SDWebimage滚动

Question

我使用SDWebimage加载和缓存图片，现在我正在寻找一种滑动/滚动图片的方法。我尝试了不同的方法，但我似乎不能让它工作，有人能帮助我吗？

Answer 1

您只需像使用其他方法一样使用滚动图像浏览器，但并不是同步设置image属性，而是调用SDWebImage方法setImageWithURL (从其UIImageView类别)。

为了向您展示一个快速而粗糙的实现，请创建一个UIScrollView，打开分页，在viewDidLoad中，您可以设置内容大小并加载第一个图像，如下所示：

[self.scrollView setContentSize:CGSizeMake(self.view.bounds.size.width * [self.objects count],
                                           self.view.bounds.size.height)];

dispatch_async(dispatch_get_main_queue(), ^{
    ImageBrowserObject *object = self.objects[0];
    [object scrollView:self.scrollView addImageViewIfNeededForIndex:0];
});

您还希望将控制器设置为该滚动视图的代理，然后处理scrollViewDidScroll事件：

- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
    static NSInteger lastKnownIndex = -1;

    NSInteger currentIndex  = scrollView.contentOffset.x / scrollView.frame.size.width + 0.5f;
    NSInteger nextIndex = currentIndex + 1;
    NSInteger prevIndex = currentIndex - 1;
    if (prevIndex < 0) prevIndex = 0;

    if (currentIndex == lastKnownIndex)
        return;

    // add the imageviews we need, remove the ones we don't

    [self.objects enumerateObjectsUsingBlock:^(ImageBrowserObject *object, NSUInteger idx, BOOL *stop) {
        if (idx >= prevIndex && idx <= nextIndex)
            [object scrollView:scrollView addImageViewIfNeededForIndex:idx];
        else
            [object scrollView:scrollView removeImageViewIfNeededForIndex:idx];
    }];

    lastKnownIndex = currentIndex;
}

我的ImageBrowserObject定义如下：

@interface ImageBrowserObject : NSObject

@property (nonatomic, strong) NSString *title;
@property (nonatomic, strong) NSURL *url;
@property (nonatomic, weak) UIImageView *imageView;

@end

@implementation ImageBrowserObject

- (id)initWithTitle:(NSString *)title URL:(NSURL *)url
{
    self = [super init];
    if (self) {
        _title = title;
        _url = url;
    }
    return self;
}

- (void)scrollView:(UIScrollView *)scrollView addImageViewIfNeededForIndex:(NSInteger)index
{
    if (self.imageView)
        return;

    CGRect frame = CGRectMake(index * scrollView.frame.size.width,
                              0.0,
                              scrollView.frame.size.width,
                              scrollView.frame.size.height);
    UIImageView *imageView = [[UIImageView alloc] initWithFrame:frame];
    [scrollView addSubview:imageView];
    [imageView setImageWithURL:self.url placeholderImage:[UIImage imageNamed:@"placeholder.png"]];
    self.imageView = imageView;
}

- (void)scrollView:(UIScrollView *)scrollView removeImageViewIfNeededForIndex:(NSInteger)index
{
    if (!self.imageView)
        return;

    [self.imageView removeFromSuperview];
    self.imageView = nil;
}

@end

这是一个非常简单的实现，但是我想您应该已经明白了。