NSTimeInterval delay = 2;
for (NSString* sentence in sentences) {
   [sentenceHandler performSelector:@selector(parseSentence:)
                         withObject:sentence
                         afterDelay:delay];
   delay += 2;
}

如何从上面停止这个电话？我试过了：

[NSObject cancelPrevIoUsPerformRequestsWithTarget:sentenceHandler 
    selector:@selector(parseSentence) object:nil];

但没有效果？它只会退出循环中的许多调用之一吗？