ios - 使用 NSURLConnection 运行多个 NSOperation 实例？
<p><p>我们有一个大型项目，需要将大型文件从服务器同步到后台的“库”中。我读过子类化 NSOperation 是多线程 iOS 任务的最灵活方式，并尝试过。因此，该函数接收要下载和保存的 URL 列表，初始化同一 NSOperation 类的实例并将每个实例添加到 NSOperation 队列(一次只能下载一个文件)。</p>
<pre><code>-(void) LibSyncOperation {
// Initialize download list. Download the homepage of some popular websites
downloadArray = [ initWithObjects:@"www.google.com",
@"www.stackoverflow.com",
@"www.reddit.com",
@"www.facebook.com", nil];
operationQueue = [[init]autorelease];
; // Only download 1 file at a time
;
for (int i = 0; i < ; i++) {
LibSyncOperation *libSyncOperation = [[ initWithURL:]autorelease];
;
}
}
</code></pre>
<p>现在，这些类实例都可以正常创建，并且都添加到 NSOperationQueue 并开始执行。但问题是何时开始下载，第一个文件永远不会开始下载(使用带有委托(delegate)方法的 NSURLConnection )。我使用了我在另一个线程中看到的 runLoop 技巧，它应该允许操作继续运行，直到下载完成。 NSURLConnection 已建立，但它从未开始将数据附加到 NSMutableData 对象!</p>
<pre><code>@synthesize downloadURL, downloadData, downloadPath;
@synthesize downloadDone, executing, finished;
/* Function to initialize the NSOperation with the URL to download */
- (id)initWithURL:(NSString *)downloadString {
if (!) return nil;
// Construct the URL to be downloaded
downloadURL = [[initWithString:downloadString]autorelease];
downloadData = [[ init] autorelease];
NSLog(@"downloadURL: %@",);
// Create the download path
downloadPath = ;
return self;
}
-(void)dealloc {
;
}
-(void)main {
// Create ARC pool instance for this thread.
// NSAutoreleasePool *pool = [init]; //--> COMMENTED OUT, MAY BE PART OF ISSUE
if (!) {
;
executing = YES;
NSURLRequest *downloadRequest = ;
NSLog(@"%s: downloadRequest: %@",__FUNCTION__,downloadURL);
NSURLConnection *downloadConnection = [ initWithRequest:downloadRequest delegate:self startImmediately:NO];
// This block SHOULD keep the NSOperation from releasing before the download has been finished
if (downloadConnection) {
NSLog(@"connection established!");
do {
[ runMode:NSDefaultRunLoopMode beforeDate:];
} while (!downloadDone);
} else {
NSLog(@"couldn't establish connection for: %@", downloadURL);
// Cleanup Operation so next one (if any) can run
;
}
}
else { // Operation has been cancelled, clean up
;
}
// Release the ARC pool to clean out this thread
//; //--> COMMENTED OUT, MAY BE PART OF ISSUE
}
#pragma mark -
#pragma mark NSURLConnection Delegate methods
// NSURLConnectionDelegate method: handle the initial connection
-(void)connection:(NSURLConnection *)connection didReceiveResponse:(NSHTTPURLResponse*)response {
NSLog(@"%s: Received response!", __FUNCTION__);
}
// NSURLConnectionDelegate method: handle data being received during connection
-(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
;
NSLog(@"downloaded %d bytes", );
}
// NSURLConnectionDelegate method: What to do once request is completed
-(void)connectionDidFinishLoading:(NSURLConnection *)connection {
NSLog(@"%s: Download finished! File: %@", __FUNCTION__, downloadURL);
NSFileManager *fileManager = ;
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *docDir = ;
NSString *targetPath = ;
BOOL isDir;
// If target folder path doesn't exist, create it
if (! isDirectory:&isDir]) {
NSError *makeDirError = nil;
withIntermediateDirectories:YES attributes:nil error:&makeDirError];
if (makeDirError != nil) {
NSLog(@"MAKE DIR ERROR: %@", );
;
}
}
NSError *saveError = nil;
//NSLog(@"downloadData: %@",downloadData);
;
if (saveError != nil) {
NSLog(@"Download save failed! Error: %@", );
;
}
else {
NSLog(@"file has been saved!: %@", targetPath);
}
downloadDone = true;
}
// NSURLConnectionDelegate method: Handle the connection failing
-(void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
NSLog(@"%s: File download failed! Error: %@", __FUNCTION__, );
;
}
// Function to clean up the variables and mark Operation as finished
-(void) terminateOperation {
;
;
finished = YES;
executing = NO;
downloadDone = YES;
;
;
}
#pragma mark -
#pragma mark NSOperation state Delegate methods
// NSOperation state methods
- (BOOL)isConcurrent {
return YES;
}
- (BOOL)isExecuting {
return executing;
}
- (BOOL)isFinished {
return finished;
}
</code></pre>
<p>注意:如果这太难以理解，我设置了 <a href="https://github.com/APPronaut/iOS-Simultaneous-Async-NSURLConnections" rel="noreferrer noopener nofollow">QUICK GITHUB PROJECT HERE</a>你可以看看。请注意，我不希望任何人为我工作，只是为我的问题寻找答案!</p>
<p>我怀疑它与保留/释放类变量有关，但我不能确定这一点，因为我认为实例化一个类会给每个实例自己的一组类变量。我已经尝试了一切，但我找不到答案，任何帮助/建议将不胜感激!</p>
<p><strong>更新:根据我下面的回答，我不久前解决了这个问题并更新了 <a href="https://github.com/APPronaut/iOS-Simultaneous-Async-NSURLConnections" rel="noreferrer noopener nofollow">GitHub project</a>与工作代码。希望如果您来这里是为了寻找同样的东西，它会有所帮助!</strong></p></p>
<br><hr><h1><strong>Best Answer-推荐答案</ strong></h1><br>
<p><p>出于良好的社区实践和帮助可能遇到同样问题的其他人的利益，我最终解决了这个问题并更新了 <a href="https://github.com/andy-cam/iOS-Simultaneous-Async-NSURLConnections" rel="noreferrer noopener nofollow"><strong>GitHub sample project here</strong></a>现在可以正常工作，即使是多个并发的 NSOperations!</p>
<p>最好查看 GitHub 代码，因为我进行了大量更改，但我必须进行的关键修复是:</p>
<pre><code> forMode:NSDefaultRunLoopMode];
</code></pre>
<p>这在 NSURLConnection 初始化之后调用，就在它启动之前。它将连接的执行附加到当前的主运行循环，以便 NSOperation 在下载完成之前不会过早终止。我很想感谢第一次发布这个聪明的修复的地方，但是太久了，我忘记了在哪里，道歉。希望这对某人有帮助!</p></p>
<p style="font-size: 20px;">关于ios - 使用 NSURLConnection 运行多个 NSOperation 实例？，我们在Stack Overflow上找到一个类似的问题：
<a href="https://stackoverflow.com/questions/9684770/" rel="noreferrer noopener nofollow" style="color: red;">
https://stackoverflow.com/questions/9684770/
</a>
</p>
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