request.predicate = NSPredicate(format: "username = %@", txtUserName.text!)

request.predicate = NSPredicate(format: "username = %@ AND password = %@", txtUserName.text!, txtPassword.text!)

let p1 = NSPredicate(format: "username = %@", "user")
let p2 = NSPredicate(format: "password = %@", "password")
let predicate = NSCompoundPredicate(andPredicateWithSubpredicates: [p1, p2])

request.predicate = NSPredicate(format: "username = %@ AND password = %@", txtUserName.text!, txtPassWord.text!)