c# – 静态对象在正确的时间为空/未初始化

2023年3月3日 335次阅读

我正在使用这里概述的
type-safe enum pattern.我需要将一个类型安全的枚举嵌套到另一个中.在创建父构造函数时,子属性(静态对象)为NULL.似乎没有调用子构造函数,我遇到了一些错误.(父母和孩子我很困惑,但它解释了层次结构)

这是一个例子(我正在使用netMF)：

public class MyDeviceSetting //parent
{
        public readonly string Name;
        public MyUnit SettingUnit;
        public readonly MyUnit.UnitPurpose UnitPurpose;

          #region MY STATIC SETTINGS
        //UNIT SETTINGS
        public static MyDeviceSetting TempUnits = new MyDeviceSetting("TempUnits", MyUnit.mm); //MyUnit.mm is null. Why?
        public static MyDeviceSetting BLAH = new MyDeviceSetting("BLAH", MyUnit.inch);//MyUnit.inch is null. Why?
          #endregion



        /// <summary>
        /// This is the MAIN PRIVATE Constructor
        /// </summary>
        /// <param name="?"></param>
        private MyDeviceSetting(string name, MyUnit defaultUnit)
        {
            Name = name;
            SettingUnit = defaultUnit;//NULL
            UnitPurpose = SettingUnit.Purpose; //fails because SettingUnit is NULL


        }


    }


public sealed class MyUnit
{
    private static int Count = 0;

    //these are used to store and identify the unit in memory
    public readonly int UnitID;
    public readonly int TestID;

    public enum UnitPurpose
    {
        DISTANCE,
        SPEED,
        TEMPERATURE,
        TIME,
        CLOCK,
        NO_UNITS
    }

    public readonly string DisplayName;
    public readonly string Abbreviation;
    public readonly string Name;
    public readonly UnitPurpose Purpose;

    #region My Units
    public static readonly MyUnit mm = new MyUnit("Milimeters", "mm", "mm", UnitPurpose.DISTANCE, 1);
    public static readonly MyUnit inch = new MyUnit("inch", "inch", "in", UnitPurpose.DISTANCE, 2);



    #endregion

    private MyUnit(string name,
                   string displayName,
                   string abbreviation,
                   UnitPurpose unitPurpose,
                   int unitID)
    {
        Name = name;
        DisplayName = displayName;
        Abbreviation = abbreviation;
        Purpose = unitPurpose;
        UnitID = unitID;
        TestID = Count;
        Count++;

    }


}

如何确保孩子不为空？有解决方法吗？编辑：This Post确保这应该工作,但在我的情况下,它不起作用.
《c# – 静态对象在正确的时间为空/未初始化》

最佳答案 这似乎是.Net Micro框架的错误/限制.它不完全支持静态构造函数.这是报告相同问题的人：
https://msdn.microsoft.com/en-us/library/Cc533032.aspx

NetCF 3.0的documentation包含以下警告：

Do not use static constructors. They are not yet fully supported by the .NET Micro Framework.

从这个blog post也似乎说(至少从2.0开始)对静态构造函数的调用是序列化的：

There are some things that cannot be done in .NET Compact Framework in
a static constructor which are possible in the full .NET Framework.
Basically, all static constructors when are executed in a serialized
fashion in .NET Compact Framework V2

该帖子在死锁的背景下讨论它,但我相信这是不起作用的原因.

不幸的是,这意味着你不能依赖静态并且必须自己处理初始化和锁定.这样的事情应该有效：

private static MyUnit inch;

public static MyUnit Inch
{
    get
    {
        if (inch == null)
            inch = new MyUnit("inch", "inch", "in", UnitPurpose.DISTANCE, 2);
         return inch;
    }
}

遗憾的是,这会失去静态构造函数给你的线程安全性.这很难修复,因为你不能依赖静态成员,因为我们已经看到你不能依赖它们被初始化.

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