为什么不能更改向量中的对象？ [英] Why can't I change objects in a vector?

问题描述

我有一个 TileGrid ，它包含 std :: vector< std :: vector< Tile> > 。访问向量中的 Tile 对象可以工作，但是我不能更改它们的属性？为了完成，以下是所有相关的类：

I have a class TileGrid that holds an std::vector< std::vector<Tile> >. Accessing the Tile objects in the vector works, but I can't change their properties? For the sake of completion, here are all the relevant classes:

tilegrid.h

tilegrid.h

#include <vector>
#include "tile.h"

class TileGrid {

public:
  TileGrid();
  TileGrid(unsigned int rows, unsigned int cols);
  virtual ~TileGrid();
  unsigned int getRows() const { return rows_; };
  unsigned int getCols() const { return cols_; };
  Tile atIndex(unsigned int row, unsigned int col) const { return tiles_[row].at(col); };

private:
  std::vector< std::vector<Tile> > tiles_;
  unsigned int rows_;
  unsigned int cols_;

};

tilegrid.cpp

tilegrid.cpp

#include "tilegrid.h"

TileGrid::TileGrid() : rows_(0), cols_(0) {
}

TileGrid::TileGrid(unsigned int rows, unsigned int cols) : rows_(rows), cols_(cols) {
  tiles_.clear();
  for (unsigned int y = 0; y < rows_; y++) {
    std::vector<Tile> horizontalTiles;
    for (unsigned int x = 0; x < cols_; x++) {
      horizontalTiles.push_back(Tile());
    }
    tiles_.push_back(horizontalTiles);
  }
}

TileGrid::~TileGrid() {
}

tile.h

class Tile {

public:
  Tile();
  virtual ~Tile();
  bool isActive() const { return isActive_; };
  void setActive(bool status) { isActive_ = status; };

private:
  bool isActive_;

};

tile.cpp

#include "tile.h"

Tile::Tile() : isActive_(false) {
}

Tile::~Tile() {
}

main.cpp

#include "tilegrid.h"
#include <iostream>

int main() {

  TileGrid tg(20, 20);

  for (unsigned int i = 0; i < tg.getRows(); i++) {
    for (unsigned int j = 0; j < tg.getCols(); j++) {
      if (tg.atIndex(i, j).isActive()) {
        std::cout << i << "," << j << " is active" << std::endl;
      } else {
        std::cout << i << "," << j << " is NOT active" << std::endl;
      }
    }
  }

  // This is all working. But when I for example use the setActive function, nothing changes:

  tg.atIndex(1, 0).setActive(true);

  // When I print it again, the values are still the ones that were set in the constructor

  for (unsigned int i = 0; i < tg.getRows(); i++) {
    for (unsigned int j = 0; j < tg.getCols(); j++) {
      if (tg.atIndex(i, j).isActive()) {
        std::cout << i << "," << j << " is active" << std::endl;
      } else {
        std::cout << i << "," << j << " is NOT active" << std::endl;
      }
    }
  }

  return 0;

}

我真的很抱歉所有这些代码...我尝试保持尽可能短，但我认为它会更好，所有！

I'm really sorry for all this code... I tried to keep it as short as possible, but I thought it'd be better to post it all!

所以是的，我的问题是 setActive 函数。当我创建一个 Tile 并调用它的 setActive 函数，一切正常，但当我通过< c $ c> TileGrid 对象，它不会。

So yeah, my problem is the setActive function. When I just create a Tile and call its setActive function, everything works, but when I call it through the TileGrid object, it won't.

我已经试图解决这个问题我自己几个小时，直觉了。

I have tried to solve this on my own for hours and I can't think straight anymore. I'm really desperate here, could you please have a look and maybe help me?

推荐答案

在您的方法中：

Tile atIndex(unsigned int row, unsigned int col) const

您应该返回对Tile的引用：

you should return a reference to Tile:

Tile& atIndex(unsigned int row, unsigned int col)

现在你正在返回副本，这就是为什么修改不工作。也不应该是 const ，否则会得到编译错误。

now you are returning copy, and that is why modifications does not work. Also it should not be const, otherwise you will get compiler error.

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