如何发出代码通过调用类的构造函数来为类的静态字段分配值/引用？

Question

（我的代码有些混乱，由 C# 和 VB.NET 组成）我试图发出如下所示的类：

public class SWTTFields
{
    private string fieldName;
    private int startPosition;
    private int endPosition;

    public static readonly SWTTFields ISO = new SWTTFields("ISO", 1, 2);
    public static readonly SWTTFields EPC = new SWTTFields("EPC", 3, 4);

    private SWTTFields(String fieldName, Int32 startPositon, Int32 endPositon)
    {
        this.fieldName = fieldName;
        this.startPosition = startPositon;
        this.endPosition = endPositon;
    }
}

但是，我正在堆栈分配对两个静态成员的引用。到目前为止，我得到了这一点（下面的代码是在 VB.NET 中，但是我很乐意接受 VB.NET 或 C# 中的答案）：

Dim typeBuilder As TypeBuilder = GetTypeBuilder()

'Definition of three private variables
'TODO: you need one more private field that would represent "Bank" particular field belongs to

'Private String fieldName
Dim fieldName As FieldBuilder = typeBuilder.DefineField("fieldName",
                                                         GetType(String),
                                                            FieldAttributes.Private)
'Private Int32 startPosition
Dim startPosition As FieldBuilder = typeBuilder.DefineField("startPosition",
                                                            GetType(Int32),
                                                              FieldAttributes.Private)
'Private Int32 endPosition
Dim endPosition As FieldBuilder = typeBuilder.DefineField("endPosition",
                                                          GetType(Int32), FieldAttributes.Private)

'Type is taken from the current TypeBuilder
Dim ISO As FieldBuilder = typeBuilder.DefineField("ISO", typeBuilder.GetType, FieldAttributes.Public)                                                           
Dim EPC As FieldBuilder = typeBuilder.DefineField("EPC", typeBuilder.GetType, FieldAttributes.Public)

'Constructor parameters are
Dim constructorParams() As Type = {GetType(String), GetType(Int32), GetType(Int32)}

'constructor for the class 
Dim ctorBuilder As ConstructorBuilder = typeBuilder.DefineConstructor(MethodAttributes.Public Or
                                                                     MethodAttributes.SpecialName Or
                                                                     MethodAttributes.RTSpecialName,
                                                                     CallingConventions.Standard,
                                                                     constructorParams)

Dim objType As Type = Type.GetType("System.Object")
'pulls out info about Object constructor. It will be called later 
Dim objCtor As ConstructorInfo = objType.GetConstructor(Type.EmptyTypes)

'Generating code (some of the code and comments came from ConstructorBuilder class)
Dim ctorIL As ILGenerator = ctorBuilder.GetILGenerator()

'place "this" on the stack 
ctorIL.Emit(OpCodes.Ldarg_0)
'Create instance of System.Object by invokign its ctor
ctorIL.Emit(OpCodes.Call, objCtor)

'store fieldName parameter 
ctorIL.Emit(OpCodes.Ldarg_0)
ctorIL.Emit(OpCodes.Ldarg_1)
ctorIL.Emit(OpCodes.Stfld, fieldName)

'store startPosition
ctorIL.Emit(OpCodes.Ldarg_0)
ctorIL.Emit(OpCodes.Ldarg_2)
ctorIL.Emit(OpCodes.Stfld, startPosition)

'stored endPosition
ctorIL.Emit(OpCodes.Ldarg_0)
ctorIL.Emit(OpCodes.Ldarg_3)
ctorIL.Emit(OpCodes.Stfld, endPosition)
'Done. Return
ctorIL.Emit(OpCodes.Ret)

Answer 1

我自己没有使用过TypeBuilder，所以这更多的是一个提示，而不是完整的代码，但基本上我相信你想要TypeBuilder.DefineTypeInitializer，并在那里执行作业。

换句话说，就其静态成员而言，将该类视为如下所示：

public class SWTTFields
{
    public static readonly SWTTFields ISO;
    public static readonly SWTTFields EPC;

    static SWTTFields()
    {
        ISO = new SWTTFields("ISO", 1, 2);
        EPC = new SWTTFields("EPC", 3, 4);
    }
}

（由于静态构造函数造成的差异，这并不完全等同于原始代码，但它已经足够接近了。）

看起来您已经知道如何为该类型初始值设定项主体生成相关的 IL - 只需像对待任何其他方法/构造函数主体一样对待它即可。