TableView重新加載，當你離開然後返回

Question

我已經構建了一個使用故事板的iOS 7應用程序。在我的offersViewController內，我有一個UIView和一個UITableView。 UIView作爲一個子視圖，在我的feed被解析的時候顯示一個加載消息。一旦完成子視圖被刪除，我的分析數據呈現在我的UITableView。

@interface OffersViewController() 

@end 

@implementation OffersViewController 
@synthesize loadingView; 

MoreCobaltOffers *currentFeed; 
AppDelegate *appDelegate; 

- (void)viewDidAppear:(BOOL)animated 
{ 
    [self.tableView addSubview:loadingView]; 

    self.navigationItem.titleView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"Navigation"]]; 

    CustomStringParser *customStringParser = [[CustomStringParser alloc] init]; 

    // Download and parse XML data 
    RXMLElement *rxml = [RXMLElement elementFromXMLData:[NSData dataWithContentsOfURL:[NSURL URLWithString:@"http://www.myrssfeed.com"]]]; 

    // Create an reference to AppDelegate 
    appDelegate = [[UIApplication sharedApplication] delegate]; 

    // Create an array to store each feed 
    appDelegate.offersFeeds = [[NSMutableArray alloc] init]; 

    // Loop Through XML Data 
    [rxml iterate:@"channel" usingBlock:^(RXMLElement *supportElement) { 

     [supportElement iterate:@"item" usingBlock:^(RXMLElement *repElement) { 

      // Assign element to string 
      NSString *title = [repElement child:@"title"].text; 
      NSString *subtitle = [repElement child:@"tagline"].text; 
      NSString *description = [repElement child:@"description"].text; 
      NSString *imageurl = [repElement child:@"image"].text; 
      NSString *address = [repElement child:@"address"].text; 

      // Assign element value to MoreCobalt.h propertys 
      currentFeed = [MoreCobaltOffers alloc]; 
      currentFeed.title = title; 
      currentFeed.imageurl = imageurl; 
      currentFeed.addressline = address; 

      // DESCRIPTION FORMATTING 
      description = [customStringParser parseHTML:description]; 
      description = [customStringParser parseLinesMultiple:description]; 
      description = [customStringParser removeSocialSignifiers:description]; 
      description = [customStringParser appendTermsOfUse:description]; 
      currentFeed.description = description; 

      // SUBTITLE FORMATTING 
      subtitle = [customStringParser parseHTML:subtitle]; 
      subtitle = [customStringParser parseLinesSingle:subtitle]; 
      subtitle = [customStringParser removeSocialSignifiers:subtitle]; 
      currentFeed.subtitle = subtitle; 

      // Add a new object to the feeds array 
      [[appDelegate offersFeeds] addObject:currentFeed]; 
     }]; 

     //Remove the loading screen 
     [loadingView removeFromSuperview]; 

     //Show table data, if this is not here the table is empty. 
     [self.tableView reloadData]; 
    }]; 
} 

當我運行應用程序時，加載屏幕出現，然後表中顯示數據。如果我從此視圖控制器導航到另一個選項卡，然後導航回來，表格將閃爍。不太好的用戶體驗。該代碼行是[self.tableView reloadData];。我需要這個或者表格變空。我究竟做錯了什麼？

Answer 1

ViewWillAppear在任何時候視圖出現時被調用。爲了每次不重新載入表，請移動viewDidAppear中的代碼。

對於示出的裝載視圖僅一次解析移動到像另一個方法：

- (void)parseFeed { 
    [self.loadingIndicator startAnimating]; 
    self.loadingIndicator.hidesWhenStopped = YES; 
    self.navigationItem.titleView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"Navigation"]]; 

    CustomStringParser *customStringParser = [[CustomStringParser alloc] init]; 

    // Download and parse XML data 
    RXMLElement *rxml = [RXMLElement elementFromXMLData:[NSData dataWithContentsOfURL:[NSURL URLWithString:@"http://www.morecobalt.co.uk/rss/?t=offers"]]]; 

    // Create an reference to AppDelegate 
    appDelegate = [[UIApplication sharedApplication] delegate]; 

    // Create an array to store each feed 
    appDelegate.offersFeeds = [[NSMutableArray alloc] init]; 

    // Loop Through XML Data 
    [rxml iterate:@"channel" usingBlock:^(RXMLElement *supportElement) { 

     [supportElement iterate:@"item" usingBlock:^(RXMLElement *repElement) { 

      // Assign element to string 
      NSString *title = [repElement child:@"title"].text; 
      NSString *subtitle = [repElement child:@"tagline"].text; 
      NSString *description = [repElement child:@"description"].text; 
      NSString *imageurl = [repElement child:@"image"].text; 
      NSString *address = [repElement child:@"address"].text; 

      // Assign element value to MoreCobalt.h propertys 
      currentFeed = [MoreCobaltOffers alloc]; 
      currentFeed.title = title; 
      currentFeed.imageurl = imageurl; 
      currentFeed.addressline = address; 

      // DESCRIPTION FORMATTING 
      description = [customStringParser parseHTML:description]; 
      description = [customStringParser parseLinesMultiple:description]; 
      description = [customStringParser removeSocialSignifiers:description]; 
      description = [customStringParser appendTermsOfUse:description]; 
      currentFeed.description = description; 

      // SUBTITLE FORMATTING 
      subtitle = [customStringParser parseHTML:subtitle]; 
      subtitle = [customStringParser parseLinesSingle:subtitle]; 
      subtitle = [customStringParser removeSocialSignifiers:subtitle]; 
      currentFeed.subtitle = subtitle; 

      // Add a new object to the feeds array 
      [[appDelegate offersFeeds] addObject:currentFeed]; 
     }]; 
     [loadingView removeFromSuperview]; 
     [self.loadingIndicator stopAnimating]; 
     [self.tableView reloadData]; 
    }]; 
    [loadingView removeFromSuperview]; 
    [self.loadingIndicator stopAnimating]; 
    isFirstLoad = NO; 
} 

聲明一個BOOL判斷是否是第一負載和執行此檢查：

-(void)viewDidAppear:(BOOL)animated { 
    if (isFirstLoad){ 
    [self parseFeed]; 
    } 
    [super viewDidAppear:animated]; 
} 

Answer 2

很少沒有價值的東西：

1. 你應該提取所有的代碼解析你的XML到另一個班級。您不應該在視圖控制器內部解析來自XML的數據。

2. 現在您正在運行網絡調用並在每次出現視圖時解析XML數據。你可能會認爲只有做它時，認爲負載，從而運行你的代碼viewDidLoad

3. 當你最終感動你可以考慮有一個臨時的本地陣列和填充，隨着XML返回值的代碼，然後使用isEqualToArray將其與您的值的屬性進行比較，看看它的不同。如果是，重新加載表並重新設置屬性，如果沒有，則不要。