雏菊NSOperation main变成超级可以接受吗？

Question

- (void)main
{
IDBAssert0(self.bestCapture.webpCandidate);
self.finished = NO;
self.executing = YES;

NSTimeInterval now = [NSDate timeIntervalSinceReferenceDate];
UIImage *possiblycorrupted = [UIImage imageWithWebPData:self.bestCapture.webpCandidate];
NSTimeInterval  webpInterval = [NSDate timeIntervalSinceReferenceDate]-now;
NSDLog(@"it tooke %.2f sec to unpack webp", webpInterval);

self.microblinkCandidate = possiblycorrupted; // data superclass nsoperation processes

[super main];
}

基类中的首要任务自然是将finished设置为no，然后将执行设置为yes：

- (void)main
{
self.finished = NO;
self.executing = YES;
NSTimeInterval now = [NSDate timeIntervalSinceReferenceDate];
start = now;

CGSize size = [self.microblinkCandidate size];
IDBAssert0(size.width && size.height);
IDBAssert0(self.microblink);
// this starts async processing
[self.microblink processImage:self.microblinkCandidate
           scanningRegion:CGRectMake(0.0, 0.0, 1.0, 1.0)
                 delegate:self];

while (![self isCancelled])
{
    sleep(1);
    NSTimeInterval now = [NSDate timeIntervalSinceReferenceDate];
    if(now - start > 5) {
        // #5677 microblink watchdog to detect hangs
        [self cancel];
        break;
    }

}
[self done];
}

因为它不是抽象的，也会单独使用。

该循环仅用于调试/监视狗。

在正常操作中，如果此回调：

- (void)scanningViewController:       (UIViewController<PPScanningViewController>*)scanningViewController
          didOutputResults:(NSArray*)results
{
if([results count]>0) {
    NSTimeInterval now = [NSDate timeIntervalSinceReferenceDate];
    NSDLog(@"found barcode in %.1fs", now - start);
    self.microblinkSuccessHandler();
}else{
    IDBAssert0(self.microblinkFailureHandler);
    self.microblinkFailureHandler();
}
[self done];
}

在"processImage:“完成时(以及时的方式)调用。

基类是

@implementation IDBAsynchronousOperation

@synthesize executing = _executing;
@synthesize finished = _finished;

-(BOOL)isFinished
{
return _finished;
}

- (void)setFinished:(BOOL)finished
{
[self willChangeValueForKey:@"isFinished"];
_finished = finished;
[self didChangeValueForKey:@"isFinished"];
}

-(BOOL)isExecuting
{
return _executing;
}

- (void)setExecuting:(BOOL)executing
{
[self willChangeValueForKey:@"isExecuting"];
_executing = executing;
[self didChangeValueForKey:@"isExecuting"];
}

- (instancetype)init
{
self = [super init];
if (self) {
    //      self.completionBlock = ^{
    //          NSDLog(@"image barcode search has finished");
    //      };
    IDBAssert0(sizeof(_executing)<2);
}
return self;
}

-(BOOL)isAsynchronous
{
return YES;
}

@end

Answer 1

您当然可以(而且我们经常这样做)子类您自己的具体NSOperation子类。

要使基类子类可以使用，您需要确保只执行一次self.executing = true。现在，基类和子类中的main都执行此操作，因此您将执行两次。典型的解决方案是将其从这两个main实现中提取出来，并在基类的start中执行。无论如何，苹果建议你在start上做这件事。

因此，在从两个self.finished实现中删除了self.executing和self.executing之后，您就可以实现start了。

- (void)start {
    if ([self isCancelled]) {
        self.finished = YES;
        return;
    }

    self.executing = YES;

    [self main];
}

注意，操作启动时不必调用self.finished = false，因为这将发送不必要的KVO。

不相关的意见：

如果您将while循环保留在基类中，那么如果调用了[self isCancelled]或processImage委托完成方法，我建议退出该循环(也许您可以更新一些状态属性以指定何时调用该委托方法)。现在，如果processImage在超时之前完成，它将使操作持续运行5秒。

就我个人而言，取决于processImage是如何设计的，我可能倾向于完全切除while循环。您通常希望避免任何这样的轮询。例如，我可以将[self done]放在适当的委托方法中，然后为超时设置一个定时器或dispatch_after。

- (void)main {
    NSTimeInterval now = [NSDate timeIntervalSinceReferenceDate];
    start = now;

    CGSize size = [self.microblinkCandidate size];
    IDBAssert0(size.width && size.height);
    IDBAssert0(self.microblink);

    // this starts async processing

    [self.microblink processImage:self.microblinkCandidate
                   scanningRegion:CGRectMake(0.0, 0.0, 1.0, 1.0)
                         delegate:self];

    // cancel upon timeout

    typeof(self) __weak weakSelf = self;
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(5 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        typeof(self) __strong strongSelf = weakSelf;
        if ([strongSelf isExecuting]) {
            [strongSelf cancel];
            [strongSelf done];   // if canceling calls the delegate method that calls `done`, then you don't need this here
        }
    });
}