為什么UITableView在同時滾動和更新時會丟失對標題標題的跟蹤？

Question

我遇到了一個錯誤，其中表視圖可能會丟失對標題標題的跟蹤，並在其位置創建新的標題標題。 （請參見下圖;右側屏幕截圖顯示丟失的標題。）

雖然我不知道確切原因，但是當我以編程方式滾動表視圖並通過調用“beginUpdates”和“endUpdates”同時更新它時，似乎會發生這種情況。 任何人都可以解釋為什么表視圖失去了節標題的跟蹤？ 什么時候發生這種情況？

下面，我提供了一個演示此問題的視圖控制器的代碼。 代碼顯示一個表視圖，其數據模型是一個字符串數組的數組。 按下添加按鈕時，會向表中添加一個新行並滾動到視圖中。 在添加一小段時間后，新行比其他單元格更高，以顯示它是新添加的單元格。 要重現該錯誤，請按幾次“添加”按鈕，然后滾動到頂部。 （我在4英寸64位iPhone模擬器中對此進行了測試。）

可能導致錯誤的代碼在“ pressedAddButton： ”方法中，因為它是在那里我同時滾動和更新表視圖。 （編輯：許多其他代碼只是用於設置數據模型並為表視圖提供數據源和委托方法的樣板。）

注意：要使代碼運行，請將視圖控制器放在UINavigationController中並顯示導航控制器：

ABCTestViewController * testViewController = [[ABCTestViewController alloc] initWithNibName:nil bundle:nil];
UINavigationController * navigationController = [[UINavigationController alloc] initWithRootViewController:testViewController];
// Now show the navigation controller.

在ABCTestViewController.h中 ：

#import <UIKit/UIKit.h>

@interface ABCTestViewController : UIViewController <UITableViewDataSource, UITableViewDelegate>

@property (weak, nonatomic) UITableView * tableView;

// The data model is an array of arrays of strings.
@property (strong, nonatomic) NSMutableArray * dataModel;

// The special row will be shown as being taller than the other rows.
@property (strong, nonatomic) NSIndexPath * indexPathOfSpecialRow;

@end

在ABCTestViewController.m中 ：

#import "ABCTestViewController.h"

#import <QuartzCore/QuartzCore.h>

@interface ABCTestViewController ()

@end

@implementation ABCTestViewController

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        [self initializeNavigationItem];
        [self initializeDataModel];
    }
    return self;
}

- (void)initializeNavigationItem
{
    self.title = @"Test";

    self.navigationItem.rightBarButtonItem = [[UIBarButtonItem alloc] initWithTitle:@"Add" style:UIBarButtonItemStylePlain target:self action:@selector(pressedAddButton:)];
}

- (void)initializeDataModel
{
    self->_dataModel = [[NSMutableArray alloc] init];

    // Add strings to section 0.
    NSMutableArray * section0 = [[self class] stringsForSection:0 numberOfStrings:2];
    [self.dataModel addObject:section0];

    // Add strings to section 1.
    NSMutableArray * section1 = [[self class] stringsForSection:1 numberOfStrings:10];
    [self.dataModel addObject:section1];
}

// Utility.
+ (NSMutableArray *)stringsForSection:(NSUInteger)section numberOfStrings:(NSUInteger)numberOfStrings
{
    NSMutableArray * strings = [[NSMutableArray alloc] initWithCapacity:numberOfStrings];
    for (NSUInteger i = 0; i < numberOfStrings; ++i) {
        NSString * string = [NSString stringWithFormat:@"%d-%d", section, i];
        [strings addObject:string];
    }
    return strings;
}

- (void)loadView
{
    [super loadView];
}

- (void)viewDidLoad
{
    [super viewDidLoad];

    // Add a table view.
    UITableView * tableView = [[UITableView alloc] initWithFrame:self.view.bounds];
    self.tableView = tableView;
    self.tableView.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
    [self.view addSubview:self.tableView];

    // Configure the table view.
    self.tableView.sectionHeaderHeight = 40;
    self.tableView.allowsSelection = NO;

    self.tableView.dataSource = self;
    self.tableView.delegate = self;
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

