我正在try 将我的应用升级到Firebase的新版本.我阅读了安装指南，编辑了所有代码，以匹配新语法.然而，当我运行应用程序时，我会出现以下两个错误.
The default app has not been configured yet.
Terminating app due to uncaught exception 'MissingDatabaseURL', reason: 'Failed to get FIRDatabase instance: FIRApp object has no databaseURL in its FirebaseOptions object.'
我在AppDelegate中有FIRApp.configure()个，我有谷歌服务信息.plist导入到我的项目中.plist也有所有正确的信息.还有谁遇到这个问题或者知道怎么解决吗？
以下是你问题的答案:
你必须在某个地方配置Firebase FIRApp.configure().完成后，可以使用let firebaseDatabaseReference = FIRDatabase.database().reference()获取对该数据库的引用并开始使用它.问题不在于Firebase本身，而在于Swift的行为.
如果在AppDelegate func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool中放入FIRApp.configure()，然后在MyDatabase class中使用let firebaseDatabaseReference = FIRDatabase.database().reference() outside个已声明函数sometimes，则代码FIRDatabase.database().reference()在执行application didFinishLaunchingWithOptions函数之前执行.
基本上，您的类正在try 获取对Firebase数据库before的引用，它有机会自行配置，并在控制台中生成错误"默认应用尚未配置"
Note: This doesn't happen all the time, sometimes the application is slow to start, in iOS Simulator for example, and it doesn't have a chance to finish before MyDatabase "let" executes and tries to get a reference.
这就是为什么要移动FIRApp.configure()代码覆盖AppDelegate中的init()，本质上它确保在初始化AppDelegate时执行configure代码(在这种和大多数情况下，在初始化MyDatabase之前)
override init() {
super.init()
FIRApp.configure()
// not really needed unless you really need it FIRDatabase.database().persistenceEnabled = true
}
还要确保你超棒.init().