Cannot open new .mdf file to C# project

I cannot attach a new Service based database(.mdf) to a C# project that I started. It shows开发者_开发百科:

Connections to SQL Server Database file(.mdf) require sql server 2008 express to be installed and running on a local computer.The current version of the SQL express can be downloaded.

But I already have SQl Server 2008 R2 installed.I've learned that a .mdf file cannot be "just" attached if the SQl server is a full version, then do I have to create a new database to accomplish the task?Or is there anything else that I can do?

As it's mentioned by Mostafa you should go to Tools->Options->Database Tools->Data Connections->SQL Server Instance Name and blank the SQLEXPRESS in that field. actually there is no need for instance name just blank it.

Use the VS 2010 menu Tools/Connect to database and, in the dialog that opens, fill the field "Attach a database file". AFAIK it's a known problem of VS 2010.

The visual studio has a default sql server instance name to connect to. The installer sets it up to point to the SQL Server Express by default. You have to change the Tools->Options->Database Tools->Data Connections->SQL Server Instance Name to point to your installed SQL Server instance name.