实现方式请参照 SealTalk 中的 ServiceExtension。
具体步骤如下：
给工程添加一个 target ：Notification Service Extension。
主工程开启 Push Notifications 和 Background Modes 功能。
Service Extension target 开启 Push Notifications 功能。
NotificationService.m 中实现 - (void)didReceiveNotificationRequest:(UNNotificationRequest *)request withContentHandler:(void (^)(UNNotificationContent * _Nonnull))contentHandler :
-(void)didReceiveNotificationRequest:(UNNotificationRequest *)request withContentHandler:(void (^)(UNNotificationContent * _Nonnull))contentHandler {
UNNotificationContent *content1 = request.content; NSDictionary *userInfo = content1.userInfo; NSDictionary *aps = [userInfo objectForKey:@"aps"]; NSString *category = [aps objectForKey:@"category"]; if (aps && category && [category isEqualToString:@"RC:RcCmd"]) { NSString *appData = [userInfo objectForKey:@"appData"]; NSDictionary *appDataDic = [NSJSONSerialization JSONObjectWithData:[appData dataUsingEncoding:NSUTF8StringEncoding] options:NSJSONReadingMutableContainers error:nil]; NSString *idString = [appDataDic objectForKey:@"rc-dlt-identifier"]; if (idString) { [[UNUserNotificationCenter currentNotificationCenter] getDeliveredNotificationsWithCompletionHandler:^(NSArray<UNNotification *> * _Nonnull notifications) { if (notifications.count == 0) { dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.2 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{ self.contentHandler = contentHandler; self.bestAttemptContent = [request.content mutableCopy]; self.contentHandler(self.bestAttemptContent); }); return; }
for (UNNotification *notice in notifications) { UNNotificationRequest *request = notice.request; UNNotificationContent *content = request.content; NSDictionary *userInfo1 = content.userInfo; NSString *identifier = userInfo1[@"rc"][@"id"]; if ([idString isEqualToString:identifier]) { [[UNUserNotificationCenter currentNotificationCenter] removeDeliveredNotificationsWithIdentifiers:@[request.identifier]]; } } dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.2 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{ self.contentHandler = contentHandler; self.bestAttemptContent = [request.content mutableCopy]; self.contentHandler(self.bestAttemptContent);
});
}]; } } else { self.contentHandler = contentHandler; self.bestAttemptContent = [request.content mutableCopy]; self.contentHandler(self.bestAttemptContent); } } 撤回消息的推送内容示例：
{ appData = "{"rc-dlt-identifier":"B7EE-8T9S-OI44-8NSS"}"; aps = { alert = { body = "\U4f60\U6536\U5230\U4e86\U4e00\U6761\U6d88\U606f"; }; badge = 2; category = "RC:RcCmd"; "mutable-content" = 1; sound = "aaaaaa.caf"; }; rc = { cType = PR; fId = 1xTlsmAn9; id = "B7EE-918C-GI64-8NSS"; oName = "RC:RcCmd"; sourceType = 0; tId = 1xTlsmAn9; }; richMediaUri = ""; } 其中通过 aps 中的 category 判断是不是撤回消息，如果是撤回消息，appData 中的 rc-dlt-identifier 表示要撤回消息的 id 。
注：
只有公有云支持该功能；
该功能只在 iOS 10 以上有效。
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