C＃循环子类

Question

Very new to C# so forgive me if this is a silly question.

If I have a base class called Validator, and a number of classes which inherit from this class such as validateFirstname, validateSecondname etc... is it possible to write a method which will loop through each of these subclasses and instantiate each?

Something along the lines of

public class loadValidators
{
  public loadValidators()
  {
   foreach (subclass in class)
     {
       // instantiate class here
     }
  }
}

Any help is much appreciated as always.

Answer 1

Try this:

var validator_type = typeof (Validator);

var sub_validator_types = 
    validator_type
    .Assembly
    .DefinedTypes
    .Where(x => validator_type.IsAssignableFrom(x) && x != validator_type)
    .ToList();


foreach (var sub_validator_type in sub_validator_types)
{
    Validator sub_validator = (Validator)Activator.CreateInstance(sub_validator_type);
}

This code assumes that all the sub classes live in the same assembly/project as the Validator class.

Also, it assumes that each of the subclasses have a public parameterless constructor.

Please note that I would not recommend this approach.

Instead you should do something like this to solve your problem (of modeling/using multiple validators):

public interface IValidator
{
    bool Validate(SomeObject something);
}

public class FirstNameValidator : IValidator
{
    public bool Validate(SomeObject something)
    {
        ...
    }
}

public class LastNameValidator : IValidator
{
    public bool Validate(SomeObject something)
    {
        ...
    }
}

public class CompositeValidator : IValidator
{
    private readonly IValidator[] m_Validators;

    public CompositeValidator(params IValidator[] validators)
    {
        m_Validators = validators;
    }

    public bool Validate(SomeObject something)
    {
        foreach (IValidator validator in m_Validators)
        {
            if (!validator.Validate(something))
                return false;
        }

        return true;
    }
}

The CompositeValidator wraps multiple validators and knows how to validate objects using those validators.

You can use it like this:

var composite_validator = new CompositeValidator(new FirstNameValidator() , new LastNameValidator());

composite_validator.Validate(obj);