如何:定义和执行动态方法How to: Define and Execute Dynamic Methods

以下过程介绍如何定义和执行简单的动态方法和绑定到类实例的动态方法。The following procedures show how to define and execute a simple dynamic method and a dynamic method bound to an instance of a class. 有关动态方法的更多信息,请参阅 DynamicMethod 类和反射发出动态方法应用场景For more information on dynamic methods, see the DynamicMethod class and Reflection Emit Dynamic Method Scenarios.

定义和执行动态方法To define and execute a dynamic method

  1. 声明用于执行方法的委托类型。Declare a delegate type to execute the method. 考虑使用泛型委托,将需要声明的委托类型数降到最低。Consider using a generic delegate to minimize the number of delegate types you need to declare. 以下代码声明两种可用于 SquareIt 方法的委托类型,其中一个是泛型。The following code declares two delegate types that could be used for the SquareIt method, and one of them is generic.

    private: 
        delegate long long SquareItInvoker(int input);
    
        generic<typename TReturn, typename TParameter0> 
            delegate TReturn OneParameter(TParameter0 p0);
    
    private delegate long SquareItInvoker(int input);
    
    private delegate TReturn OneParameter<TReturn, TParameter0>
        (TParameter0 p0);
    
    Private Delegate Function _
        SquareItInvoker(ByVal input As Integer) As Long 
    
    Private Delegate Function _
        OneParameter(Of TReturn, TParameter0) _
        (ByVal p0 As TParameter0) As TReturn 
    
  2. 创建用于为动态方法指定参数类型的数组。Create an array that specifies the parameter types for the dynamic method. 在此示例中,唯一的参数为 int(在 Visual Basic 中为 Integer),所以数组只有一个元素。In this example, the only parameter is an int (Integer in Visual Basic), so the array has only one element.

    array<Type^>^ methodArgs = { int::typeid };
    
    Type[] methodArgs = {typeof(int)};
    
    Dim methodArgs As Type() = { GetType(Integer) }
    
  3. 创建 DynamicMethodCreate a DynamicMethod. 在此示例中,该方法命名为 SquareItIn this example the method is named SquareIt.

    备注

    不需要为动态方法命名,并且不能通过名称调用它们。It is not necessary to give dynamic methods names, and they cannot be invoked by name. 多个动态方法可以具有相同的名称。Multiple dynamic methods can have the same name. 但是,名称将在调用堆栈中显示并且可用于调试。However, the name appears in call stacks and can be useful for debugging.

    返回值的类型指定为 longThe type of the return value is specified as long. 该方法与包含 Example 类的模块关联,该类包含代码示例。The method is associated with the module that contains the Example class, which contains the example code. 可以指定任何加载的模块。Any loaded module could be specified. 动态方法的行为类似于模块级的 static 方法(在 Visual Basic 中为 Shared)。The dynamic method acts like a module-level static method (Shared in Visual Basic).

    DynamicMethod^ squareIt = gcnew DynamicMethod(
        "SquareIt", 
        long long::typeid, 
        methodArgs, 
        Example::typeid->Module);
    
    DynamicMethod squareIt = new DynamicMethod(
        "SquareIt", 
        typeof(long), 
        methodArgs, 
        typeof(Example).Module);
    
    Dim squareIt As New DynamicMethod( _
        "SquareIt", _
        GetType(Long), _
        methodArgs, _
        GetType(Example).Module)
    
  4. 发出方法主体。Emit the method body. 在此示例中,使用 ILGenerator 对象发出 Microsoft 中间语言 (MSIL)。In this example, an ILGenerator object is used to emit the Microsoft intermediate language (MSIL). 也可以结合使用 DynamicILInfo 对象与非托管代码生成器,发出 DynamicMethod 的方法主体。Alternatively, a DynamicILInfo object can be used in conjunction with unmanaged code generators to emit the method body for a DynamicMethod.

    此示例中的 MSIL 将该参数(一个 int)加载到堆栈上,将其转换为 long,复制 long,然后将这两个数字相乘。The MSIL in this example loads the argument, which is an int, onto the stack, converts it to a long, duplicates the long, and multiplies the two numbers. 这会将平方结果保留在堆栈中,方法只需返回即可。This leaves the squared result on the stack, and all the method has to do is return.

