MinValue & MaxValue attribute for properties

Question

Is it possible to make attribute which can limit minimum or maximum value of numbers.

Example:

[MinValue(1), MaxValue(50)]
public int Size { get; set         


        

Answer 1

Yes, it is possible with (already pointed) CustomAttributes, but mind, that you will loose the comfort of the auto-properties - because you need to apply resp. check the attribute restriction somewhere and in this case an appropriate place would be the getter of the property, so the interesting part of the problem is the application of the attributes. You can read how to access custom attributes in this MSDN article.

A possible solution for the MaxValue custom attribute can look like this:

// simple class for the example
public class DataHolder
{
    private int a;

    [MaxValue(10)]
    public int A 
    { 
        get
        {
            var memberInfo = this.GetType().GetMember("A");
            if (memberInfo.Length > 0)
            {
                // name of property could be retrieved via reflection
                var mia = this.GetType().GetMember("A")[0];
                var attributes = System.Attribute.GetCustomAttributes(mia);
                if (attributes.Length > 0)
                {
                    // TODO: iterate over all attributes and check attribute name
                    var maxValueAttribute = (MaxValue)attributes[0];
                    if (a > maxValueAttribute.Max) { a = maxValueAttribute.Max; }
                }
            }
            return a;
        }
        set
        {
            a = value;
        }
    }
}


// max attribute
public class MaxValue : Attribute
{
    public int Max;

    public MaxValue(int max)
    {
        Max = max;  
    }
}

The sample usage:

var data = new DataHolder();
data.A = 12;
Console.WriteLine(data.A);

creates the output:

10

The code for the MinValue will look the same as for the MaxValue but the if condition will be less than instead of greater than.