如何在使用IL Emit动态生成的类中使用本地对象

时间:2017-03-08 16:01:34

标签: c# .net reflection.emit dynamic-assemblies

我甚至不确定这是否可行。在一个方法中,我正在创建一个动态程序集,定义一个类型,并为该类型的构造函数发出IL。此方法将IEnumerable<Action>作为参数,我希望能够在我生成的类中使用该引用。

我已经编写了一些数据库迁移帮助程序来使用FluentMigrator或MigratorDotNet,我正在尝试实现单元测试以验证功能是否正确。使用FluentMigrator,我可以实例化一个运行器并传递它的Migration类实例。但是,对于MigratorDotNet,它要求我传递一个程序集,它扫描Migration类以实例化并运行 - 因此动态生成。

这是我动态子类化的基类:

    public class ActionMigration : Migration
    {
        private readonly IEnumerable<Action<Migration>> _up;
        private readonly IEnumerable<Action<Migration>> _down;
        public ActionMigration(Action<Migration> migration) : this(migration, migration) { }
        public ActionMigration(Action<Migration> up, Action<Migration> down) : this(new[] { up }, new[] { down }) { }
        public ActionMigration(IEnumerable<Action<Migration>> actions) : this(actions, actions) { }
        public ActionMigration(IEnumerable<Action<Migration>> up, IEnumerable<Action<Migration>> down) { _up = up; _down = down; }
        public override void Down() => _down?.ForEach(m => m(this));
        public override void Up() => _up?.ForEach(m => m(this));
    }

这是我生成动态实现的代码:

    private Assembly BuildMigrationAssembly(IEnumerable<Action<Migration>> actions)
    {
        var assemblyName = $"mdn_test_{Guid.NewGuid()}";
        var assemblyBuilder = AppDomain.CurrentDomain.DefineDynamicAssembly(new AssemblyName(assemblyName), AssemblyBuilderAccess.RunAndSave);
        var moduleBuilder = assemblyBuilder.DefineDynamicModule(assemblyBuilder.GetName().Name, assemblyName + ".dll");
        BuildMigrationClass(moduleBuilder, 1, actions);

        return assemblyBuilder;
    }

    private void BuildMigrationClass(ModuleBuilder moduleBuilder, long version, IEnumerable<Action<Migration>> actions)
    {
        var baseType = typeof(ActionMigration);
        var typeBuilder = moduleBuilder.DefineType($"Migration{version}",
            TypeAttributes.Public | TypeAttributes.Class |
            TypeAttributes.AutoClass | TypeAttributes.AnsiClass |
            TypeAttributes.BeforeFieldInit | TypeAttributes.AutoLayout,
            baseType);

        var migAttrType = typeof(MigrationAttribute);
        var migAttrCtor = migAttrType.GetConstructor(new[] { typeof(long) });
        typeBuilder.SetCustomAttribute(migAttrCtor, BitConverter.GetBytes(version));

        var baseCtor = baseType.GetConstructor(new[] { typeof(IEnumerable<Action<Migration>>) });
        var ctor = typeBuilder.DefineConstructor(MethodAttributes.Public, CallingConventions.Standard, null);
        var ilg = ctor.GetILGenerator();
        ilg.Emit(OpCodes.Ldarg_0);
        // how can I pass the local 'actions' object to the base constructor here?
        ilg.Emit(OpCodes.Call, baseCtor);
        ilg.Emit(OpCodes.Nop);
        ilg.Emit(OpCodes.Nop);
        ilg.Emit(OpCodes.Ret);
    }

我打开了一个项目并创建了一些样本子类来检查:

namespace MdnTest
{
    [Migration(1)]
    public class Migration1 : EasyMigrator.Tests.Integration.Migrators.MigratorDotNet.ActionMigration
    {
        public Migration1() : base(new List<Action<Migration>>()) { }
    }
}

或者:

namespace MdnTest
{
    [Migration(1)]
    public class Migration1 : EasyMigrator.Tests.Integration.Migrators.MigratorDotNet.ActionMigration
    {
        static private readonly IEnumerable<Action<Migration>> _actions;
        public Migration1() : base(_actions) { }
    }
}

这是他们产生的IL:

.class public auto ansi beforefieldinit 
  MdnTest.Migration1
    extends [EasyMigrator.Tests]EasyMigrator.Tests.Integration.Migrators.MigratorDotNet/ActionMigration
{
  .custom instance void [Migrator.Framework]Migrator.Framework.MigrationAttribute::.ctor(int64) 
    = (01 00 01 00 00 00 00 00 00 00 00 00 ) // ............
    // int64(1) // 0x0000000000000001