    ILGenerator^ il = squareIt->GetILGenerator();
    il->Emit(OpCodes::Ldarg_0);
    il->Emit(OpCodes::Conv_I8);
    il->Emit(OpCodes::Dup);
    il->Emit(OpCodes::Mul);
    il->Emit(OpCodes::Ret);
    
    ILGenerator il = squareIt.GetILGenerator();
    il.Emit(OpCodes.Ldarg_0);
    il.Emit(OpCodes.Conv_I8);
    il.Emit(OpCodes.Dup);
    il.Emit(OpCodes.Mul);
    il.Emit(OpCodes.Ret);
    
    Dim il As ILGenerator = squareIt.GetILGenerator()
    il.Emit(OpCodes.Ldarg_0)
    il.Emit(OpCodes.Conv_I8)
    il.Emit(OpCodes.Dup)
    il.Emit(OpCodes.Mul)
    il.Emit(OpCodes.Ret)
    
  5. 通过调用 CreateDelegate 方法创建表示动态方法的委托(在步骤 1 中声明)的实例。Create an instance of the delegate (declared in step 1) that represents the dynamic method by calling the CreateDelegate method. 创建委托即完成该方法,任何更改方法的进一步尝试(例如,添加更多 MSIL)都将被忽略。Creating the delegate completes the method, and any further attempts to change the method — for example, adding more MSIL — are ignored. 以下代码使用泛型委托创建委托并调用它。The following code creates the delegate and invokes it, using a generic delegate.

    OneParameter<long long, int>^ invokeSquareIt = 
        (OneParameter<long long, int>^)
        squareIt->CreateDelegate(OneParameter<long long, int>::typeid);
    
    Console::WriteLine("123456789 squared = {0}",
        invokeSquareIt(123456789));
    
    OneParameter<long, int> invokeSquareIt = 
        (OneParameter<long, int>)
        squareIt.CreateDelegate(typeof(OneParameter<long, int>));
    
    Console.WriteLine("123456789 squared = {0}",
        invokeSquareIt(123456789));
    
    Dim invokeSquareIt As OneParameter(Of Long, Integer) = _
        CType( _
            squareIt.CreateDelegate( _
                GetType(OneParameter(Of Long, Integer))), _
            OneParameter(Of Long, Integer) _
        )
    
    Console.WriteLine("123456789 squared = {0}", _ 
        invokeSquareIt(123456789))
    

定义和执行绑定到对象的动态方法To define and execute a dynamic method that is bound to an object

  1. 声明用于执行方法的委托类型。Declare a delegate type to execute the method. 考虑使用泛型委托,将需要声明的委托类型数降到最低。Consider using a generic delegate to minimize the number of delegate types you need to declare. 以下代码声明一个泛型委托类型,可使用该类型执行任何具有一个参数和一个返回值的方法,如果委托绑定到对象,则该类型也可以执行具有两个参数和一个返回值的方法。The following code declares a generic delegate type that can be used to execute any method with one parameter and a return value, or a method with two parameters and a return value if the delegate is bound to an object.

    generic<typename TReturn, typename TParameter0> 
        delegate TReturn OneParameter(TParameter0 p0);
    
    private delegate TReturn OneParameter<TReturn, TParameter0>
        (TParameter0 p0);
    
    Private Delegate Function _
        OneParameter(Of TReturn, TParameter0) _
        (ByVal p0 As TParameter0) As TReturn 
    
  2. 创建用于为动态方法指定参数类型的数组。Create an array that specifies the parameter types for the dynamic method. 如果表示方法的委托要绑定到对象,则第一个参数必须与委托绑定到的类型相匹配。If the delegate representing the method is to be bound to an object, the first parameter must match the type the delegate is bound to. 在此示例中,存在两个参数,分别属于 Exampleint(在 Visual Basic 中为 Integer)类型。In this example, there are two parameters, of type Example and type int (Integer in Visual Basic).

    array<Type^>^ methodArgs2 = { Example::typeid, int::typeid };
    
    Type[] methodArgs2 = { typeof(Example), typeof(int) };
    
    Dim methodArgs2 As Type() = _
        { GetType(Example), GetType(Integer) }
    
  3. 创建 DynamicMethodCreate a DynamicMethod. 在此示例中,方法没有名称。In this example the method has no name. 返回值的类型指定为 int(在 Visual Basic 中为 Integer)。The type of the return value is specified as int (Integer in Visual Basic). 该方法可以访问 Example 类的私有成员和受保护成员。The method has access to the private and protected members of the Example class.

    DynamicMethod^ multiplyHidden = gcnew DynamicMethod(
        "", 
        int::typeid, 
        methodArgs2, 
        Example::typeid);
    
    DynamicMethod multiplyHidden = new DynamicMethod(
        "", 
        typeof(int), 
        methodArgs2, 
        typeof(Example));
    
    Dim multiplyPrivate As New DynamicMethod( _
        "", _
        GetType(Integer), _
        methodArgs2, _
        GetType(Example))
    
  4. 发出方法主体。Emit the method body. 在此示例中,使用 ILGenerator 对象发出 Microsoft 中间语言 (MSIL)。In this example, an ILGenerator object is used to emit the Microsoft intermediate language (MSIL). 也可以结合使用 DynamicILInfo 对象与非托管代码生成器,发出 DynamicMethod 的方法主体。Alternatively, a DynamicILInfo object can be used in conjunction with unmanaged code generators to emit the method body for a DynamicMethod.

    此示例中的 MSIL 加载第一个参数(一个 Example 类的实例),然后使用该参数加载类型 int 的专用实例字段的值。The MSIL in this example loads the first argument, which is an instance of the Example class, and uses it to load the value of a private instance field of type int. 然后加载第二个参数,并将两个数相乘。The second argument is loaded, and the two numbers are multiplied. 如果结果大于 int,将截断该值且丢弃最高有效位。If the result is larger than int, the value is truncated and the most significant bits are discarded. 该方法返回,返回值保留在堆栈中。The method returns, with the return value on the stack.

    ILGenerator^ ilMH = multiplyHidden->GetILGenerator();
    ilMH->Emit(OpCodes::Ldarg_0);
    
    FieldInfo^ testInfo = Example::typeid->GetField("test",
        BindingFlags::NonPublic | BindingFlags::Instance);
    
    ilMH->Emit(OpCodes::Ldfld, testInfo);
    ilMH->Emit(OpCodes::Ldarg_1);
    ilMH->Emit(OpCodes::Mul);
    ilMH->Emit(OpCodes::Ret);
    
    ILGenerator ilMH = multiplyHidden.GetILGenerator();
    ilMH.Emit(OpCodes.Ldarg_0);
    
    FieldInfo testInfo = typeof(Example).GetField("test",
        BindingFlags.NonPublic | BindingFlags.Instance);
    
    ilMH.Emit(OpCodes.Ldfld, testInfo);
    ilMH.Emit(OpCodes.Ldarg_1);
    ilMH.Emit(OpCodes.Mul);
    ilMH.Emit(OpCodes.Ret);
    
    Dim ilMP As ILGenerator = multiplyPrivate.GetILGenerator()
    ilMP.Emit(OpCodes.Ldarg_0)
    
    Dim testInfo As FieldInfo = _
        GetType(Example).GetField("test", _
            BindingFlags.NonPublic Or BindingFlags.Instance)
    
    ilMP.Emit(OpCodes.Ldfld, testInfo)
    ilMP.Emit(OpCodes.Ldarg_1)
    ilMP.Emit(OpCodes.Mul)
    ilMP.Emit(OpCodes.Ret)
    
  5. 通过调用 CreateDelegate(Type, Object) 方法重载创建表示动态方法的委托(在步骤 1 中声明)的实例。Create an instance of the delegate (declared in step 1) that represents the dynamic method by calling the CreateDelegate(Type, Object) method overload. 创建委托即完成该方法,任何更改方法的进一步尝试(例如,添加更多 MSIL)都将被忽略。Creating the delegate completes the method, and any further attempts to change the method — for example, adding more MSIL — are ignored.

