1

We want to download image and data async to our tableview and we want to cache it not to download it again. We found a code for caching.Here is our code. It works asynchronously but when we scroll table view, images gone and come back(we cant see image for a while). Sometimes wrong image come to wrong cell. What might be the reasons and how can we solve it ?

 NSURL *imageURL = [NSURL URLWithString:[NSString stringWithFormat:@"%@%@",[userInfo[0] serverUrl],[estateList[indexPath.row] imgUrl]]];

    NSString *key = [imageURL absoluteString];
    NSData *data = [FTWCache objectForKey:key];
    if (data) {
        UIImage *image = [UIImage imageWithData:data];
        cell.imageView.image = image;
    } else {
        cell.imageView.image = [UIImage imageNamed:@"yukleniyor"];
        dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul);
        dispatch_async(queue, ^{
            NSData *data = [NSData dataWithContentsOfURL:imageURL];
            [FTWCache setObject:data forKey:key];
            UIImage *image = [UIImage imageWithData:data];
            dispatch_async(dispatch_get_main_queue(), ^{
                cell.imageView.image = image;
            });
        });
    }

Here is that code we found for caching

Header is like this

#import <Foundation/Foundation.h>

@interface FTWCache : NSObject

+ (void) resetCache;

+ (void) setObject:(NSData*)data forKey:(NSString*)key;
+ (id) objectForKey:(NSString*)key;

@end

And .m file is like this

#import "FTWCache.h"

static NSTimeInterval cacheTime =  (double)604800;

@implementation FTWCache

+ (void) resetCache {
    [[NSFileManager defaultManager] removeItemAtPath:[FTWCache cacheDirectory] error:nil];
}

+ (NSString*) cacheDirectory {
    NSArray* paths = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES);
    NSString *cacheDirectory = [paths objectAtIndex:0];
    cacheDirectory = [cacheDirectory stringByAppendingPathComponent:@"FTWCaches"];
    return cacheDirectory;
}

+ (NSData*) objectForKey:(NSString*)key {
    NSFileManager *fileManager = [NSFileManager defaultManager];
    NSString *filename = [self.cacheDirectory stringByAppendingPathComponent:key];

    if ([fileManager fileExistsAtPath:filename])
    {
        NSDate *modificationDate = [[fileManager attributesOfItemAtPath:filename error:nil] objectForKey:NSFileModificationDate];
        if ([modificationDate timeIntervalSinceNow] > cacheTime) {
            [fileManager removeItemAtPath:filename error:nil];
        } else {
            NSData *data = [NSData dataWithContentsOfFile:filename];
            return data;
        }
    }
    return nil;
}

+ (void) setObject:(NSData*)data forKey:(NSString*)key {
    NSFileManager *fileManager = [NSFileManager defaultManager];
    NSString *filename = [self.cacheDirectory stringByAppendingPathComponent:key];

    BOOL isDir = YES;
    if (![fileManager fileExistsAtPath:self.cacheDirectory isDirectory:&isDir]) {
        [fileManager createDirectoryAtPath:self.cacheDirectory withIntermediateDirectories:NO attributes:nil error:nil];
    }

    NSError *error;
    @try {
        [data writeToFile:filename options:NSDataWritingAtomic error:&error];
    }
    @catch (NSException * e) {
        //TODO: error handling maybe
    }
}


@end
4

1 回答 1

0

对不起我之前的回答。我将尝试解释问题：我们有TableView 的总行数和显示的保留区域的行数。结果，异步加载的图像无法加载到它们的单元格中（因为它是在从内存中下载时插入的）。

解决方案非常简单，您必须为每个 ImageView 分配键，并且此键与表格的单元格相关联。

我通过使用此 git ( https://gist.github.com/khanlou/4998479 )中的代码解决了这个问题

上面有两个文件

UIImageView+Network.h
UIImageView+Network.m

您必须将它们包含在您的项目中，或者创建自己的类并粘贴到其中。

此类使用来自 ( https://github.com/FTW/FTWCache/tree/master/FTWCache ) 的 FTW/FTWCache。因此，您也必须将这个添加到您的项目中。

之后你必须导入

#import "UIImageView+Network.h"

在将使用异步图像加载和缓存的文件中。

以及使用 TableView 的简短代码部分

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *simpleTableIdentifier = @"MyTableCell";

    MyTableCell *cell = (MyTableCell *)[tableView dequeueReusableCellWithIdentifier:simpleTableIdentifier];
    if (cell == nil){
        NSArray *nib = [[NSBundle mainBundle] loadNibNamed:@"MyTableCell" owner:self options:nil];
        cell = [nib objectAtIndex:0];
    }
    // construction to call method 
    // [cell.imageView loadImageFromURL:(NSURL*)url placeholderImage:(UIImage*)placeholder cachingKey:(NSString*)key ];

    [cell.thumbnailImageView loadImageFromURL:(NSURL*)url placeholderImage:[UIImage imageNamed:@"no_foto.gif"]  cachingKey:(NSString*)[NSString stringWithFormat:@"%d",indexPath.row]];

    return cell;
}
于 2015-07-15T15:55:47.443 回答