Question

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

这个问题众所周知;尽管正确显示了viewControllers，但很难跟踪当前索引。

我认为在SO社区中更新此主题会很好，因为它仍然由于某种原因尚未解决

我在这里浏览了很多帖子，但大多数答案都已过时或标记为不可靠（结果取决于用户是否进行了完全滑动或只是半滑等）

我已访问this帖子，但它没有提供任何明确正确的答案。

我试过了：

1）跟踪viewController的视图标记 - link - 始终返回0

2）在UIPageViewController方法中查看索引变量viewControllerBeforeViewController和viewControllerAfterViewControlle

其结果无法预测，有时会跳过一个索引等。

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

我很欣赏obj-c和swift的实现，但很快就是我正在寻找的。

Answer 1

与@ 0yeoj建议一样，委托设计模式就是解决方案。它需要在盒子外面思考一下。

让我们添加协议IndexDelegate并修改一下PageContentViewController

protocol IndexDelegate {
func showIndex(index:Int)
 }

import UIKit

class PageContentViewController: UIViewController {

@IBOutlet weak var imageView: UIImageView!
var delegate:IndexDelegate?
var pageIndex:Int = 0
var imageFile:String!
override func viewDidLoad() {
    super.viewDidLoad()
    self.imageView.image = UIImage(named: self.imageFile)
    }
override func viewDidAppear(animated: Bool) {
    self.delegate!.showIndex(self.pageIndex)
    }

现在在我们的父视图控制器中，我们符合协议

func showIndex(index: Int) {
  print(index)
  }

不要忘记设置yourPageContentViewControllerInstance.delegate = self 并继承协议YourParentViewController:UIViewController, UIPageViewControllerDataSourceDelegate, IndexDelegate {}

那就是它！工作完美可靠，并且完全没有延迟！

Answer 2

这适用于ObjC

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

@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

获取UIPageViewController当前索引的可靠方法

2 个答案: