IOS队列异步下载

我面临一个问题，使异步下载3个文件的队列

我想当我完成下载并保存第一个文件开始下载第二个然后第三个

目前，我正在使用3 iAction下载到Documents文件夹中，它工作得很好，但要使它自动用于所有文件，却无法工作

实现此文件下载队列的最佳方法是什么？ 我知道我必须对didReceiveData进行声明，但我需要帮助才能使其正常工作

这是我正在使用的代码：

// Download song 1
- (IBAction)download {

[self performSelector:@selector(downloadmusic) withObject:nil afterDelay:0.0];

}


- (void)downloadmusic
{
self.log = [NSMutableString string];
[self doLog:@"1/13"];

// Retrieve the URL string
int which = [(UISegmentedControl *)self.navigationItem.titleView selectedSegmentIndex];
NSArray *urlArray = [NSArray arrayWithObjects: SONG1_URL, nil];
NSString *urlString = [urlArray objectAtIndex:which];

// Prepare for download
[[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:YES];

// Set up the Download Helper and start download
[DownloadHelper sharedInstance].delegate = self;
[DownloadHelper download:urlString];

}

// Download song 2
- (void)downloadmusic2 
{

self.log = [NSMutableString string];
[self doLog:@"2/13"];

// Retrieve the URL string
int which = [(UISegmentedControl *)self.navigationItem.titleView        selectedSegmentIndex];
NSArray *urlArray = [NSArray arrayWithObjects: SONG2_URL, nil];
NSString *urlString = [urlArray objectAtIndex:which];

// Prepare for download
[[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:YES];

// Set up the Download Helper and start download
[DownloadHelper sharedInstance].delegate = self;
[DownloadHelper download:urlString];


}


// Download song 3
- (void)downloadmusic3 
{

self.log = [NSMutableString string];
[self doLog:@"3/13"];

// Retrieve the URL string
int which = [(UISegmentedControl *)self.navigationItem.titleView selectedSegmentIndex];
NSArray *urlArray = [NSArray arrayWithObjects: SONG3_URL, nil];
NSString *urlString = [urlArray objectAtIndex:which];

// Prepare for download
[[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:YES];

// Set up the Download Helper and start download
[DownloadHelper sharedInstance].delegate = self;
[DownloadHelper download:urlString];


}



- (void) doLog: (NSString *) formatstring, ...
{
va_list arglist;
if (!formatstring) return;
va_start(arglist, formatstring);
NSString *outstring = [[[NSString alloc] initWithFormat:formatstring arguments:arglist] autorelease];
va_end(arglist);
[self.log appendString:outstring];
[self.log appendString:@"\n"];
[textView setText:self.log];
}

- (void) restoreGUI
{
self.navigationItem.rightBarButtonItem = BARBUTTON(@"Get Data", @selector(action:));
if ([[NSFileManager defaultManager] fileExistsAtPath:DEST_PATH])
    self.navigationItem.leftBarButtonItem = BARBUTTON(@"Play", @selector(startPlayback:));  
[[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:NO];
[(UISegmentedControl *)self.navigationItem.titleView setEnabled:YES];
[progress setHidden:YES];

}

- (void) dataDownloadAtPercent: (NSNumber *) aPercent
{
[progress setHidden:NO];
[progress setProgress:[aPercent floatValue]];
}

- (void) dataDownloadFailed: (NSString *) reason
{
[self restoreGUI];
if (reason) [self doLog:@"Download failed: %@", reason];
}

- (void) didReceiveFilename: (NSString *) aName
{
self.savePath = [DEST_PATH stringByAppendingString:aName];


}

- (void) didReceiveData: (NSData *) theData
{
if (![theData writeToFile:self.savePath atomically:YES])
    [self doLog:@"Error writing data to file"];

[theData release];
[self restoreGUI];
[self doLog:@"Download succeeded"];


//[self performSelector:@selector(downloadmusic2) withObject:nil afterDelay:1.0];


    //[self performSelector:@selector(downloadmusic3) withObject:nil afterDelay:1.0];


}

---

在控制器中，创建三个块并将它们复制到一个数组中，该数组将用作队列。该数组需要存储为实例变量，以便以后调用控制器类中的方法可以访问它。三个块中的每一个都应该创建并执行一个NSURLConnection，该连接异步下载相应的文件。每个NSURLConnection的委托可以是您的控制器，它应该实现

-connectiondFinishLoading:

委托方法。从这个方法中，调用一个从队列中弹出第一个块并执行它的方法

然后第一次调用该方法就可以开始这个过程。显然，您需要提供一些边缘情况和错误处理，但这是基本思想