一种获取UIPageViewController当前索引的可靠方法 [英] A reliable way to get UIPageViewController current index

问题描述

我正在寻找一种可靠的方式来跟踪UIPageViewController当前索引.

I'm looking for a reliable way to keep track of UIPageViewController current index.

这个问题是众所周知的；尽管viewControllers可以正确显示，但是很难跟踪当前索引.

The problem is well known; Although viewControllers are being presented properly, it hard to keep track of the current index.

我认为最好在整个SO社区中刷新此主题，因为由于某些原因该主题仍未解决

I thought it will be good to refresh this topic across SO community since it remains unsolved for some reason

我在这里浏览了很多主题，但是大多数答案已经过时或标记为不可靠(结果取决于用户是完全滑动还是只滑动了一半等等)

I've browsed through many threads here, but most answers are outdated or marked as unreliable(The result depends on if user did a full swipe or just half swiped etc)

我已经访问过此线程，但是它没有提供任何明确正确的答案.

I've visited this thread, but it doesn't provide any explicitly correct answer.

我尝试过:

1)跟踪viewController的视图标签-链接-始终返回0

1) Keeping track of viewController's view tag - link - always returns 0

2)在两个UIPageViewController方法viewControllerBeforeViewController和viewControllerAfterViewControlle

2) Looking at index variable in both UIPageViewController methods, viewControllerBeforeViewController and viewControllerAfterViewControlle

其结果不可预测，有时会跳过一个索引，等等.

its results is unpredictable, sometimes it skips over one index etc.

是否有人想出一种很好的方法来跟踪UIPageCiewController索引以利用它(例如打印当前索引)?

我很欣赏obj-c和swift的实现，但是swift是我想要的.

I'd appreciate both obj-c and swift implementation, but swift is the one I'm looking for.

推荐答案

这是针对ObjC

ParentViewController

ParentViewController

#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

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

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

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