如何在iOS中实现离线缓存阅文app？

Question

我正在构建一篇阅读and的文章，我正在从服务器获取JSON格式的数据，并将其加载到UITableView和UIWebView中。

一篇文章包含图像、视频和文本。我想做离线缓存手段，如果没有互联网用户可以阅读以前加载的文章。我已经使用了图像的异步线程。

下面是我的代码：

- (void)viewDidLoad
{
    [super viewDidLoad];
    [self checkInternetConnection];
    UILabel *titleLabel = [[UILabel alloc] initWithFrame:CGRectMake(20,10,0,20)];
    titleLabel.textColor = [UIColor blackColor];
    titleLabel.backgroundColor = [UIColor clearColor];
    titleLabel.text = @"Story";
    [self.navigationItem setTitleView:titleLabel];

    UIActivityIndicatorView *spinner = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray];
    spinner.center = CGPointMake(160, 240);
    spinner.hidesWhenStopped = YES;
    [self.view addSubview:spinner];
    [spinner startAnimating];
    BOOL myBool = [self isNetworkAvailable];
    if (myBool)
    {
        @try {

            self.tableView.separatorColor = [UIColor colorWithRed:190/255.0 green:190/255.0 blue:190/255.0 alpha:1.0];

            // for displaying the previous screen lable with back button in details view controller        UIBarButtonItem *backbutton1 = [[UIBarButtonItem alloc] initWithTitle:@"" style:UIBarButtonItemStyleBordered target:nil action:nil];
            [[self navigationItem] setBackBarButtonItem:backbutton1];
            _Title1 = [[NSMutableArray alloc] init];
            _Author1 = [[NSMutableArray alloc] init];
            _Images1 = [[NSMutableArray alloc] init];
            _Details1 = [[NSMutableArray alloc] init];
            _link1 = [[NSMutableArray alloc] init];
            _Date1 = [[NSMutableArray alloc] init];
            pageNumber=1;
            NSData* data = [NSData dataWithContentsOfURL:ysURL];
            NSArray *ys_avatars = [NSJSONSerialization JSONObjectWithData:data options:0 error:nil];
            if(ys_avatars){
                for (int j=0;j<ys_avatars.count;j++)
                {
                    [_Title1 addObject:ys_avatars[j][@"title"]];
                    [_Author1 addObject: ys_avatars[j][@"author"]];
                    [_Images1 addObject: ys_avatars[j][@"featured_img"]];
                    [_Details1 addObject:ys_avatars[j][@"content"]];
                    [_link1 addObject:ys_avatars[j][@"permalink"]];
                    NSString *newStr=[ys_avatars[j][@"date"] substringToIndex:[ys_avatars[j]        [@"date"] length]-3];
                    [_Date1 addObject:newStr];
                }
            }
            else
            {
                NSLog(@"asd");
            }
        }
        @catch (NSException *exception) {

        }
        dispatch_queue_t downloadQueue = dispatch_queue_create("downloader", NULL);
        dispatch_async(downloadQueue, ^{
            // do our long running process here
            [NSThread sleepForTimeInterval:3];
            // do any UI stuff on the main UI thread
            dispatch_async(dispatch_get_main_queue(), ^{
                [spinner stopAnimating];
            });
        });
    }
}

- (UITableViewCell *)tableView:(UITableView *)tableView
         cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *Cellidentifier1 = @"ysTableViewCell";
    ysTableViewCell *cell1 = [tableView      dequeueReusableCellWithIdentifier:Cellidentifier1 forIndexPath:indexPath];
    long row = [indexPath row];
    cell1.TitleLabel1.text = _Title1[row];
    cell1.AuthorLabel1.text = _Author1[row];
    NSString *yourStoryUrl = [_Images1[indexPath.row]  stringByAddingPercentEscapesUsingEncoding:NSASCIIStringEncoding];
    if(yourStoryUrl) {
        NSArray *subStringsUrl = [yourStoryUrl componentsSeparatedByString:@"/"];
        NSString *stripedName = [subStringsUrl lastObject];
        NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,  NSUserDomainMask, YES);
        NSString *documentsDirectory = [paths objectAtIndex:0];
        NSString* filePath =[documentsDirectory stringByAppendingPathComponent:[NSString stringWithFormat:@"%@",stripedName]];
        NSLog(@"File Path retrieved %@", filePath);
        if(filePath) {
            UIImage *image = [UIImage imageWithContentsOfFile:filePath];
            if(image) {
                ysTableViewCell  *updateCell =(id)[tableView cellForRowAtIndexPath:indexPath];
                if(updateCell)
                    updateCell.ThumbImage1.image=image;
                cell1.ThumbImage1.image=image;
            } else {
                dispatch_queue_t taskQ = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
                dispatch_async(taskQ, ^{
                    NSURL *Imageurl = [NSURL URLWithString:yourStoryUrl];
                    NSData *data =  [NSData dataWithContentsOfURL:Imageurl];
                    UIImage *images1 = [[UIImage alloc] initWithData:data];
                    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
                    NSString *documentsDirectory = [paths objectAtIndex:0];
                    NSData *imageData = UIImagePNGRepresentation(images1);
                    //_imagePath =[documentsDirectory stringByAppendingPathComponent:[NSString stringWithFormat:@"%@.png",stripedName]];
                    if (![imageData writeToFile:filePath atomically:NO])
                    {
                        NSLog((@"Failed to cache image data to disk"));
                    }
                    else
                    {
                        NSLog((@"the cachedImagedPath is %@",filePath));
                    }
                    dispatch_sync(dispatch_get_main_queue(), ^{
                        ysTableViewCell  *updateCell =(id)[tableView cellForRowAtIndexPath:indexPath];
                        if(updateCell)
                            updateCell.ThumbImage1.image=images1;
                        cell1.ThumbImage1.image=images1;
                    });
                });
                return cell1;
            }

Answer 1

对于离线存储，您已经创建了一个sqlite文件，将从JSON获得的所有详细信息存储到数据库中。在数据库中只存储图像和视频的文件路径。下载这些资源并将其存储在文档目录中。

谢谢。

Answer 2

您可以使用键控归档(NSKeyedArchiver/NSKeyedUnarchiver)

这是一个tutorial