src/com/android/calendar/StickyHeaderListView.java

/*
 * Copyright (C) 2011 The Android Open Source Project
 *
 * 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 com.android.calendar;

import android.content.Context;
import android.graphics.Color;
import android.util.AttributeSet;
import android.view.Gravity;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AbsListView;
import android.widget.AbsListView.OnScrollListener;
import android.widget.Adapter;
import android.widget.FrameLayout;
import android.widget.ListView;

/**
 * Implements a ListView class with a sticky header at the top. The header is
 * per section and it is pinned to the top as long as its section is at the top
 * of the view. If it is not, the header slides up or down (depending on the
 * scroll movement) and the header of the current section slides to the top.
 * Notes:
 * 1. The class uses the first available child ListView as the working
 *    ListView. If no ListView child exists, the class will create a default one.
 * 2. The ListView's adapter must be passed to this class using the 'setAdapter'
 *    method. The adapter must implement the HeaderIndexer interface. If no adapter
 *    is specified, the class will try to extract it from the ListView
 * 3. The class registers itself as a listener to scroll events (OnScrollListener), if the
 *    ListView needs to receive scroll events, it must register its listener using
 *    this class' setOnScrollListener method.
 * 4. Headers for the list view must be added before using the StickyHeaderListView
 * 5. The implementation should register to listen to dataset changes. Right now this is not done
 *    since a change the dataset in a listview forces a call to OnScroll. The needed code is
 *    commented out.
 */
public class StickyHeaderListView extends FrameLayout implements OnScrollListener {

    private static final String TAG = "StickyHeaderListView";
    protected boolean mChildViewsCreated = false;
    protected boolean mDoHeaderReset = false;

    protected Context mContext = null;
    protected Adapter mAdapter = null;
    protected HeaderIndexer mIndexer = null;
    protected HeaderHeightListener mHeaderHeightListener = null;
    protected View mStickyHeader = null;
    protected View mNonessentialHeader = null; // A invisible header used when a section has no header
    protected ListView mListView = null;
    protected ListView.OnScrollListener mListener = null;

    private int mSeparatorWidth;
    private View mSeparatorView;
    private int mLastStickyHeaderHeight = 0;

    // This code is needed only if dataset changes do not force a call to OnScroll
    // protected DataSetObserver mListDataObserver = null;


    protected int mCurrentSectionPos = -1; // Position of section that has its header on the
                                           // top of the view
    protected int mNextSectionPosition = -1; // Position of next section's header
    protected int mListViewHeadersCount = 0;

    /**
     * Interface that must be implemented by the ListView adapter to provide headers locations
     * and number of items under each header.
     *
     */
    public interface HeaderIndexer {
        /**
         * Calculates the position of the header of a specific item in the adapter's data set.
         * For example: Assuming you have a list with albums and songs names:
         * Album A, song 1, song 2, ...., song 10, Album B, song 1, ..., song 7. A call to
         * this method with the position of song 5 in Album B, should return  the position
         * of Album B.
         * @param position - Position of the item in the ListView dataset
         * @return Position of header. -1 if the is no header
         */

        int getHeaderPositionFromItemPosition(int position);

        /**
         * Calculates the number of items in the section defined by the header (not including
         * the header).
         * For example: A list with albums and songs, the method should return
         * the number of songs names (without the album name).
         *
         * @param headerPosition - the value returned by 'getHeaderPositionFromItemPosition'
         * @return Number of items. -1 on error.
         */
        int getHeaderItemsNumber(int headerPosition);
    }

    /***
    *
    * Interface that is used to update the sticky header's height
    *
    */
   public interface HeaderHeightListener {

       /***
        * Updated a change in the sticky header's size
        *
        * @param height - new height of sticky header
        */
       void OnHeaderHeightChanged(int height);
   }

    /**
     * Sets the adapter to be used by the class to get views of headers
     *
     * @param adapter - The adapter.
     */

    public void setAdapter(Adapter adapter) {

        // This code is needed only if dataset changes do not force a call to
        // OnScroll
        // if (mAdapter != null && mListDataObserver != null) {
        // mAdapter.unregisterDataSetObserver(mListDataObserver);
        // }

        if (adapter != null) {
            mAdapter = adapter;
            // This code is needed only if dataset changes do not force a call
            // to OnScroll
            // mAdapter.registerDataSetObserver(mListDataObserver);
        }
    }

