停止 UITableView 在方向更改时重新加载数据

Posted 2023-03-04

【中文标题】停止 UITableView 在方向更改时重新加载数据

【英文标题】：Stop a UITableView from reloading data on orientation change

【发布时间】：2013-12-19 09:48:27

【问题描述】：

当设备的方向发生变化时，我的uitableview 调用reloaddata（这是有道理的，因为显示的单元格数量发生了变化，据我从文档中可以理解，在布局子视图中调用），但是这是有问题的对我来说，因为我在后台执行下载，我不希望某些文件突然出现。有没有办法停止默认行为并让我在需要时手动重新加载？

编辑： 我会尽力解释得更好。在我的 tableview 顶部，我有一个名为“sync”的按钮，它从服务器启动一个同步请求，这个同步请求首先得到一个 JSON 对象，它包含我想在 tableview 中显示的信息，但是每个uitableview items 代表我从 Internet 下载的文件。

在下载文件时，屏幕上有一个活动指示器，只有在文件下载完成后，我才想重新加载表格。问题是，UITableview 在用户改变方向时会自动调用reloaddata，所以在下载的文件完成下载之前，单元格会填充来自 json 的信息。

代码：

@implementation BIDManageFilesViewController

- (id)initWithStyle:(UITableViewStyle)style

    self = [super initWithStyle:style];
    if (self) 
        // Custom initialization
    
    return self;


- (void)viewDidLoad

    [super viewDidLoad];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(newDataFinishedDownloading) name:kBIDContentManagerContentDidChangeNotification object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(newDataStartedDownloading:) name:kBIDContentManagerStartedDownloadingContent object:nil];
     [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(contentAlreadyUpToDate) name:kBIDContentUpToDate object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(contentStartingSync) name:kBIDContentStartingSync object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(contentEndingSync) name:kBIDContentEndingSync object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(singleDownloadFinished) name:kBIDFinishedDownloadingSingleContent object:nil];
    self.navigationController.navigationBarHidden = NO;
    UIBarButtonItem *leftButton = [[UIBarButtonItem alloc] initWithTitle:@"Sync"
                                                                    style:UIBarButtonItemStyleDone target:self action:@selector(Sync)];
    self.navigationItem.leftBarButtonItem = leftButton;
    UIBarButtonItem *rightButton = [[UIBarButtonItem alloc] initWithTitle:@"Display Mode"
                                                                   style:UIBarButtonItemStyleDone target:self action:@selector(dismissSelf)];
    self.navigationItem.rightBarButtonItem = rightButton;

    self.navigationItem.title = @"Content Manager";
    self.navigationBar = [[UINavigationBar alloc] initWithFrame:CGRectZero];
    [self.view addSubview:_navigationBar];
    [self.navigationBar pushNavigationItem:self.navigationItem animated:NO];


-(void)viewWillAppear:(BOOL)animated

    [super viewWillAppear:animated];
    [[UIApplication sharedApplication] setStatusBarHidden:NO withAnimation:UIStatusBarAnimationFade];


-(void)layoutNavigationBar
    if([[UIApplication sharedApplication] statusBarOrientation] == UIInterfaceOrientationPortrait || [[UIApplication sharedApplication] statusBarOrientation] == UIInterfaceOrientationPortraitUpsideDown)
    
    self.navigationBar.frame = CGRectMake(0, self.tableView.contentOffset.y, self.view.frame.size.width, self.topLayoutGuide.length + 44);
    
    else
    
        self.navigationBar.frame = CGRectMake(0, self.tableView.contentOffset.y, self.view.frame.size.height, self.topLayoutGuide.length + 44);
    
    NSLog(@"width: %f", self.view.frame.size.width);
    NSLog(@"height: %f", self.view.frame.size.height);
    self.tableView.contentInset = UIEdgeInsetsMake(self.navigationBar.frame.size.height, 0, 0, 0);


-(void)scrollViewDidScroll:(UIScrollView *)scrollView
    //no need to call super
    [self layoutNavigationBar];

-(void)willRotateToInterfaceOrientation:(UIInterfaceOrientation)toInterfaceOrientation duration:(NSTimeInterval)duration

    [self layoutNavigationBar];
    [super willRotateToInterfaceOrientation:toInterfaceOrientation duration:duration];


-(void)viewDidLayoutSubviews
    [super viewDidLayoutSubviews];
    [self layoutNavigationBar];

- (void)didReceiveMemoryWarning

    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.





