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];
}

基类中的第一件事主要是将完成设置为no并执行到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。

循环仅用于调试/监视程序

在正常操作中，它没有跳闸，操作完成如果这个回调：

- (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];
}

当“processImage：”完成（及时）时，将调用

。

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（我们经常这样做）继承您自己的具体NSOperation子类。

要使基类可子类化，您需要确保只执行一次self.executing = true。现在，基类和子类中的main都可以做到，因此您将执行两次。典型的解决方案是将其从两个main实现中拉出来，并在基类的start中执行。无论如何，Apple建议您在start中执行此操作。

因此，从self.finished个实施中移除self.executing和main内容后，您就可以实施start：

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

    self.executing = YES;

    [self main];
}

注意，操作开始时您不必调用self.finished = false，因为这会发送不必要的KVO。

无关的观察：

如果你在基类中保留while循环，我建议退出循环，如果[self isCancelled]或processImage委托完成方法被调用（也许你可以更新）一些状态属性，用于指定何时调用该委托方法）。现在，如果processImage在超时之前完成，它将使操作保持运行整整5秒。

就个人而言，根据processImage的设计方式，我可能完全倾向于切除while循环。您通常希望避免任何类似的轮询。例如，我可能会将[self done]置于适当的委托方法中，然后为超时设置计时器或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
        }
    });
}

雏菊NSOperation主要进入超级是否可以接受？

1 个答案: