把NSOperation主要变成超级可以接受吗？
- (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];
}
第一件事主要在基类中不自然地被设置完毕没有和执行为yes：把NSOperation主要变成超级可以接受吗？
- (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];
}
因为它不是一个抽象的，将在其自身的使用。
循环是调试/看门狗仅供参考
在正常操作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];
}
被调用时“processImage来：”将完成（及时）。
非常基类是
@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
回答：
您当然可以（并且我们经常这样做）继承自己的具体NSOperation子类。
要使基类具有可分类性，您需要确保只执行一次self.executing = true。现在，基类和子类中的main都这样做了，因此你会做两次。典型的解决方案是将它从这两个main实现中拉出来，并在基类的start中执行。无论如何，苹果建议你在start这个东西。
因此已经从两个main实现去除self.finished和self.executing的东西，你就可以实现start：
- (void)start { if ([self isCancelled]) {
self.finished = YES;
return;
}
self.executing = YES;
[self main];
}
注意，你不必叫self.finished = false当操作开始，因为这将发送不必要的KVO。
一个无关的观察：
如果保持while环基类，我建议退出循环，如果任一[self isCancelled]或者如果processImage委托完成的方法被称为（也许你可以更新某些状态属性指定何时调用委托方法）。现在，如果processImage在超时之前完成，它将使操作持续运行整整5秒钟。
就个人而言，根据processImage的设计，我可能会倾向于完全消除while循环。你通常希望避免这样的投票。例如，我可能会将[self done]置于适当的委托方法中，然后设置一个计时器或dispatch_after来进行超时。
- (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) __span spanSelf = weakSelf;
if ([spanSelf isExecuting]) {
[spanSelf cancel];
[spanSelf done]; // if canceling calls the delegate method that calls `done`, then you don't need this here
}
});
}
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