[iOS] performSelector:withObject:afterDelay:調用沒有作用的問題及解決方案

這個問題找了將近一天，baidu、google了很久，竟然沒有人遇到同樣問題？

performSelector:withObject:afterDelay:和[NSTimer timerWithTimeInterval:invocation:repeats:]都存在此問題：調用後，延遲後（延遲0也一樣）沒有進入指定的@selecter()中。反覆驗證發現，這種現象出現在子線程中，主線程中可正常使用。因此必須保證調用performSelector:withObject:afterDelay:是在主線程中。
但沒有測試在子線程中再建立個NSTimer用來延遲，應該也可以，反正直接用
[NSTimer timerWithTimeInterval:invocation:repeats:]是不行的。
特實現
- (void)performSelectorOnMainThread:(SEL)aSelector withObject:(id)anArgument afterDelay:(NSTimeInterval)delay
方法，保證在主線程中調用成功
//  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