iOS 获取全局唯一标示符

这个方法用来产生一个唯一的标示符，每次调用都会不一样，所以可以用当作一些临时缓存文件的名字

        NSString *identifier = [[NSProcessInfo processInfo] globallyUniqueString];
        NSLog(@"identifier1 ====== %@",identifier);
        identifier = [[NSProcessInfo processInfo] globallyUniqueString];
        NSLog(@"identifier2 ====== %@",identifier);
        identifier = [[NSProcessInfo processInfo] globallyUniqueString];
        NSLog(@"identifier3 ====== %@",identifier);
        identifier = [[NSProcessInfo processInfo] globallyUniqueString];
        NSLog(@"identifier4 ====== %@",identifier);