Reason for Order of Execution

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C#

public class child:parent
    {
        public child()
        {
            System.Windows.Forms.MessageBox.Show("child ns");
        }
        static child()
        {
            System.Windows.Forms.MessageBox.Show("child s");
        }

    }
    public class parent
    {
        public parent()
        {
            System.Windows.Forms.MessageBox.Show("parent ns");
        }
        static parent()
        {
            System.Windows.Forms.MessageBox.Show("parent s");
        }
    }

I have this code and when i make object of the child class... The order of execution of constructor is child static,parent static,parent non static and child non static... All i want to know is the reason for this...
Thanks...

Posted 31-Mar-12 5:05am

Rahul_Patel

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OriginalGriff · Accepted Answer · 2012-03-31T05:26:00

Static has to precede non-static - otherwise the non-static constructor could not rely on (or even access!) static elements of the class. So all static construction needs to precede all non-static.

Child construction must follow parent in non-static classes, so that child instances can rely on parent properties. In actual fact, the constructor for the child is called first - this triggers the parent constructor before any child code is executed.

The only one which looks odd is the child-first static, which is actually following the same order as the public: child constructor first, but the parent constructor is called the first time it is needed - so if you change your code slightly:

C#

public class child : parent
    {
    public child()
        {
        Console.WriteLine("child ns");
        }
    static child()
        {
        Console.WriteLine("child s");
        X = "goodbye";
        Console.WriteLine("child s end");
        }

    }
public class parent
    {
    public static string X = "hello";
    public parent()
        {
        Console.WriteLine("parent ns");
        }
    static parent()
        {
        Console.WriteLine("parent s");
        }

You will get:

child s
parent s
child s end
parent ns
child ns

Because the parent static constructor is called when the child references a parent static property, or at the end of the child constructor if it hasn't been needed before then. Remember, Static constructors are called once, the first time a static property or method is referenced.

[edit]Typo: "public" instead of "parent" and a spare "the" - OriginalGriff[/edit]