我目前正在使用dispatch_group在所有并发任务完成时获取通知。我正在[TWReaderDocument documentFileURL：url withCompletionBlock：]类方法中的一个并发队列上卸载一些繁重的任务。
我已实现以下代码但从未收到任何通知。我在下面的代码中看不到我可能做错了什么：
dispatch_group_t readingGroup = dispatch_group_create();
NSFileManager* manager = [NSFileManager defaultManager];
NSString *docsDir = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"Data"];
NSDirectoryEnumerator *dirEnumerator = [manager enumeratorAtURL:[NSURL fileURLWithPath:docsDir]
includingPropertiesForKeys:[NSArray arrayWithObjects:NSURLNameKey,
NSURLIsDirectoryKey,nil]
options:NSDirectoryEnumerationSkipsHiddenFiles
errorHandler:nil];
// An array to store the all the enumerated file names in
NSMutableArray *arrayFiles;
// Enumerate the dirEnumerator results, each value is stored in allURLs
for (NSURL *url in dirEnumerator) {
// Retrieve the file name. From NSURLNameKey, cached during the enumeration.
NSString *fileName;
[url getResourceValue:&fileName forKey:NSURLNameKey error:NULL];
// Retrieve whether a directory. From NSURLIsDirectoryKey, also cached during the enumeration.
NSNumber *isDirectory;
[url getResourceValue:&isDirectory forKey:NSURLIsDirectoryKey error:NULL];
if (![isDirectory boolValue]) {
dispatch_group_enter(readingGroup);
TWReaderDocument* doc = [TWReaderDocument documentFileURL:url withCompletionBlock:^(BOOL success) {
dispatch_group_leave(readingGroup);
}];
[arrayFiles addObject:doc];
}
else if ([[[fileName componentsSeparatedByString:@"_" ] objectAtIndex:0] isEqualToString:@"XXXXXX"]) {
TreeItem* treeItem = [[TreeItem alloc] init];
arrayFiles = [NSMutableArray arrayWithCapacity:10];
treeItem.child = arrayFiles;
treeItem.nodeName = [[fileName componentsSeparatedByString:@"_" ] lastObject];
[self addItem:treeItem];
}
}
dispatch_group_notify(readingGroup, dispatch_get_main_queue(), ^{ // 4
NSLog(@"All concurrent tasks completed");
});
dispatch_group_enter和dispatch_group_leave是否必须在同一个线程上执行？
修改 我工厂方法的代码片段可能也有帮助：
+ (TWReaderDocument *)documentFileURL:(NSURL *)url withCompletionBlock:(readingCompletionBlock)completionBlock{
TWReaderDocument * twDoc = [[TWReaderDocument alloc] init];
twDoc.status = ReaderDocCreated;
twDoc.doc = [ReaderDocument withDocumentFilePath:[url path] withURL:url withLoadingCompletionBLock:^(BOOL completed) {
twDoc.status = completed ? ReaderDocReady : ReaderDocFailed;
completionBlock(completed);
}];
return twDoc;
}
TWReaderDocument是一个包装类，它在内部调用第三方库的以下方法（它是一个PDF阅读器）
+ (ReaderDocument *)withDocumentFilePath:(NSString *)filePath withURL:(NSURL*)url withLoadingCompletionBLock:(readingCompletionBlock)completionBlock{
ReaderDocument *document = [[ReaderDocument alloc] initWithFilePath:filePath withURL:url withLoadingCompletionBLock:[completionBlock copy]];
return document;
}
- (id)initWithFilePath:(NSString *)fullFilePath withURL:(NSURL*)url withLoadingCompletionBLock:(readingCompletionBlock)completionBlock {
id object = nil; // ReaderDocument object;
if ([ReaderDocument isPDF:fullFilePath] == YES) // File must exist
{
if ((self = [super init])) // Initialize superclass object first
{
_fileName = [ReaderDocument relativeApplicationFilePath:fullFilePath]; // File name
dispatch_async([ReaderDocument concurrentLoadingQueue], ^{
self.guid = [ReaderDocument GUID]; // Create a document GUID
self.password = nil; // Keep copy of any document password
self.bookmarks = [NSMutableIndexSet indexSet]; // Bookmarked pages index set
self.pageNumber = [NSNumber numberWithInteger:1]; // Start on page 1
CFURLRef docURLRef = (__bridge CFURLRef)url;// CFURLRef from NSURL
self.fileURL = url;
CGPDFDocumentRef thePDFDocRef = CGPDFDocumentCreateX(docURLRef, self.password);
BOOL success;
if (thePDFDocRef != NULL) // Get the number of pages in the document
{
NSInteger pageCount = CGPDFDocumentGetNumberOfPages(thePDFDocRef);
self.pageCount = [NSNumber numberWithInteger:pageCount];
CGPDFDocumentRelease(thePDFDocRef); // Cleanup
success = YES;
}
else // Cupertino, we have a problem with the document
{
// NSAssert(NO, @"CGPDFDocumentRef == NULL");
success = NO;
}
NSFileManager *fileManager = [NSFileManager new]; // File manager instance
self.lastOpen = [NSDate dateWithTimeIntervalSinceReferenceDate:0.0]; // Last opened
NSDictionary *fileAttributes = [fileManager attributesOfItemAtPath:fullFilePath error:NULL];
self.fileDate = [fileAttributes objectForKey:NSFileModificationDate]; // File date
self.fileSize = [fileAttributes objectForKey:NSFileSize]; // File size (bytes)
completionBlock(success);
});
//[self saveReaderDocument]; // Save the ReaderDocument object
object = self; // Return initialized ReaderDocument object
}
}
return object;
}
答案 0 :(得分：1)
如果不了解更多有关TWReaderDocument的信息，很难说这里发生了什么，但我怀疑......
首先，不，dispatch_group_enter和dispatch_group_leave 不必须在同一个线程上执行。当然不。
根据此处的信息，我的最佳猜测是，对于某些输入，[TWReaderDocument documentFileURL:withCompletionBlock:]正在返回nil。您可以尝试这样做：
if (![isDirectory boolValue]) {
dispatch_group_enter(readingGroup);
TWReaderDocument* doc = [TWReaderDocument documentFileURL:url withCompletionBlock:^(BOOL success) {
dispatch_group_leave(readingGroup);
}];
// If the doc wasn't created, leave might never be called.
if (nil == doc) {
dispatch_group_leave(readingGroup);
}
[arrayFiles addObject:doc];
}
试一试。
修改 它完全符合我的预期。在某些情况下，此工厂方法不会调用完成。例如：
if ([ReaderDocument isPDF:fullFilePath] == YES) // File must exist
如果-isPDF:返回NO，则永远不会调用completionBlock，返回的值将为nil。
顺便说一句，你永远不应该比较== YES。 （任何非零都等于YES，但YES定义为1。只需if ([ReaderDocument isPDF:fullFilePath])。它等同，更安全。