问使用Firebase时使用无法解析的标识符'FIRDatabase‘

EN

import UIKit
import Firebase

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?

    func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
        FIRApp.configure()
        FIRDatabase.database().persistenceEnabled = true // Use of unresolved identifier 'FIRDatabase'
        return true
    }
}

source 'https://github.com/CocoaPods/Specs.git'
platform :ios, '8.0'
use_frameworks!

target 'myapp' do
pod 'IQKeyboardManagerSwift', '<= 4.0.0'
pod 'JSQMessagesViewController', '<= 7.3.1'
pod 'Firebase'
end