Codesign error ,What can I do?

When I debug my application on device,i开发者_如何学Ct alert the info " Codesign error: no certificate was found in your keychain for the specified identifier "(null)"

You may not have an application identifier set. Make sure that in your Target Settings > Properties, you have a valid reverse DNS identifier (com.apple.myapp, for example) entered into your Identifier field. Also make sure your Code Signing Identity is set to the correct certificate (Target Settings > Build).