实例化我的类时需要运行一个受保护的方法

Question

I have a base class with some Custom Attributes, this class is the base class for many other clases This is my class:

[CustomAttribute1("First")]
[CustomAttribute2("Other")]
public class Foo
{
    protected void checkAttributes()
    {
        // Need to run this code when the class and derived classes are instantiated 
    }
}

Then if I créate an instance

Foo MyClass = new Foo();

or build a dereived class:

[CustomAttribute1("FirstDerived")]
public CustClass : Foo
{
    public CustClass(int MyVar)
    {
        //Something here
    }
    public void OtherMethod()
    {
    }
}

CustClass MyClass = new CustClass(5);

I need the method checkAttributes() allways run.

IS that Posible?

There is another aproach ?

NOTE: I need to be shure checkAttributes() runs even if in derived classes the constructor is redefined:

Answer 1

Yes, just define a constructor that calls this method:

public class Foo
{
    public Foo()
    {
        checkAttributes();
    }

    protected void checkAttributes()
    {
        throw new NotImplementedException();
    }
}

As long as every constructor on Foo winds up calling checkAttributes() (either directly or by chaining to a constructor that does) derived classes will not be able to avoid the check.

(It's unclear why this method would be protected, though. Consider making it private, as it sounds like it is a one-time check run when an object is constructed, and shouldn't need to be run later.)

---

One of Foo 's constructors must be called (directly or indirectly) by any type that derives from Foo (directly or indirectly).

From section 10.11.1 of the C# 5 language specification:

All instance constructors (except those for class object ) implicitly include an invocation of another instance constructor immediately before the constructor-body .

...

If an instance constructor has no constructor initializer, a constructor initializer of the form base() is implicitly provided.

The only way that a derived type can avoid calling a constructor on Foo would be to infinitely recurse into one of its own constructors, which would eventually lead to a StackOverflowException .

Answer 2

If you want to run it on each object creation of the object you will have to call it in a normal constructor .

  public Foo()
  {
     //Your normal method call
  }

However if you want it to run only once during your application lifetime you can call in a static constructor Like

static Foo()
{
    // your static method that needs to be run only once
}