如何創建可用於兩個不同對象的基類？

Question

我有兩個類， PersonAdapter和AnimalAdapter 。

這兩個類幾乎是相同的，因此我正在嘗試減少盡可能多的樣板代碼。

PersonAdapter從RecyclerView.Adapter擴展。

AnimalAdapter從RecyclerView.Adapter擴展。 這兩個類都實現了Filterable接口。

PersonAdapter定義了從Filter擴展的內部類PersonFilter 。

AnimalAdapter定義了從Filter擴展的內部類AnimalFilter 。

我想用某種通用類替換PersonFilter和AnimalFilter ，但是我不知道如何，因為這是兩個類之間的區別：

PersonFilter 
    - works with a List<Person>
    - uses Person#getName() to make a string comparison

AnimalFilter 
    - works with a List<Animal>
    - uses Animal#getType() to make a string comparison

請快速瀏覽以下兩個類別：

PersonAdapter

public class PersonAdapter extends RecyclerView.Adapter<PersonViewHolder> implements Filterable {
    private List<Person> persons;
    private PersonFilter personFilter;

    public PersonAdapter(List<Person> persons) {
        this.persons = persons;
    }

    ...

    @Override
    public Filter getFilter() {
        if(personFilter == null)
            personFilter = new PersonFilter(this, persons);
        return personFilter;
    }


    public static class PersonFilter extends Filter {
        private final PersonAdapter adapter;

        private final List<Person> originalList;

        private final List<Person> filteredList;

        private PersonFilter(PersonAdapter adapter, List<Person> originalList) {
            super();
            this.adapter = adapter;
            this.originalList = new LinkedList<>(originalList);
            this.filteredList = new ArrayList<>();
        }

        @Override
        protected FilterResults performFiltering(CharSequence constraint) {
            filteredList.clear();
            final FilterResults results = new FilterResults();

            if (constraint.length() == 0) {
                filteredList.addAll(originalList);
            } else {
                final String filterPattern = constraint.toString().toLowerCase().trim();

                for (final Person person : originalList) {
                    if (person.getName().toLowerCase().contains(filterPattern.toLowerCase())) {
                        filteredList.add(person);
                    }
                }
            }
            results.values = filteredList;
            results.count = filteredList.size();
            return results;
        }

        @Override
        protected void publishResults(CharSequence constraint, FilterResults results) {
            adapter.persons.clear();
            adapter.persons.addAll((ArrayList<Person>) results.values);
            adapter.notifyDataSetChanged();
        }
    }
}

AnimalAdapter

public class AnimalAdapter extends RecyclerView.Adapter<AnimalViewHolder> implements Filterable {
    private List<Animal> animals;
    private AnimalFilter animalFilter;

    public AnimalAdapter(List<Animal> animals) {
        this.animals = animals;
    }

    ...


    public static class AnimalFilter extends Filter {
        private final AnimalAdapter adapter;

        private final List<Animal> originalList;

        private final List<Animal> filteredList;

        private AnimalFilter(AnimalAdapter adapter, List<Animal> originalList) {
            super();
            this.adapter = adapter;
            this.originalList = new LinkedList<>(originalList);
            this.filteredList = new ArrayList<>();
        }

        @Override
        protected FilterResults performFiltering(CharSequence constraint) {
            filteredList.clear();
            final FilterResults results = new FilterResults();

            if (constraint.length() == 0) {
                filteredList.addAll(originalList);
            } else {
                final String filterPattern = constraint.toString().toLowerCase().trim();

                for (final Animal animal : originalList) {
                    if (animal.getType().toLowerCase().contains(filterPattern.toLowerCase())) {
                        filteredList.add(animal);
                    }
                }
            }
            results.values = filteredList;
            results.count = filteredList.size();
            return results;
        }

        @Override
        protected void publishResults(CharSequence constraint, FilterResults results) {
            adapter.animals.clear();
            adapter.animals.addAll((ArrayList<Animal>) results.values);
            adapter.notifyDataSetChanged();
        }
    }
}

我應該如何創建既可以與Animal對象又可以與Animal對象一起使用並且可以被PersonAdapter和AnimalAdapter使用的Filter的通用子類？

Answer 1

這是一個使用泛型和謂詞的過濾器，從問題中拉出兩個過濾器。 通過使用類似於Guava Iterable.filter（）的方法，可以進一步減少代碼。

MyAdapterInterface將需要是適配器的接口或共享父類，這些適配器共享此過濾器需要調用的所有適配器方法。

    public class MyFilter<A extends MyAdapterInterface,T> extends Filter {
        private final A adapter;
        private final Predicate<T> comparator; // Java 8 class - can easily be created by hand if you are using pre Java 8
        // see https://docs.oracle.com/javase/8/docs/api/java/util/function/Predicate.html

        private final List<T> originalList;
        private final List<T> filteredList;

        private MyFilter(A adapter, List<T> originalList, Predicate<T> predicate) {
            super();
            this.adapter = adapter;
            this.comparator = comparator;
            this.originalList = new LinkedList<>(originalList);
            this.filteredList = new ArrayList<>();
        }

        @Override
        protected FilterResults performFiltering(CharSequence constraint) {
            filteredList.clear();
            final FilterResults results = new FilterResults();

            if (constraint.length() == 0) {
                filteredList.addAll(originalList);
            } else {
                final String filterPattern = constraint.toString().toLowerCase().trim();

                for (final T animal : originalList) {
                    if (predicate.test(animal)) {
                        filteredList.add(animal);
                    }
                }
            }
            results.values = filteredList;
            results.count = filteredList.size();
            return results;
        }

        @Override
        protected void publishResults(CharSequence constraint, FilterResults results) {
            adapter.clearResults();   // method to be added to MyAdapterInterface
            adapter.addResults(results.values);  // method to be added to MyAdapterInterface
            adapter.notifyDataSetChanged();
        }
    }