Can we interrupt creating an object in constructor

Question

Could you help me please. I have one idea but don\'t know how can I implement it.

So the question is: Can we interrupt creating an object in constructor i.e.

Answer 1

If the parameters to your constructor are invalid, consider throwing ArgumentException or one of its descendant classes (e.g. ArgumentOutOfRangeException).

Answer 2

You may want to use a factory class that creates instances of SomeClass returning null if the someCriteria is invalid.

Answer 3

No it is not possible directly.

You could throw an exception and add the required code to check for the exception and assign null to you variable.

A better solution would be to use a Factory that would return null if some condition fail.

var someClass = SomeClassFactory.Create(someCriteria);
if(someClass != null)
{
}

Answer 4

The new construct guarantees that an object will be returned (or an exception thrown). So as bleeeah recommended, a factory or similar concept will allow you to apply your logic.

Answer 5

Best way is a factory class but if your class is so small you can use this:

class SomeClass
    {
        private string _someCriteria;

        private SomeClass(string someCriteria)
        {
            _someCriteria = someCriteria;
        }

        public static SomeClass CreateInstance(string someCriteria)
        {
            if (someCriteria.Length > 2)
            {
                return new SomeClass(someCriteria);
            }
            return null;
        }
    }

    class Program
    {
        static void Main(string[] args)
        {

            // returns null
            SomeClass someClass = SomeClass.CreateInstance("t");

            // returns object
            SomeClass someClass2 = SomeClass.CreateInstance("test");
        }
    }

Answer 6

That would be possible. Another way would be to put your checking in before you create the object. Like so

SomeClass someClass = null;

if (someCriteria == VALID)
{
    someClass = new SomeClass(someCriteria);
}

Hope this helps.