传递 class 成员 object - SFML draw()

Question

这似乎是一个非常奇怪的情况。我只想在主循环之外绘制一个 sf::Text object 句柄（在另一个 class 中）。

我只给你看最重要的。这段代码有效（它绘制了直接在 main 中处理的其他内容），因此可以编译。

主要 :

int main()
{

//we handle the creation of the window //
//...

//Example where the sf::Text is handle in the main (it works)
sf::Font font;
font.loadFromFile("arial.ttf");
sf::Text mainTxt("It works !!",font);
mainTxt.setPosition(sf::Vector2f(64,"It works !!"));
mainTxt.setCharacterSize(25);
mainTxt.setFillColor(sf::Color::Blue);

TextManager textManager(); //My class that don't work...    

sf::Event event;
while (window.isOpen())
{
    // We handle event (we don't care here)
    // ... 
    
    window.draw(mainTxt); // it works
    window.draw(textManager.getMyText()); // do nothing

    window.display();
    window.clear();

}

return 0;

}

文本管理器header:

#ifndef TEXTMANAGER_H
#define TEXTMANAGER_H

#include <SFML/Graphics.hpp>

class TextManager 
{
    public:
        TextManager();
        virtual ~TextManager();
        sf::Text getMyText();

    private:
         sf::Text myText;
};

#endif // TEXTMANAGER_H

TextManager cpp

#include "TextManager.h"

TextManager::TextManager()
{
    sf::Font font;
    font.loadFromFile("arial.ttf");
    sf::Text myText("Not drawn on the screen :-(",font);
    myText.setPosition(sf::Vector2f(164,0));
    myText.setCharacterSize(25);
    myText.setFillColor(sf::Color::Blue);
}

// in this example (that do not work) I do not change fspText. But, I want to update         it at each call of the get function. So, it is not a constant class member.
sf::Text TextManager::getMyText() {        
    return myText;
}

TextManager::~TextManager()
{
    //dtor
}

我真的不明白的是，通过我的自定义 class，我可以使用这种 getter 访问 class 成员 object ].我也做了一些研究，我觉得应该return一份sf::Textobject。我尝试了很多东西，比如 return 参考或 const 参考等...我不明白。

希望我的问题得到很好的展示。谢谢您的帮助 ;-）祝你有美好的一天！

Answer 1

这个

TextManager textManager(); //My class that don't work...

是函数声明，不是对象的构造。应该是：

TextManager textManager; //My class that don't work...

由

sf::Text myText("Not drawn on the screen :-(",font);

您定义了一个名为 myText 的局部变量，与您的数据成员相同。因此，getMyText 返回的 myText 不受影响。

编码前阅读文档：

It is important to note that the sf::Text instance doesn't copy the font that it uses, it only keeps a reference to it. Thus, a sf::Font must not be destructed while it is used by a sf::Text (i.e. never write a function that uses a local sf::Font instance for creating a text).

取自 SFML reference.

class TextManager 
{
    public:
        TextManager();
        virtual ~TextManager();
        sf::Text& getMyText(); // <- pass by reference
    private:
         sf::Font myFont;
         sf::Text myText;
};

和

TextManager::TextManager()
{
    myFont.loadFromFile("arial.ttf");
    myText.setString("Not drawn on the screen :-(");
    myText.setFont(myFont);
    myText.setPosition(sf::Vector2f(164,0));
    myText.setCharacterSize(25);
    myText.setFillColor(sf::Color::Blue);
}

可能有用。

传递 class 成员 object - SFML draw()

Passing class member object - SFML draw()

c++

getter

class

object

sfml