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[操作系统]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]; } } } } }}

 

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