Calling base constuctor with alternative argument

rodmcleay · January 11th, 2005, 01:08 AM

Hi All,

I have been looking for some examples of how to call a a classes base constructor using a different argument than the derived class.

I have noted from the examples I have found that when calling the base class like so:

Code:

public MyDerivedClass(int myInt):base(myInt){}

The base class constructor is executed first.

I wish to use a SQLDatareader from the derived class constructor in the base class constructor.
Something like this:

Code:

public MyDerivedClass(int myInt)
{
//Call a method that selects returns a datareader containing the fields for the objects properties 
SLQDataReader reader = this.Select();
if(reader.read())
{
//Set a few variables here
this.MyVariable = reader[""];

//Then I want to load the base class properties with fields from this reader.
base(reader);

}
 }

But I get an error:
"Use of keyword base is not valid in this context."

So my question is: How do I call the base constructor explicitly???

Many thanks for taking the time to read this.

======================================
They say, best men are molded out of faults,
And, for the most, become much more the better
For being a little bad.
======================================

Kep · January 11th, 2005, 11:13 PM

As far as I'm aware the only way to do what you want is to make your derived class have a private constructor. You would then create the object using a public static method.

Something like...

Code:

public class MyDerivedClass : MyBaseClass
{
    private MyDerivedClass(SqlDataReader reader) : base(reader)
    {
        // do your initialization
    }

    public static MyDerivedClass Create(int myInt)
    {  
        SqlDataReader reader = this.Select();

        // do some work

        // return a newly created object
        return new MyDerivedClass(reader);
    }
}

Kep.

rodmcleay · January 12th, 2005, 08:21 PM

Thanks Kep,
That is just the solution I was after.
I had not though of a private constructor at all.

Although I now realise that my need for such an implementation is due to a design floor.
I really needed to make the the primay field of the base class protected, then I could set it, and call the base classes Select() method directly.

Thanks again

======================================
They say, best men are molded out of faults,
And, for the most, become much more the better
For being a little bad.
======================================