performSelector 的使用

一、方法集

1、同步执行

这三个方法，均为同步执行，与线程无关，主线程和子线程中均可调用成功。等同于直接调用该方法。在需要动态的去调用方法的时候去使用。
例如：[self performSelector:@selector(test2)];与[self test2];执行效果上完全相同。

- (id)performSelector:(SEL)aSelector;
- (id)performSelector:(SEL)aSelector withObject:(id)object;
- (id)performSelector:(SEL)aSelector withObject:(id)object1 withObject:(id)object2;

2、异步执行

这两个方法为异步执行，即使delay传参为0，仍为异步执行。只能在主线程中执行，在子线程中不会调到aSelector方法。
由于是在主线程中执行aSelector，所以不会开启子线程。

- (void)performSelector:(SEL)aSelector withObject:(id)anArgument afterDelay:(NSTimeInterval)delay inModes:(NSArray *)modes;
- (void)performSelector:(SEL)aSelector withObject:(id)anArgument afterDelay:(NSTimeInterval)delay;

在方法未到执行时间之前，取消方法为：

+ (void)cancelPreviousPerformRequestsWithTarget:(id)aTarget selector:(SEL)aSelector object:(id)anArgument;
+ (void)cancelPreviousPerformRequestsWithTarget:(id)aTarget;

注意：调用该方法之前或在该方法所在的viewController生命周期结束的时候去调用取消函数，以确保不会引起内存泄露。

3、主线程执行

这两个方法，在主线程和子线程中均可执行，均会调用主线程的aSelector方法；

• 当前线程为主线程
  • 如果设置wait为YES，等待主线程执行完aSelector以后，继续执行主线程；
  • 如果设置wait为NO，执行完主线程之后，执行aSelector；
• 当前线程为子线程
  • 如果设置wait为YES，等待主线程执行完aSelector以后，继续执行子线程；
  • 如果设置wait为NO，不等待主线程执行完aSelector，继续执行子线程；

- (void)performSelectorOnMainThread:(SEL)aSelector withObject:(id)arg waitUntilDone:(BOOL)wait modes:(nullable NSArray<NSString *> *)array;
// equivalent to the first method with kCFRunLoopCommonModes
- (void)performSelectorOnMainThread:(SEL)aSelector withObject:(id)arg waitUntilDone:(BOOL)wait;

4、子线程执行

- (void)performSelector:(SEL)aSelector onThread:(NSThread *)thr withObject:(id)arg waitUntilDone:(BOOL)wait modes:(NSArray *)array;
- (void)performSelector:(SEL)aSelector onThread:(NSThread *)thr withObject:(id)arg waitUntilDone:(BOOL)wait;

5、开启子线程在后台运行

- (void)performSelectorInBackground:(SEL)aSelector withObject:(id)arg

二、performSelectorOnMainThread支持多个参数

@interface NSObject(PGPerformSelectorOnMainThreadWithTwoObjects)
- (void) performSelectorOnMainThread:(SEL)selector withObject:(id)arg1 withObject:(id)arg2 waitUntilDone:(BOOL)wait;
@end

@implementation(PGPerformSelectorOnMainThreadWithTwoObjects)
- (void) performSelectorOnMainThread:(SEL)selector withObject:(id)arg1 withObject:(id)arg2 waitUntilDone:(BOOL)wait {
    NSMethodSignature *sig = [self methodSignatureForSelector:selector];
    if (!sig) return;

    NSInvocation* invo = [[NSInvocation] invocationWithMethodSignature:sig];
    [invo setTarget:self];
    [invo setSelector:selector];
    [invo setArgument:&arg1 atIndex:2];
    [invo setArgument:&arg2 atIndex:3];
    [invo retainArguments];
    [invo performSelectorOnMainThread:@selector(invoke) withObject:nil waitUntilDone:wait];
}
@end