问题
I get this error when compiling a C# application. Looks like a trivial error, but I can't get around it.
My setup is Windows 7 64 bit. Visual-Studio 2010 C# express B2Rel.
I added a reference to System.Web.dll located at C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.0, but it has a yellow exclamation symbol and I still get the above error. I also have the using System.Web declaration.
What am I doing wrong?
Update: After getting the prompt answer pointing me at the root cause, I searched a bit in Google to where it states that System.Web.dll is for the full framework. I did not find such a reference.
For newbies like me, this blog summarizes the difference between the frameworks (client and full) nicely. I could not find a spot that says whether a certain Dll is supported in the client framework or not. I guess the exclamation mark in Visual Studio should be the first signal...
回答1:
You're probably targeting the Client Profile, in which System.Web.dll is not available.
You can target the full framework in project's Properties.
回答2:
You need to add the System.Web reference;
- Right click the "Reference" in the Solution Explorer
- Choose "Add Reference"
- Check the ".NET" tab is selected.
- Search for, and add "System.Web".
回答3:
SLaks has the right answer... but let me be a bit more specific for people, like me, who are annoyed by this and can't find it right away :
Project -> Properties -> Application -> Target Framework -> select ".Net Framework 4"
the project will then save and reload.
回答4:
In order to resolve this, Kindly go to the below path
Project-->Properties-->Application-->TargetFramework
and change the Framework to ".NET Framework 4".
Once you do this, the project will close and re-open.
This should solve the error
(but for some reason @Karan Modi's answer does not...)
next right-click the references tab in the solution explorer and choose add reference,
choose "System.Web"
(declaring the namespace directly by "using System.Web;" doesnt seems to be enough...you have to add it to the solution explorer...i cant understand why - which is no surprise because i am a cobol programmer..
回答5:
After following the answers above , and did
Project -> Properties -> Application -> Target Framework -> select ".Net Framework 4"
It still didn't work until I went to Project -> Add Reference
And selected System.web.
And everything worked link a charm.
回答6:
In order to resolve this, Kindly go to the below path
Project-->Properties-->Application-->TargetFramework
and change the Framework to ".NET Framework 4".
Once you do this, the project will close and re-open.
This should solve the error.
回答7:
Agrega System.web a las referencias del proyecto.
[Edit]
According to Google Translate, this translates to:
Add System.Web to the project references.
回答8:
I had the same problem what I did, I copied web.dll from Microsoft.NET framework, then paste in root of project, then add dll refrence to app, it worked
回答9:
It worked for by following process:
Add Reference:
system.net
system.web
also, include the namespace
using system.net
using system.web
回答10:
Adding a reference to Sysem.Web.Dll did it for me.
来源：https://stackoverflow.com/questions/2405182/httputility-does-not-exist-in-the-current-context