Unity单例MonoBehaviour类中如何通过[SerializeField]获取Camera？

你的核心矛盾在于：自动创建的单例GameObject无法通过Inspector给[SerializeField]字段赋值，同时想避免手动挂载脚本的操作。以下是三种实用解决方案：

方案1：通过预制体初始化单例 #

提前在预制体中配置好Camera等参数，让单例自动加载预制体而非创建空对象，完美保留Inspector赋值的便利性。

修改SingletonMono基类 #

添加预制体加载逻辑，允许子类指定预制体路径：

public abstract class SingletonMono<T>: MonoBehaviour where T: MonoBehaviour
{
    private static T _instance;
    protected static bool ApplicationIsQuitting;
    protected static bool IsGlobal;

    static SingletonMono()
    {
        ApplicationIsQuitting = false;
        IsGlobal = false;
    }

    // 子类重写此方法返回预制体路径
    protected virtual string GetPrefabPath() => string.Empty;

    public static T Instance
    {
        get
        {
            if (ApplicationIsQuitting)
            {
                Debug.LogWarning($"Application is quitting, you cant operate a singleton mono object: [{typeof(T)}]");
                return _instance;
            }
            
            _instance = FindObjectOfType<T>();
            if (FindObjectsOfType<T>().Length > 1)
            {
                Debug.LogError($"the singleton type [{typeof(T)}] has more than one instances");
                return _instance;
            }
            
            if (_instance != null) return _instance;
            
            GameObject obj = null;
            // 尝试加载子类指定的预制体
            var prefabPath = ((SingletonMono<T>)Activator.CreateInstance(typeof(T), true)).GetPrefabPath();
            if (!string.IsNullOrEmpty(prefabPath))
            {
                obj = Resources.Load<GameObject>(prefabPath);
                if (obj != null)
                {
                    obj = Instantiate(obj);
                    obj.name = typeof(T).ToString();
                }
            }
            
            // 预制体不存在时创建空对象
            obj ??= new GameObject(typeof(T).ToString());
            _instance = obj.GetComponent<T>() ?? obj.AddComponent<T>();
            
            if(IsGlobal) DontDestroyOnLoad(obj);
            return _instance;
        }
    }

    public void OnApplicationQuit()
    {
        ApplicationIsQuitting = true;
    }
}

修改StageManager子类 #

重写GetPrefabPath方法指定预制体位置：

public class StageManager: SingletonMono<StageManager>
{
    [SerializeField] private float spaceOffset;
    [SerializeField] private Camera mainCam;

    // 假设预制体放在Resources/StageManagerPrefab路径下
    protected override string GetPrefabPath() => "StageManagerPrefab";

    public Vector3 GetWorldPositionByScreenPoint(Vector2 pos)
    {
        var z = -mainCam.transform.position.z;
        return mainCam.ScreenToWorldPoint(new Vector3(pos.x, pos.y, z));
    }
}

操作步骤：创建StageManager预制体，在Inspector中给mainCam赋值，将预制体放入Resources目录即可。

方案2：代码自动获取Camera（无需Inspector赋值） #

如果只需使用主相机或特定标签的相机，直接通过代码获取，完全跳过手动赋值环节。

修改StageManager类 #

public class StageManager: SingletonMono<StageManager>
{
    [SerializeField] private float spaceOffset;
    private Camera mainCam;

    private void Awake()
    {
        // 方式1：获取标签为"MainCamera"的主相机（会缓存结果，性能优）
        mainCam = Camera.main;
        
        // 方式2：获取指定标签的相机（适合多相机场景）
        // mainCam = GameObject.FindWithTag("GameCamera").GetComponent<Camera>();
        
        // 方式3：获取场景中第一个Camera组件（适合单相机场景）
        // mainCam = FindObjectOfType<Camera>();
    }

    public Vector3 GetWorldPositionByScreenPoint(Vector2 pos)
    {
        if (mainCam == null)
        {
            Debug.LogError("Main Camera not found!");
            return Vector3.zero;
        }
        var z = -mainCam.transform.position.z;
        return mainCam.ScreenToWorldPoint(new Vector3(pos.x, pos.y, z));
    }
}

注意：使用Camera.main时确保目标相机的标签设为"MainCamera"。

方案3：允许场景中存在预设实例（自动检测） #

优化单例逻辑，优先使用场景中已有的实例，只有当场景中无实例时才自动创建。这样你可以在场景中放置一个挂载了StageManager的GameObject，提前在Inspector中赋值Camera，单例会自动复用该实例。

修改SingletonMono基类 #

添加Awake阶段的实例检测逻辑：

public abstract class SingletonMono<T>: MonoBehaviour where T: MonoBehaviour
{
    private static T _instance;
    protected static bool ApplicationIsQuitting;
    protected static bool IsGlobal;

    static SingletonMono()
    {
        ApplicationIsQuitting = false;
        IsGlobal = false;
    }

    protected virtual void Awake()
    {
        if (_instance == null)
        {
            _instance = this as T;
            if (IsGlobal) DontDestroyOnLoad(gameObject);
        }
        else
        {
            Destroy(gameObject);
            Debug.LogWarning($"Duplicate singleton instance of {typeof(T)} destroyed.");
        }
    }

    public static T Instance
    {
        get
        {
            if (ApplicationIsQuitting)
            {
                Debug.LogWarning($"Application is quitting, you cant operate a singleton mono object: [{typeof(T)}]");
                return _instance;
            }
            
            if (_instance == null)
            {
                _instance = FindObjectOfType<T>();
                if (_instance == null)
                {
                    var obj = new GameObject(typeof(T).ToString());
                    _instance = obj.AddComponent<T>();
                    if(IsGlobal) DontDestroyOnLoad(obj);
                }
            }
            
            if (FindObjectsOfType<T>().Length > 1)
            {
                Debug.LogError($"the singleton type [{typeof(T)}] has more than one instances");
            }
            
            return _instance;
        }
    }

    public void OnApplicationQuit()
    {
        ApplicationIsQuitting = true;
    }
}

操作步骤：在场景中创建一个GameObject，挂载StageManager，在Inspector中给mainCam赋值即可。游戏启动时单例会自动识别并复用这个实例，不会创建新对象。

内容的提问来源于stack exchange，提问作者Wiosier