Вопросы Теги

изменение состояния в определенном / выбранном массиве при отображении массива

Короче: «Как удалить с карты во время ее итерации?»

  • С помощью старой карты impl: вы не можете
  • с новым отображением карты: почти как предложил @KerrekSB.

Из GCC map impl (примечание GXX_EXPERIMENTAL_CXX0X): 

#ifdef __GXX_EXPERIMENTAL_CXX0X__
      // _GLIBCXX_RESOLVE_LIB_DEFECTS
      // DR 130. Associative erase should return an iterator.
      /**
       *  @brief Erases an element from a %map.
       *  @param  position  An iterator pointing to the element to be erased.
       *  @return An iterator pointing to the element immediately following
       *          @a position prior to the element being erased. If no such 
       *          element exists, end() is returned.
       *
       *  This function erases an element, pointed to by the given
       *  iterator, from a %map.  Note that this function only erases
       *  the element, and that if the element is itself a pointer,
       *  the pointed-to memory is not touched in any way.  Managing
       *  the pointer is the user's responsibility.
       */
      iterator
      erase(iterator __position)
      { return _M_t.erase(__position); }
#else
      /**
       *  @brief Erases an element from a %map.
       *  @param  position  An iterator pointing to the element to be erased.
       *
       *  This function erases an element, pointed to by the given
       *  iterator, from a %map.  Note that this function only erases
       *  the element, and that if the element is itself a pointer,
       *  the pointed-to memory is not touched in any way.  Managing
       *  the pointer is the user's responsibility.
       */
      void
      erase(iterator __position)
      { _M_t.erase(__position); }
#endif

Пример со старым и новым стилем: 

#include <iostream>
#include <map>
#include <vector>
#include <algorithm>

using namespace std;
typedef map<int, int> t_myMap;
typedef vector<t_myMap::key_type>  t_myVec;

int main() {

    cout << "main() ENTRY" << endl;

    t_myMap mi;
    mi.insert(t_myMap::value_type(1,1));
    mi.insert(t_myMap::value_type(2,1));
    mi.insert(t_myMap::value_type(3,1));
    mi.insert(t_myMap::value_type(4,1));
    mi.insert(t_myMap::value_type(5,1));
    mi.insert(t_myMap::value_type(6,1));

    cout << "Init" << endl;
    for(t_myMap::const_iterator i = mi.begin(); i != mi.end(); i++)
        cout << '\t' << i->first << '-' << i->second << endl;

    t_myVec markedForDeath;

    for (t_myMap::const_iterator it = mi.begin(); it != mi.end() ; it++)
        if (it->first > 2 && it->first < 5)
            markedForDeath.push_back(it->first);

    for(size_t i = 0; i < markedForDeath.size(); i++)
        // old erase, returns void...
        mi.erase(markedForDeath[i]);

    cout << "after old style erase of 3 & 4.." << endl;
    for(t_myMap::const_iterator i = mi.begin(); i != mi.end(); i++)
        cout << '\t' << i->first << '-' << i->second << endl;

    for (auto it = mi.begin(); it != mi.end(); ) {
        if (it->first == 5)
            // new erase() that returns iter..
            it = mi.erase(it);
        else
            ++it;
    }

    cout << "after new style erase of 5" << endl;
    // new cend/cbegin and lambda..
    for_each(mi.cbegin(), mi.cend(), [](t_myMap::const_reference it){cout << '\t' << it.first << '-' << it.second << endl;});

    return 0;
}

печатает: 

main() ENTRY
Init
        1-1
        2-1
        3-1
        4-1
        5-1
        6-1
after old style erase of 3 & 4..
        1-1
        2-1
        5-1
        6-1
after new style erase of 5
        1-1
        2-1
        6-1

Process returned 0 (0x0)   execution time : 0.021 s
Press any key to continue.
0
задан Akza 17 January 2019 в 11:05
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1 ответ

Вы можете использовать идентификатор данных в качестве состояния вместо логического значения (например, openedMenuId) 

import React, { Component } from 'react'
import Menu from '@material-ui/core/Menu'
import MenuItem from '@material-ui/core/MenuItem'

const dataMap = [
    {
        id: 1,
        name: "john"
    }, {
        id: 2,
        name: "Doe"
    }
]

export default class MyComponent extends Component {

    state = {
        openedMenuId: null
    }

    handleClick(newOpenedMenuId) {
        this.setState({
            openedMenuId: newOpenedMenuId
        })
    }

    render() {
        const mapResult = dataMap.map((item, index) => {
            const id = item.id;
            const name = item.name;
            return <span key={index}>
                {name}
                <Menu
                    open={this.state.openedMenuId === item.id}
                >
                    <MenuItem id={id}>First</MenuItem>
                    <MenuItem id={id}>Second</MenuItem>
                    <MenuItem id={id}>Third</MenuItem>
                </Menu>
            </span>
        })
        return (
            <div>
                {mapResult}
            </div>
        )
    }
}
0
ответ дан Mohamed Ramrami 17 January 2019 в 11:05
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