
Solution:
These keywords are not supported in VB.NET. Simply remove them and your code should work.
Problem:
The name '
N
' is not declared.
even though you have declared it.
Description:
The declaration for a variable in one part of your page is not accessible by another part of your page.
Solution:
In VBScript,
variables
declared within blocks (any set of statements
terminated
with
End
,
Next
, or
Loop
) are viewable outside the block. For example, the following code will write
11
to the browser:
dim I as integer
For I = 1 To 10
Dim N As Double
N = N + I
Next
Response.write(N)
In VB.NET, the variable
N
in the
preceding
code has block scope, meaning it is not accessible outside the code block (the
for
loop, in this case). Thus, this code will produce an error. Instead, declare your variable outside the loop.
Problem:
Optional parameters must always specify a default value.
Description:
You've declared a function with the
optional
keyword, specifying that a parameter is optional.
Solution:
In VB.NET, optional parameters must specify a default value. For instance, change the following VBScript code:
sub MySub(Optional MyParam as String)
to
sub MySub(Optional MyParam as String = "HI")
Also, the
IsMissing
function, used to detect whether an optional parameter was specified in VBScript, is not supported in VB.NET.
Problem:
Argument lists in all call statements must now be
enclosed
in parentheses.
Description:
You tried to call a function or sub without using parentheses. For example:
Response.Write "Hello World"
Solution:
In VB.NET, all function and sub calls must enclose any parameters in parentheses, whether or not they return values. Instead of the preceding code, use the following:
Response.Write("Hello World")
Problem:
Type-declaration character & does not match declared data type
type
.
Description:
You are trying to use the ampersand to concatenate strings.
Solution:
In VBScript, it was possible to concatenate strings using the ampersand, without any spaces between variable
names
. For example, the following code in VBScript would write
HI there everyone
to the browser:
dim a as string = "HI "
dim b as string = "there "
dim c as string = "everyone"
Response.Write(a&b&c)
This will cause an error in ASP.NET. Instead, use
Response.Write(a & b & c)
Problems with Classic ASP
Problem:
Syntax Error
or
Expected variable, constant, Enum, Type, or procedural declaration.
Description:
Method and global variable declarations don't work properly. You are trying to declare a method or variable within a code render block. For example:
<%
dim I as Integer
sub HelloWorld
...
end sub
%>
Solution:
In VB.NET, all method and global variable declarations must be contained within code declaration blocks (within
<script>
tags). Also, any non-assignment statements must be placed within another method, such as
Page_Load
.
Problem:
Request
doesn't return what you expect it to.
Description:
You are using the
Request
object to return data from the HTTP request; for example,
Request.Form
or
Request.QueryString
.
Solution:
In classic ASP, the
Request
object would return strings containing the entire collection of variables. For example, given the URL
http://localhost/test/Test.asp?values=45&values=600
and the following code:
Response.Write(Request.Querystring(values)
classic ASP would display a single string,
45, 600
, in the browser. In ASP.NET, the
Request
object returns arrays of strings instead of one
concatenated
string. For example, with the earlier URL and the code
Response.Write(Request.Querystring(values)(0)
ASP.NET would display
45
, and the following:
Response.Write(Request.Querystring(values)(1)
would display
600
. This functionality is the same for
Request
,
Request.Querystring
, and
Request.Form
.
|
