IOS UITableView 加载未知宽高图片的解决方案

在开发中遇到了UITableView列表 UITableViewCell装载图片但不知Image的宽高 问题。

在解决该问题的时候，首先想到的是异步加载图片 采用第三方框架SDWebImage 实现对图片异步下载和缓存

以下是我采用的方法几个关键地方

1.计算UITableView的高度

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath{        NSString *imgURL  = self.electionPictureArray.count > indexPath.row ? self.electionPictureArray[indexPath.row] :nil;    if (imgURL) {
        //根据当前Row的ImageUrl作为Key获取图片缓存        UIImage *img = [[SDImageCache sharedImageCache] imageFromDiskCacheForKey: imgURL ];        if (!img) {            img = [UIImage resizedImageWithName:@"childshow_placeholder"];;                    }        CGFloat height = img.size.height *Main_Screen_Width/img.size.width;//Image宽度为屏幕宽度 ，计算宽高比求得对应的高度        NSLog(@"----------------return Height:%f",height);        return height;            }    return 0; }

2.在UITableViewCell中实现图片的下载，回调下载完成刷新页面代理

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{    ElectronicBookCell *cell = [ElectronicBookCell cellWithTableView:tableView];    cell.imageUrl = self.electionPictureArray.count > indexPath.row ? self.electionPictureArray[indexPath.row] :nil;    cell.selectionStyle = UITableViewCellSelectionStyleNone;    return cell;    }

在cell中的setImageUrl中进行下载图片

-(void) setImageUrl:(NSString *)imageUrl{    if (imageUrl) {        _imageUrl = imageUrl;        UIImage *cachedImage = [[SDImageCache sharedImageCache] imageFromDiskCacheForKey:imageUrl];        // 没有缓存图片        if (!cachedImage) {            __weak typeof(self) target = self;            // 利用 SDWebImage 框架提供的功能下载图片            [[SDWebImageDownloader sharedDownloader] downloadImageWithURL:[NSURL URLWithString:imageUrl] options:SDWebImageDownloaderUseNSURLCache progress:^(NSInteger receivedSize, NSInteger expectedSize) {                            } completed:^(UIImage *image, NSData *data, NSError *error, BOOL finished) {                // 保存图片                [[SDImageCache sharedImageCache] storeImage:image forKey:imageUrl toDisk:YES]; // 保存到磁盘                if (imageUrl == target.imageUrl) {                     [target configPreviewImageViewWithImage:image];                }                if ([self.delegate respondsToSelector:@selector(reloadCellAtIndexPathWithUrl:)]) {                    [self.delegate reloadCellAtIndexPathWithUrl:imageUrl];                }            }];        }else        {            [self configPreviewImageViewWithImage:cachedImage];        }    }}

/** * 加载图片成功后设置image's frame */- (void)configPreviewImageViewWithImage:(UIImage *)image{    _previewWidth = Main_Screen_Width;    _previewHeight =  image.size.height *Main_Screen_Width/image.size.width;    CGRect rect = _previewImageView.frame;    rect.size.width = _previewWidth;// image.size.width;    rect.size.height = _previewHeight;    _previewImageView.frame = rect;    _previewImageView.image = image;    [self resetLayoutByPreviewImageView];}

3.在Controller中实现代理方法，

-(void)reloadCellAtIndexPathWithUrl:(NSString *)url{        if (url) {        for (int i = 0; i< self.electionPictureArray.count; i++) {
            //遍历当前数据源中并找到ImageUrl             NSString *imgURL  =   self.electionPictureArray.count >i ? self.electionPictureArray[i] :nil;            if ([imgURL isEqualToString:url]) {                //获取当前可见的Cell NSIndexPaths                NSArray *paths  = self.tableView.indexPathsForVisibleRows;
                //判断回调的NSIndexPath 是否在可见中如果存在则刷新页面                NSIndexPath *pathLoad = [NSIndexPath indexPathForItem:i inSection:0];                for (NSIndexPath *path in paths) {                    if (path && path == pathLoad ) {                        [self.tableView reloadData];                    }                }            }        }    }}