Abit/app/src/main/java/ch/dissem/apps/abit/AbstractItemListFragment.java

/*
 * Copyright 2015 Christian Basler
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package ch.dissem.apps.abit;

import android.content.Context;
import android.os.Bundle;
import android.support.v4.app.ListFragment;
import android.view.View;
import android.widget.ListView;

import ch.dissem.apps.abit.listener.ListSelectionListener;

/**
 * @author Christian Basler
 */
public abstract class AbstractItemListFragment<L, T> extends ListFragment implements ListHolder<L> {
    /**
     * The serialization (saved instance state) Bundle key representing the
     * activated item position. Only used on tablets.
     */
    private static final String STATE_ACTIVATED_POSITION = "activated_position";
    /**
     * A dummy implementation of the {@link ListSelectionListener} interface that does
     * nothing. Used only when this fragment is not attached to an activity.
     */
    private static final ListSelectionListener<Object> dummyCallbacks =
        new ListSelectionListener<Object>() {
            @Override
            public void onItemSelected(Object item) {
                // NO OP
            }
        };
    /**
     * The fragment's current callback object, which is notified of list item
     * clicks.
     */
    private ListSelectionListener<? super T> callbacks = dummyCallbacks;
    /**
     * The current activated item position. Only used on tablets.
     */
    private int activatedPosition = ListView.INVALID_POSITION;
    private boolean activateOnItemClick;

    @Override
    public void onViewCreated(View view, Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);

        // Restore the previously serialized activated item position.
        if (savedInstanceState != null
            && savedInstanceState.containsKey(STATE_ACTIVATED_POSITION)) {
            setActivatedPosition(savedInstanceState.getInt(STATE_ACTIVATED_POSITION));
        }
    }

    @Override
    public void onResume() {
        super.onResume();

        // When setting CHOICE_MODE_SINGLE, ListView will automatically
        // give items the 'activated' state when touched.
        getListView().setChoiceMode(activateOnItemClick
            ? ListView.CHOICE_MODE_SINGLE
            : ListView.CHOICE_MODE_NONE);
    }

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);

        // Activities containing this fragment must implement its callbacks.
        if (context instanceof ListSelectionListener) {
            //noinspection unchecked
            callbacks = (ListSelectionListener) context;
        } else {
            throw new IllegalStateException("Activity must implement fragment's callbacks.");
        }

    }

    @Override
    public void onDetach() {
        super.onDetach();

        // Reset the active callbacks interface to the dummy implementation.
        callbacks = dummyCallbacks;
    }

    @Override
    public void onListItemClick(ListView listView, View view, int position, long id) {
        super.onListItemClick(listView, view, position, id);

        // Notify the active callbacks interface (the activity, if the
        // fragment is attached to one) that an item has been selected.
        //noinspection unchecked
        callbacks.onItemSelected((T) listView.getItemAtPosition(position));
    }

    @Override
    public void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        if (activatedPosition != ListView.INVALID_POSITION) {
            // Serialize and persist the activated item position.
            outState.putInt(STATE_ACTIVATED_POSITION, activatedPosition);
        }
    }

    /**
     * Turns on activate-on-click mode. When this mode is on, list items will be
     * given the 'activated' state when touched.
     */
    public void setActivateOnItemClick(boolean activateOnItemClick) {
        this.activateOnItemClick = activateOnItemClick;

        if (isVisible()) {
            // When setting CHOICE_MODE_SINGLE, ListView will automatically
            // give items the 'activated' state when touched.
            getListView().setChoiceMode(activateOnItemClick
                ? ListView.CHOICE_MODE_SINGLE
                : ListView.CHOICE_MODE_NONE);
        }
    }

    private void setActivatedPosition(int position) {
        if (position == ListView.INVALID_POSITION) {
            getListView().setItemChecked(activatedPosition, false);
        } else {
            getListView().setItemChecked(position, true);
        }

        activatedPosition = position;
    }

    @Override
    public L getCurrentLabel() {
        return null;
    }

    @Override
    public boolean showPreviousList() {
        return false;
    }
}