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Question

我的代码有一个小问题。 当我尝试在我的应用程序中有两个页面视图控制器时，不断出现以下消息。 两者都被用于不同的事物。 我复制并粘贴了我实现的第一个页面控制器的代码，然后更改了名称以防止发生冲突。 我最近开始收到此错误消息，现在我的程序不再起作用。 谁能告诉我为什么会这样？

我还收到一条错误，指出协议中的方法“ pageViewController：viewControllerBeforeViewController：”未实现。 我不太确定这是否是一个链接问题，但是有人知道我为什么得到这个吗？

#import "StorageViewController.h"
#import "InstructionContentViewController.h"

@interface StorageViewController ()

@end

@implementation StorageViewController


- (void)viewDidLoad
{
        [super viewDidLoad];
        // Create the data model
        _pageInstructTitles = @[@"Over 200 Tips and Tricks", @"Discover Hidden Features", @"Bookmark Favorite Tip", @"Free Regular Update"];
        _pageInstructImages = @[@"instructions1.png", @"instructions2.png", @"instructions3.png", @"instructions4.png"];

        // Create page view controller
        self.instructViewController = [self.storyboard instantiateViewControllerWithIdentifier:@"InstructionViewController"];
        self.instructViewController.dataSource = self;

        InstructionContentViewController *startingInstructViewController = [self viewControllerAtIndex:0];
        NSArray *viewInstructControllers = @[startingInstructViewController];
        [self.instructViewController setViewControllers:viewInstructControllers direction:UIPageViewControllerNavigationDirectionForward animated:NO completion:nil];

        // Change the size of page view controller
        self.instructViewController.view.frame = CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height - 30);

        [self addChildViewController:_instructViewController];
        [self.view addSubview:_instructViewController.view];
        [self.instructViewController didMoveToParentViewController:self];

}

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

- (IBAction)startInstructWalkthrough:(id)sender {

    InstructionContentViewController *startingInstructViewController = [self viewControllerAtIndex:0];
    NSArray *viewControllers = @[startingInstructViewController];
    [self.instructViewController setViewControllers:viewControllers direction:UIPageViewControllerNavigationDirectionReverse animated:NO completion:nil];
}


#pragma mark - Page View Controller Data Source Methods:

- (UIViewController *)instructViewController:(UIPageViewController *)instructViewController viewControllerBeforeViewController:(UIViewController *)viewInstructController
{
    NSUInteger index = ((InstructionContentViewController*) viewInstructController).instructPageIndex;

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

    index--;
    return [self viewControllerAtIndex:index];
}


- (UIViewController *)instructViewController:(UIPageViewController *)instructViewController viewControllerAfterViewController:(UIViewController *)viewInstructController
{
    NSUInteger index = ((InstructionContentViewController*) viewInstructController).instructPageIndex;

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

    index++;
    if (index == [self.pageInstructTitles count]) {
        return nil;
    }
    return [self viewControllerAtIndex:index];
}

- (InstructionContentViewController *)viewControllerAtIndex:(NSUInteger)index
{
    if (([self.pageInstructTitles count] == 0) || (index >= [self.pageInstructTitles count])) {
        return nil;
    }

    // Create a new view controller and pass suitable data.
    InstructionContentViewController *instructionContentViewController = [self.storyboard instantiateViewControllerWithIdentifier:@"InstructionContentViewController"];
    instructionContentViewController.instructImageFile = self.pageInstructImages[index];
    instructionContentViewController.instructTitleText = self.pageInstructTitles[index];
    instructionContentViewController.instructPageIndex = index;

    return instructionContentViewController;


}

- (NSInteger)presentationCountForPageViewController:(UIPageViewController *)instructViewController
{
    return [self.pageInstructTitles count];
}

- (NSInteger)presentationIndexForPageViewController:(UIPageViewController *)instructViewController
{
    return 0;
}



@end