Cascading Constructors

rodmcleay · May 16th, 2007, 04:13 AM

Hi All,
I wish to have a class call the constuctor from the class it inherits in within its own constuctor.
I have understand the constuct
public class myClass():Base(){}
But I wish to use a paramter for the class that is not determined untill the child constructor is executed.
Can anyone advise me of how this is done.

This is an example of what Im after but it doesnot seem to recognise the base class constuctors.

Code:

class Class1
    {
        int _c1id;
        int _field1;
        int _field2;
        public Class1() { }
        public Class1(int c1id) 
        { 
            _c1id = c1id;

            //Get Data From DB
            _field1 = 456;
            _field2 = 789;
        }
    }
    class Class2 : Class1
    {
        int _c2id;
        public Class2(int c2id) 
        {
            _c2id = c2id;
            //Get C1 ID from DB
            _c1id = 1;//FROM DB
            base(_c1id);
        }
    }

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

planoie · May 16th, 2007, 07:26 AM

You can pass constructor arguments to the super class construct:

Code:

public class SubClass : SuperClass{

   public SubClass(int someInt) : base(someInt){
      //do stuff
   }

}

-Peter

rodmcleay · May 16th, 2007, 07:23 PM

Hi Peter,
Thanks for that.
I thought that will execute the base constructor first.
I need the base contructors paramter to be obtained by the subclass.
Its not the same variable.

Code:

public class SubClass : SuperClass{

   public SubClass(int someInt) : base(anotherInt){
      //do stuff
      anotherInt = 31;//Obtained from DB lookup
   }

}

Should I just create a protected method to populate the super class variables?

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

planoie · May 16th, 2007, 10:31 PM

You've discovered one of the pitfalls of putting too much smarts into a constructor. All super class constructor's are called before the subclass ones.

You would probably be better off making a method outside of the constructor that loads the database info so you can control it more.

-Peter

rodmcleay · May 18th, 2007, 03:57 AM

Thanks Peter, I had thought as much but had hoped for some wierd and wonderful work around.
thanks all the same.

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