Question

我正面临着制作3个文件的异步下载队列的问题。

我希望当我完成下载并保存第一个文件以开始下载第二个文件然后第三个...

目前我正在使用3 IBAction下载到Documents文件夹中，它可以正常工作，但是为所有文件自动生成它不起作用。

实现此文件的下载队列的最佳方法是什么？我知道我必须在didReceiveData上发表声明，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];


}

Answer 1

在控制器中，创建三个块并将它们复制到一个阵列，该阵列将作为您的队列。此数组需要存储为实例变量，以便稍后可以通过调用控制器类中的方法来访问它。三个块中的每一个都应该创建并执行NSURLConnection，它会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-connectionDidFinishLoading:委托方法。从这个方法中，调用一个方法，将第一个块从队列中弹出并执行它。

然后只是第一次调用该方法来启动该过程。显然，您需要提供一些边缘案例和错误处理，但这是基本的想法。

IOS队列异步下载

1 个答案: