使用LocalAuthentication有问题，支持iOS7.0当我尝试importLocalAuthentication如果目标iOS版本低于8.0，我会崩溃。我试图在构建阶段将LocalAuthentication.framework标记为可选，并通过调用检查类可用性:varisTouchIDSupported:Bool{ifletcontextClass:AnyClass=NSClassFromString("LAContext"){returnLAContext().canEvaluatePolicy(.DeviceOwnerAuthenticationWithBiometr