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 17 package com.android.contacts.list; 18 19 import android.content.Context; 20 import android.os.Build; 21 import android.util.AttributeSet; 22 import android.widget.ListView; 23 24 /** 25 * A ListView that can be asked to scroll (smoothly or otherwise) to a specific 26 * position. This class takes advantage of similar functionality that exists 27 * in {@link ListView} and enhances it. 28 */ 29 public class AutoScrollListView extends ListView { 30 31 /** 32 * Position the element at about 1/3 of the list height 33 */ 34 private static final float PREFERRED_SELECTION_OFFSET_FROM_TOP = 0.33f; 35 36 private int mRequestedScrollPosition = -1; 37 private boolean mSmoothScrollRequested; 38 AutoScrollListView(Context context)39 public AutoScrollListView(Context context) { 40 super(context); 41 } 42 AutoScrollListView(Context context, AttributeSet attrs)43 public AutoScrollListView(Context context, AttributeSet attrs) { 44 super(context, attrs); 45 } 46 AutoScrollListView(Context context, AttributeSet attrs, int defStyle)47 public AutoScrollListView(Context context, AttributeSet attrs, int defStyle) { 48 super(context, attrs, defStyle); 49 } 50 51 /** 52 * Brings the specified position to view by optionally performing a jump-scroll maneuver: 53 * first it jumps to some position near the one requested and then does a smooth 54 * scroll to the requested position. This creates an impression of full smooth 55 * scrolling without actually traversing the entire list. If smooth scrolling is 56 * not requested, instantly positions the requested item at a preferred offset. 57 */ requestPositionToScreen(int position, boolean smoothScroll)58 public void requestPositionToScreen(int position, boolean smoothScroll) { 59 mRequestedScrollPosition = position; 60 mSmoothScrollRequested = smoothScroll; 61 requestLayout(); 62 } 63 64 @Override layoutChildren()65 protected void layoutChildren() { 66 super.layoutChildren(); 67 if (mRequestedScrollPosition == -1) { 68 return; 69 } 70 71 final int position = mRequestedScrollPosition; 72 mRequestedScrollPosition = -1; 73 74 int firstPosition = getFirstVisiblePosition() + 1; 75 int lastPosition = getLastVisiblePosition(); 76 if (position >= firstPosition && position <= lastPosition) { 77 return; // Already on screen 78 } 79 80 final int offset = (int) (getHeight() * PREFERRED_SELECTION_OFFSET_FROM_TOP); 81 if (!mSmoothScrollRequested) { 82 setSelectionFromTop(position, offset); 83 84 // Since we have changed the scrolling position, we need to redo child layout 85 // Calling "requestLayout" in the middle of a layout pass has no effect, 86 // so we call layoutChildren explicitly 87 super.layoutChildren(); 88 89 } else { 90 // We will first position the list a couple of screens before or after 91 // the new selection and then scroll smoothly to it. 92 int twoScreens = (lastPosition - firstPosition) * 2; 93 int preliminaryPosition; 94 if (position < firstPosition) { 95 preliminaryPosition = position + twoScreens; 96 if (preliminaryPosition >= getCount()) { 97 preliminaryPosition = getCount() - 1; 98 } 99 if (preliminaryPosition < firstPosition) { 100 setSelection(preliminaryPosition); 101 super.layoutChildren(); 102 } 103 } else { 104 preliminaryPosition = position - twoScreens; 105 if (preliminaryPosition < 0) { 106 preliminaryPosition = 0; 107 } 108 if (preliminaryPosition > lastPosition) { 109 setSelection(preliminaryPosition); 110 super.layoutChildren(); 111 } 112 } 113 114 115 smoothScrollToPositionFromTop(position, offset); 116 } 117 } 118 119 @Override onLayout(boolean changed, int l, int t, int r, int b)120 protected void onLayout(boolean changed, int l, int t, int r, int b) { 121 super.onLayout(changed, l, t, r, b); 122 123 // Workaround for b/31160338. 124 if (android.os.Build.VERSION.SDK_INT == Build.VERSION_CODES.N 125 || android.os.Build.VERSION.SDK_INT == Build.VERSION_CODES.N_MR1) { 126 layoutChildren(); 127 } 128 } 129 } 130