无法通过错误LNK2001：未解析的外部符号，即使我似乎已经包含了所需的内容

我正试图用c++和SMFL 2.0创建一个游戏，我无法通过这个错误，它让我发疯。我一直在网上阅读，似乎这可能是因为忘记了包括，但我仍然看不出我错在哪里。我已经在项目属性部分的c++ -> general -> additional include目录和linker -> general -> additional library目录下包含了SMFL 2.0库。

我完全空白，这是我得到的错误信息:

1>------ Build started: Project: Pang, Configuration: Debug Win32 ------
1>  Game.cpp
1>  Generating Code...
1>  Skipping... (no relevant changes detected)
1>  Pang.cpp
1>Game.obj : warning LNK4075: ignoring '/EDITANDCONTINUE' due to '/INCREMENTAL:NO' specification
1>Game.obj : error LNK2001: unresolved external symbol "private: static class PlayerPaddle Game::_player1" (?_player1@Game@@0VPlayerPaddle@@A)
1>C:UsersAlexanderDesktopC++ProjectsPangDebugPang.exe : fatal error LNK1120: 1 unresolved externals
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

Microsoft Visual c++没有显示任何语法语法错误与红色下划线，当我环顾四周的代码，所以它看起来像语法是好的。以下是相关的代码行:

我的大部分一般内容都在这里:

stdafx.h

#pragma once
#include "targetver.h"
#include <stdio.h>
#include <tchar.h>
#include <windows.h>
#include <SFML/System.hpp>
#include <SFML/Graphics.hpp>
#include <SFML/Window.hpp>
#include <SFML/Audio.hpp>
#include <map>
#include <iostream>
#include <cassert>
#include <list>

VisibleGameObject.h

#pragma once
class VisibleGameObject {
    public:
        VisibleGameObject();
        virtual ~VisibleGameObject();
        virtual void Load(std::string filename);
        virtual void Draw(sf::RenderWindow &window);
        virtual void SetPosition(float x, float y);
    private:
        sf::Sprite  _sprite;
        sf::Texture _image;
        std::string _filename;
        bool _isLoaded;
};

VisibleGameObject.cpp

#include "stdafx.h"
#include "VisibleGameObject.h"
VisibleGameObject::VisibleGameObject() {
    _isLoaded = false;
}
VisibleGameObject::~VisibleGameObject() {
}
void VisibleGameObject::Load(std::string filename) {
    if (_image.loadFromFile(filename) == false) {
        _filename = "";
        _isLoaded = false;
    }
    else {
        _filename = filename;
        _sprite.setTexture(_image);
    }
}
void VisibleGameObject::Draw(sf::RenderWindow &renderWindow) {
    if (_isLoaded) {
        renderWindow.draw(_sprite);
    }
}
void VisibleGameObject::SetPosition(float x, float y) {
    if (_isLoaded) {
        _sprite.setPosition(x,y);
    }
}

这个类帮助我使用SMFL库在渲染窗口上绘制图像。

PlayerPaddle.h

#pragma once
#include "VisibleGameObject.h"
class PlayerPaddle : public VisibleGameObject {
    public:
        PlayerPaddle();
        ~PlayerPaddle();
};

PlayerPaddle.cpp

#include "stdafx.h"
#include "VisibleGameObject.h"
#include "PlayerPaddle.h"
PlayerPaddle::PlayerPaddle() {
}
PlayerPaddle::~PlayerPaddle() {
}

Game.h

#pragma once
#include "PlayerPaddle.h"
class Game {
public:
    static void Start();
private:
    static bool IsExiting();
    static void GameLoop();
    static void ShowSplashScreen();
    static void ShowMenu();
    enum GameState { Uninitialized, ShowingSplash, Paused, ShowingMenu, Playing, Exiting };
    static GameState _gameState;
    static sf::RenderWindow _mainWindow;
    static PlayerPaddle _player1;
};

Game.cpp

#include "stdafx.h"
#include "Game.h"
#include "SplashScreen.h"
#include "MainMenu.h"

void Game::Start(void) {
    if(_gameState != Uninitialized) {
        return;
    }
    _mainWindow.create(sf::VideoMode(1024,768,32),"Pang!");
    //_player1.Load("images/paddle.png");
    //_player1.SetPosition((1024/2)-45, 700);
    _gameState = Game::ShowingSplash;
    while(!IsExiting()) {
        GameLoop();
    }
    _mainWindow.close();
}
bool Game::IsExiting() {
    if(_gameState == Game::Exiting) {
        return true;
    }
    else {
        return false;
    }
}
void Game::GameLoop() {
    switch(_gameState) {
        case Game::ShowingMenu: {
            ShowMenu();
            break;
        }
        case Game::ShowingSplash: {
            ShowSplashScreen();
            break;
        }
        case Game::Playing: {
            sf::Event currentEvent;
            while (_mainWindow.pollEvent(currentEvent)) {
                _mainWindow.clear(sf::Color(0,0,0));
                //_player1.Draw(_mainWindow);
                _mainWindow.display();
                if (currentEvent.type == sf::Event::Closed) {
                    _gameState = Game::Exiting;
                }
                if (currentEvent.type == sf::Event::KeyPressed) {
                    return;
                    if(currentEvent.key.code == sf::Keyboard::Escape) {
                        ShowMenu();
                    }
                }
            }
            break;
        }
    }
}
void Game::ShowSplashScreen() {
    SplashScreen splashScreen;
    splashScreen.Show(_mainWindow);
    _gameState = Game::ShowingMenu;
}
void Game::ShowMenu() {
    MainMenu mainMenu;
    MainMenu::MenuResult result = mainMenu.Show(_mainWindow);
    switch(result) {
        case MainMenu::Exit: {
            _gameState = Game::Exiting;
            break;
        }
        case MainMenu::Play: {
            _gameState = Game::Playing;
            break;
        }
    }
}
Game::GameState Game::_gameState = Uninitialized;
sf::RenderWindow Game::_mainWindow;

这段代码只有在Game.cpp中以_player1开头的3行代码被注释掉时才能编译和运行。当没有注释掉时，我得到这个LNK2001错误，我只是不能通过这个，这是相当令人沮丧的。

如果有人能告诉我这里有什么问题就好了。

敬上亚历山大