c++ - 尝试获取用户输入以在 Cocos2D-X 中移动精灵

Question

我试图让 WASD 的用户输入在 Cocos2D-X 中移动精灵。我很确定我做的一切都是正确的，但它给了我这个错误： 表达式必须是一个可修改的左值。

这是我的代码（注意：我是 Cocos2D-X 的新手，所以可能有点乱）

float playerX = visibleSize.width / 2 + origin.x;
float playerY = visibleSize.height / 2 + origin.y;
    
auto player = Sprite::create("sprites/player.png");
if (player == nullptr)
{
    problemLoading("'sprites/player.png'");
}
else
{
    // position the sprite on the center of the screen
    player->setPosition(Vec2(playerX, playerY));

    // add the sprite as a child to this layer
    this->addChild(player, 0);
}

    // Keyboard events
auto keyboardListener = EventListenerKeyboard::create();
keyboardListener->onKeyPressed = [playerX, playerY](EventKeyboard::KeyCode keyCode, Event* event)
{
    switch (keyCode)
    {
    case EventKeyboard::KeyCode::KEY_W:
        playerY += 5.0f;
        break;
    case EventKeyboard::KeyCode::KEY_A:
        playerX -= 5.0f;
        break;
    case EventKeyboard::KeyCode::KEY_S:
        playerY -= 5.0f;
        break;
    case EventKeyboard::KeyCode::KEY_D:
        playerX += 5.0f;
        break;
    case EventKeyboard::KeyCode::KEY_ESCAPE:
        Director::getInstance()->end();
        break;
    }
};
    _eventDispatcher->addEventListenerWithSceneGraphPriority(keyboardListener, this);

有四个错误，它们都指向不同的玩家X/Y +=/-= 5.0f

标签： c++cocos2d-x

Answer 1

尝试使用mutable说明符（它允许 lambdas 主体修改通过复制捕获的对象，并调用它们的非常量成员函数）：

float playerX = visibleSize.width / 2 + origin.x;
float playerY = visibleSize.height / 2 + origin.y;
    
auto player = Sprite::create("sprites/player.png");
if (player == nullptr)
{
    problemLoading("'sprites/player.png'");
}
else
{
    // position the sprite on the center of the screen
    player->setPosition(Vec2(playerX, playerY));

    // add the sprite as a child to this layer
    this->addChild(player, 0);
}

    // Keyboard events
auto keyboardListener = EventListenerKeyboard::create();

// add mutable specifier
keyboardListener->onKeyPressed = [playerX, playerY, player](EventKeyboard::KeyCode keyCode, Event* event) mutable
{
    switch (keyCode)
    {
    case EventKeyboard::KeyCode::KEY_W:
        playerY += 5.0f;
        break;
    case EventKeyboard::KeyCode::KEY_A:
        playerX -= 5.0f;
        break;
    case EventKeyboard::KeyCode::KEY_S:
        playerY -= 5.0f;
        break;
    case EventKeyboard::KeyCode::KEY_D:
        playerX += 5.0f;
        break;
    case EventKeyboard::KeyCode::KEY_ESCAPE:
        Director::getInstance()->end();
        break;
    }
    
    player->setPosition(playerX, playerY);
};
    _eventDispatcher->addEventListenerWithSceneGraphPriority(keyboardListener, this);