Question

I have some classes inherit from existing Windows Controls like TextBox and DateTimePicker, ..etc

I want to add custom functionalities for these classes like (Read, Alert, …etc)
these added functionalities are the same in all these classes

The problem is: these classes inherited from difference parents so I can’t put my added functionalities in the parent class,

What’s the best practice in this case:

• repeat the code in each inherited
  class

• Use a separated class have the
  functionalities as Static Methods
  with parameter from an interface, implement this interface for the classes and
  then pass them.

• Use a separated class like the second approach but with Dynamic parameter (which added in C# 4.0)

  or other !!

Thanks in advance

Answer 1

I’d consider option 4: composition.

First, define your set of functionality. We’ll assume that your partial list is exclusive, so “Read” and “Alert.”

Second, create a single class that implements this functionality, something like MyCommonControlBehaviors. I’d prefer this implementation not be static if possible, though, it may be generic.

public MyCommonControlBehaviors
{
    public Whatever Read() { /* ... */ }
    public void Alert() {}
}

Third, use composition to add an instance of this class to each of your custom control types and expose that functionality through your custom control:

public class MyCustomControl
{
    private MyCommonControlBehaviors common; // Composition

    public Whatever Read() { return this.common.Read(); }
    public void Alert() { this.common.Alert(); }
}

Depending on specifics, you can get creative to the degree necessary. E.g., perhaps your custom behaviors need to interact with private control data. In that case, make your control implement a common ICommonBehaviorHost interface that your common behaviors need. Then pass the control into the behavior class on construction as an instance of ICommonBehaviorHost:

public interface ICommonBehaviorHost
{
    void Notify();
}

public class MyCommonControlBehaviors
{
    ICommonBehaviorHost hst = null;

    public MyCommonControlBehaviors(ICommonBehaviorHost host) 
    {
        this.hst = host;
    }

    public void Alert() { this.hst.Notify(); }  // Calls back into the hosting control
    // ...
}

public class MyCustomControl : ICommonBehaviorHost
{
    private MyCommonControlBehaviors common = null;

    public MyCustomControl() { common = new MyCommonControlBehaviors(this); }
    public Whatever Read() { return this.common.Read(); }
    public void Alert() { this.common.Alert(); }

    void ICommonBehaviorHost.Notify() { /* called by this.common */ }
}