1 /* 2 * Copyright (C) 2011 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 17 package com.android.contacts; 18 19 import android.view.View; 20 import android.widget.AbsListView; 21 import android.widget.ListView; 22 23 /** 24 * Handles scrolling back of a list tied to a header. 25 * <p> 26 * This is used to implement a header that scrolls up with the content of a list to be partially 27 * obscured. 28 */ 29 public class BackScrollManager { 30 /** Defines the header to be scrolled. */ 31 public interface ScrollableHeader { 32 /** Sets the offset by which to scroll. */ setOffset(int offset)33 public void setOffset(int offset); 34 /** Gets the maximum offset that should be applied to the header. */ getMaximumScrollableHeaderOffset()35 public int getMaximumScrollableHeaderOffset(); 36 } 37 38 private final ScrollableHeader mHeader; 39 private final ListView mListView; 40 41 private final AbsListView.OnScrollListener mScrollListener = 42 new AbsListView.OnScrollListener() { 43 @Override 44 public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, 45 int totalItemCount) { 46 if (firstVisibleItem != 0) { 47 // The first item is not shown, the header should be pinned at the top. 48 mHeader.setOffset(mHeader.getMaximumScrollableHeaderOffset()); 49 return; 50 } 51 52 View firstVisibleItemView = view.getChildAt(firstVisibleItem); 53 if (firstVisibleItemView == null) { 54 return; 55 } 56 // We scroll the header up, but at most pin it to the top of the screen. 57 int offset = Math.min( 58 (int) -view.getChildAt(firstVisibleItem).getY(), 59 mHeader.getMaximumScrollableHeaderOffset()); 60 mHeader.setOffset(offset); 61 } 62 63 @Override 64 public void onScrollStateChanged(AbsListView view, int scrollState) { 65 // Nothing to do here. 66 } 67 }; 68 69 /** 70 * Creates a new instance of a {@link BackScrollManager} that connected the header and the list 71 * view. 72 */ bind(ScrollableHeader header, ListView listView)73 public static void bind(ScrollableHeader header, ListView listView) { 74 BackScrollManager backScrollManager = new BackScrollManager(header, listView); 75 backScrollManager.bind(); 76 } 77 BackScrollManager(ScrollableHeader header, ListView listView)78 private BackScrollManager(ScrollableHeader header, ListView listView) { 79 mHeader = header; 80 mListView = listView; 81 } 82 bind()83 private void bind() { 84 mListView.setOnScrollListener(mScrollListener); 85 // We disable the scroll bar because it would otherwise be incorrect because of the hidden 86 // header. 87 mListView.setVerticalScrollBarEnabled(false); 88 } 89 } 90