从TypeBuilder创建具有基类和附加字段的动态类型会生成异常

Question

我正在尝试基于仅包含公共字段的现有类型创建动态类型.新的动态类型还必须从仅具有完全实现的方法的不同基类型继承.

我创建了TypeBuilder指定基类型然后我将公共字段添加到它,最后我调用CreateType().生成的错误消息是:

"无法从程序集'MyDynamicAssembly,Version = 0.0.0.0,Culture = neutral,PublicKeyToken = null'加载类型'InternalType',因为字段'first'未被赋予显式偏移量."

对我来说这意味着该CreateType方法在基类中寻找公共字段"first",这是一个问题,因为它不在那里.为什么它认为添加的字段应该在基类中？或者,我是否误解了这个例外？

这是代码:

public class sourceClass
{
    public Int32 first = 1;
    public Int32 second = 2;
    public Int32 third = 3;
}

public static class MyConvert
{
    public static object ToDynamic(object sourceObject, out Type outType)
    {
        // get the public fields from the source object
        FieldInfo[] sourceFields = sourceObject.GetType().GetFields();

        // get a dynamic TypeBuilder and inherit from the base type
        AssemblyName assemblyName
            = new AssemblyName("MyDynamicAssembly");
        AssemblyBuilder assemblyBuilder
            = AppDomain.CurrentDomain.DefineDynamicAssembly(
                assemblyName,
                AssemblyBuilderAccess.Run);
        ModuleBuilder moduleBuilder
            = assemblyBuilder.DefineDynamicModule("MyDynamicModule");
        TypeBuilder typeBuilder
            = moduleBuilder.DefineType(
                "InternalType",
                TypeAttributes.Public
                | TypeAttributes.Class
                | TypeAttributes.AutoClass
                | TypeAttributes.AnsiClass
                | TypeAttributes.ExplicitLayout,
                typeof(SomeOtherNamespace.MyBase));

        // add public fields to match the source object
        foreach (FieldInfo sourceField in sourceFields)
        {
            FieldBuilder fieldBuilder
                = typeBuilder.DefineField(
                    sourceField.Name,
                    sourceField.FieldType,
                    FieldAttributes.Public);
        }

        // THIS IS WHERE THE EXCEPTION OCCURS
        // create the dynamic class
        Type dynamicType = typeBuilder.CreateType();

        // create an instance of the class
        object destObject = Activator.CreateInstance(dynamicType);

        // copy the values of the public fields of the
        // source object to the dynamic object
        foreach (FieldInfo sourceField in sourceFields)
        {
            FieldInfo destField
                = destObject.GetType().GetField(sourceField.Name);
            destField.SetValue(
                destObject,
                sourceField.GetValue(sourceField));
        }

        // give the new class to the caller for casting purposes
        outType = dynamicType;

        // return the new object
        return destObject;
    }

Answer 1

好的,我在发布后想出了这个.我确实误读了错误信息.事实上,它与继承的基类无关.

当我创建类型时,我指定了所需的属性"TypeAttributes.ExplicitLayout".不幸的是,我没有意识到在创建它们时我还必须为每个字段添加一个偏移量.异常消息完全准确.对不起,误报了.更正后的代码如下:

public class SourceClass
{
    public Int32 first = 1;
    public Int32 second = 2;
    public Int32 third = 3;
}

public static class MyConvert
{
    public static object ToDynamic(object sourceObject, out Type outType)
    {
        Int32 fieldOffset = 0;

        // get the public fields from the source object
        FieldInfo[] sourceFields = sourceObject.GetType().GetFields();

        // get a dynamic TypeBuilder and inherit from the base type
        AssemblyName assemblyName
            = new AssemblyName("MyDynamicAssembly");
        AssemblyBuilder assemblyBuilder
            = AppDomain.CurrentDomain.DefineDynamicAssembly(
                assemblyName,
                AssemblyBuilderAccess.Run);
        ModuleBuilder moduleBuilder
            = assemblyBuilder.DefineDynamicModule("MyDynamicModule");
        TypeBuilder typeBuilder
            = moduleBuilder.DefineType(
                "InternalType",
                TypeAttributes.Public
                | TypeAttributes.Class
                | TypeAttributes.AutoClass
                | TypeAttributes.AnsiClass
                | TypeAttributes.ExplicitLayout,
                typeof(SomeOtherNamespace.MyBase));

        // add public fields to match the source object
        foreach (FieldInfo sourceField in sourceFields)
        {
            FieldBuilder fieldBuilder
                = typeBuilder.DefineField(
                    sourceField.Name,
                    sourceField.FieldType,
                    FieldAttributes.Public);
            fieldBuilder.SetOffset(fieldOffset);
            fieldOffset++;
        }

        // create the dynamic class
        Type dynamicType = typeBuilder.CreateType();

        // create an instance of the class
        object destObject = Activator.CreateInstance(dynamicType);

        // copy the values of the public fields of the
        // source object to the dynamic object
        foreach (FieldInfo sourceField in sourceFields)
        {
            FieldInfo destField
                = destObject.GetType().GetField(sourceField.Name);
            destField.SetValue(
                destObject,
                sourceField.GetValue(sourceObject));
        }

        // give the new class to the caller for casting purposes
        outType = dynamicType;

        // return the new object
        return destObject;
    }

编辑:上面的代码将无法正常工作.字段索引以字节为单位,因此当您增加偏移时,您应该按字段大小这样做​​:

fieldOffset += sizeof(Int32);