BaseSectionAdapter.java

/*
 * Copyright (c) 2011. WillowTree Apps
 *
 * 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 oak;

import android.view.View;
import android.view.ViewGroup;
import android.widget.AbsListView;
import android.widget.AbsListView.OnScrollListener;
import android.widget.BaseAdapter;
import android.widget.SectionIndexer;

import oak.widget.SectionListView;

public abstract class BaseSectionAdapter extends BaseAdapter
        implements SectionIndexer, OnScrollListener {

    public static final String TAG = BaseSectionAdapter.class.getSimpleName();


    /**
     * Pinned header state: don't show the header.
     */
    public static final int PINNED_HEADER_GONE = 0;

    /**
     * Pinned header state: show the header at the top of the list.
     */
    public static final int PINNED_HEADER_VISIBLE = 1;

    /**
     * Pinned header state: show the header. If the header extends beyond the bottom of the first shown element, push it
     * up and clip.
     */
    public static final int PINNED_HEADER_PUSHED_UP = 2;

    /**
     * Computes the desired state of the pinned header for the given position of the first visible list item. Allowed
     * return values are {@link #PINNED_HEADER_GONE}, {@link #PINNED_HEADER_VISIBLE} or {@link
     * #PINNED_HEADER_PUSHED_UP}.
     */
    public int getPinnedHeaderState(int position) {
        if (position < 0 || getCount() == 0) {
            return PINNED_HEADER_GONE;
        }

        // The header should get pushed up if the top item shown
        // is the last item in a section for a particular letter.
        int section = getSectionForPosition(position);
        int nextSectionPosition = getPositionForSection(section + 1);
        if (nextSectionPosition != -1 && position == nextSectionPosition - 1) {
            return PINNED_HEADER_PUSHED_UP;
        }

        return PINNED_HEADER_VISIBLE;
    }

    @Override
    public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
        if (view instanceof SectionListView) {
            ((SectionListView) view).configureHeaderView(firstVisibleItem);
        }
    }

    @Override
    public void onScrollStateChanged(AbsListView view, int scrollState) {
        // nop
    }

    @Override
    public final View getView(int position, View convertView, ViewGroup parent) {
        View res = getAmazingView(position, convertView, parent);

        final int section = getSectionForPosition(position);
        boolean displaySectionHeaders = (getPositionForSection(section) == position);

        bindSectionHeader(res, position, displaySectionHeaders);

        return res;
    }


    /**
     * Configure the view (a listview item) to display headers or not based on displaySectionHeader (e.g. if
     * displaySectionHeader header.setVisibility(VISIBLE) else header.setVisibility(GONE)).
     */
    protected abstract void bindSectionHeader(View view, int position, boolean displaySectionHeader);

    /**
     * read: get view too
     */
    public abstract View getAmazingView(int position, View convertView, ViewGroup parent);

    /**
     * Configures the pinned header view to match the first visible list item.
     *
     * @param header pinned header view.
     * @param position position of the first visible list item.
     * @param alpha fading of the header view, between 0 and 255.
     */
    public abstract void configurePinnedHeader(View header, int position, int alpha);

    @Override
    public abstract int getPositionForSection(int section);

    @Override
    public abstract int getSectionForPosition(int position);

    @Override
    public abstract Object[] getSections();
}