// ---------------------

// Event Handers

- (void)pressedAddButton:(id)sender
{
    // Update data model: add a new string to the second section.
    NSUInteger section = 1;
    NSMutableArray * strings = [self.dataModel objectAtIndex:section];
    NSUInteger newStringIndex = strings.count;
    NSString * newString = [NSString stringWithFormat:@"1-%d (New String)", newStringIndex];
    [strings insertObject:newString atIndex:newStringIndex];

    // Update display: add a new row in the table for the newly added string.
    NSIndexPath * indexPath = [NSIndexPath indexPathForRow:newStringIndex inSection:section];
    [self.tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];

    // Scroll to the newly added row.
    [self.tableView scrollToRowAtIndexPath:indexPath atScrollPosition:UITableViewScrollPositionNone animated:YES];

    // After a brief pause, show that the newly added row is "special" by making its height taller than the other rows.
    double delayInSeconds = 0.1;
    dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));
    dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
        // Update display model: set the special row to be the newly added row.
        self.indexPathOfSpecialRow = indexPath;

        // Update display: tell the table view to update the heights of the rows
        // (i.e., tableView:heightForRowAtIndexPath: will be called for each row).
        [self.tableView beginUpdates];
        [self.tableView endUpdates];
    });
}

// ---------------------

// Table View Data Source and Delegate Methods

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
    return self.dataModel.count;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    NSArray * strings = [self.dataModel objectAtIndex:section];

    return strings.count;
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    // Data from the data model.
    NSArray * strings = [self.dataModel objectAtIndex:indexPath.section];
    NSString * string = [strings objectAtIndex:indexPath.row];

    static NSString * const kCellIdentifier = @"Cell";
    UITableViewCell * cell = [tableView dequeueReusableCellWithIdentifier:kCellIdentifier];
    if (cell == nil) {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:kCellIdentifier];
    }

    cell.textLabel.text = string;

    return cell;
}

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
{
    if (self.indexPathOfSpecialRow != nil && [indexPath isEqual:self.indexPathOfSpecialRow]) {
        return tableView.rowHeight * 1.5;
    }
    else {
        return tableView.rowHeight;
    }
}

- (UIView *)tableView:(UITableView *)tableView viewForHeaderInSection:(NSInteger)section
{
    static NSString * const kHeaderIdentifier = @"Header";
    UITableViewHeaderFooterView * headerView = [tableView dequeueReusableHeaderFooterViewWithIdentifier:kHeaderIdentifier];
    if (headerView == nil) {
        headerView = [[UITableViewHeaderFooterView alloc] initWithReuseIdentifier:kHeaderIdentifier];

        // Give the header view a border (need to link to QuartzCore.framework to access layer property of UIView).
        headerView.contentView.layer.borderColor = [UIColor colorWithWhite:0 alpha:0.5].CGColor;
        headerView.contentView.layer.borderWidth = 1;
    }

    headerView.textLabel.text = [NSString stringWithFormat:@"Section %d", section];

    return headerView;
}

@end

Answer 1

我知道我的答案很晚，但我遇到了同樣的問題。 IOS所有系統動畫由CATransaction制作。 我的解決方案是：

[CATransaction begin];

[CATransaction setCompletionBlock:^{
    //scroll view here
}];

[self.tableView beginUpdates];
[self.tableView endUpdates];

[CATransaction commit];

Answer 2

嘗試這個

// Scroll to the newly added row.
[self.tableView scrollToRowAtIndexPath:indexPath atScrollPosition:UITableViewScrollPositionNone animated:YES];

比

[NSTimer scheduledTimerWithTimeInterval:0.1f target:self selector:@selector(loadFetchWithDelay) userInfo:nil repeats:NO];

- (void)loadFetchWithDelay
{    
    self.indexPathOfSpecialRow = indexPath;
    [self.tableView reloadData];
}

Answer 3

以下更新方法可能是它的重復：

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{


   NSString *DataCellId = [NSString stringWithFormat:@"Photo%d%d",indexPath.row,indexPath.section];
        cell = (cell *)[tableView dequeueReusableCellWithIdentifier:DataCellId];
        if(!cell) {
            cell = [[cell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:DataCellId];

        }
   // Data from the data model.
    NSArray * strings = [self.dataModel objectAtIndex:indexPath.section];
    NSString * string = [strings objectAtIndex:indexPath.row];

    cell.textLabel.text = string;

    return cell;
}