dispatch_source_set_cancel_handler並將nil分配給@property ivar

Question

如果您有一個定時器的cancel_handler，您是否可以直接引用和重置任何聲明爲具有'assign'屬性的ivars屬性，還是必須先將其指定爲__block？

@interface SomeClass: NSObject { } 
@property (nonatomic, assign) dispatch_source_t    timer; 
@end 

// Class implementation 
@implementation SomeClass 

@synthesize timer = _timer; 
- (void)startTimer 
{ 
    dispatch_queue_t globalQ = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0); 
    self.timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 
            0, 0, globalQ); 

    dispatch_time_t startWhen = dispatch_walltime(DISPATCH_TIME_NOW, NSEC_PER_SEC * 1); 
    dispatch_source_set_timer(_timer, startWhen, 1 * NSEC_PER_SEC, 5000ull); 

    dispatch_source_set_event_handler(_timer, ^{ 
     // timer's event handler  
    }); 

    // VERSION 1: 
    // Is it okay to reference and assign self.timer to nil 
    // or does it have to be declared as __block as in VERSION 2? 
    dispatch_source_set_cancel_handler(_timer, ^{ 
     dispatch_release(_timer);     
     self.timer = nil; 
    }); 


    // VERSION 2: 
    __block myTimer = self.timer; 
    dispatch_source_set_cancel_handler(_timer, ^{ 
     dispatch_release(myTimer);   

     myTimer = nil; 
    }); 

    dispatch_resume(_timer); 
} 

Answer 1

你可以參考ivars就好了。但是，這些參考文獻帶有對self的隱含引用，所以您需要謹慎保留週期。例如，如果您直接引用伊維爾，不要指望關閉-dealloc中的計時器，因爲永遠不會調用該計時器。