how to run nopcommerce in visual studio without publish

when I want to run(debug)my project in visual studio(offline),it throw an error "throw new ApplicationException("No database instance");"
how to fix it?

Make sure that Nop.Web is the startup project for the solution.  When you Run, the Install page should come up - where you enter the DB info.

it will show this error:
System.ApplicationException: 'No database instance'

See https://www.nopcommerce.com/boards/t/35329/no-database-instance.aspx

If you are expecting to connect to a local DB, and you've not yet done so and you want to do an "install", then be sure that there is no Settings.txt (or InstalledPlugins.txt) in the \App_Data folder.