[iOS] performSelector:withObject:afterDelay:调用没有作用的问题及解决方法

这个问题找了将近一天，baidu、google了很久，竟然没有人遇到同样问题？

performSelector:withObject:afterDelay:和[NSTimer timerWithTimeInterval:invocation:repeats:]都存在此问题：
调用后，延迟后（延迟0也一样）没有进入指定的@selecter()中。
反复验证发现，这种现象出现在子线程中，主线程中可正常使用。因此必须保证调用performSelector:withObject:afterDelay:是在主线程中。

但没有测试在子线程中再创建个NSTimer用来延迟，应该也可以，反正直接用

[NSTimer timerWithTimeInterval:invocation:repeats:]是不行的。

特实现

- (void)performSelectorOnMainThread:(SEL)aSelector withObject:(id)anArgument afterDelay:(NSTimeInterval)delay

方法，保证在主线程中调用成功

//  NSObject_performSelectorEx.h

@interface NSObject (performSelectorEx)

- (void)performSelectorOnMainThread:(SEL)aSelector withObject:(id)anArgument afterDelay:(NSTimeInterval)delay;

@end

//  NSObject_performSelectorEx.m

#import "NSObject_performSelectorEx.h"

@implementation NSObject (performSelectorEx)

- (void)performSelectorOnMainThread:(SEL)aSelector withObject:(id)anArgument afterDelay:(NSTimeInterval)delay

{

    NSMethodSignature *sig = [self methodSignatureForSelector:aSelector];

    if (!sig)

    {

        return;

    }

    

    NSInvocation *invo = [NSInvocation invocationWithMethodSignature:sig];

    [invo setTarget:self];

    [invo setSelector:aSelector];

    [invo setArgument:&anArgument atIndex:2];

    [invo retainArguments];

    NSMethodSignature *sigMT = [invo methodSignatureForSelector:@selector(performSelector:withObject:afterDelay:)];

    NSInvocation *invoMT = [NSInvocation invocationWithMethodSignature:sigMT];

    [invoMT setTarget:invo];

    [invoMT setSelector:@selector(performSelector:withObject:afterDelay:)];

    SEL arg1 = @selector(invoke);

    void *arg2 = nil;

    NSTimeInterval arg3 = delay;

    [invoMT setArgument:&arg1 atIndex:2];

    [invoMT setArgument:&arg2 atIndex:3];

    [invoMT setArgument:&arg3 atIndex:4];

    [invoMT retainArguments];

    [invoMT performSelectorOnMainThread:@selector(invoke) withObject:nil waitUntilDone:NO];

}

@end