Question

我在Pickup.h中为我的皮卡创建了一个课程。这将是：

class Pickup
{
private:
    Sprite m_Sprite;
    int m_Value;
    int m_Type;
public:
Pickup (int type)
{
    m_Type = type;
    if (m_Type == 1)
    {
        Sprite m_Sprite;
        Texture health;
        health.loadFromFile("health.png");
        m_Sprite.setTexture(health);
    }
    else ...

}
void spawn()
{
    srand((int)time(0) / m_Type);
    int x = (rand() % 1366);
    srand((int)time(0) * m_Type);
    int y = (rand() % 768);
    m_Sprite.setPosition(x, y);
}
Sprite getSprite()
{
    return m_Sprite;
}
};

如果我尝试使用

在屏幕上绘制一个使用此类创建的Sprite

Pickup healthPickup(1);
healthPickup.spawn();

进入游戏循环之前，并在游戏循环内放置

    mainScreen.draw(healthPickup.getSprite());

我从未在屏幕上看到过Sprite。我尝试使用

创建另一个Sprite

Sprite m_Sprite2;
Texture health2;
health2.loadFromFile("health.png");
m_Sprite2.setTexture(health2);
m_Sprite2.setPosition(healthPickup.getSprite().getPosition().x, healthPickup.getSprite().getPosition().y);

如果我尝试在游戏循环中显示它，一切正常。我的问题是：为什么这对我创建的类不起作用？

Answer 1

来自构造函数：

Pickup (int type)
{
    m_Type = type;
    if (m_Type == 1)
    {
        Sprite m_Sprite;
        ...

在此定义一个与成员变量同名的局部变量。这会创建一个超出范围并被破坏的局部变量。

构造函数使成员变量未初始化。

要正确解决您的问题，您需要进行两项更改：第一项是构建成员变量m_Sprite。第二个是不定义局部变量。

这样的事情：

Pickup (int type)
    : m_Sprite()    // Constructor initializer list, default-constructs the m_Sprite member
{
    m_Type = type;
    if (m_Type == 1)
    {
        // Don't define a local variable m_Sprite
        Texture health;
        health.loadFromFile("health.png");
        m_Sprite.setTexture(health);
    }
    ...
}

Answer 2

您的代码应为：

class Pickup
{
private:
    Sprite m_Sprite;
    int m_Value;
    int m_Type;
public:
Pickup (int type)
{
    m_Type = type;
    if (m_Type == 1)
    {
        Texture health; // removed the declaration of m_Sprite that was here.
        health.loadFromFile("health.png");
        m_Sprite.setTexture(health);
    }
    else ...

}
void spawn()
{
    srand((int)time(0) / m_Type);
    int x = (rand() % 1366);
    srand((int)time(0) * m_Type);
    int y = (rand() % 768);
    m_Sprite.setPosition(x, y);
}
Sprite getSprite()
{
    return m_Sprite;
}
};

不显示用类创建的Sprite

2 个答案: