关于NSOperation和NSOperationQueue，我有几个不同的问题，我知道你们的回答对我有帮助。
我必须加载大量图像，并且已经基于NSOperation，NSOperationQueue和NSURLConnection(异步加载)创建了自己的加载器；
问题:
maxConcurrentOperationCount)设置NSOperationQueue(例如3)，是否意味着即使队列有100个操作，在同一时间仅执行3个操作？ maxConcurrentOperationCount时，有时“setCompletionBlock”不起作用，并且计数(operationCount)仅增加；为什么？ MyLoader:
- (id)init
{
self = [super init];
if (self) {
_loadingFiles = [NSMutableDictionary new];
_downloadQueue = [NSOperationQueue new];
_downloadQueue.maxConcurrentOperationCount = 3;
_downloadQueue.name = @"LOADER QUEUE";
}
return self;
}
- (void)loadFile:(NSString *)fileServerUrl handler:(GetFileDataHandler)handler {
if (fileServerUrl.length == 0) {
return;
}
if ([_loadingFiles objectForKey:fileServerUrl] == nil) {
[_loadingFiles setObject:fileServerUrl forKey:fileServerUrl];
__weak NSMutableDictionary *_loadingFiles_ = _loadingFiles;
MyLoadOperation *operation = [MyLoadOperation new];
[operation fileServerUrl:fileServerUrl handler:^(NSData *fileData) {
[_loadingFiles_ removeObjectForKey:fileServerUrl];
if (fileData != nil) {
handler(fileData);
}
}];
[operation setQueuePriority:NSOperationQueuePriorityLow];
[_downloadQueue addOperation:operation];
__weak NSOperationQueue *_downloadQueue_ = _downloadQueue;
[operation setCompletionBlock:^{
NSLog(@"completion block :%i", _downloadQueue_.operationCount);
}];
}
}
我的操作:
@interface MyLoadOperation()
@property (nonatomic, assign, getter=isOperationStarted) BOOL operationStarted;
@property(nonatomic, strong)NSString *fileServerUrl;
@property(nonatomic, copy)void (^OnFinishLoading)(NSData *);
@end
@implementation MyLoadOperation
- (id)init
{
self = [super init];
if (self) {
_executing = NO;
_finished = NO;
}
return self;
}
- (void)fileServerUrl:(NSString *)fileServerUrl
handler:(void(^)(NSData *))handler {
@autoreleasepool {
self.fileServerUrl = fileServerUrl;
[self setOnFinishLoading:^(NSData *loadData) {
handler(loadData);
}];
[self setOnFailedLoading:^{
handler(nil);
}];
self.url = [[NSURL alloc] initWithString:self.fileServerUrl];
NSMutableURLRequest *request = [[NSMutableURLRequest alloc]
initWithURL:self.url
cachePolicy:NSURLRequestReloadIgnoringLocalCacheData
timeoutInterval:25];
[request setValue:@"" forHTTPHeaderField:@"Accept-Encoding"];
self.connection = [[NSURLConnection alloc] initWithRequest:request delegate:self startImmediately:NO];
[self.connection scheduleInRunLoop:[NSRunLoop mainRunLoop] forMode:NSRunLoopCommonModes];
[self.connection start];
_data = [[NSMutableData alloc] init];
}
}
- (void)main {
@autoreleasepool {
[self stop];
}
}
- (void)start {
[self setOperationStarted:YES];
[self willChangeValueForKey:@"isFinished"];
_finished = NO;
[self didChangeValueForKey:@"isFinished"];
if ([self isCancelled])
{
[self willChangeValueForKey:@"isFinished"];
_finished = YES;
_executing = NO;
[self didChangeValueForKey:@"isFinished"];
}
else
{
[self willChangeValueForKey:@"isExecuting"];
_finished = NO;
_executing = YES;
[self didChangeValueForKey:@"isExecuting"];
}
}
- (BOOL)isConcurrent {
return YES;
}
- (BOOL)isExecuting {
return _executing;
}
- (BOOL)isFinished {
return _finished;
}
- (void)cancel {
[self.connection cancel];
if ([self isExecuting])
{
[self stop];
}
[super cancel];
}
#pragma mark -NSURLConnectionDelegate
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
[_data appendData:data];
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
if ([self OnFinishLoading]) {
[self OnFinishLoading](_data);
}
if (![self isCancelled]) {
[self stop];
}
}
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
;
if (![self isCancelled]) {
[self stop];
}
}
- (void)stop {
@try {
__weak MyLoadOperation *self_ = self;
dispatch_async(dispatch_get_main_queue(), ^{
[self_ completeOperation];
});
}
@catch (NSException *exception) {
NSLog(@"Exception! %@", exception);
[self completeOperation];
}
}
- (void)completeOperation {
if (![self isOperationStarted]) return;
[self willChangeValueForKey:@"isFinished"];
[self willChangeValueForKey:@"isExecuting"];
_executing = NO;
_finished = YES;
[self didChangeValueForKey:@"isExecuting"];
[self didChangeValueForKey:@"isFinished"];
}
最佳答案
您必须使用Operation的start方法而不是fileServerUrl:handler:来启动连接。
我将完全删除此方法，仅提供带有所有必需参数的init方法，您可以在其中完全设置操作。然后，在方法start中启动连接。
此外，尚不清楚为什么要覆盖main。
修改状态变量_executing和_finished可能更简洁明了(由于它们已经初始化为NO，因此您不需要初始设置它们)。仅在包括KVO通知的“最终”方法completeOperation中设置它们。
您也不需要stop中的@ try / @ catch，因为函数dispatch_async()不会引发Objective-C异常。
您的cancel方法不是线程安全的，并且还有其他一些问题。我建议进行以下更改:
@implementation MyOperation {
BOOL _executing;
BOOL _finished;
NSError* _error; // remember the error
id _result; // the "result" of the connection, unless failed
completion_block_t _completionHandler; //(your own completion handler)
id _self; // strong reference to self
}
// Use the "main thread" as the "synchronization queue"
- (void) start
{
// Ensure start will be called only *once*:
dispatch_async(dispatch_get_main_queue(), ^{
if (!self.isCancelled && !_finished && !_executing) {
[self willChangeValueForKey:@"isExecuting"];
_executing = YES;
[self didChangeValueForKey:@"isExecuting"];
_self = self; // keep a strong reference to self in order to make
// the operation "immortal for the duration of the task
// Setup connection:
...
[self.connection start];
}
});
}
- (void) cancel
{
dispatch_async(dispatch_get_main_queue, ^{
[super cancel];
[self.connection cancel];
if (!_finished && !_executing) {
// if the op has been cancelled before we started the connection
// ensure the op will be orderly terminated:
self.error = [[NSError alloc] initWithDomain:@"MyOperation"
code:-1000
userInfo:@{NSLocalizedDescriptionKey: @"cancelled"}];
[self completeOperation];
}
});
}
- (void)completeOperation
{
[self willChangeValueForKey:@"isExecuting"];
self.isExecuting = NO;
[self didChangeValueForKey:@"isExecuting"];
[self willChangeValueForKey:@"isFinished"];
self.isFinished = YES;
[self didChangeValueForKey:@"isFinished"];
completion_block_t completionHandler = _completionHandler;
_completionHandler = nil;
id result = self.result;
NSError* error = self.error;
_self = nil;
if (completionHandler) {
dispatch_async(dispatch_get_global_queue(0, 0), ^{
completionHandler(result, error);
});
}
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
if ([self onFinishLoading]) {
[self onFinishLoading](self.result);
}
[self completeOperation];
}
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
if (self.error == nil) {
self.error = error;
}
[self completeOperation];
}
关于ios - NSOperation + setCompletionBlock，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/23033707/