MakeGenericMethod in the below code throws VerificationException: Method MyClass.Calculate: type argument CityList'violates the constraint of type parameter 'TResult'

public class MyCustomActionFilterAttribute : ActionFilterAttribute
{
    public void Calculate<TResult>(PagedResults<TResult> pagedResults) where TResult : MyDTO
    {
        foreach (TResult dto in pagedResults.Value)
        {
            //Do something to dto
        }
    }

    /// <inheritdoc />
    public override void OnActionExecuted(ActionExecutedContext context)
    {
        if (objectResult.Value.GetType().BaseType.GetGenericTypeDefinition().IsAssignableFrom(typeof(PagedResults<>)))
        {
            MethodInfo calculateMethod = this.GetType().GetMethods().Single(m => m.Name == "Calculate");
            calculateMethod = calculateMethod.MakeGenericMethod(objectResult.Value.GetType());
            calculateMethod.Invoke(this, new object[] { objectResult.Value });
        }
    }
}

Please note that CityList extends PagedResults where City extends MyDTO

What am I doing wrong to get the exception?

Thanks

CodePudding user response：

The method's generic argument is TResult whereas the parameter used with MakeGenericMethod in your code is inhertied from PagedResults<TResult>

Try something like this:

  
  Type FindGenericResultType(object pagedResults)
  {
      var type = pagedResults.GetType();

      while (type != null)
      {
          if (type.IsGenericType && typeof(PagedResults<>).IsAssignableFrom(type.GetGenericTypeDefinition())
          {
              return type.GetGenericArguments()[0];
          }    
          type = type.BaseType; 
      }
      
      return null;
  }
  
  var resultType = FindGenericResultType(objectResult.Value);
  if (resultType != null)
  {
     MethodInfo calculateMethod = this.GetType().GetMethods().Single(m => m.Name == "Calculate");
     calculateMethod = calculateMethod.MakeGenericMethod(resultType);
     calculateMethod.Invoke(this, new object[] { objectResult.Value });
  }