游戏编程模式06-设计模式-单例模式

设计模式-单例模式

参考章节：https://gpp.tkchu.me/singleton.html

脑内画面

单例模式保证某个类在进程里只有一个实例，并提供一个全局入口。它像游戏里的总控开关：大家都能摸到它，但也正因为大家都能摸到，它很容易变成隐形依赖的集合点。
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SaveSystem.Instance
UI
调试工具
存档文件

它解决的问题

有些服务在技术上确实只应存在一个，例如平台成就接口、存档管理、硬件音频设备包装层。单例提供唯一实例和延迟初始化。但在游戏架构里，单例最常见的问题是：它让依赖关系从构造函数里消失，藏进任何地方都能访问的静态属性。

C# 示例

csharp 复制代码

public sealed class SaveSystem
{
    public static SaveSystem Instance { get; } = new SaveSystem();

    private readonly Dictionary<string, string> _values = new();

    private SaveSystem()
    {
    }

    public void SetString(string key, string value)
    {
        _values[key] = value;
    }

    public string? GetString(string key)
    {
        return _values.TryGetValue(key, out var value) ? value : null;
    }
}

public sealed class SettingsMenu
{
    public void ChangeLanguage(string language)
    {
        SaveSystem.Instance.SetString("language", language);
    }
}

更可控的替代写法

csharp 复制代码

public interface ISaveSystem
{
    void SetString(string key, string value);
    string? GetString(string key);
}

public sealed class SettingsMenu2
{
    private readonly ISaveSystem _saveSystem;

    public SettingsMenu2(ISaveSystem saveSystem)
    {
        _saveSystem = saveSystem;
    }

    public void ChangeLanguage(string language)
    {
        _saveSystem.SetString("language", language);
    }
}

什么时候用

对象天然唯一，并且重复实例会造成错误。
初始化顺序清晰，生命周期贯穿整个游戏。
测试不需要频繁替换该对象，或者已经提供替换通道。

使用时的锋利边

单例常把两个概念绑在一起：唯一实例和全局访问。真正危险的是全局访问。它会让代码表面上没有依赖，实际上依赖遍布各处。大型项目里更推荐依赖注入、服务定位器或显式上下文对象。