Ios 将映像异步下载到NSData和缓存

首先，这不是一个重复的问题。我已经阅读了许多关于堆栈溢出的问题，但它们并没有帮助我完全解决问题

我正在从web服务下载图像。因为没有人喜欢UI被暂停，所以我使用线程分别下载图像

NSURL *imageUrl = [NSURL URLWithString:storyImageURL];

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

    thumbnailData = [NSData dataWithContentsOfURL:imageUrl];

    dispatch_async(dispatch_get_main_queue(), ^{
        thumbnail = [UIImage imageWithData:thumbnailData];
    });
});

如果我完全按照上面的方式使用代码，UI将不会停止，直到它从web服务获取数据，但是图像不会被缓存

如果我不使用线程，那么UI将暂停，但是使用NSCoding方法（归档）缓存图像

我的问题是：如何使用线程并同时缓存缩略图？请不要建议任何第三方图书馆

更新：反复阅读代码后，我可能会想到两个问题：

1） 看起来在线程下载完图像之前调用了NSKeyedArchiver和NSKeyedUnarchiver，但这只是一个猜测。在单独的存储文件中，我使用NSKeyedArchiver和NSKeyedUnachiver：

- (RSSChannel *)fetchRSSFeedWithCompletion:(void (^)(RSSChannel *, NSError *))block
{
    NSURL *url = [NSURL URLWithString:@"http://techcrunch.com/feed"];
    NSURLRequest *req = [NSURLRequest requestWithURL:url];

    RSSChannel *channel = [[RSSChannel alloc] init];
    TheConnection *connection = [[TheConnection alloc] initWithRequest:req];

    //[connection setCompletionBlock:block];

    NSString *cachePath = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) objectAtIndex:0];
    cachePath = [cachePath stringByAppendingPathComponent:@"HAHAHA.archive"];

    RSSChannel *cachedChannel = [NSKeyedUnarchiver unarchiveObjectWithFile:cachePath];

    if (!cachedChannel) 
        cachedChannel = [[RSSChannel alloc] init];

    RSSChannel *channelCopy = [cachedChannel copy];

    [connection setCompletionBlock:^(RSSChannel *obj, NSError *err) {
        if (!err) {

            [channelCopy addItemsFromChannel:obj];
            [NSKeyedArchiver archiveRootObject:channelCopy toFile:cachePath];
        }
        block(channelCopy, err);
    }];


    [connection setXmlRootObject:channel];
    [connection start];

    return cachedChannel;
}

---

2） 我能想到的第二个问题是，在尝试从缓存中解码缩略图后，UI没有刷新。

是否将

thumbnailData

保存为实例变量？在分派之前，请检查实例变量是否已设置，如果已设置，请返回该值。如果没有，则运行分派块并将其另存为实例变量。

假设您的目标是iOS 5+，最自然的解决方案是使用

NSURLCache

和

NSURLConnection+sendAsynchronousRequest:queue:completionHandler:

。第三方解决方案通常只是忽略这些方法，要么是出于无知，要么是出于支持iOS 4的愿望，所以您的选择要么是将这些东西的维护工作有效地外包给苹果，要么是信任第三方，要么是花自己的时间在上面

例如

NSURLCache

在iOS 5之前存在，但只是一个内存缓存。因为它也是一个磁盘缓存。

试试这个

    NSURL *imageUrl = [NSURL URLWithString:storyImageURL];

    UIButton *btnThumbnail = [[UIButton alloc] initWithFrame:CGRectMake(0, 10, 180, 280)];
    [self downloadingServerImageFromUrl:btnThumbnail AndUrl:imageUrl];
    [btnThumbnail addTarget:self action:@selector(onSelectEPaper:) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:viewPaperBg];

 - (void)onSelectEPaper:(id)sender
  {
  }


  -(void)downloadingServerImageFromUrl:(UIButton*)imgView AndUrl:(NSString*)strUrl
{
//    strUrl = [strUrl encodeUrl];
//    strUrl = [strUrl stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];

NSString* theFileName = [NSString stringWithFormat:@"%@.jpg",[[strUrl lastPathComponent] stringByDeletingPathExtension]];


NSFileManager *fileManager =[NSFileManager defaultManager];
NSString *fileName = [NSHomeDirectory() stringByAppendingPathComponent:[NSString stringWithFormat:@"tmp/%@",theFileName]];


imgView.backgroundColor = [UIColor darkGrayColor];
UIActivityIndicatorView *actView = [[UIActivityIndicatorView alloc]initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhite];
[imgView addSubview:actView];
[actView startAnimating];
CGSize boundsSize = imgView.bounds.size;
CGRect frameToCenter = actView.frame;
// center horizontally
if (frameToCenter.size.width < boundsSize.width)
    frameToCenter.origin.x = (boundsSize.width - frameToCenter.size.width) / 2;
else
    frameToCenter.origin.x = 0;