  .method public hidebysig specialname rtspecialname instance void 
    .ctor() cil managed 
  {
    .maxstack 8

    // [14 31 - 14 66]
    IL_0000: ldarg.0      // this
    IL_0001: newobj       instance void class [mscorlib]System.Collections.Generic.List`1<class [mscorlib]System.Action`1<class [Migrator.Framework]Migrator.Framework.Migration>>::.ctor()
    IL_0006: call         instance void [EasyMigrator.Tests]EasyMigrator.Tests.Integration.Migrators.MigratorDotNet/ActionMigration::.ctor(class [mscorlib]System.Collections.Generic.IEnumerable`1<class [mscorlib]System.Action`1<class [Migrator.Framework]Migrator.Framework.Migration>>)
    IL_000b: nop          

    // [14 67 - 14 68]
    IL_000c: nop          

    // [14 69 - 14 70]
    IL_000d: ret          

  } // end of method Migration1::.ctor
} // end of class MdnTest.Migration1

或者:

.class public auto ansi beforefieldinit 
  MdnTest.Migration1
    extends [EasyMigrator.Tests]EasyMigrator.Tests.Integration.Migrators.MigratorDotNet/ActionMigration
{
  .custom instance void [Migrator.Framework]Migrator.Framework.MigrationAttribute::.ctor(int64) 
    = (01 00 01 00 00 00 00 00 00 00 00 00 ) // ............
    // int64(1) // 0x0000000000000001

  .field private static initonly class [mscorlib]System.Collections.Generic.IEnumerable`1<class [mscorlib]System.Action`1<class [Migrator.Framework]Migrator.Framework.Migration>> _actions

  .method public hidebysig specialname rtspecialname instance void 
    .ctor() cil managed 
  {
    .maxstack 8

    // [15 31 - 15 45]
    IL_0000: ldarg.0      // this
    IL_0001: ldsfld       class [mscorlib]System.Collections.Generic.IEnumerable`1<class [mscorlib]System.Action`1<class [Migrator.Framework]Migrator.Framework.Migration>> MdnTest.Migration1::_actions
    IL_0006: call         instance void [EasyMigrator.Tests]EasyMigrator.Tests.Integration.Migrators.MigratorDotNet/ActionMigration::.ctor(class [mscorlib]System.Collections.Generic.IEnumerable`1<class [mscorlib]System.Action`1<class [Migrator.Framework]Migrator.Framework.Migration>>)
    IL_000b: nop          

    // [15 46 - 15 47]
    IL_000c: nop          

    // [15 48 - 15 49]
    IL_000d: ret          

  } // end of method Migration1::.ctor
} // end of class MdnTest.Migration1

我不确定如何使其适应我想要实现的目标。我可以在IL加载指令中仅仅引用存在于动态程序集上下文之外的本地对象吗?表达式有帮助吗?也许尝试在构造函数中传递它是错误的方法 - 可能改为覆盖上下实现(我可以得到一个函数句柄到一个Action并发出一个调用它,而不是传递给它的引用IEnumerable?)。

我对装配和IL非常熟悉,在审查了操作后,我开始认为我可能无法做我想做的事。

那么,这是否有可能,如果有的话,有人会朝着正确的方向推动我吗?

好奇的是,完整的代码是here

1 个答案:

答案 0 :(得分:0)

您可以通过为动态类定义类型为IEnumerable<Action<Migration>>的参数的构造函数来路径引用存在于动态程序集之外的对象:

var ctor = typeBuilder.DefineConstructor(
    MethodAttributes.Public,
    CallingConventions.Standard, 
    new[] { typeof(IEnumerable<Action<Migration>>) });

然后使用这些参数在基类构造函数中对其进行路径:

var ilg = ctor.GetILGenerator();
ilg.Emit(OpCodes.Ldarg_0);        // load 'this' onto stack 
ilg.Emit(OpCodes.Ldarg_1);        // load constructor argument onto the stack 
ilg.Emit(OpCodes.Call, baseCtor); // call base constructor
ilg.Emit(OpCodes.Ret);

在此之后,您将能够使用Activator

创建动态类的实例
var type = typeBuilder.CreateType();
var args = new object[] { new List<Action<Migration>>() };
var instance = Activator.CreateInstance(type, args);