我一直在想，你可以在你用 GCD 启动的线程中使用 cancel/cancelAllOperations/.isCancelled 吗？
目前，我只是使用布尔值作为标志，来取消后台进程。
假设您想在后台进行大量处理，同时保持 UI 响应，以便您可以捕捉取消按钮（或动画显示处理器正在工作）。这是我们如何做到的......
@interface AstoundingView : UIView
{
BOOL pleaseAbandonYourEfforts;
blah
}
@implementation AstoundingView
//
// these are the foreground routines...
// begin, abandon and all-done
//
-(void)userHasClickedToBuildASpaceship
{
[YourUIStateMachine buildShip];
[self procedurallyBuildEnormousSpaceship];
}
-(void)userHasClickedToAbandonBuildingTheSpaceship
{
[YourUIStateMachine inbetween];
pleaseAbandonYourEfforts = false; // that's it!
}
-(void)attentionBGIsAllDone
{
// you get here when the process finishes, whether by completion
// or if we have asked it to cancel itself.
[self typically setNeedsDisplay, etc];
[YourUIStateMachine nothinghappening];
}
//
// these are the background routines...
// the kickoff, the wrapper, and the guts
//
// The wrapper MUST contain a "we've finished" message to home
// The guts can contain messages to home (eg, progress messages)
//
-(void)procedurallyBuildEnormousSpaceship
{
// user has clicked button to build new spaceship
pleaseAbandonYourEfforts = FALSE;
dispatch_async(
dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0),
^{ [self actuallyProcedurallyBuildInBackground]; }
);
// as an aside, it's worth noting that this does not work if you
// use the main Q rather than a global Q as shown.
// Thus, this would not work:
// dispatch_async(dispatch_get_main_queue(), ^{ ...; });
}
-(void)actuallyProcedurallyBuildInBackground
{
// we are actually in the BG here...
[self setUpHere];
// set up any variables, contexts etc you need right here
// DO NOT open any variables, contexts etc in "buildGuts"
// when you return back here after buildGuts, CLEAN UP those
// variables, contexts etc at this level.
// (using this system, you can nest as deep as you want, and the
// one CHECKER pseudocall will always take you right out.
// You can insert CHECKERs anywhere you want.)
[self buildGuts];
// Note that any time 'CHECKER' "goes off', you must fall-
// through to exactly here. This is the common fall-through point.
// So we must now tidy-up, to match setUpHere.
[self wrapUpHere];
// when you get to here, we have finished (or, the user has cancelled
// the background operation)
// Whatever technique you use,
// MAKE SURE you clean up all your variables/contexts/etc before
// abandoning the BG process.
// and then you must do this......
// we have finished. it's critical to let the foreground know NOW,
// or else it will sit there for about 4 to 6 seconds (on 4.3/4.2)
// doing nothing until it realises you are done
dispatch_sync(
dispatch_get_main_queue(),
^{[self attentionBGIsAllDone];} // would setneedsdisplay, etc
);
return;
}
-(void)buildGuts
{
// we are actually in the BG here...
// Don't open any local variables in here.
CHECKER
[self blah blah];
CHECKER
[self blah blah];
CHECKER
[self blah blah];
// to get stuff done from time to time on the UI, something like...
CHECKER
dispatch_sync(
dispatch_get_main_queue(),
^{[supportStuff pleasePostMidwayImage:
[UIImage imageWithCGImage:halfOfShip] ];}
);
CHECKER
[self blah blah];
CHECKER
[self blah blah];
CHECKER
[self blah blah];
for ( i = 1 to 10^9 )
{
CHECKER
[self blah blah];
}
CHECKER
[self blah blah];
CHECKER
[self blah blah];
CHECKER
[self blah blah];
return;
}
CHECKER 只是检查标志是否为真......
#define CHECKER if ( pleaseAbandonYourEfforts == YES ) \
{NSLog(@"Amazing Interruption System Working!");return;}
这一切都完美无缺。
但是........是否可以在这种类型的 GCD 使用中使用 cancel/cancelAllOperations/.isCancelled？
这里有什么故事？干杯。
PS - 适用于使用此“六部分”背景模板的任何初学者。
请注意，正如 BJ 在下面强调的那样，每当您退出 bg 流程时...
你必须清理你打开的所有变量！
在我的习惯中，您必须分配所有变量、上下文、内存等，特别是在“setUpHere”中。你必须在“wrapUpHere”中释放它们。（如果你在 BG 中越深入，这个习语就会继续有效。）
或者，完全按照 BJ 在他的示例中显示的那样做。（如果你使用BJ的方法，如果你深入的话要小心。）
无论您使用什么方法，当您退出 BG 进程时，都必须清理您打开的所有变量/上下文/内存。希望它可以帮助某人，有时！