PerformSelector 相關(guān)
- (id)performSelector:(SEL)aSelector;
- (id)performSelector:(SEL)aSelector withObject:(id)object;
- (id)performSelector:(SEL)aSelector withObject:(id)object1 withObject:(id)object2;
這三個方法是同步在當前線程執(zhí)行的。會阻塞當前線程?？稍谥骶€程或者子線程執(zhí)行。
比如
- (void)viewDidLoad {
[super viewDidLoad];
[self performSelector:@selector(doSomething:) withObject:@"111"];
NSLog(@"over");
}
- (void)doSomething:(NSString *)aStr {
NSLog(@"doSomething:__%@__, currentThread = %@", aStr, [NSThread currentThread]);
sleep(2);
NSLog(@"doSomething sleep over");
}
打印結(jié)果是
doSomething:__111__, currentThread = <NSThread: 0x7fe18c904ac0>{number = 1, name = main}
(2s later...)
doSomething sleep over
over
如果在子線程里做會立即打印 over。子線程嘛，當然不會阻塞主線程。
PerformSelector:afterDelay 相關(guān)
- (void)performSelector:(SEL)aSelector withObject:(nullable id)anArgument afterDelay:(NSTimeInterval)delay;
- (void)performSelector:(SEL)aSelector withObject:(nullable id)anArgument afterDelay:(NSTimeInterval)delay inModes:(NSArray<NSString *> *)modes;
這兩個方法類似，只是第二個方法里指定了線程中 Runloop 的 Modes，這個先不說。
這個方法是異步的，而且只能在主線程中執(zhí)行。什么意思呢？
- (void)viewDidLoad {
[super viewDidLoad];
[self performSelector:@selector(doSomething:) withObject:@"ahahaha" afterDelay:0];
NSLog(@"before sleep");
sleep(4);
NSLog(@"after sleep");
}
- (void)doSomething:(NSString *)aStr {
NSLog(@"doSomething:__%@__, currentThread = %@", aStr, [NSThread currentThread]);
}
打印結(jié)果是
before sleep
(4s later...)
after sleep
doSomething:__ahahaha__, currentThread = <NSThread: 0x7fdf73706c70>{number = 1, name = main}
能看出來，這個方法不會阻塞當前線程，而是把 Selector 加到主隊列里，當 delay 之后執(zhí)行 Selector。如果主線程在執(zhí)行業(yè)務(wù)，那只能等到執(zhí)行完所有業(yè)務(wù)之后才會去執(zhí)行 Selector，就算 delay 等于 0。
那 delay 從什么時候開始計算呢？從 performSelector 的時候。就算這時主線程在阻塞也會計算時間，當阻塞結(jié)束之后，如果到了 delay 那就執(zhí)行 Selector，如果沒到就繼續(xù) delay。
PerformSelectorOnMainThread 相關(guān)
- (void)performSelectorOnMainThread:(SEL)aSelector withObject:(nullable id)arg waitUntilDone:(BOOL)wait modes:(nullable NSArray<NSString *> *)array;
- (void)performSelectorOnMainThread:(SEL)aSelector withObject:(nullable id)arg waitUntilDone:(BOOL)wait;
// 相關(guān)的指定線程方法就不提了。一個意思。
這倆方法意思很明確，可以在主或者子線程中執(zhí)行，但 Selector 肯定是在主線程中執(zhí)行。這里只提一下 waitUntilDone。
- (void)viewDidLoad {
[super viewDidLoad];
[self performSelectorOnMainThread:@selector(doSomething:) withObject:@"1111" waitUntilDone:YES];
NSLog(@"before sleep");
sleep(2);
NSLog(@"after sleep");
}
- (void)doSomething:(NSString *)aStr {
NSLog(@"doSomething:__%@__, currentThread = %@", aStr, [NSThread currentThread]);
sleep(2);
NSLog(@"doSomething sleep over");
}
打印結(jié)果是
doSomething:__1111__, currentThread = <NSThread: 0x7fc90b5038b0>{number = 1, name = main}
(2s later...)
doSomething sleep over
before sleep
(2s later);
after sleep
很明顯，waitUntilDone == YES 會阻塞當前線程，當主線程執(zhí)行完 Selector 之后才會繼續(xù)執(zhí)行當前線程。如果是 NO 呢？
before sleep
(2s later...)
after sleep
doSomething:__1111__, currentThread = <NSThread: 0x7fc90b5038b0>{number = 1, name = main}
(2s later);
doSomething sleep over
主線程不會阻塞當前線程，大家互不干擾。但上述代碼中的當前線程是主線程，那么和 performSelector:afterDelay 類似，主線程順序執(zhí)行完業(yè)務(wù)之后才會繼續(xù)執(zhí)行 Selector 的業(yè)務(wù)。如果當前線程是子線程呢？
- (void)viewDidLoad {
[super viewDidLoad];
dispatch_queue_t t1 = dispatch_queue_create("sub queue", DISPATCH_QUEUE_CONCURRENT);
dispatch_async(t1, ^{
[self performSelectorOnMainThread:@selector(doSomething:) withObject:@"1111" waitUntilDone:NO];
NSLog(@"before sleep");
sleep(2);
NSLog(@"after sleep");
});
}
- (void)doSomething:(NSString *)aStr {
NSLog(@"doSomething:__%@__, currentThread = %@", aStr, [NSThread currentThread]);
sleep(2);
NSLog(@"doSomething sleep over");
}
打印結(jié)果是
before sleep
doSomething:__1111__, currentThread = <NSThread: 0x7ff7c2603a00>{number = 1, name = main}
(after 2s...)
after sleep
doSomething sleep over
當前線程和主線程互不干擾，大家是并行的。那如果 waitUntilDone == YES 呢？
當然是等主線程執(zhí)行完之后再接著執(zhí)行子線程里的業(yè)務(wù)了。
doSomething:__1111__, currentThread = <NSThread: 0x7fd3a1f03510>{number = 1, name = main}
(2s later...)
doSomething sleep over
before sleep
(2s later...)
after sleep
大致就是這樣。
