PerformSelector 相关
- (id)performSelector:(SEL)aSelector;
- (id)performSelector:(SEL)aSelector withObject:(id)object;
- (id)performSelector:(SEL)aSelector withObject:(id)object1 withObject:(id)object2;
这三个方法是同步在当前线程执行的。会阻塞当前线程。可在主线程或者子线程执行。
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");
}
打印结果是
doSomething:__111__, currentThread = <NSThread: 0x7fe18c904ac0>{number = 1, name = main}
(2s later...)
doSomething sleep over
over
如果在子线程里做会立即打印 over。子线程嘛，当然不会阻塞主线程。
PerformSelector:afterDelay 相关
- (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;
这两个方法类似，只是第二个方法里指定了线程中 Runloop 的 Modes，这个先不说。
这个方法是异步的，而且只能在主线程中执行。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]);
}
打印结果是
before sleep
(4s later...)
after sleep
doSomething:__ahahaha__, currentThread = <NSThread: 0x7fdf73706c70>{number = 1, name = main}
能看出来，这个方法不会阻塞当前线程，而是把 Selector 加到主队列里，当 delay 之后执行 Selector。如果主线程在执行业务，那只能等到执行完所有业务之后才会去执行 Selector，就算 delay 等于 0。
那 delay 从什么时候开始计算呢？从 performSelector 的时候。就算这时主线程在阻塞也会计算时间，当阻塞结束之后，如果到了 delay 那就执行 Selector，如果没到就继续 delay。
PerformSelectorOnMainThread 相关
- (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;
// 相关的指定线程方法就不提了。一个意思。
这俩方法意思很明确，可以在主或者子线程中执行，但 Selector 肯定是在主线程中执行。这里只提一下 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");
}
打印结果是
doSomething:__1111__, currentThread = <NSThread: 0x7fc90b5038b0>{number = 1, name = main}
(2s later...)
doSomething sleep over
before sleep
(2s later);
after sleep
很明显，waitUntilDone == YES 会阻塞当前线程，当主线程执行完 Selector 之后才会继续执行当前线程。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
主线程不会阻塞当前线程，大家互不干扰。但上述代码中的当前线程是主线程，那么和 performSelector:afterDelay 类似，主线程顺序执行完业务之后才会继续执行 Selector 的业务。如果当前线程是子线程呢？
- (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");
}
打印结果是
before sleep
doSomething:__1111__, currentThread = <NSThread: 0x7ff7c2603a00>{number = 1, name = main}
(after 2s...)
after sleep
doSomething sleep over
当前线程和主线程互不干扰，大家是并行的。那如果 waitUntilDone == YES 呢？
当然是等主线程执行完之后再接着执行子线程里的业务了。
doSomething:__1111__, currentThread = <NSThread: 0x7fd3a1f03510>{number = 1, name = main}
(2s later...)
doSomething sleep over
before sleep
(2s later...)
after sleep
大致就是这样。
