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