需要帮助在故事板上的 UIScrollView / UIPageControl 中推送视图

Question

我正在尝试在情节提要上使用 UIPageControl 实现 UIScrollView 以显示多个视图。我发现的所有示例、教程或信息都使用 xib 而不是故事板。我试图改编 Apple 的示例代码，但我遗漏了一些东西。如您所见，这很简单。

但是，当我测试 if (controller.view.superview == nil) 我推送视图的地方（见下文前半部分代码）。

或者只有 UIScrollView 和 UIPageControl 工作，我无法在 UIScrollView 中推送视图：

我知道这是一个简单的问题，但是我花了很多时间来解决这个问题，我们将不胜感激。

我发布了完整的代码，因为当它像一种教程一样解决时可能会对某人有所帮助。如果/需要时，我会根据贡献更正代码。

提前致谢

AppDelegate.h

// Nothing special as I don't want to manage it through application delegate
@interface AppDelegate : UIResponder <UIApplicationDelegate>
@property (strong, nonatomic) UIWindow *window;
@end

AppDelegate.m

// Nothing special as I don't want to manage it through application delegate
#import "AppDelegate.h"

@implementation AppDelegate

@synthesize window = _window;
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    return YES;
}

- (void)applicationWillResignActive:(UIApplication *)application { }

- (void)applicationDidEnterBackground:(UIApplication *)application { }

- (void)applicationWillEnterForeground:(UIApplication *)application { }

- (void)applicationDidBecomeActive:(UIApplication *)application { }

- (void)applicationWillTerminate:(UIApplication *)application { }

@end

ContentController.h

// From Apple's PageControl sample code
#import <UIKit/UIKit.h>

@interface ContentController : UIViewController <UIScrollViewDelegate> {
    UIScrollView *scrollView;
    UIPageControl *pageControl;
    NSMutableArray *viewControllers;
    BOOL pageControlUsed;
}

@property (nonatomic, retain) IBOutlet UIScrollView *scrollView;
@property (nonatomic, retain) IBOutlet UIPageControl *pageControl;
@property (nonatomic, retain) NSMutableArray *viewControllers;

- (IBAction)changePage:(id)sender;

@end

ContentController.m

// From Apple's PageControl sample code

#import "AppDelegate.h"
#import "ContentController.h"
#import "MyViewController.h"

// Private methods
@interface ContentController (PrivateMethods)
- (void)loadScrollViewWithPage:(int)page;
- (void)scrollViewDidScroll:(UIScrollView *)sender;
@end

@implementation ContentController

@synthesize scrollView, pageControl, viewControllers;

static NSUInteger kNumberOfPages = 6;

- (void)viewDidLoad {
    [super viewDidLoad];

    // Do any additional setup after loading the view, typically from a nib.
    self.navigationController.navigationBar.hidden=YES;

    // view controllers are created lazily in the meantime, load the array with
    // placeholders which will be replaced on demand
    NSMutableArray *controllers = [[NSMutableArray alloc] init];
    for (unsigned i = 0; i < kNumberOfPages; i++) {
        [controllers addObject:[NSNull null]];
    }
    self.viewControllers = controllers;

    // a page is the width of the scroll view
    scrollView.pagingEnabled = YES;
    scrollView.contentSize = CGSizeMake(scrollView.frame.size.width * kNumberOfPages, scrollView.frame.size.height);
    scrollView.showsHorizontalScrollIndicator = NO;
    scrollView.showsVerticalScrollIndicator = NO;
    scrollView.scrollsToTop = NO;
    scrollView.delegate = self;

    pageControl.numberOfPages = kNumberOfPages;
    pageControl.currentPage = 0;

    // pages are created on demand
    // load the visible page
    // load the page on either side to avoid flashes when the user starts scrolling
    [self loadScrollViewWithPage:0];
    [self loadScrollViewWithPage:1];
}

- (void)viewDidUnload {
    [super viewDidUnload];

