在iOS中定期在後臺線程中運行任務

Question

我是iOS新手。我正在研究應用程序需要在後臺線程中運行從服務器獲取數據的任務，因爲我不想在主線程中鎖定UI。這個任務將需要很長時間，我嘗試使用NSTimer，但它仍然鎖定用戶界面。我的任務是在聊天屏幕中查看新消息，我需要每5秒調用一次這個任務。如果我使用NSTimer，當輸入文本時，文本似乎在執行此任務時凍結一會兒。有沒有辦法在沒有鎖定UI的情況下處理這個任務。請給我一些建議。非常感謝。

==更新代碼==

- (void)performBackgroundTask 
{ 
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ 
     //Do background work 

     if([[NSUserDefaults standardUserDefaults] boolForKey:@"LoggedIn"]) { 
      NSDictionary * userDictionary = [[NSUserDefaults standardUserDefaults] dictionaryForKey:@"SessionDictionary"]; 

      NSString *authenKey= [userDictionary valueForKey:@"authToken"]; 

      NSString* limit = @"1000"; 

      [[LSDataManager sharedDataManager] getLatestMessagesWithAuthKey:authenKey andLimit:limit withBlock:^ (NSDictionary* responseDict) 
      { 
       if (responseDict) { 
        [self loadDataFromServer:responseDict]; 

        NSArray* lastMessageArray= nil; 

        //filter message data 
        if (self.MessagesArray.count >0) { 

         if (!self.isSeller) { 

          lastMessageArray = [self filterMessageData:self.MessagesArray withProductID:self.productID withSellerID:self.receiverID withBuyerID:self.senderID]; 
         } 
         else 
         { 
          lastMessageArray = [self filterMessageData:self.MessagesArray withProductID:self.productID withSellerID:self.senderID withBuyerID:self.receiverID]; 
         } 

         NSLog(@"filter array %@",lastMessageArray); 

         if([lastMessageArray count] >0){ 
          //[self loadMessages:lastMessageArray]; 
          if (self.TempdataSource == nil) { 
           self.TempdataSource = [NSMutableArray array]; 
          } 
          else 
          { 
           [self.TempdataSource removeAllObjects]; 
          } 

          self.TempdataSource = [[[ContentManager sharedManager] generateConversation:lastMessageArray withSenderID:self.senderID] mutableCopy]; 

         } 
        } 
       } 
      }]; 
     } 


     dispatch_async(dispatch_get_main_queue(), ^{ 
      //Update UI 

      //compare 2 arrays 
      if ([self.TempdataSource count] == [self.dataSource count]) { 
       NSLog(@"both are same"); 
      } 
      else{ 
       NSLog(@"both are different"); 
       self.dataSource = [self.TempdataSource mutableCopy]; 

       [self refreshMessages]; 
      } 

     }); 
    }); 
} 

Answer 1

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^(void){ 
    //Background Thread 
    dispatch_async(dispatch_get_main_queue(), ^(void){ 
     //Run UI Updates 
    }); 
}); 

試試這個

Answer 2

安排使用一個NSTimer確實是正確的方式去的任務。你只需要確保你在後臺線程上運行沉重的非UI代碼。下面是一個例子

- (void)viewDidLoad { 
    [super viewDidLoad];  
    [self startTimedTask]; 
} 

- (void)startTimedTask 
{ 
    NSTimer *fiveSecondTimer = [NSTimer scheduledTimerWithTimeInterval:5.0 target:self selector:@selector(performBackgroundTask) userInfo:nil repeats:YES]; 
} 

- (void)performBackgroundTask 
{ 
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ 
     //Do background work 
     dispatch_async(dispatch_get_main_queue(), ^{ 
      //Update UI 
     }); 
    }); 
}