PinnedHeaderListView.java revision 1a848b1f6ab34d9cfe90ed13f20bb9b5131246d0 
1/*
2 * Copyright (C) 2010 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package com.android.contacts.widget;
18
19import android.content.Context;
20import android.graphics.Canvas;
21import android.util.AttributeSet;
22import android.view.View;
23import android.view.ViewGroup;
24import android.widget.AbsListView;
25import android.widget.ListAdapter;
26import android.widget.ListView;
27import android.widget.AbsListView.OnScrollListener;
28
29/**
30 * A ListView that maintains a header pinned at the top of the list. The
31 * pinned header can be pushed up and dissolved as needed.
32 */
33public class PinnedHeaderListView extends ListView implements OnScrollListener {
34
35    /**
36     * Adapter interface.  The list adapter must implement this interface.
37     */
38    public interface PinnedHeaderAdapter {
39
40        /**
41         * Pinned header state: don't show the header.
42         */
43        public static final int PINNED_HEADER_GONE = 0;
44
45        /**
46         * Pinned header state: show the header at the top of the list.
47         */
48        public static final int PINNED_HEADER_VISIBLE = 1;
49
50        /**
51         * Pinned header state: show the header. If the header extends beyond
52         * the bottom of the first shown element, push it up and clip.
53         */
54        public static final int PINNED_HEADER_PUSHED_UP = 2;
55
56        /**
57         * Creates the pinned header view.
58         */
59        View createPinnedHeaderView(ViewGroup parent);
60
61        /**
62         * Computes the desired state of the pinned header for the given
63         * position of the first visible list item. Allowed return values are
64         * {@link #PINNED_HEADER_GONE}, {@link #PINNED_HEADER_VISIBLE} or
65         * {@link #PINNED_HEADER_PUSHED_UP}.
66         */
67        int getPinnedHeaderState(int position);
68
69        /**
70         * Configures the pinned header view to match the first visible list item.
71         *
72         * @param header pinned header view.
73         * @param position position of the first visible list item.
74         * @param alpha fading of the header view, between 0 and 255.
75         */
76        void configurePinnedHeader(View header, int position, int alpha);
77    }
78
79    private static final int MAX_ALPHA = 255;
80
81    private PinnedHeaderAdapter mAdapter;
82    private View mHeaderView;
83    private boolean mHeaderViewVisible;
84    private int mHeaderViewWidth;
85    private int mHeaderViewHeight;
86
87    private OnScrollListener mOnScrollListener;
88
89    public PinnedHeaderListView(Context context) {
90        super(context);
91    }
92
93    public PinnedHeaderListView(Context context, AttributeSet attrs) {
94        super(context, attrs);
95        super.setOnScrollListener(this);
96    }
97
98    public PinnedHeaderListView(Context context, AttributeSet attrs, int defStyle) {
99        super(context, attrs, defStyle);
100        super.setOnScrollListener(this);
101    }
102
103    public void setPinnedHeaderView(View view) {
104        mHeaderView = view;
105
106        // Disable vertical fading when the pinned header is present
107        // TODO change ListView to allow separate measures for top and bottom fading edge;
108        // in this particular case we would like to disable the top, but not the bottom edge.
109        if (mHeaderView != null) {
110            setFadingEdgeLength(0);
111        }
112        requestLayout();
113    }
114
115    @Override
116    public void setAdapter(ListAdapter adapter) {
117        super.setAdapter(adapter);
118        mAdapter = (PinnedHeaderAdapter)adapter;
119        View headerView = mAdapter.createPinnedHeaderView(this);
120        setPinnedHeaderView(headerView);
121    }
122
123    @Override
124    public void setOnScrollListener(OnScrollListener onScrollListener) {
125        mOnScrollListener = onScrollListener;
126        super.setOnScrollListener(this);
127    }
128
129    @Override
130    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
131        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
132        if (mHeaderView != null) {
133            configureHeaderView(getFirstVisiblePosition() - getHeaderViewsCount());
134            measureChild(mHeaderView, widthMeasureSpec, heightMeasureSpec);
135            mHeaderViewWidth = mHeaderView.getMeasuredWidth();
136            mHeaderViewHeight = mHeaderView.getMeasuredHeight();
137        }
138    }
139
140    @Override
141    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
142        super.onLayout(changed, left, top, right, bottom);
143        if (mHeaderView != null) {
144            mHeaderView.layout(0, mHeaderView.getTop(), mHeaderViewWidth, mHeaderViewHeight);
145        }
146    }
147
148    public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount,
149            int totalItemCount) {
150        configureHeaderView(firstVisibleItem - getHeaderViewsCount());
151        if (mOnScrollListener != null) {
152            mOnScrollListener.onScroll(this, firstVisibleItem, visibleItemCount, totalItemCount);
153        }
154    }
155
156    public void onScrollStateChanged(AbsListView view, int scrollState) {
157        if (mOnScrollListener != null) {
158            mOnScrollListener.onScrollStateChanged(this, scrollState);
159        }
160    }
161
162    public void configureHeaderView(int position) {
163        if (mHeaderView == null) {
164            return;
165        }
166
167        int state = mAdapter.getPinnedHeaderState(position);
168        switch (state) {
169            case PinnedHeaderAdapter.PINNED_HEADER_GONE: {
170                mHeaderViewVisible = false;
171                break;
172            }
173
174            case PinnedHeaderAdapter.PINNED_HEADER_VISIBLE: {
175                mAdapter.configurePinnedHeader(mHeaderView, position, MAX_ALPHA);
176                if (mHeaderView.getTop() != 0) {
177                    mHeaderView.layout(0, 0, mHeaderViewWidth, mHeaderViewHeight);
178                }
179                mHeaderViewVisible = true;
180                break;
181            }
182
183            case PinnedHeaderAdapter.PINNED_HEADER_PUSHED_UP: {
184                View firstView = getChildAt(0);
185                int bottom = firstView.getBottom();
186                int headerHeight = mHeaderViewHeight;
187                int y;
188                int alpha;
189                if (bottom < headerHeight) {
190                    y = (bottom - headerHeight);
191                    alpha = MAX_ALPHA * (headerHeight + y) / headerHeight;
192                } else {
193                    y = 0;
194                    alpha = MAX_ALPHA;
195                }
196                mAdapter.configurePinnedHeader(mHeaderView, position, alpha);
197                if (mHeaderView.getTop() != y) {
198                    mHeaderView.layout(0, y, headerHeight, headerHeight + y);
199                }
200                mHeaderViewVisible = true;
201                break;
202            }
203        }
204    }
205
206    @Override
207    protected void dispatchDraw(Canvas canvas) {
208        super.dispatchDraw(canvas);
209        if (mHeaderViewVisible) {
210            drawChild(canvas, mHeaderView, getDrawingTime());
211        }
212    }
213}
214