// center vertically
if (frameToCenter.size.height < boundsSize.height)
    frameToCenter.origin.y = (boundsSize.height - frameToCenter.size.height) / 2;
else
    frameToCenter.origin.y = 0;

actView.frame = frameToCenter;


dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_async(queue, ^{

    NSData *dataFromFile = nil;
    NSData *dataFromUrl = nil;

    dataFromFile = [fileManager contentsAtPath:fileName];
    //      NSLog(@"%@",fileName);
    if(dataFromFile==nil){
        //      NSLog(@"%@",strUrl);
        NSString *url =[strUrl stringByReplacingOccurrencesOfString:@"\n" withString:@""];
        url=[url stringByReplacingOccurrencesOfString:@"\t" withString:@""];
        url=[url stringByReplacingOccurrencesOfString:@" " withString:@""];

        url = [url stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
        //       dataFromUrl=[[[NSData alloc] initWithContentsOfURL:[NSURL URLWithString:url]] autorelease];
        //       dataFromUrl=[[NSData dataWithContentsOfURL:[NSURL URLWithString:url]] autorelease];
        NSError* error = nil;
        //     NSLog(@"%@", [NSURL URLWithString:url]);
        dataFromUrl = [NSData dataWithContentsOfURL:[NSURL URLWithString:url] options:NSDataReadingUncached error:&error];

        if (error) {
            NSLog(@"%@", [error localizedDescription]);
        } else {
            //    NSLog(@"Data has loaded successfully.");
        }
    }

    dispatch_sync(dispatch_get_main_queue(), ^{

        if(dataFromFile!=nil){
            //    imgView.image = [UIImage imageWithData:dataFromFile];
            [imgView setBackgroundImage:[UIImage imageWithData:dataFromFile] forState:UIControlStateNormal];
        }else if(dataFromUrl!=nil){
            //    imgView.image = [UIImage imageWithData:dataFromUrl];
            [imgView setBackgroundImage:[UIImage imageWithData:dataFromUrl] forState:UIControlStateNormal];
            NSString *fileName = [NSHomeDirectory() stringByAppendingPathComponent:[NSString stringWithFormat:@"tmp/%@",theFileName]];

            BOOL filecreationSuccess = [fileManager createFileAtPath:fileName contents:dataFromUrl attributes:nil];
            if(filecreationSuccess == NO){
                //    NSLog(@"Failed to create the html file");
            }

        }else{
            //     imgView.image = [UIImage imageNamed:@"no_image.jpg"];
            [imgView setBackgroundImage:[UIImage imageNamed:@"no_image.jpg"] forState:UIControlStateNormal];
        }
        [actView removeFromSuperview];
        //            [actView release];
        //    [imgView setBackgroundColor:[UIColor clearColor]];
    });
});
}

NSURL*imageUrl=[NSURL-URLWithString:storyImageURL]；
UIButton*btnThumbnail=[[UIButton alloc]initWithFrame:CGRectMake（0,10,180,280）]；
[自下载ServerImageFromURL:BTN缩略图和URL:imageUrl]；
[btnThumbnail addTarget:self action:@selector（onselectepper:）for controlEvents:UIControlEventTouchUpInside]；
[self.view addSubview:viewPaperBg]；
-（无效）onSelectEPaper:（id）发件人
{
}
-（void）下载ServerImagefromURL:（UIButton*）imgView和URL:（NSString*）strUrl
{
//strUrl=[strUrl encodeUrl]；
//strUrl=[strUrl stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]；
NSString*文件名=[NSString stringWithFormat:@“%@.jpg”，[[strUrl lastPathComponent]stringByDeletingPathExtension]；
NSFileManager*fileManager=[NSFileManager defaultManager]；
NSString*文件名=[NSHomeDirectory（）stringByAppendingPathComponent:[NSString stringWithFormat:@“tmp/%@”，文件名]]；
imgView.backgroundColor=[UIColor darkGrayColor]；
UIActivityIndicatorView*actView=[[UIActivityIndicatorView alloc]initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhite]；
[imgView添加子视图：actView]；
[actView startAnimating]；
CGSize boundsSize=imgView.bounds.size；
CGRect frameToCenter=actView.frame；
//水平居中
if（frameToCenter.size.width    NSURL *imageUrl = [NSURL URLWithString:storyImageURL];

    UIButton *btnThumbnail = [[UIButton alloc] initWithFrame:CGRectMake(0, 10, 180, 280)];
    [self downloadingServerImageFromUrl:btnThumbnail AndUrl:imageUrl];
    [btnThumbnail addTarget:self action:@selector(onSelectEPaper:) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:viewPaperBg];

