Here's how to accomplish what I was trying to do.

Validatable class:

public class ValidateMe : IValidatableObject

{

    [Required]

    public bool Enable { get; set; }

    [Range(1, 5)]

    public int Prop1 { get; set; }

    [Range(1, 5)]

    public int Prop2 { get; set; }

    public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)

    {

        var results = new List<ValidationResult>();

        if (this.Enable)

        {

            Validator.TryValidateProperty(this.Prop1,

                new ValidationContext(this, null, null) { MemberName = "Prop1" },

                results);

            Validator.TryValidateProperty(this.Prop2,

                new ValidationContext(this, null, null) { MemberName = "Prop2" },

                results);

            // some other random test

            if (this.Prop1 > this.Prop2)

            {

                results.Add(new ValidationResult("Prop1 must be larger than Prop2"));

            }

        }

        return results;

    }

}

Using Validator.TryValidateProperty() will add to the results collection if there are failed validations. If there is not a failed validation then nothing will be add to the result collection which is an indication of success.

Doing the validation:

    public void DoValidation()

    {

        var toValidate = new ValidateMe()

        {

            Enable = true,

            Prop1 = 1,

            Prop2 = 2

        };

        bool validateAllProperties = false;

        var results = new List<ValidationResult>();

        bool isValid = Validator.TryValidateObject(

            toValidate,

            new ValidationContext(toValidate, null, null),

            results,

            validateAllProperties);

    }

It is important to set validateAllProperties to false for this method to work. When validateAllProperties is false only properties with a [Required] attribute are checked. This allows the IValidatableObject.Validate() method handle the conditional validations.

https://*.com/questions/3400542/how-do-i-use-ivalidatableobject