获取 UIPageViewController 当前索引的可靠方法

Question

我正在寻找一种可靠的方法来跟踪 UIPageViewController 当前索引。

这个问题是众所周知的；尽管 viewController 被正确呈现，但很难跟踪当前索引。

我认为在 SO 社区中刷新这个主题会很好，因为它由于某种原因仍未解决

我在这里浏览了许多线程，但大多数答案都已过时或标记为不可靠（结果取决于用户是完全滑动还是仅滑动了一半等）

我访问过这个线程，但它没有提供任何明确正确的答案。

我试过了：

1) 跟踪 viewController 的视图标签 -链接- 总是返回 0

2）查看两个 UIPageViewController 方法中的索引变量，viewControllerBeforeViewController以及viewControllerAfterViewControlle

它的结果是不可预测的，有时它会跳过一个索引等。

有没有人想出一个好方法，可靠的方法来跟踪 UIPageCiewController 索引以利用它（例如打印当前索引）？

我很欣赏 obj-c 和 swift 实现，但 swift 是我正在寻找的。

Answer 1

这是为了ObjC

父视图控制器

#import "PagesViewController.h"

// Delegate: PageViewDelegate
// Declared inside `PagesViewController`
//
@interface ParentViewController () <UIPageViewControllerDataSource, UIPageViewControllerDelegate, PageViewDelegate>

@property (nonatomic) UIPageViewController *pageViewController;

@end

@implementation ViewController

- (void)viewDidLoad 
{
    [super viewDidLoad];

    self.pageViewController = [[UIPageViewController alloc] initWithTransitionStyle:UIPageViewControllerTransitionStyleScroll navigationOrientation:UIPageViewControllerNavigationOrientationHorizontal options:nil];
    self.pageViewController.dataSource = self;
    self.pageViewController.view.frame = self.view.frame;

    // im setting page 3 as the default page
    //
    [self.pageViewController setViewControllers:[NSArray arrayWithObject:[self viewControllerAtIndex:3]] direction:UIPageViewControllerNavigationDirectionForward animated:YES completion:nil];
    [self addChildViewController:self.pageViewController];
    [self.view addSubview:self.pageViewController.view];
}

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerBeforeViewController:(UIViewController *)viewController 
{
    NSUInteger index = [(PagesViewController *)viewController index];

    if (index == 0) {
        return nil;
    }

    index--;

    return [self viewControllerAtIndex:index];
}

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerAfterViewController:(UIViewController *)viewController {

    NSUInteger index = [(PagesViewController *)viewController index];

    index++;

    if (index == 5) {
        return nil;
    }

    return [self viewControllerAtIndex:index];
}

- (PagesViewController *)viewControllerAtIndex:(NSInteger)index
{
    PagesViewController *vc = [[PagesViewController alloc] init];

    // set delegate here..
    //
    vc.delegate = self;

    // other data
    //
    vc.index = index;
    vc.titleLabel = [NSString stringWithFormat:@"Screen :%ld", (long)index];

    return vc;
}

- (NSInteger)presentationCountForPageViewController:(UIPageViewController *)pageViewController 
{ // The number of items reflected in the page indicator. return x; }

- (NSInteger)presentationIndexForPageViewController:(UIPageViewController *)pageViewController
{ // The selected item reflected in the page indicator. return x; }

// This is what you need
//
- (void)viewController:(id)VC didShowWithIndex:(long)index
{
    NSLog(@"didShowWithIndex: %ld", index);
}

PagesViewController.h

@protocol PageViewDelegate <NSObject>

- (void)viewController:(id)VC didShowWithIndex:(long)index;

@end


@interface PagesViewController : UIViewController

@property (weak) id <PageViewDelegate> delegate;

@property (nonatomic) NSInteger index;

@property (nonatomic) NSString *titleLabel;

@end

PagesViewController.m

@implementation PagesViewController

- (void)viewDidLoad
{
    [super viewDidLoad];

    self.view.backgroundColor = [UIColor blackColor];

    UILabel *titleLabel = [[UILabel alloc] initWithFrame:self.view.frame];
    titleLabel.textAlignment = NSTextAlignmentCenter;
    titleLabel.textColor = [UIColor whiteColor];
    titleLabel.text = self.titleLabel;
    [self.view addSubview:titleLabel];
}

// Trigger delegate here
//
- (void)viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];

    [self.delegate viewController:self didShowWithIndex:self.index];
}

@end