I am trying to use
the equivalent of
the C# “??” operator in some VB.NET code that I am working in. This StackOverflow article for “Is there a VB.NET equivalent for C#'s ?? operator?” explains
the VB.NET IF() statement syntax which is exactly what I am looking for... and I thought I was going to be done pretty quickly and could move on. But after implementing
the IF() statement in my code I started to receive this error:
Compiler Error Message: BC30201: Expression expected. And no matter how I tried using
the “IF()” statement, whenever I tried to visit
the aspx page that I was working on I received
the same error. This other StackOverflow article Using VB.NET If vs. IIf in binding/rendering expression indicated that
the VB.NET IF() operator was not available until VS2008 or .NET Framework 3.5. So I checked
the Web Application project properties but it was targeting
the .NET Framework 3.5: So I was still not understanding what was going on, but then I noticed
the version information in
the detailed
compiler output of
the error page: This happened to be a C# project, but with an ASPX page with inline VB.NET code (yes, it is strange to have that but that is
the project I am working on). So even though
the project file was targeting
the .NET Framework 3.5,
the ASPX page was being compiled using
the .NET Framework 2.0. But why? Where does this get set? How does ASP.NET know which version of
the compiler to use for
the inline code? For this I turned to
the web.config. Here is
the system.codedom/compilers section that was in
the web.config for this project: <system.codedom> <compilers> <compiler language="c#;cs;csharp" extension=".cs" warningLevel="4" type="Microsoft.CSharp.CSharpCodeProvider, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"> <providerOption name="CompilerVersion" value="v3.5" /> <providerOption name="WarnAsError" value="false" /> </compiler> </compilers> </system.codedom> Keep in mind that this is a C# web application project file but my aspx file has inline VB.NET code.
The web.config does not have any information for how to compile for VB.NET so it defaults to .NET 2.0 (instead of 3.5 which is what I need). So
the web.config needed to include
the VB.NET
compiler option. Here it is with both
the C# and VB.NET options (I copied
the VB.NET config from a new VB.NET Web Application project file). <system.codedom> <compilers> <compiler language="c#;cs;csharp" extension=".cs" warningLevel="4" type="Microsoft.CSharp.CSharpCodeProvider, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"> <providerOption name="CompilerVersion" value="v3.5" /> <providerOption name="WarnAsError" value="false" /> </compiler> <compiler language="vb;vbs;visualbasic;vbscript" extension=".vb" warningLevel="4" type="Microsoft.VisualBasic.VBCodeProvider, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"> <providerOption name="CompilerVersion" value="v3.5"/> <providerOption name="OptionInfer" value="true"/> <providerOption name="WarnAsError" value="false"/> </compiler> </compilers> </system.codedom> So
the inline VB.NET code on my aspx page was being compiled using
the .NET Framework 2.0 when it really needed to be compiled with
the .NET Framework 3.5
compiler in order to take advantage of
the VB.NET IF() coalesce statement. Without
the VB.NET web.config
compiler option,
the default is to compile using
the .NET Framework 2.0 and
the VB.NET IF() coalesce statement does not exist (at least in
the form that I want it in). FYI, there is an older IF statement in VB.NET 2.0
compiler which is why it is giving me
the unusual “Expression Expected” error message – see this article for when VB.NET got
the new updated version. EDIT (2011-06-20): I had made a wrong assumption in
the first version of this blog post. After a little more research and investigation I was able to figure out that
the issue was in
the web.config and not with
the IIS App Pool. Thanks to
the comment from James which forced me to look into this again.
