1. 添加您要安装的 Pod，在 Podfile 中纳入 Pod：

pod 'Firebase/Core'
pod 'Firebase/Messaging'

2. 从 Firebase 控制台中下载一个 GoogleService-Info.plist 文件并将其添加到您的应用中。

将您的 APNs 身份验证密钥上传到 Firebase。如果您还没有 APNs 身份验证密钥，请参阅配置 FCM APNs。

1. 在 Firebase 控制台中，在您的项目内依次选择齿轮图标、项目设置以及云消息传递标签。
2. 在 iOS 应用配置下的 APNs 身份验证密钥中，点击上传按钮。
3. 转到您保存密钥的位置，选择该密钥，然后点击打开。添加该密钥的密钥 ID（可在 Apple 开发者会员中心的 Certificates, Identifiers & Profiles 中找到），然后点击上传。

3. 在 UIApplicationDelegate 中导入 Firebase 模块：

@import  Firebase;
//添加代理
@interface AppDelegate ()<FIRMessagingDelegate,UNUserNotificationCenterDelegate>

4. 在您的应用中初始化 Firebase,配置一个 FirebaseApp 共享实例（通常在应用的 application:didFinishLaunchingWithOptions: 方法中配置）：

// Use Firebase library to configure APIs
[FIRApp configure];
[FIRMessaging messaging].delegate = self;

5. // 注册接收远程通知

    if (@available(iOS 10.0, *)) {
        UNUserNotificationCenter *center = [UNUserNotificationCenter currentNotificationCenter];
        center.delegate = self;
        [center requestAuthorizationWithOptions:(UNAuthorizationOptionBadge | UNAuthorizationOptionSound | UNAuthorizationOptionAlert | UNAuthorizationOptionCarPlay) completionHandler:^(BOOL granted, NSError *_Nullable error) {
            if (!error) {
                NSLog(@"request authorization succeeded!");
            }
        }];
    } else {
        // Fallback on earlier versions
        UIUserNotificationType types = (UIUserNotificationTypeAlert | UIUserNotificationTypeSound | UIUserNotificationTypeBadge);
        UIUserNotificationSettings *settings = [UIUserNotificationSettings settingsForTypes:types categories:nil];
        [[UIApplication sharedApplication] registerUserNotificationSettings:settings];
        [[UIApplication sharedApplication] registerForRemoteNotifications];
    }
    [[UIApplication sharedApplication] registerForRemoteNotifications];

6. 实现的FIRMessaging代理方法

// [END ios_10_message_handling]
// [START refresh_token]
//获取注册令牌
- (void)messaging:(FIRMessaging *)messaging didReceiveRegistrationToken:(NSString *)fcmToken {
    NSLog(@"FCM registration token: %@", fcmToken);
    // Notify about received token.
    NSDictionary *dataDict = [NSDictionary dictionaryWithObject:fcmToken forKey:@"token"];
    [[NSNotificationCenter defaultCenter] postNotificationName:@"FCMToken" object:nil userInfo:dataDict];
    // TODO: If necessary send token to application server.
    // Note: This callback is fired at each app startup and whenever a new token is generated.
}
// [END refresh_token]

// [START ios_10_data_message]
// Receive data messages on iOS 10+ directly from FCM (bypassing APNs) when the app is in the foreground.
// To enable direct data messages, you can set [Messaging messaging].shouldEstablishDirectChannel to YES.
- (void)messaging:(FIRMessaging *)messaging didReceiveMessage:(FIRMessagingRemoteMessage *)remoteMessage {
    NSLog(@"Received data message: %@", remoteMessage.appData);
}
// [END ios_10_data_message]

- (void)application:(UIApplication *)application didFailToRegisterForRemoteNotificationsWithError:(NSError *)error {
    NSLog(@"Unable to register for remote notifications: %@", error);
}

pragma mark - 通知相关方法

// 需要将您的 APNs 令牌明确映射到 FCM 注册令牌

- (void)application:(UIApplication *)application didRegisterForRemoteNotificationsWithDeviceToken:(NSData *)deviceToken {
    //firebase
    [FIRMessaging messaging].APNSToken = deviceToken;
}

//接收通知消息
- (void)application:(UIApplication *)application didReceiveRemoteNotification:(NSDictionary *)userInfo fetchCompletionHandler:(void (^)(UIBackgroundFetchResult))completionHandler {
    NSLog(@"userInfo=%@",userInfo);
    
    // firebase推送
    // Print message ID.
    if (userInfo[kGCMMessageIDKey]) {
        NSLog(@"Message ID: %@", userInfo[kGCMMessageIDKey]);
    }    
    completionHandler(UIBackgroundFetchResultNewData);
    if(application.applicationState==UIApplicationStateInactive){//点击
       [self showClickPushNotice:userInfo];
    }
}

FireBase使用过程注意事项及可能出现的问题

注册令牌会在发生下列情况时更改：
用户卸载/重新安装应用
用户清除应用数据

出现不执行messaging didReceiveRegistrationToken的代理方法原因如下：

1. 这是由于该服务是谷歌提供的，会因为网络问题无法执行代理方法获得token，国内需要使用VPN翻墙工具.
2. pod 'Firebase/Core' 的版本过低，需要pod最新版本，如果pod还是旧版本，可以 如：pod 'Firebase/Core',  '5.15.0'

可以参考Firebase官方文档
Firebase SDK版本