    备注

    可以多次调用 CreateDelegate 方法,创建绑定到目标类型的其他实例的委托。You can call the CreateDelegate method multiple times to create delegates bound to other instances of the target type.

    以下代码将该方法绑定到 Example 类的一个新实例,该类的专用测试字段设置为 42。The following code binds the method to a new instance of the Example class whose private test field is set to 42. 也就是说,每次调用委托时,都会将 Example 的实例传递给该方法的第一个参数。That is, each time the delegate is invoked the instance of Example is passed to the first parameter of the method.

    使用委托 OneParameter 的原因是该方法的第一个参数始终会接收 Example 的实例。The delegate OneParameter is used because the first parameter of the method always receives the instance of Example. 调用委托时,只需要使用第二个参数。When the delegate is invoked, only the second parameter is required.

    OneParameter<int, int>^ invoke = (OneParameter<int, int>^)
        multiplyHidden->CreateDelegate(
            OneParameter<int, int>::typeid, 
            gcnew Example(42)
        );
    
    Console::WriteLine("3 * test = {0}", invoke(3));
    
    OneParameter<int, int> invoke = (OneParameter<int, int>)
        multiplyHidden.CreateDelegate(
            typeof(OneParameter<int, int>), 
            new Example(42)
        );
    
    Console.WriteLine("3 * test = {0}", invoke(3));
    
    Dim invoke As OneParameter(Of Integer, Integer) = _
        CType( _
            multiplyPrivate.CreateDelegate( _
                GetType(OneParameter(Of Integer, Integer)), _
                new Example(42) _
            ), _
            OneParameter(Of Integer, Integer) _
        )
    
    Console.WriteLine("3 * test = {0}", invoke(3))
    

示例Example

以下代码示例演示一个简单的动态方法和一个绑定到类实例的动态方法。The following code example demonstrates a simple dynamic method and a dynamic method bound to an instance of a class.

简单动态方法具有一个 32 位整数参数,返回该整数的 64 位平方。The simple dynamic method takes one argument, a 32-bit integer, and returns the 64-bit square of that integer. 使用泛型委托来调用该方法。A generic delegate is used to invoke the method.

第二个动态方法有两个参数,分别属于 Exampleint(在 Visual Basic 中为 Integer)类型。The second dynamic method has two parameters, of type Example and type int (Integer in Visual Basic). 创建动态方法后,将使用具有一个 int 类型参数的泛型委托将其绑定到 Example 的实例。When the dynamic method has been created, it is bound to an instance of Example, using a generic delegate that has one argument of type int. 该委托没有 Example 类型的参数,因为方法的第一个参数始终接收 Example 的绑定实例。The delegate does not have an argument of type Example because the first parameter of the method always receives the bound instance of Example. 调用委托时,只提供 int 参数。When the delegate is invoked, only the int argument is supplied. 此动态方法访问 Example 类的专用字段,并返回专用字段和 int 参数的乘积。This dynamic method accesses a private field of the Example class and returns the product of the private field and the int argument.

该代码示例定义可用于执行方法的委托。The code example defines delegates that can be used to execute the methods.

using namespace System;
using namespace System::Reflection;
using namespace System::Reflection::Emit;

public ref class Example
{
    // The following constructor and private field are used to
    // demonstrate a method bound to an object.
private:
    int test;
    
public:
    Example(int test) { this->test = test; }

    // Declare delegates that can be used to execute the completed 
    // SquareIt dynamic method. The OneParameter delegate can be 
    // used to execute any method with one parameter and a return
    // value, or a method with two parameters and a return value
    // if the delegate is bound to an object.
    //
private: 
    delegate long long SquareItInvoker(int input);

    generic<typename TReturn, typename TParameter0> 
        delegate TReturn OneParameter(TParameter0 p0);

public:
    static void Main()
    {
        // Example 1: A simple dynamic method.
        //
        // Create an array that specifies the parameter types for the
        // dynamic method. In this example the only parameter is an 
        // int, so the array has only one element.
        //
        array<Type^>^ methodArgs = { int::typeid };

        // Create a DynamicMethod. In this example the method is
        // named SquareIt. It is not necessary to give dynamic 
        // methods names. They cannot be invoked by name, and two
        // dynamic methods can have the same name. However, the 
        // name appears in calls stacks and can be useful for
        // debugging. 
        //
        // In this example the return type of the dynamic method is
        // long long. The method is associated with the module that 
        // contains the Example class. Any loaded module could be
        // specified. The dynamic method is like a module-level
        // static method.
        //
        DynamicMethod^ squareIt = gcnew DynamicMethod(
            "SquareIt", 
            long long::typeid, 
            methodArgs, 
            Example::typeid->Module);

        // Emit the method body. In this example ILGenerator is used
        // to emit the MSIL. DynamicMethod has an associated type
        // DynamicILInfo that can be used in conjunction with 
        // unmanaged code generators.
        //
        // The MSIL loads the argument, which is an int, onto the 
        // stack, converts the int to a long long, duplicates the top
        // item on the stack, and multiplies the top two items on the
        // stack. This leaves the squared number on the stack, and 
        // all the method has to do is return.
        //
        ILGenerator^ il = squareIt->GetILGenerator();
        il->Emit(OpCodes::Ldarg_0);
        il->Emit(OpCodes::Conv_I8);
        il->Emit(OpCodes::Dup);
        il->Emit(OpCodes::Mul);
        il->Emit(OpCodes::Ret);

        // Create a delegate that represents the dynamic method. 
        // Creating the delegate completes the method, and any further 
        // attempts to change the method (for example, by adding more
        // MSIL) are ignored. The following code uses a generic 
        // delegate that can produce delegate types matching any
        // single-parameter method that has a return type.
        //
        OneParameter<long long, int>^ invokeSquareIt = 
            (OneParameter<long long, int>^)
            squareIt->CreateDelegate(OneParameter<long long, int>::typeid);

        Console::WriteLine("123456789 squared = {0}",
            invokeSquareIt(123456789));

        // Example 2: A dynamic method bound to an instance.
        //
        // Create an array that specifies the parameter types for a
        // dynamic method. If the delegate representing the method
        // is to be bound to an object, the first parameter must 
        // match the type the delegate is bound to. In the following
        // code the bound instance is of the Example class. 
        //
        array<Type^>^ methodArgs2 = { Example::typeid, int::typeid };

        // Create a DynamicMethod. In this example the method has no
        // name. The return type of the method is int. The method 
        // has access to the protected and private data of the 
        // Example class.
        //
        DynamicMethod^ multiplyHidden = gcnew DynamicMethod(
            "", 
            int::typeid, 
            methodArgs2, 
            Example::typeid);

        // Emit the method body. In this example ILGenerator is used
        // to emit the MSIL. DynamicMethod has an associated type
        // DynamicILInfo that can be used in conjunction with 
        // unmanaged code generators.
        //
        // The MSIL loads the first argument, which is an instance of
        // the Example class, and uses it to load the value of a 
        // private instance field of type int. The second argument is
        // loaded, and the two numbers are multiplied. If the result
        // is larger than int, the value is truncated and the most 
        // significant bits are discarded. The method returns, with
        // the return value on the stack.
        //
        ILGenerator^ ilMH = multiplyHidden->GetILGenerator();
        ilMH->Emit(OpCodes::Ldarg_0);

        FieldInfo^ testInfo = Example::typeid->GetField("test",
            BindingFlags::NonPublic | BindingFlags::Instance);

        ilMH->Emit(OpCodes::Ldfld, testInfo);
        ilMH->Emit(OpCodes::Ldarg_1);
        ilMH->Emit(OpCodes::Mul);
        ilMH->Emit(OpCodes::Ret);

        // Create a delegate that represents the dynamic method. 
        // Creating the delegate completes the method, and any further 
        // attempts to change the method � for example, by adding more
        // MSIL � are ignored. 
        // 
        // The following code binds the method to a new instance
        // of the Example class whose private test field is set to 42.
        // That is, each time the delegate is invoked the instance of
        // Example is passed to the first parameter of the method.
        //
        // The delegate OneParameter is used, because the first
        // parameter of the method receives the instance of Example.
        // When the delegate is invoked, only the second parameter is
        // required. 
        //
        OneParameter<int, int>^ invoke = (OneParameter<int, int>^)
            multiplyHidden->CreateDelegate(
                OneParameter<int, int>::typeid, 
                gcnew Example(42)
            );

        Console::WriteLine("3 * test = {0}", invoke(3));
    }
};

void main()
{
    Example::Main();
}
/* This code example produces the following output:

123456789 squared = 15241578750190521
3 * test = 126
 */
using System;
using System.Reflection;
using System.Reflection.Emit;

public class Example
{
    // The following constructor and private field are used to
    // demonstrate a method bound to an object.
    private int test;
    public Example(int test) { this.test = test; }

    // Declare delegates that can be used to execute the completed 
    // SquareIt dynamic method. The OneParameter delegate can be 
    // used to execute any method with one parameter and a return
    // value, or a method with two parameters and a return value
    // if the delegate is bound to an object.
    //
    private delegate long SquareItInvoker(int input);

    private delegate TReturn OneParameter<TReturn, TParameter0>
        (TParameter0 p0);

    public static void Main()
    {
        // Example 1: A simple dynamic method.
        //
        // Create an array that specifies the parameter types for the
        // dynamic method. In this example the only parameter is an 
        // int, so the array has only one element.
        //
        Type[] methodArgs = {typeof(int)};

        // Create a DynamicMethod. In this example the method is
        // named SquareIt. It is not necessary to give dynamic 
        // methods names. They cannot be invoked by name, and two
        // dynamic methods can have the same name. However, the 
        // name appears in calls stacks and can be useful for
        // debugging. 
        //
        // In this example the return type of the dynamic method
        // is long. The method is associated with the module that 
        // contains the Example class. Any loaded module could be
        // specified. The dynamic method is like a module-level
        // static method.
        //
        DynamicMethod squareIt = new DynamicMethod(
            "SquareIt", 
            typeof(long), 
            methodArgs, 
            typeof(Example).Module);

        // Emit the method body. In this example ILGenerator is used
        // to emit the MSIL. DynamicMethod has an associated type
        // DynamicILInfo that can be used in conjunction with 
        // unmanaged code generators.
        //
        // The MSIL loads the argument, which is an int, onto the 
        // stack, converts the int to a long, duplicates the top
        // item on the stack, and multiplies the top two items on the
        // stack. This leaves the squared number on the stack, and 
        // all the method has to do is return.
        //
        ILGenerator il = squareIt.GetILGenerator();
        il.Emit(OpCodes.Ldarg_0);
        il.Emit(OpCodes.Conv_I8);
        il.Emit(OpCodes.Dup);
        il.Emit(OpCodes.Mul);
        il.Emit(OpCodes.Ret);

        // Create a delegate that represents the dynamic method. 
        // Creating the delegate completes the method, and any further 
        // attempts to change the method (for example, by adding more
        // MSIL) are ignored. The following code uses a generic 
        // delegate that can produce delegate types matching any
        // single-parameter method that has a return type.
        //
        OneParameter<long, int> invokeSquareIt = 
            (OneParameter<long, int>)
            squareIt.CreateDelegate(typeof(OneParameter<long, int>));

        Console.WriteLine("123456789 squared = {0}",
            invokeSquareIt(123456789));

        // Example 2: A dynamic method bound to an instance.
        //
        // Create an array that specifies the parameter types for a
        // dynamic method. If the delegate representing the method
        // is to be bound to an object, the first parameter must 
        // match the type the delegate is bound to. In the following
        // code the bound instance is of the Example class. 
        //
        Type[] methodArgs2 = { typeof(Example), typeof(int) };

        // Create a DynamicMethod. In this example the method has no
        // name. The return type of the method is int. The method 
        // has access to the protected and private data of the 
        // Example class.
        //
        DynamicMethod multiplyHidden = new DynamicMethod(
            "", 
            typeof(int), 
            methodArgs2, 
            typeof(Example));

        // Emit the method body. In this example ILGenerator is used
        // to emit the MSIL. DynamicMethod has an associated type
        // DynamicILInfo that can be used in conjunction with 
        // unmanaged code generators.
        //
        // The MSIL loads the first argument, which is an instance of
        // the Example class, and uses it to load the value of a 
        // private instance field of type int. The second argument is
        // loaded, and the two numbers are multiplied. If the result
        // is larger than int, the value is truncated and the most 
        // significant bits are discarded. The method returns, with
        // the return value on the stack.
        //
        ILGenerator ilMH = multiplyHidden.GetILGenerator();
        ilMH.Emit(OpCodes.Ldarg_0);

        FieldInfo testInfo = typeof(Example).GetField("test",
            BindingFlags.NonPublic | BindingFlags.Instance);

        ilMH.Emit(OpCodes.Ldfld, testInfo);
        ilMH.Emit(OpCodes.Ldarg_1);
        ilMH.Emit(OpCodes.Mul);
        ilMH.Emit(OpCodes.Ret);

        // Create a delegate that represents the dynamic method. 
        // Creating the delegate completes the method, and any further 
        // attempts to change the method — for example, by adding more
        // MSIL — are ignored. 
        // 
        // The following code binds the method to a new instance
        // of the Example class whose private test field is set to 42.
        // That is, each time the delegate is invoked the instance of
        // Example is passed to the first parameter of the method.
        //
        // The delegate OneParameter is used, because the first
        // parameter of the method receives the instance of Example.
        // When the delegate is invoked, only the second parameter is
        // required. 
        //
        OneParameter<int, int> invoke = (OneParameter<int, int>)
            multiplyHidden.CreateDelegate(
                typeof(OneParameter<int, int>), 
                new Example(42)
            );

        Console.WriteLine("3 * test = {0}", invoke(3));
    }
}
/* This code example produces the following output:

123456789 squared = 15241578750190521
3 * test = 126
 */
Imports System.Reflection
Imports System.Reflection.Emit

Public Class Example

    ' The following constructor and private field are used to
    ' demonstrate a method bound to an object.
    '
    Private test As Integer
    Public Sub New(ByVal test As Integer) 
        Me.test = test 
    End Sub
    
    ' Declare delegates that can be used to execute the completed 
    ' SquareIt dynamic method. The OneParameter delegate can be 
    ' used to execute any method with one parameter and a return
    ' value, or a method with two parameters and a return value
    ' if the delegate is bound to an object.
    '
    Private Delegate Function _
        SquareItInvoker(ByVal input As Integer) As Long 
    
    Private Delegate Function _
        OneParameter(Of TReturn, TParameter0) _
        (ByVal p0 As TParameter0) As TReturn 

    Public Shared Sub Main() 

        ' Example 1: A simple dynamic method.
        '
        ' Create an array that specifies the parameter types for the
        ' dynamic method. In this example the only parameter is an 
        ' Integer, so the array has only one element.
        '
        Dim methodArgs As Type() = { GetType(Integer) }

        ' Create a DynamicMethod. In this example the method is
        ' named SquareIt. It is not necessary to give dynamic 
        ' methods names. They cannot be invoked by name, and two
        ' dynamic methods can have the same name. However, the 
        ' name appears in calls stacks and can be useful for
        ' debugging. 
        '
        ' In this example the return type of the dynamic method
        ' is Long. The method is associated with the module that 
        ' contains the Example class. Any loaded module could be
        ' specified. The dynamic method is like a module-level
        ' Shared method.
        '
        Dim squareIt As New DynamicMethod( _
            "SquareIt", _
            GetType(Long), _
            methodArgs, _
            GetType(Example).Module)

