带参数的C＃反射发射调用

由 DJHongKong发布于 2020-05-18 06:11:01

I want to call a function with a parameter with the reflection.emit API. In the following is what I have at the moment. But when I run it, it throws the following exception: System.InvalidProgramException : Common Language Runtime detected an invalid program. So my question is what I have wrong in my code snippet below? Can someone help me out?

public class Test
{

    public void test()
    {
        Func<int, long> realSquareFunc = (val) => val * val;
        Type[] methodArgs = { typeof(int) };

        DynamicMethod squareIt = new DynamicMethod(
            "SquareIt",
            typeof(long),
            methodArgs,
            typeof(Test).Module)
        ;

        ILGenerator il = squareIt.GetILGenerator();
        il.Emit(OpCodes.Ldarg_0); // Save parameter on stack
        il.Emit(OpCodes.Call, realSquareFunc.Method); // Call function with input as parameter
        il.Emit(OpCodes.Ret); // Return value from function call before

        var myMethod = (Func<int, long>)squareIt.CreateDelegate(realSquareFunc.GetType());
        var result = myMethod.Invoke(4); // Should be 16 (4*4)
    }

}

det

2020-05-18 06:11:01

如果被调用的方法是静态方法，您的代码将按原样工作：

public static long RealSquare(int val) => val * val;

public void test()
{
    Func<int, long> realSquareFunc = RealSquare;
    // ...

However, the realSquareFunc = (val) => val * val lambda is actually compiled as an instance method of a hidden class. To call an instance method, the instance must be pushed onto the stack first, before the method arguments. Instance method calls also typically use the Callvirt opcode (regardless of whether they're virtual, because this opcode does null reference checking):

public class Test
{
    public long RealSquare(int val) => val * val;

    public void test()
    {
        Func<int, long> realSquareFunc = RealSquare;
        // pass the instance we want to call the method on in as well
        Type[] methodArgs = { typeof(Test), typeof(int) };

        DynamicMethod squareIt = new DynamicMethod(
            "SquareIt",
            typeof(long),
            methodArgs,
            typeof(Test).Module)
        ;

        ILGenerator il = squareIt.GetILGenerator();
        il.Emit(OpCodes.Ldarg_0); // Push the target instance onto stack      
        il.Emit(OpCodes.Ldarg_1); // Save parameter on stack
        il.Emit(OpCodes.Callvirt, realSquareFunc.Method); // Call function with input as parameter
        il.Emit(OpCodes.Ret); // Return value from function call before

        var myMethod = (Func<Test, int, long>)squareIt.CreateDelegate(typeof(Func<Test, int, long>));
        var result = myMethod.Invoke(this, 4); // Should be 16 (4*4)
    }  
}

由于涉及到编译器生成的类，因此直接调用lambda的target方法更为复杂，但是如果您通常要调用委托，则它的工作方式如下：

public class Test
{        
    public void test()
    {
        Func<int, long> realSquareFunc = (val) => val * val;
        // pass the delegate we want to call into the method
        Type[] methodArgs = { realSquareFunc.GetType(), typeof(int) };

        DynamicMethod squareIt = new DynamicMethod(
            "SquareIt",
            typeof(long),
            methodArgs,
            typeof(Test).Module)
        ;

        ILGenerator il = squareIt.GetILGenerator();
        il.Emit(OpCodes.Ldarg_0); // Push the delegate onto stack        
        il.Emit(OpCodes.Ldarg_1); // Save parameter on stack
        il.Emit(OpCodes.Callvirt, realSquareFunc.GetType().GetMethod("Invoke")); // Invoke delegate
        il.Emit(OpCodes.Ret); // Return value from function call before

        var myMethod = (Func<Func<int, long>, int, long>)squareIt
            .CreateDelegate(typeof(Func<Func<int, long>, int, long>));
        var result = myMethod.Invoke(realSquareFunc, 4); // Should be 16 (4*4)
    }  
}

DJHongKong

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