 - (void)onSelectEPaper:(id)sender
  {
  }


  -(void)downloadingServerImageFromUrl:(UIButton*)imgView AndUrl:(NSString*)strUrl
{
//    strUrl = [strUrl encodeUrl];
//    strUrl = [strUrl stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];

NSString* theFileName = [NSString stringWithFormat:@"%@.jpg",[[strUrl lastPathComponent] stringByDeletingPathExtension]];


NSFileManager *fileManager =[NSFileManager defaultManager];
NSString *fileName = [NSHomeDirectory() stringByAppendingPathComponent:[NSString stringWithFormat:@"tmp/%@",theFileName]];


imgView.backgroundColor = [UIColor darkGrayColor];
UIActivityIndicatorView *actView = [[UIActivityIndicatorView alloc]initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhite];
[imgView addSubview:actView];
[actView startAnimating];
CGSize boundsSize = imgView.bounds.size;
CGRect frameToCenter = actView.frame;
// center horizontally
if (frameToCenter.size.width < boundsSize.width)
    frameToCenter.origin.x = (boundsSize.width - frameToCenter.size.width) / 2;
else
    frameToCenter.origin.x = 0;

// center vertically
if (frameToCenter.size.height < boundsSize.height)
    frameToCenter.origin.y = (boundsSize.height - frameToCenter.size.height) / 2;
else
    frameToCenter.origin.y = 0;

actView.frame = frameToCenter;


dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_async(queue, ^{

    NSData *dataFromFile = nil;
    NSData *dataFromUrl = nil;

    dataFromFile = [fileManager contentsAtPath:fileName];
    //      NSLog(@"%@",fileName);
    if(dataFromFile==nil){
        //      NSLog(@"%@",strUrl);
        NSString *url =[strUrl stringByReplacingOccurrencesOfString:@"\n" withString:@""];
        url=[url stringByReplacingOccurrencesOfString:@"\t" withString:@""];
        url=[url stringByReplacingOccurrencesOfString:@" " withString:@""];

        url = [url stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
        //       dataFromUrl=[[[NSData alloc] initWithContentsOfURL:[NSURL URLWithString:url]] autorelease];
        //       dataFromUrl=[[NSData dataWithContentsOfURL:[NSURL URLWithString:url]] autorelease];
        NSError* error = nil;
        //     NSLog(@"%@", [NSURL URLWithString:url]);
        dataFromUrl = [NSData dataWithContentsOfURL:[NSURL URLWithString:url] options:NSDataReadingUncached error:&error];

        if (error) {
            NSLog(@"%@", [error localizedDescription]);
        } else {
            //    NSLog(@"Data has loaded successfully.");
        }
    }

    dispatch_sync(dispatch_get_main_queue(), ^{

        if(dataFromFile!=nil){
            //    imgView.image = [UIImage imageWithData:dataFromFile];
            [imgView setBackgroundImage:[UIImage imageWithData:dataFromFile] forState:UIControlStateNormal];
        }else if(dataFromUrl!=nil){
            //    imgView.image = [UIImage imageWithData:dataFromUrl];
            [imgView setBackgroundImage:[UIImage imageWithData:dataFromUrl] forState:UIControlStateNormal];
            NSString *fileName = [NSHomeDirectory() stringByAppendingPathComponent:[NSString stringWithFormat:@"tmp/%@",theFileName]];

            BOOL filecreationSuccess = [fileManager createFileAtPath:fileName contents:dataFromUrl attributes:nil];
            if(filecreationSuccess == NO){
                //    NSLog(@"Failed to create the html file");
            }

        }else{
            //     imgView.image = [UIImage imageNamed:@"no_image.jpg"];
            [imgView setBackgroundImage:[UIImage imageNamed:@"no_image.jpg"] forState:UIControlStateNormal];
        }
        [actView removeFromSuperview];
        //            [actView release];
        //    [imgView setBackgroundColor:[UIColor clearColor]];
    });
});
}

RSSChannel *channelCopy = [cachedChannel copy];

INCREMENT_COUNTER

    [channelCopy addItemsFromChannel:obj];
    DECREMENT_COUNTER;
 }
block(channelCopy, err);
}];

NSURL *imageUrl = [NSURL URLWithString:storyImageURL];

INCREMENT_COUNTER;

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

thumbnailData = [NSData dataWithContentsOfURL:imageUrl];

dispatch_async(dispatch_get_main_queue(), ^{
  thumbnail = [UIImage imageWithData:thumbnailData];
  DECREMENT_COUNTER;
  if (COUNTER_REACHED_ZERO)
    CALL_ARCHIVE_METHOD_ON_CHANNEL OBJECT
  });
});