Question

每次滚动到新图像时，我的应用程序的“实时字节数”会继续增加约600kb。我懒洋洋地加载我的图像，一次只有3个，加载到水平页面的UIScrollView。我已经运行了Xcode仪器，我相信我已经将问题跟踪到了这一行：

newPageView = [[UIImageView alloc] initWithImage:[self.album objectAtIndex:page]];

每个加载的页面都会创建一个新的UIImageView实例，由于某种原因，该空间将保存在内存中。我正在使用ARC和XCode5。由于ARC中没有办法'dealloc'对象，释放这些内存的最佳方法是什么？

这是我的乐器的快照，显示了不断占用记忆的图像： enter image description here

我已经在网上看到了其他领域提出的这个问题，但找不到有帮助的答案。我对编码很新，但非常愿意学习，任何参考文献都将非常感谢！谢谢！

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

    self.pageCount = self.album.count;

    // Set up the array to hold the views for each page
    self.pageViews = [[NSMutableArray alloc] init];
    for (NSInteger i = 0; i < self.pageCount; ++i) {
        [self.pageViews addObject:[NSNull null]];
    }

    NSInteger p = self.page;
    CGFloat w = self.scrollView.bounds.size.width;
    [self.scrollView setContentOffset:CGPointMake(p*w,0) animated:YES];

    // Set up the content size of the scroll view
    CGSize pagesScrollViewSize = self.scrollView.frame.size;
    self.scrollView.contentSize = CGSizeMake(pagesScrollViewSize.width * self.pageCount, pagesScrollViewSize.height);

    // Load the initial set of pages that are on screen
    [self loadVisiblePages];
}

- (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));

    // Keeps track of which image is showing, for passing to child view controller
    self.currentImage = [self.album objectAtIndex:page];
    self.title =[NSString stringWithFormat:@"%d of %d", [self.album indexOfObject:self.currentImage]+1, self.pageCount];

    // Work out which pages we 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];
    }
    for (NSInteger i=firstPage; i<=lastPage; i++) {
        [self loadPage:i];
    }
    for (NSInteger i=lastPage+1; i<self.pageCount; i++) {
        [self purgePage:i];
    }
}

- (void)loadPage:(NSInteger)page {

    if (page < 0 || page >= self.pageCount) {
        // If it's outside the range of what we have to display, then do nothing
        return;
    }

    // Load an individual page, first seeing if we've already loaded it
    UIView *pageView = [self.pageViews objectAtIndex:page];
    // create an instance of imageView to be used as the newPageView
    UIImageView *newPageView;

    if ((NSNull*)pageView == [NSNull null]) {
        CGRect frame = self.scrollView.bounds;
        frame.origin.x = frame.size.width * page;
        frame.origin.y = 0.0f;

        newPageView = [[UIImageView alloc] initWithImage:[self.album objectAtIndex:page]];

        newPageView.contentMode = UIViewContentModeScaleAspectFit;
        newPageView.frame = frame;
        [self.scrollView addSubview:newPageView];

        [self.pageViews replaceObjectAtIndex:page withObject:newPageView];
    }
}

- (void)purgePage:(NSInteger)page {
    if (page < 0 || page >= self.pageCount) {
        // If it's outside the range of what we 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]];
        [self.album replaceObjectAtIndex:page withObject:[NSNull null]];
    }

}

#pragma mark - UIScrollViewDelegate
- (void)scrollViewDidScroll:(UIScrollView *)scrollView {

    [self loadVisiblePages];
}

Answer 1

ARC尝试自动释放内存，因此您不必担心这样做。

但是，您可以“标记”对象，以便通过“弄脏”它们来释放它们：

yourobject = nil;

这种告诉IOS设备该对象未被使用并且可以被释放。如果您正在将图像加载到滚动视图中，这意味着当用户向下滚动时，内存中仍有内容不在屏幕上，因此不需要。您可以摆脱这些图像，然后在滚动视图接近某一点时再次加载它们您可以在此问题中找到答案（与您的问题非常相似）：Memory pressure in app

Answer 2

如果没有看到您的代码，很难给出答案，但我想当您谈到“延迟加载”时，您的意思是您只在需要时将图像添加到滚动视图中。但是，如果没有显示滚动视图中的图像，是否将其删除？

我不知道您想要哪种显示方式，但请查看UICollectionView。集合视图管理内存本身，仅在需要时显示单元格，UICollectionViewLayout允许您自定义集合视图。

Answer 3

我已经更改了我的代码，以便在按照以下方式加载图片时调整图片大小：

   - (void)loadPage:(NSInteger)page {

    if (page < 0 || page >= self.pageCount) {
        // If it's outside the range of what we have to display, then do nothing
        return;
    }

    // Load an individual page, first seeing if we've already loaded it
    UIView *pageView = [self.pageViews objectAtIndex:page];
    // create an instance of imageView to be used as the newPageView
    UIImageView *newPageView;

    if ((NSNull*)pageView == [NSNull null]) {
        CGRect frame = self.scrollView.bounds;
        frame.origin.x = frame.size.width * page;
        frame.origin.y = 0.0f;

        self.resizeImage = [self.album objectAtIndex:page];
        UIImage *theImage = [self resizeImage:self.resizeImage toWidth:320.0f andHeight:480.0f];

        newPageView = [[UIImageView alloc] initWithImage:theImage];

        newPageView.contentMode = UIViewContentModeScaleAspectFit;
        newPageView.frame = frame;
        [self.scrollView addSubview:newPageView];

        [self.pageViews replaceObjectAtIndex:page withObject:newPageView];
    }
}

- (UIImage *)resizeImage:(UIImage *)image toWidth:(float)width andHeight:(float)height  {
    CGSize newSize = CGSizeMake(width, height);
    CGRect newRectangle = CGRectMake(0, 0, width, height);
    UIGraphicsBeginImageContext(newSize);
    [self.resizeImage drawInRect:newRectangle];
    UIImage *resizedImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return resizedImage;
}

这似乎将内存保持在稳定的位置，而内存消耗没有永久性增加。我不确定这是否是解决此问题的最佳方法，所以如果有人有任何更好的想法，请提供帮助。

在UIScrollView iOS7中延迟加载图像时，内存会增加

3 个答案: