抽象类和多态问题

Question

I am trying to do the following:

public abstract class MyBaseFragment extends Fragment {
    private FloatingActionButton fab;

    protected void initFab(View contentView, int resourceId) {
        fab = (FloatingActionButton) contentView.findViewById(resourceId);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                launchDetailsDialogFragment(new Animal());
            }
        });
    }

    private void launchDetailsDialogFragment(Animal animal) {
        //... 
    }
}

The key point here being the line about making a new Animal.

I have various types of Animals -- Cat, Dog, etc. The page about Cats, the page about Dogs, etc, they will all extend MyBaseFragment. So clicking the FloatingActionButton on the Cat page will execute a function that passes in a new Cat() to the DialogFragment where you can edit its details. Same for Dogs. But each details DialogFragment is a little different, since Cats and Dogs have different properties from each other even though they are both Animals.

However I don't know how to apply polymorphism here. Right now all MyBaseFragment knows is that it will make a new Animal, but really I want it to make a new Cat, or a new Dog, etc, depending on where I am extending the base fragment.

How do I do this?

Answer 1

Just make the called method abstract ad have each concrete class fill in its own implementation

public abstract class MyBaseFragment extends Fragment {
    private FloatingActionButton fab;

    protected void initFab(View contentView, int resourceId) {
        fab = (FloatingActionButton) contentView.findViewById(resourceId);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                launchDetailsDialogFragment();
            }
        });
    }

    protected abstract void launchDetailsDialogFragment();
}

Answer 2

是的，您可以使用“访问者”模式处理对象系列： https : //en.wikipedia.org/wiki/Visitor_pattern

Answer 3

Make launchDetailsDialogFragment abstract:

protected abstract void launchDetailsDialogFragment();

And implement it in the subclasses like you want.

Answer 4

You must let the MyBaseFragment specific implementations decide which animal to instantiate while launching the detail fragment.As far as I can understand the MyBaseFragment abstract class only knows that there should be a detailfragment which should be launched on click event of fabbutton, it does not know of the the type of fragment which should be launched.This would be decided by the specific implementation of the fragment. So, mark the method responsible for creating the detailfragment as protected abstract and override them in the specific implementations to create the specific animal.