        ' Emit the method body. In this example ILGenerator is used
        ' to emit the MSIL. DynamicMethod has an associated type
        ' DynamicILInfo that can be used in conjunction with 
        ' unmanaged code generators.
        '
        ' The MSIL loads the argument, which is an Integer, onto the 
        ' stack, converts the Integer to a Long, duplicates the top
        ' item on the stack, and multiplies the top two items on the
        ' stack. This leaves the squared number on the stack, and 
        ' all the method has to do is return.
        '
        Dim il As ILGenerator = squareIt.GetILGenerator()
        il.Emit(OpCodes.Ldarg_0)
        il.Emit(OpCodes.Conv_I8)
        il.Emit(OpCodes.Dup)
        il.Emit(OpCodes.Mul)
        il.Emit(OpCodes.Ret)

        ' Create a delegate that represents the dynamic method. 
        ' Creating the delegate completes the method, and any further 
        ' attempts to change the method (for example, by adding more
        ' MSIL) are ignored. The following code uses a generic 
        ' delegate that can produce delegate types matching any
        ' single-parameter method that has a return type.
        '
        Dim invokeSquareIt As OneParameter(Of Long, Integer) = _
            CType( _
                squareIt.CreateDelegate( _
                    GetType(OneParameter(Of Long, Integer))), _
                OneParameter(Of Long, Integer) _
            )
        
        Console.WriteLine("123456789 squared = {0}", _ 
            invokeSquareIt(123456789))


        ' Example 2: A dynamic method bound to an instance.
        '
        ' Create an array that specifies the parameter types for a
        ' dynamic method. If the delegate representing the method
        ' is to be bound to an object, the first parameter must 
        ' match the type the delegate is bound to. In the following
        ' code the bound instance is of the Example class. 
        '
        Dim methodArgs2 As Type() = _
            { GetType(Example), GetType(Integer) }

        ' Create a DynamicMethod. In this example the method has no
        ' name. The return type of the method is Integer. The method 
        ' has access to the protected and private members of the 
        ' Example class. 
        '
        Dim multiplyPrivate As New DynamicMethod( _
            "", _
            GetType(Integer), _
            methodArgs2, _
            GetType(Example))

        ' Emit the method body. In this example ILGenerator is used
        ' to emit the MSIL. DynamicMethod has an associated type
        ' DynamicILInfo that can be used in conjunction with 
        ' unmanaged code generators.
        '
        ' The MSIL loads the first argument, which is an instance of
        ' the Example class, and uses it to load the value of a 
        ' private instance field of type Integer. The second argument 
        ' is loaded, and the two numbers are multiplied. If the result
        ' is larger than Integer, the value is truncated and the most 
        ' significant bits are discarded. The method returns, with
        ' the return value on the stack.
        '
        Dim ilMP As ILGenerator = multiplyPrivate.GetILGenerator()
        ilMP.Emit(OpCodes.Ldarg_0)
        
        Dim testInfo As FieldInfo = _
            GetType(Example).GetField("test", _
                BindingFlags.NonPublic Or BindingFlags.Instance)

        ilMP.Emit(OpCodes.Ldfld, testInfo)
        ilMP.Emit(OpCodes.Ldarg_1)
        ilMP.Emit(OpCodes.Mul)
        ilMP.Emit(OpCodes.Ret)

        ' Create a delegate that represents the dynamic method. 
        ' Creating the delegate completes the method, and any further 
        ' attempts to change the method  for example, by adding more
        ' MSIL  are ignored. 
        ' 
        ' The following code binds the method to a new instance
        ' of the Example class whose private test field is set to 42.
        ' That is, each time the delegate is invoked the instance of
        ' Example is passed to the first parameter of the method.
        '
        ' The delegate OneParameter is used, because the first
        ' parameter of the method receives the instance of Example.
        ' When the delegate is invoked, only the second parameter is
        ' required. 
        '
        Dim invoke As OneParameter(Of Integer, Integer) = _
            CType( _
                multiplyPrivate.CreateDelegate( _
                    GetType(OneParameter(Of Integer, Integer)), _
                    new Example(42) _
                ), _
                OneParameter(Of Integer, Integer) _
            )
        
        Console.WriteLine("3 * test = {0}", invoke(3))

    End Sub 

End Class

' This code example produces the following output:
'
'123456789 squared = 15241578750190521
'3 * test = 126
' 

请参阅See also