How to pass in a generic type using a variable working it out at runtime?

Question

I wish to make a generic extension method :

public static IList<ValidationResult> ValidateMany<T>(this IValidator validator, IList objectsToValidate)
{
    var results = new List<ValidationResult>();
    foreach (var obj in objectsToValidate)
    {
        var validationResult = validator.Validate((T) obj);
        results.Add(validationResult);
    }
    return results;
}

I would like T to be passed in. That may seem easy by adding a template param, but then from the calling code I would like to do :

// calling code
var typeOfT = WorkOutTypeFromObjects(objectsToValidate);
var objectsToValidate = RowsToObjectsFactory.Create(typeName, tableRows);
var results = validator.ValidateMany<typeOfT>(objectsToValidate);

the top line there is the critical part that is hard to get, I need some dynamic way of working out the type and passing it in the T param. Or is there a good alternative?

Answer 1

You can call the method using reflection. With the following extension-class

static class ValidatorExtension
{
    public static IList<ValidationResult> ValidateMany<T>(this IValidator validator, IList objectsToValidate)
    {
        var results = new List<ValidationResult>();
        foreach (var obj in objectsToValidate)
        {
            var validationResult = validator.Validate((T)obj);
            results.Add(validationResult);
        }
        return results;
    }
}

call the method like

    public void DoIt()
    {
        // Samplearray of type string
        var typeOfT = typeof(String);
        String[] objectsToValidate = new string[] { "AA", "BB" };

        MethodInfo methodInfo = typeof(ValidatorExtension).GetMethod("ValidateMany");
        MethodInfo genericMethod = methodInfo.MakeGenericMethod(new[] { typeOfT });
        IList<ValidationResult> forTheResult = new List<ValidationResult>();
        genericMethod.Invoke(forTheResult , objectsToValidate);
    }