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NECperation子类是多线程iOS任务最灵活的方式，并试图这样做。因此，该功能接收要下载的URL列表。保存，初始化同一个NSOperation类的实例，并将每个添加到NSOperation队列（一次只能下载1个文件）。
-(void) LibSyncOperation {
// Initialize download list. Download the homepage of some popular websites
downloadArray = [[NSArray alloc] initWithObjects:@"www.google.com",
@"www.stackoverflow.com",
@"www.reddit.com",
@"www.facebook.com", nil];
operationQueue = [[[NSOperationQueue alloc]init]autorelease];
[operationQueue setMaxConcurrentOperationCount:1]; // Only download 1 file at a time
[operationQueue waitUntilAllOperationsAreFinished];
for (int i = 0; i < [downloadArray count]; i++) {
LibSyncOperation *libSyncOperation = [[[LibSyncOperation alloc] initWithURL:[downloadArray objectAtIndex:i]]autorelease];
[operationQueue addOperation:libSyncOperation];
}
}
现在，这些类实例都被创建得很好，并且都被添加到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（使用带有委托方法的NSURLConnection）。我已经使用了我在另一个线程中看到的runLoop技巧，该技巧应该允许操作继续运行直到下载完成。 NSURLConnection已建立，但它永远不会开始将数据附加到NSMutableData对象！
@synthesize downloadURL, downloadData, downloadPath;
@synthesize downloadDone, executing, finished;
/* Function to initialize the NSOperation with the URL to download */
- (id)initWithURL:(NSString *)downloadString {
if (![super init]) return nil;
// Construct the URL to be downloaded
downloadURL = [[[NSURL alloc]initWithString:downloadString]autorelease];
downloadData = [[[NSMutableData alloc] init] autorelease];
NSLog(@"downloadURL: %@",[downloadURL path]);
// Create the download path
downloadPath = [NSString stringWithFormat:@"%@.txt",downloadString];
return self;
}
-(void)dealloc {
[super dealloc];
}
-(void)main {
// Create ARC pool instance for this thread.
// NSAutoreleasePool *pool = [[NSAutoreleasePool alloc]init]; //--> COMMENTED OUT, MAY BE PART OF ISSUE
if (![self isCancelled]) {
[self willChangeValueForKey:@"isExecuting"];
executing = YES;
NSURLRequest *downloadRequest = [NSURLRequest requestWithURL:downloadURL];
NSLog(@"%s: downloadRequest: %@",__FUNCTION__,downloadURL);
NSURLConnection *downloadConnection = [[NSURLConnection alloc] 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 {
[[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]];
} while (!downloadDone);
} else {
NSLog(@"couldn't establish connection for: %@", downloadURL);
// Cleanup Operation so next one (if any) can run
[self terminateOperation];
}
}
else { // Operation has been cancelled, clean up
[self terminateOperation];
}
// Release the ARC pool to clean out this thread
//[pool release]; //--> 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 {
[downloadData appendData:data];
NSLog(@"downloaded %d bytes", [data length]);
}
// NSURLConnectionDelegate method: What to do once request is completed
-(void)connectionDidFinishLoading:(NSURLConnection *)connection {
NSLog(@"%s: Download finished! File: %@", __FUNCTION__, downloadURL);
NSFileManager *fileManager = [NSFileManager defaultManager];
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *docDir = [paths objectAtIndex:0];
NSString *targetPath = [docDir stringByAppendingPathComponent:downloadPath];
BOOL isDir;
// If target folder path doesn't exist, create it
if (![fileManager fileExistsAtPath:[targetPath stringByDeletingLastPathComponent] isDirectory:&isDir]) {
NSError *makeDirError = nil;
[fileManager createDirectoryAtPath:[targetPath stringByDeletingLastPathComponent] withIntermediateDirectories:YES attributes:nil error:&makeDirError];
if (makeDirError != nil) {
NSLog(@"MAKE DIR ERROR: %@", [makeDirError description]);
[self terminateOperation];
}
}
NSError *saveError = nil;
//NSLog(@"downloadData: %@",downloadData);
[downloadData writeToFile:targetPath options:NSDataWritingAtomic error:&saveError];
if (saveError != nil) {
NSLog(@"Download save failed! Error: %@", [saveError description]);
[self terminateOperation];
}
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__, [error description]);
[self terminateOperation];
}
// Function to clean up the variables and mark Operation as finished
-(void) terminateOperation {
[self willChangeValueForKey:@"isFinished"];
[self willChangeValueForKey:@"isExecuting"];
finished = YES;
executing = NO;
downloadDone = YES;
[self didChangeValueForKey:@"isExecuting"];
[self didChangeValueForKey:@"isFinished"];
}
#pragma mark -
#pragma mark NSOperation state Delegate methods
// NSOperation state methods
- (BOOL)isConcurrent {
return YES;
}
- (BOOL)isExecuting {
return executing;
}
- (BOOL)isFinished {
return finished;
}
注意：如果那太难以理解，我设置了QUICK GITHUB PROJECT HERE你可以查看。请注意我不希望任何人为我做我的工作，只是寻找我的问题的答案！
我怀疑它与保留/释放类变量有关，但我不能确定，因为我认为实例化一个类会给每个实例提供一组自己的类变量。我已经尝试了一切，我找不到答案，任何帮助/建议将不胜感激！
更新：根据我在下面的回答，我不久前解决了这个问题，并使用工作代码更新了GitHub project。希望如果你来这里寻找相同的东西它会有所帮助！
答案 0 :(得分：4)
为了良好的社区实践并帮助可能最终遇到同样问题的其他人，我最终解决了这个问题并更新了现在正常工作的GitHub sample project here，即使对于多个并发的NSOperations也是如此！
最好查看GitHub代码，因为我进行了大量更改，但我必须做的关键修复就是：
[downloadConnection scheduleInRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];
在NSURLConnection初始化之后，就在它启动之前调用它。它将连接的执行附加到当前主运行循环，以便NSOperation在下载完成之前不会过早终止。我很乐意在第一次发布这个聪明的解决方案时给予赞扬，但是已经很久了，我已经忘记了哪里，道歉。希望这有助于某人！