When editing C# files, Source Insight can perform symbol completion for the .NET Framework class library symbols. This is accomplished by importing symbols from the .NET Framework assemblies on your machine.
To import the .NET Framework assemblies, use the Project > Import External Symbols command, or use the Preferences: Symbol Lookups dialog box and click the Import Symbols button.
To import .NET Framework symbols:
1.In the Options > Preferences: Symbol Lookups dialog box, click the Import Symbols button.
2.In the Import External Symbols dialog box, click on the Add... button. Click next on Import a directory tree of .NET assemblies. Navigate to the directory that contains the .NET Framework assemblies. This is typically in a location like C:\Windows\Microsoft.NET\Framework\v2.0.50727. Select the directory and click OK.
3.The directory tree containing .NET dlls will be scanned and symbol declarations will be extracted into a special project called an import library. This may take a few minutes since there are many .NET Framework assemblies.
Now, auto-complete should work for the packages that have been imported into the C# source file using the using statement.