Is there a way to initialize properties after construction of object?

Question

I have a Conversion class like this:

public class Conversion
{
    public memorySource MSource { get; set; }
    public Rule[] Rules { get; set; }
    public Conversion(XElement xElement)
    {
       // I use Rules property here 
       // From Rules property and xElement parameter i initialize MSource Property
    }

    public Conversion(ExcelPackage)
    {
       // Also i use Rules property here 
       // From Rules property and xElement parameter i initialize MSource Property
    }
}

When I want to construct an instance of the Conversion class, I do this:

Conversion cvr = new Conversion(xElement) { Rules = rules };

Then I get this error:

Object reference not set to an instance of an object

I know that construction of object begins before initializing of properties, but is there a way to do inverse?

I can use Rules property as parameter of constructor but it is not suitable for performance because I have several constructors.

you have to initialize rules in the constructor or add another constructor that takes Rules as you said. there is no other way — Selman Genç, Dec 04 '14 at 10:54

Patrick Hofman · Accepted Answer · 2014-12-04T14:25:01.000

2

Yes, simply pass the value as parameter in the constructor. It's the only way:

Conversion cvr = new Conversion(rules, package);

Where the constructor is:

public Conversion(Rule[] rules, ExcelPackage package)
{
   this.Rules = rules;

   ...
}

You can default the rules parameter for your other constructor, so you don't have to duplicate code:

public Conversion(ExcelPackage package) : this(new Rule[] { ... }, package)
{
   ...
}

edited Dec 04 '14 at 14:25

answered Dec 04 '14 at 10:55

Patrick Hofman

153,850
22
249
325

Oh, I didn't see you've already shown an example with `: this` so I removed mine. – t3chb0t Dec 04 '14 at 11:07
the way OP doing is not possible?? – Ehsan Sajjad Dec 04 '14 at 11:08
@EhsanSajjad: Not if you intend to use `Rules` inside the constructor. Object initializers are post-constructor actions. – Patrick Hofman Dec 04 '14 at 11:08
@PatrickHofman i studied in Albahari book and what i remember we can write that way – Ehsan Sajjad Dec 04 '14 at 11:19
@EhsanSajjad: You can, but that will initialize the `Rules` **after** the constructor. OP needs the `Rules` **in** the constructor. – Patrick Hofman Dec 04 '14 at 11:23
The order is Class initialization => Constructor initialization – Bouam Dec 04 '14 at 13:59
@Bouam: And then object intializers. That's where this question is about. – Patrick Hofman Dec 04 '14 at 14:00

Is there a way to initialize properties after construction of object?

1 Answers1