ios - 需要帮助在 Storyboard上推送 UIScrollView/UIPageControl 中的 View

Question

我正在尝试在 Storyboard上使用 UIPageControl 实现 UIScrollView 以显示多个 View 。我找到的所有示例、教程或信息都使用 xib 而不是 Storyboard。我试图改编 Apple 的示例代码，但我遗漏了一些东西。如您所见，它非常简单。

但是，当我测试 if (controller.view.superview == nil) 我在其中推送 View (请参阅上半部分代码后的下方)。

或者只有 UIScrollView 和 UIPageControl 在工作，我无法在 UIScrollView 中推送 View :

我知道这是一个简单的问题，但是我在这个问题上花了很多时间，我们将不胜感激。

我发布了完整的代码，因为它可能会像一种教程一样解决问题时对某人有所帮助。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 语句中重新声明了您的局部变量“controller”:因为您这样做，所以新的 Controller 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 Controller 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];
}