    // Release any retained subviews of the main view.
    // e.g. self.myOutlet = nil;
    self.pageControl=nil;
    self.pageControl = nil;
    self.viewControllers = nil;
}

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];
}

- (void)viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];
}

- (void)viewWillDisappear:(BOOL)animated {
    [super viewWillDisappear:animated];
}

- (void)viewDidDisappear:(BOOL)animated {
    [super viewDidDisappear:animated];
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation {
    // Return YES for supported orientations
    return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Release any cached data, images, etc that aren't in use.
}

- (void)loadScrollViewWithPage:(int)page {
    if (page < 0)
        return;
    if (page >= kNumberOfPages)
        return;

    // replace the placeholder if necessary
    MyViewController *controller = [viewControllers objectAtIndex:page];

    if ((NSNull *)controller == [NSNull null]) // <== *** HERE SEEMS TO BE THE ERROR ***
    {
        controller = [[MyViewController alloc] initWithPageNumber:page
                                                  initWithNibName:nil
                                                           bundle:nil];

        [viewControllers replaceObjectAtIndex:page withObject:controller];
    }

    // add the controller's view to the scroll view
    if (controller.view.superview == nil)
    {
        CGRect frame = scrollView.frame;
        frame.origin.x = frame.size.width * page;
        frame.origin.y = 0;
        controller.view.frame = frame;
        [scrollView addSubview:controller.view];
    }
}

- (void)scrollViewDidScroll:(UIScrollView *)sender {
    // We don't want a "feedback loop" between the UIPageControl and the scroll delegate in
    // which a scroll event generated from the user hitting the page control triggers updates from
    // the delegate method. We use a boolean to disable the delegate logic when the page control is used.
    if (pageControlUsed) {
        // do nothing - the scroll was initiated from the page control, not the user dragging
        return;
    }

    // Switch the indicator when more than 50% of the previous/next page is visible
    CGFloat pageWidth = scrollView.frame.size.width;
    int page = floor((scrollView.contentOffset.x - pageWidth / 2) / pageWidth) + 1;
    pageControl.currentPage = page;

    // load the visible page and the page on either side of it (to avoid flashes when the user starts scrolling)
    [self loadScrollViewWithPage:page - 1];
    [self loadScrollViewWithPage:page];
    [self loadScrollViewWithPage:page + 1];

    // A possible optimization would be to unload the views+controllers which are no longer visible
}

// At the begin of scroll dragging, reset the boolean used when scrolls originate from the UIPageControl
- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView {
    pageControlUsed = NO;
}

- (IBAction)changePage:(id)sender {
    int page = pageControl.currentPage;

    // load the visible page and the page on either side of it (to avoid flashes when the user starts scrolling)
    [self loadScrollViewWithPage:page - 1];
    [self loadScrollViewWithPage:page];
    [self loadScrollViewWithPage:page + 1];

    // update the scroll view to the appropriate page
    CGRect frame = scrollView.frame;
    frame.origin.x = frame.size.width * page;
    frame.origin.y = 0;
    [scrollView scrollRectToVisible:frame animated:YES];

    // Set the boolean used when scrolls originate from the UIPageControl. See scrollViewDidScroll: above.
    pageControlUsed = YES;
}

@end

MyViewController.h

#import <UIKit/UIKit.h>

@interface MyViewController : UIViewController {
    UILabel *pageNumberLabel;
    int pageNumber;
}

@property (nonatomic, retain) IBOutlet UILabel *pageNumberLabel;

- (id)initWithPageNumber:(int)page initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil;

@end

MyViewController.m

#import "MyViewController.h"

@implementation MyViewController

@synthesize pageNumberLabel;

- (void)loadView {
}

- (void)viewDidLoad {
    [super viewDidLoad];

    // Set the label and background color when the view has finished loading
    pageNumberLabel.text = [NSString stringWithFormat:@"Page %d", pageNumber + 1];
}

- (void)viewDidUnload {
    [super viewDidUnload];
    // Release any retained subviews of the main view.
    // e.g. self.myOutlet = nil;
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation {
    // Return YES for supported orientations
    return (interfaceOrientation == UIInterfaceOrientationPortrait);
}

// Load the view nib and initialize the pageNumber ivar
// classic initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
// class adapted to init the page number
// /!\ be careful, I'm not sure it's working properly
- (id)initWithPageNumber:(int)page initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil {
    pageNumber = page;
    NSLog(@"pageNumber = %i", pageNumber);
}

- (void)didReceiveMemoryWarning {
// Releases the view if it doesn't have a superview.
[super didReceiveMemoryWarning];
// Release any cached data, images, etc that aren't in use.
}

@end

Answer 1

发生无法识别的选择器错误是因为您在 loadScrollViewWithPage 的 if 语句中重新声明了局部变量“控制器”：因为您这样做了，所以新的控制器变量仅存在于 if 语句的范围内，并且当您退出时if 语句该范围之外的控制器变量仍然是 NSNull。

您可以通过删除 if 语句中的变量定义来修复：

if ((NSNull *)controller == [NSNull null])
{
    controller = [self.storyboard instantiateViewControllerWithIdentifier:@"MVC"];
    [controller initWithPageNumber:page];

    [viewControllers replaceObjectAtIndex:page withObject:controller];
}

Answer 2

所以我遇到了和你一样的问题，但我只是做了一些可能效果很好的事情。

简短的回答是对 Jonkroll 关于在 if 语句中启动控制器的回答的补充。出于某种原因，我无法解释空占位符不为空，因此 if 语句不会像您在代码中指出的那样执行。所以我所做的是修改 if 并将 else 添加到相同的 if 并从情节提要加载 ViewController。

if ((NSNull *)controller == [NSNull null]) {
        controller = [self.storyboard instantiateViewControllerWithIdentifier:@"MVC"];        
        [viewControllers replaceObjectAtIndex:page withObject:[controller initWithPageNumber:page]];
}
else {
        controller = [self.storyboard instantiateViewControllerWithIdentifier:@"MVC"];        
        [viewControllers replaceObjectAtIndex:page withObject:[controller initWithPageNumber:page]];
}

我的其余代码与您的完全相同。我知道这不是有史以来最好的代码，我可能只需在没有 if/else 语句的情况下启动 ViewController 就可以了，但我不知道为什么需要这样做，或者最糟糕的是为什么实际上没有按我预期的那样工作.如果有人知道，请分享。

Answer 3

首先，感谢这个帖子，它确实是一种教程或对我的参考。

我所做的一切几乎和你一样，除了在内容控制器中我输入了以下代码（基于@jonkroll 的回答）：

    if ((NSNull *)controller == [NSNull null]){
    controller = [[self.storyboard instantiateViewControllerWithIdentifier:@"MyViewController"] initWithPageNumber:page initWithNibName:nil bundle:nil];
    [viewControllers replaceObjectAtIndex:page withObject:controller];
}

MyViewController（在我的例子中具有不同的名称，但没有相关性）继承自 UITableViewController，因为它是我需要的东西。 我的 initWithPageNumber 方法如下所示：

    - (id)initWithPageNumber:(int)page initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil {
pageNumber = page;
NSLog(@"PageNumber = %i", pageNumber);
return self;

}

添加了return.self，注意这一点。

最后一件事是，我通过编辑器->嵌入->导航控制器将 ContentController 嵌入到导航控制器中。

这几乎就是一切。后来，我什至设法从 MyViewController 导航到另一个视图，一切正常。

如果您需要进一步的帮助，您可以在这里提问。

问候。

Answer 4

当我尝试遵循 Apple Documents 中的 UIPageController 示例代码时，我遇到了同样的问题。因为我以编程方式完成了 MyViewController，所以我直接使用以下代码

if ((NSNull *)controller == [NSNull null])
{
  MyViewController * controller = [[MyViewController alloc]init];
  [viewControllers replaceObjectAtIndex:page withObject:controller];
}

我在 MyViewController 中什么也没做。