performSelector系列方法

• 編譯器并不知道將要執(zhí)行的選擇器是什么，也不知道該選擇器是否有返回值，所以沒有辦法運用ARC的內(nèi)存管理規(guī)則判斷返回值是不是應(yīng)該釋放
• 這些方法的返回值只能是void或者對象類型（id）
• 使用起來傳入?yún)?shù)有限

- (id)performSelector:(SEL)aSelector;
- (id)performSelector:(SEL)aSelector withObject:(id)object;
- (id)performSelector:(SEL)aSelector withObject:(id)object1 withObject:(id)object2;
- (void)performSelector:(SEL)aSelector withObject:(id)anArgument afterDelay:(NSTimeInterval)delay;
- (void)performSelector:(SEL)aSelector onThread:(NSThread *)thr withObject:(id)arg waitUntilDone:(BOOL)wait;
- (void)performSelectorOnMainThread:(SEL)aSelector withObject:(id)arg waitUntilDone:(BOOL)wait;

GCD與performSelector方法對比(盡可能使用GCD)

• 延時

//performSelector
[NSObject performSelector:@selector(dosomething) withObject:nil afterDelay:0.5];

//GCD
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.5 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        [self dosomething];
});

• 主線程執(zhí)行任務(wù)

//performSelector
[NSObject performSelectorOnMainThread:@selector(dosomething) withObject:nil waitUntilDone:NO];
    
//GCD
dispatch_async(dispatch_get_main_queue(), ^{
        [self dosomething];
});