NSInvocationOperation的cancelAllOperations不会取消正在运行的operation

原来以为cancelAllOperations时，正在运行的operation的会停止，旦实际发现是不会的。

并且在operation运行结束前，ViewController是不会dealloc的。

实际上，cancelAllOperations的作用是将在队列里排队的operation从对列里移除。

测试代码如下：

#import "ViewController.h"

@interface ViewController ()

@property (retain,nonatomic)NSOperationQueue *pQueue;

@end

@implementation ViewController

- (void)viewDidLoad

{

    [superviewDidLoad];

    self.pQueue =[[NSOperationQueuealloc]init];

    

   NSInvocationOperation *Invocation = [[NSInvocationOperationalloc]initWithTarget:selfselector:@selector(downLoadImage)object:nil];

    

    [self.pQueueaddOperation:Invocation];

    

    

    UIButton* btn = [UIButtonbuttonWithType:UIButtonTypeRoundedRect];

    btn.frame =CGRectMake(10,100,300, 30);

    [btn setTitle:@"pop back"forState:UIControlStateNormal];

    [btn addTarget:selfaction:@selector(popBack)forControlEvents:UIControlEventTouchUpInside];

    [self.viewaddSubview:btn];

}

-(void)popBack{

    

    [self.pQueuecancelAllOperations];

    [self.navigationControllerpopViewControllerAnimated:YES];

}

-(void)dealloc{

    NSLog(@"ViewController dealloced");

}

- (void)downLoadImage

{

   sleep(5);

   NSLog(@"operation ended");

}

@end