UIScrollView-来自网址的图片未显示

Question

在我的项目中，我有一个UITableView视图，如果单击该单元格，它将转到详细信息页面。在详细页面中，它有一个显示图像的UIScrollView。

我面临的问题是来自网址的图片没有显示。它只显示占位符图像。但是在我将其单击回UITableView视图并再次单击相同的单元格之后。它将显示URL中的图像。

这是我的代码

- (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;
    self.scrollView.pagingEnabled = YES;

    // 3   

    UIImageView *newPageView = [[UIImageView alloc] initWithImage:[self.pageImages objectAtIndex:page]];
    //Fit the Screen
    //newPageView.contentMode = UIViewContentModeScaleToFill;
    newPageView.contentMode = UIViewContentModeScaleAspectFit;
    newPageView.frame = frame;

    newPageView.userInteractionEnabled = YES;

    [self.scrollView addSubview:newPageView];

    // 4
    [self.pageViews replaceObjectAtIndex:page withObject:newPageView];

    UITapGestureRecognizer *SingleTap = [[UITapGestureRecognizer alloc]initWithTarget:self action:@selector(actionHandleTapOnImageView:)];
    [SingleTap setNumberOfTapsRequired:1];

    [newPageView addGestureRecognizer:SingleTap];



}
}

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

- (void)viewDidLoad {

[super viewDidLoad]




// Add image into slide image
if([data.gallery count] == 1){


    _imageView1 = [[UIImageView alloc] init];

    [_imageView1 sd_setImageWithURL:[NSURL URLWithString:[NSString stringWithFormat:@"%@", data.gallery[0]]]placeholderImage:[UIImage imageNamed:@"placeholder.png"]];

    self.pageImages = [[NSMutableArray alloc] initWithObjects:_imageView1.image, nil];


}else if([data.gallery count] == 2){

    // Load image from server



    _imageView1 = [[UIImageView alloc] init];

    [_imageView1 sd_setImageWithURL:[NSURL URLWithString:[NSString stringWithFormat:@"%@", data.gallery[0]]]placeholderImage:[UIImage imageNamed:@"placeholder.png"]];

    self.pageImages = [[NSMutableArray alloc] initWithObjects:_imageView1.image, nil];

    _imageView2 = [[UIImageView alloc] init];

    [_imageView2 sd_setImageWithURL:[NSURL URLWithString:[NSString stringWithFormat:@"%@", data.gallery[1]]]placeholderImage:[UIImage imageNamed:@"placeholder.png"]];



    // Add image to page

    self.pageImages = [[NSMutableArray alloc] initWithObjects:_imageView1.image,_imageView2.image, 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];

}