设备就绪ios无法正常工作(Device Ready ios not working)

 我过去成功使用了Boost.Multi_index。 从第一眼看你可能会觉得很奇怪，但实际上它已经退出了有趣的图书馆。 请记住，使用它时，你不会在你的定制容器中提供“如何”，而是“什么”。 假设你有以下类型： 
 
struct user_t
{
    string id, name, email;
    int age;
    friend ostream& operator<<(ostream& output_stream, const user_t& user)
    {
        return output_stream
            << user.id    << " "
            << user.name  << " "
            << user.age   << " "
            << user.email << "\n";
    }
    friend istream& operator>>(istream& input_stream, user_t& user)
    {
        return input_stream >> user.id >> user.name >> user.age >> user.email;
    }
};
 
 会发生什么是您创建一个容器，它包含对象和任意数量的索引。 在我们开始之前，让我们定义索引的标签。 标签只是标签！ 你用来通过名称而不是神奇数字来访问你的指数： 
 
struct by_id    { };
struct by_name  { };
struct by_age   { };
struct by_email { };
 
 然后我们用所需的索引定义我们的“数据库”： 
 
typedef multi_index_container<
    user_t,
    indexed_by
    <
      ordered_unique<tag<by_id>, member<user_t, string, &user_t::id> >,
      ordered_non_unique<tag<by_name>, member<user_t, string, &user_t::name> >,
      ordered_non_unique<tag<by_age>, member<user_t, int, &user_t::age> >,
      ordered_non_unique<tag<by_email>, member<user_t, string, &user_t::email> >
    >
> user_db;
 
 首先是容器中元素的类型。 然后，你说我想通过以下索引这个容器： 
 
indexed_by
<
  ordered_unique<tag<by_id>, member<user_t, string, &user_t::id> >,
  ordered_non_unique<tag<by_name>, member<user_t, string, &user_t::name> >,
  ordered_non_unique<tag<by_age>, member<user_t, int, &user_t::age> >,
  ordered_non_unique<tag<by_email>, member<user_t, string, &user_t::email> >
>
 
 您只需指定要公开的索引类型即可。 实际上有各种类型，它取决于你拥有的数据的语义。 给每个索引（第一个参数）赋予一个标签是很好的，并且您指定要通过第二个模板参数的内容来索引该类型。 实际上有多种方式来选择数据的“关键”。 关键并不要求实际上是唯一的！ 
 
 从现在起，你只需要像普通的std::multi_set那样处理std::multi_set ！ 实际上有所不同;）让我们假设你想从文件中加载系列化用户的信息，并根据我们创建的indecies预订有序的信息： 
 
 user_db load_information()
{
    ifstream info_file("information.txt");
    user_db db;
    user_t user;
    while(info_file >> user)
        db.insert(user);
    return db;
}
template <typename index_t>
void save_information_by(ostream& output_stream, const index_t& index)
{
    ostream_iterator<user_t> serializer(output_stream);
    copy(index.begin(), index.end(), serializer);
}
int main()
{
    ofstream
        by_id_file("by_id.txt"),
        by_name_file("by_name.txt"),
        by_age_file("by_age.txt"),
        by_email_file("by_email.txt");
    user_db db = load_information();
    // You see why we created the tags,
    // if we didn't we had to specify the index like the following:
    // const auto& name_index  = db.get<by_name>(); ==
    // const auto& name_index  = db.get<1>();
    const auto& id_index    = db.get<by_id>();
    const auto& name_index  = db.get<by_name>();
    const auto& age_index   = db.get<by_age>();
    const auto& email_index = db.get<by_email>();
    save_information_by(by_id_file, id_index);
    save_information_by(by_name_file, name_index);
    save_information_by(by_age_file, age_index);
    save_information_by(by_email_file, email_index);
}

I have used Boost.Multi_index successfully in the past. You might find it strange from a first look but in reality it is quit interesting library. Keep in mind when using it, that you don't provide "how" but "what" in your customized container. Assume that you have the following type:
 
struct user_t
{
    string id, name, email;
    int age;
    friend ostream& operator<<(ostream& output_stream, const user_t& user)
    {
        return output_stream
            << user.id    << " "
            << user.name  << " "
            << user.age   << " "
            << user.email << "\n";
    }
    friend istream& operator>>(istream& input_stream, user_t& user)
    {
        return input_stream >> user.id >> user.name >> user.age >> user.email;
    }
};
 
What will happen is that you create one container, that holds the objects and as many indices as you want. Before we start lets define the tags of indices. The tags are simply tags! that you use to access your indices by name instead of by magical numbers:
 
struct by_id    { };
struct by_name  { };
struct by_age   { };
struct by_email { };
 
Then we define our "data base" with the required indices:
 
typedef multi_index_container<
    user_t,
    indexed_by
    <
      ordered_unique<tag<by_id>, member<user_t, string, &user_t::id> >,
      ordered_non_unique<tag<by_name>, member<user_t, string, &user_t::name> >,
      ordered_non_unique<tag<by_age>, member<user_t, int, &user_t::age> >,
      ordered_non_unique<tag<by_email>, member<user_t, string, &user_t::email> >
    >
> user_db;
 
First thing is the type of elements in the container. Then, you say I want to index this container by the following:
 
indexed_by
<
  ordered_unique<tag<by_id>, member<user_t, string, &user_t::id> >,
  ordered_non_unique<tag<by_name>, member<user_t, string, &user_t::name> >,
  ordered_non_unique<tag<by_age>, member<user_t, int, &user_t::age> >,
  ordered_non_unique<tag<by_email>, member<user_t, string, &user_t::email> >
>
 
You just specify the type of index you want expose. There are various types actually, and it depends on the semantics of the data you have. It is good to give a tag for each index(the first parameter), and you specify you want to index the type by what through the second template parameter. There are various ways actually to choose the "key" of the data. The key is not required to be unique actually!
 
From now on, you just deal with user_db just like regular std::multi_set! with a small difference that makes the difference actually ;) Lets say you want to load serilaized users' information from a file, and reserlize ordered information according to the indecies we created:
 
 user_db load_information()
{
    ifstream info_file("information.txt");
    user_db db;
    user_t user;
    while(info_file >> user)
        db.insert(user);
    return db;
}
template <typename index_t>
void save_information_by(ostream& output_stream, const index_t& index)
{
    ostream_iterator<user_t> serializer(output_stream);
    copy(index.begin(), index.end(), serializer);
}
int main()
{
    ofstream
        by_id_file("by_id.txt"),
        by_name_file("by_name.txt"),
        by_age_file("by_age.txt"),
        by_email_file("by_email.txt");
    user_db db = load_information();
    // You see why we created the tags,
    // if we didn't we had to specify the index like the following:
    // const auto& name_index  = db.get<by_name>(); ==
    // const auto& name_index  = db.get<1>();
    const auto& id_index    = db.get<by_id>();
    const auto& name_index  = db.get<by_name>();
    const auto& age_index   = db.get<by_age>();
    const auto& email_index = db.get<by_email>();
    save_information_by(by_id_file, id_index);
    save_information_by(by_name_file, name_index);
    save_information_by(by_age_file, age_index);
    save_information_by(by_email_file, email_index);
}