我遇到了一个错误，表格视图可能会丢失部分标题，在其位置创建一个新的部分标题。（见下图；右边的屏幕截图显示了丢失的标题。）
虽然我不知道确切的原因，但当我以编程方式滚动表格视图并通过调用“beginUpdates”和“endUpdates”同时更新它时，似乎会发生这种情况。谁能解释为什么表格视图会丢失部分标题？这究竟是什么时候发生的？
下面，我提供了演示此问题的视图控制器的代码。该代码显示了一个表视图，其数据模型是一个字符串数组。当您按下添加按钮时，会在表格中添加一个新行并滚动到视图中。在添加了片刻之后，新行将变得比其他单元格高，以表明它是新添加的单元格。要重现该错误，请按几次“添加”按钮，然后滚动到顶部。（我在 4 英寸 64 位 iPhone 模拟器中对此进行了测试。）
可能导致该错误的代码在“ pressedAddButton: ”方法中，因为它在那里我同时滚动和更新表格视图。（编辑：许多其他代码只是设置数据模型并为表视图提供数据源和委托方法的样板。）
注意：要运行代码，请将视图控制器放在 UINavigationController 中并显示导航控制器：
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