2

我正在开发一个非常简单直接的应用程序，它使用几个带有滚动视图的页面。我在 ViewDidLoad 中有一个图像数组，然后是一个可变数组，显示当前页面加减 1。有一个清除页面方法应该从超级视图中删除额外的图像。在具有大量图像的实际设备上运行此程序时，滚动浏览 50 左右图像后会出现内存警告，然后应用程序崩溃。我通过仪器运行了这个，发现每次滑动都会显着增加内存。在创建数组时，我使用了 imageNamed 和 imageWithContentsOfFile ，无论哪种方式都接近相同的结果。我意识到这里有多个滚动视图问题，但不知何故我似乎无法解决这个问题。至少可以说令人沮丧。我希望有人能以全新的眼光看待这个问题，并对我的问题有所了解。首先十分感谢。

编辑：忘了提及 ARC 的使用。是的，我使用 ARC。

代码：.h 文件

#import <UIKit/UIKit.h>

@interface FirstViewController : UIViewController <UIScrollViewDelegate>

@property (nonatomic, strong) IBOutlet UIScrollView *scrollView;
@property (nonatomic, strong) IBOutlet UIPageControl *pageControl;

@end

和 .m 文件

#import "FirstViewController.h"

@interface FirstViewController ()

@property (nonatomic, strong) NSArray *pageImages;
@property (nonatomic, strong) NSMutableArray *pageViews;

- (void)loadVisiblePages;
- (void)loadPage:(NSInteger)page;
- (void)purgePage:(NSInteger)page;
@end

@implementation FirstViewController


@synthesize scrollView = _scrollView;
@synthesize pageControl = _pageControl;

@synthesize pageImages = _pageImages;
@synthesize pageViews = _pageViews;

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (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.
}

- (void)loadVisiblePages {
    // First, determine which page is currently visible
    CGFloat pageWidth = self.scrollView.frame.size.width;
    NSInteger page = (NSInteger)floor((self.scrollView.contentOffset.x * 2.0f + pageWidth)     / (pageWidth * 2.0f));

// Update the page control
self.pageControl.currentPage = page;

// Work out which pages you want to load
NSInteger firstPage = page - 1;
NSInteger lastPage = page + 1;

// Purge anything before the first page
for (NSInteger i=0; i<firstPage; i++) {
    [self purgePage:i];
}

// Load pages in our range
for (NSInteger i=firstPage; i<=lastPage; i++) {
    [self loadPage:i];
}

// Purge anything after the last page
for (NSInteger i=lastPage+1; i<self.pageImages.count; i++) {
    [self purgePage:i];
}

}

- (void)purgePage:(NSInteger)page {
    if (page < 0 || page >= self.pageImages.count) {
    // If it's outside the range of what you have to display, then do nothing
    return;
    }

    // Remove a page from the scroll view and reset the container array
    UIView *pageView = [self.pageViews objectAtIndex:page];
    if ((NSNull*)pageView != [NSNull null]) {
        [pageView removeFromSuperview];
        [self.pageViews replaceObjectAtIndex:page withObject:[NSNull null]];


    }

}


- (void)loadPage:(NSInteger)page {
    if (page < 0 || page >= self.pageImages.count) {
        // If it's outside the range of what you have to display, then do nothing
        return;
    }

    // 1
    UIView *pageView = [self.pageViews objectAtIndex:page];
    if ((NSNull*)pageView == [NSNull null]) {
        // 2
        CGRect frame = self.scrollView.bounds;
        frame.origin.x = frame.size.width * page;
        frame.origin.y = 0.0f;

        // 3
        UIImageView *newPageView = [[UIImageView alloc] initWithImage:[self.pageImages objectAtIndex:page]];
        newPageView.contentMode = UIViewContentModeScaleAspectFit;
        newPageView.frame = frame;
        [self.scrollView addSubview:newPageView];
        // 4
       [self.pageViews replaceObjectAtIndex:page withObject:newPageView];

    }
}

- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
    // Load the pages that are now on screen
    [self loadVisiblePages];
}

- (void)viewDidLoad {
    [super viewDidLoad];

    // 1
    self.pageImages = [NSArray arrayWithObjects:
                       [UIImage imageNamed:@"BBD1.jpg"],
                       [UIImage imageNamed:@"BBD2.jpg"],
                       [UIImage imageNamed:@"BBD3.jpg"],
                       [UIImage imageNamed:@"BBD4.jpg"],
                       [UIImage imageNamed:@"BBD5.jpg"],
                       [UIImage imageNamed:@"BBD6.jpg"],
                       [UIImage imageNamed:@"BBD7.jpg"],
                  .....
                       [UIImage imageNamed:@"BBD292.jpg"],
                       [UIImage imageNamed:@"BBD293.jpg"],
                       [UIImage imageNamed:@"BBD294.jpg"],
                       [UIImage imageNamed:@"BBD295.jpg"],
                       [UIImage imageNamed:@"BBD296.jpg"],
                       [UIImage imageNamed:@"BBD297.jpg"],
                       [UIImage imageNamed:@"BBD298.jpg"],
                       [UIImage imageNamed:@"BBD299.jpg"],
                       [UIImage imageNamed:@"BBD300.jpg"],                       


                       nil];

    NSInteger pageCount = self.pageImages.count;

    // 2
    self.pageControl.currentPage = 0;
    self.pageControl.numberOfPages = pageCount;

    // 3
    self.pageViews = [[NSMutableArray alloc] init];
    for (NSInteger i = 0; i < pageCount; ++i) {
        [self.pageViews addObject:[NSNull null]];
    } 
}

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

    // 4
    CGSize pagesScrollViewSize = self.scrollView.frame.size;
    self.scrollView.contentSize = CGSizeMake(pagesScrollViewSize.width *     self.pageImages.count, pagesScrollViewSize.height);

    // 5
    [self loadVisiblePages];
}

- (void)viewDidUnload
{
    [super viewDidUnload];
    // Release any retained subviews of the main view.
}

- (BOOL)shouldAutorotateToInterfaceOrientation:    (UIInterfaceOrientation)interfaceOrientation
{
    if ([[UIDevice currentDevice] userInterfaceIdiom] == UIUserInterfaceIdiomPhone) {
        return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
    } else {
        return YES;
    }
}

@end

我真的很感谢你花时间来看看这个，并希望有人可以为我指明正确的方向。

谢谢！

4

2 回答 2

3

将实际图像加载到数组中会比仅将名称存储在数组中并像加载图像那样加载更大的开销

UIImage *image = [[UIImage alloc] initWithContentsOfFile:[self.pageImages objectAtIndex:page]];
UIImageView *newPageView = [[UIImageView alloc] initWithImage:image];
[image release];

此时，只有 newPageView 会持有对内存中图像的引用，当 newPageView 从其父视图中删除时，内存中的图像将被释放。

于 2012-12-08T21:00:45.147 回答
0

你没有说你是否使用了 ARC，但是没有 ARC，内存管理就会出现明显的问题。在loadPage:注释“// 3”中，您创建newPageView的保留计数为 1，然后将其作为 和 的子视图添加self.scrollView到数组self.pageViews中。因此，它的总体保留计数为 +3。在purgePage:您从中删除它self.scrollView，self.pageViews但仍然保留 +1 的总体保留计数。因此，UIImageViewfor each page 被遗忘但没有被释放。

您可以通过在项目中使用 ARC 或修改您创建的行来解决此问题newPageView：

UIImageView *newPageView = [[[UIImageView alloc] initWithImage:[self.pageImages objectAtIndex:page]] autorelease];
于 2012-07-21T18:04:27.433 回答