objective-c 延迟执行某个函数，类似于jquery中的延迟执行

/*
performSelector:withObject:afterDelay:
Invokes a method of the receiver on the current thread using the default mode after a delay.

- (void)performSelector:(SEL)aSelector withObject:(id)anArgument afterDelay:(NSTimeInterval)delay
Parameters
aSelector
A selector that identifies the method to invoke. The method should not have a significant return value and should take a single argument of type id, or no arguments.
See “Selectors” for a description of the SEL type.
anArgument
The argument to pass to the method when it is invoked. Pass nil if the method does not take an argument.
delay
The minimum time before which the message is sent. Specifying a delay of 0 does not necessarily cause the selector to be performed immediately. The selector is still queued on the thread’s run loop and performed as soon as possible.
Discussion
This method sets up a timer to perform the aSelector message on the current thread’s run loop. The timer is configured to run in the default mode (NSDefaultRunLoopMode). When the timer fires, the thread attempts to dequeue the message from the run loop and perform the selector. It succeeds if the run loop is running and in the default mode; otherwise, the timer waits until the run loop is in the default mode.
*/
//loadTimeline是要延迟执行的方法，afterDelay:是要延迟的时间。这里是0.5秒
[self performSelector:@selector(loadTimeline) withObject:nil afterDelay:0.5];