    /**
     * Sets the indexer object (that implements the HeaderIndexer interface).
     *
     * @param indexer - The indexer.
     */

    public void setIndexer(HeaderIndexer indexer) {
        mIndexer = indexer;
    }

    /**
     * Sets the list view that is displayed
     * @param lv - The list view.
     */

    public void setListView(ListView lv) {
        mListView = lv;
        mListView.setOnScrollListener(this);
        mListViewHeadersCount = mListView.getHeaderViewsCount();
    }

    /**
     * Sets an external OnScroll listener. Since the StickyHeaderListView sets
     * itself as the scroll events listener of the listview, this method allows
     * the user to register another listener that will be called after this
     * class listener is called.
     *
     * @param listener - The external listener.
     */
    public void setOnScrollListener(ListView.OnScrollListener listener) {
        mListener = listener;
    }

    public void setHeaderHeightListener(HeaderHeightListener listener) {
        mHeaderHeightListener = listener;
    }

    // This code is needed only if dataset changes do not force a call to OnScroll
    // protected void createDataListener() {
    //    mListDataObserver = new DataSetObserver() {
    //        @Override
    //        public void onChanged() {
    //            onDataChanged();
    //        }
    //    };
    // }

    /**
     * Constructor
     *
     * @param context - application context.
     * @param attrs - layout attributes.
     */
    public StickyHeaderListView(Context context, AttributeSet attrs) {
        super(context, attrs);
        mContext = context;
        // This code is needed only if dataset changes do not force a call to OnScroll
        // createDataListener();
     }

    /**
     * Scroll status changes listener
     *
     * @param view - the scrolled view
     * @param scrollState - new scroll state.
     */
    @Override
    public void onScrollStateChanged(AbsListView view, int scrollState) {
        if (mListener != null) {
            mListener.onScrollStateChanged(view, scrollState);
        }
    }

    /**
     * Scroll events listener
     *
     * @param view - the scrolled view
     * @param firstVisibleItem - the index (in the list's adapter) of the top
     *            visible item.
     * @param visibleItemCount - the number of visible items in the list
     * @param totalItemCount - the total number items in the list
     */
    @Override
    public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount,
            int totalItemCount) {

        updateStickyHeader(firstVisibleItem);

        if (mListener != null) {
            mListener.onScroll(view, firstVisibleItem, visibleItemCount, totalItemCount);
        }
    }

    /**
     * Sets a separator below the sticky header, which will be visible while the sticky header
     * is not scrolling up.
     * @param color - color of separator
     * @param width - width in pixels of separator
     */
    public void setHeaderSeparator(int color, int width) {
        mSeparatorView = new View(mContext);
        ViewGroup.LayoutParams params = new LayoutParams(LayoutParams.MATCH_PARENT,
                width, Gravity.TOP);
        mSeparatorView.setLayoutParams(params);
        mSeparatorView.setBackgroundColor(color);
        mSeparatorWidth = width;
        this.addView(mSeparatorView);
    }

    protected void updateStickyHeader(int firstVisibleItem) {

        // Try to make sure we have an adapter to work with (may not succeed).
        if (mAdapter == null && mListView != null) {
            setAdapter(mListView.getAdapter());
        }

        firstVisibleItem -= mListViewHeadersCount;
        if (mAdapter != null && mIndexer != null && mDoHeaderReset) {

            // Get the section header position
            int sectionSize = 0;
            int sectionPos = mIndexer.getHeaderPositionFromItemPosition(firstVisibleItem);

            // New section - set it in the header view
            boolean newView = false;
            if (sectionPos != mCurrentSectionPos) {

