Inheritance question / problem

Question

I'm creating a custom Layout for android. The layout implementation is exactly the same, but once I need to extend from RelativeLayout, and once from LinearLayout.

class Layout1 extends LinearLayout {
// methods and fields
}

class Layout2 extends RelativeLayout {
// the same EXACT methods and fields
}

How can I use inheritance to avoid code duplication and implement my methods once.

Answer 1

I do not know if it will fit your use case, but you might consider using delegation by adding a field of the "other" class.

I am pessimistic though as tha classes are too closely related.

Answer 2

You could use composition and something like the "strategy" pattern:

class YourLayout extends ViewGroup {
    ViewGroup strategy;
    public YourLayout( Condition someCondition ) {
       if( someCondition.useLinear() ) {
            strategy = new LinearLayout(); // or Layout1
       } else {
            strategy = new RelativeLayout();
       }
    }
    public View findFocus() {
        return strategy.findFocus();
    }
    .... rest of the methods:
    / rest of specific EXACT methods and fields
 }

You may even change the strategy at runtime.

This way your YourLayout class may use both scenarios.

Answer 3

I used delegation, although somewhat differently. The only overloaded method I have in my class was an overloaded dispatchDraw. So I moved it to a different class and included an instance of it in each of the classes that extend.

 class MyLinearLayout extends LinearLayout {
        MyDraw md = new MyDraw();

        @Override
        protected void dispatchDraw(Canvas canvas) {    
            md.draw(canvas);
            super.dispatchDraw(canvas);
        }
 }

 class MyRelativeLayout extends RelativeLayout {
      //    as above
 }

Although I still have two classes that extend, but I'm not duplicating the code that was duplicated before which was what I wanted to achieve.