/*
#pragma mark - Navigation

// In a story board-based application, you will often want to do a little preparation before navigation
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender

    // Get the new view controller using [segue destinationViewController].
    // Pass the selected object to the new view controller.


 */
-(void)viewDidDisappear:(BOOL)animated

    [super viewDidDisappear:animated];
    self.navigationController.navigationBarHidden = YES;


-(void)newDataStartedDownloading: (NSNotification *)notif

    self.hud = [MBProgressHUD showHUDAddedTo:self.view animated:YES];
    _hud.labelText = @"Downloading...";
    _hud.detailsLabelText = [NSString stringWithFormat:@"1/%@",[notif.userInfo objectForKey:@"downloadFileNumber"]];


-(void)singleDownloadFinished

    NSString *currentText = _hud.detailsLabelText;
    NSArray *subStrings = [currentText componentsSeparatedByString:@"/"];
    NSInteger downloadsPlusOne = [[subStrings objectAtIndex:0] integerValue]+1;
    NSString *newTextForLabel = [NSString stringWithFormat:@"%d/%@", downloadsPlusOne, [subStrings objectAtIndex:1]];
    _hud.detailsLabelText = newTextForLabel;

-(void)newDataFinishedDownloading

    _thereIsNewInfo = TRUE;
    [MBProgressHUD hideHUDForView:self.view animated:YES];
    [self.tableView reloadData];
    [[NSNotificationCenter defaultCenter] postNotificationName:kBIDnewDownloadedContentReadyToBeDispayedNotification object:nil userInfo:nil];


-(void)contentAlreadyUpToDate

    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Sync Alert"
                                                    message:@"Files Are Already Up To Date"
                                                   delegate:nil
                                          cancelButtonTitle:@"OK"
                                          otherButtonTitles: nil];
    [alert show];


-(void)contentStartingSync

    MBProgressHUD *hud = [MBProgressHUD showHUDAddedTo:self.view animated:YES];
    hud.labelText = @"Syncing...";


-(void)contentEndingSync

     [MBProgressHUD hideHUDForView:self.view animated:YES];


-(void)Sync

    [AppDelegate.appContentManager downloadContent];

-(void)dismissSelf

    if (![AppDelegate.appContentManager subsetArrayFromFileArrayWithNonVidContentThatShouldDisplay] && ![AppDelegate.appContentManager subsetArrayFromFileArrayWithVideoContentThatShouldDisplay]) 
        UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"No Files to Display"
                                                        message:@"Please update or enable content"
                                                       delegate:nil
                                              cancelButtonTitle:@"OK"
                                              otherButtonTitles: nil];
        [alert show];
        return;
    
    else if ([AppDelegate.appContentManager subsetArrayFromFileArrayWithNonVidContentThatShouldDisplay])
    
        [self dismissViewControllerAnimated:YES completion:Nil];

    
    else
    
    [self performSegueWithIdentifier:@"goToVideos" sender:self];
    

-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender

    if ([segue.identifier isEqualToString:@"goToVideos"])
    
        ((BIDViewController *)segue.destinationViewController).stackedByManager = TRUE;
    



@end

【问题讨论】：

我不明白表格视图与下载文件有什么关系。您能否更好地解释问题或显示一些代码？

【参考方案1】：

没有必要在方向改变时重新加载数据，但是如果你想重新加载表格，请在后台下载完成后尝试调用 [myTable reloadData] 并且只有在方向改变时（你可以在 orient.改变）。

【讨论】：

反之，我不希望它重新加载方向变化的数据。

tableview 不会在方向改变时自动重新加载数据。也许你将它设置在 didRotateFromInterfaceOrientation 上。请粘贴您的代码，以便我提供更好的帮助！