                // No header for current position , use the nonessential invisible one, hide the separator
                if (sectionPos == -1) {
                    sectionSize = 0;
                    this.removeView(mStickyHeader);
                    mStickyHeader = mNonessentialHeader;
                    if (mSeparatorView != null) {
                        mSeparatorView.setVisibility(View.GONE);
                    }
                    newView = true;
                } else {
                    // Create a copy of the header view to show on top
                    sectionSize = mIndexer.getHeaderItemsNumber(sectionPos);
                    View v = mAdapter.getView(sectionPos + mListViewHeadersCount, null, mListView);
                    v.measure(MeasureSpec.makeMeasureSpec(mListView.getWidth(),
                            MeasureSpec.EXACTLY), MeasureSpec.makeMeasureSpec(mListView.getHeight(),
                                    MeasureSpec.AT_MOST));
                    this.removeView(mStickyHeader);
                    mStickyHeader = v;
                    newView = true;
                }
                mCurrentSectionPos = sectionPos;
                mNextSectionPosition = sectionSize + sectionPos + 1;
            }


            // Do transitions
            // If position of bottom of last item in a section is smaller than the height of the
            // sticky header - shift drawable of header.
            if (mStickyHeader != null) {
                int sectionLastItemPosition =  mNextSectionPosition - firstVisibleItem - 1;
                int stickyHeaderHeight = mStickyHeader.getHeight();
                if (stickyHeaderHeight == 0) {
                    stickyHeaderHeight = mStickyHeader.getMeasuredHeight();
                }

                // Update new header height
                if (mHeaderHeightListener != null &&
                        mLastStickyHeaderHeight != stickyHeaderHeight) {
                    mLastStickyHeaderHeight = stickyHeaderHeight;
                    mHeaderHeightListener.OnHeaderHeightChanged(stickyHeaderHeight);
                }

                View SectionLastView = mListView.getChildAt(sectionLastItemPosition);
                if (SectionLastView != null && SectionLastView.getBottom() <= stickyHeaderHeight) {
                    int lastViewBottom = SectionLastView.getBottom();
                    mStickyHeader.setTranslationY(lastViewBottom - stickyHeaderHeight);
                    if (mSeparatorView != null) {
                        mSeparatorView.setVisibility(View.GONE);
                    }
                } else if (stickyHeaderHeight != 0) {
                    mStickyHeader.setTranslationY(0);
                    if (mSeparatorView != null && !mStickyHeader.equals(mNonessentialHeader)) {
                        mSeparatorView.setVisibility(View.VISIBLE);
                    }
                }
                if (newView) {
                    mStickyHeader.setVisibility(View.INVISIBLE);
                    this.addView(mStickyHeader);
                    if (mSeparatorView != null && !mStickyHeader.equals(mNonessentialHeader)){
                        FrameLayout.LayoutParams params =
                                new FrameLayout.LayoutParams(LayoutParams.MATCH_PARENT,
                                        mSeparatorWidth);
                        params.setMargins(0, mStickyHeader.getMeasuredHeight(), 0, 0);
                        mSeparatorView.setLayoutParams(params);
                        mSeparatorView.setVisibility(View.VISIBLE);
                    }
                    mStickyHeader.setVisibility(View.VISIBLE);
                }
            }
        }
    }

    @Override
    protected void onFinishInflate() {
        super.onFinishInflate();
        if (!mChildViewsCreated) {
            setChildViews();
        }
        mDoHeaderReset = true;
    }

    @Override
    protected void onAttachedToWindow() {
        super.onAttachedToWindow();
        if (!mChildViewsCreated) {
            setChildViews();
        }
        mDoHeaderReset = true;
    }


    // Resets the sticky header when the adapter data set was changed
    // This code is needed only if dataset changes do not force a call to OnScroll
    // protected void onDataChanged() {
    // Should do a call to updateStickyHeader if needed
    // }

    private void setChildViews() {

        // Find a child ListView (if any)
        int iChildNum = getChildCount();
        for (int i = 0; i < iChildNum; i++) {
            Object v = getChildAt(i);
            if (v instanceof ListView) {
                setListView((ListView) v);
            }
        }

        // No child ListView - add one
        if (mListView == null) {
            setListView(new ListView(mContext));
        }

        // Create a nonessential view , it will be used in case a section has no header
        mNonessentialHeader = new View (mContext);
        ViewGroup.LayoutParams params = new LayoutParams(LayoutParams.MATCH_PARENT,
                1, Gravity.TOP);
        mNonessentialHeader.setLayoutParams(params);
        mNonessentialHeader.setBackgroundColor(Color.TRANSPARENT);

        mChildViewsCreated = true;
    }

}