1/* 2 * Copyright (C) 2013 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 android.support.v4.widget; 18 19import android.view.View; 20import android.widget.ListView; 21 22/** 23 * An implementation of {@link AutoScrollHelper} that knows how to scroll 24 * through a {@link ListView}. 25 */ 26public class ListViewAutoScrollHelper extends AutoScrollHelper { 27 private final ListView mTarget; 28 29 public ListViewAutoScrollHelper(ListView target) { 30 super(target); 31 32 mTarget = target; 33 } 34 35 @Override 36 public void scrollTargetBy(int deltaX, int deltaY) { 37 final ListView target = mTarget; 38 final int firstPosition = target.getFirstVisiblePosition(); 39 if (firstPosition == ListView.INVALID_POSITION) { 40 return; 41 } 42 43 final View firstView = target.getChildAt(0); 44 if (firstView == null) { 45 return; 46 } 47 48 final int newTop = firstView.getTop() - deltaY; 49 target.setSelectionFromTop(firstPosition, newTop); 50 } 51 52 @Override 53 public boolean canTargetScrollHorizontally(int direction) { 54 // List do not scroll horizontally. 55 return false; 56 } 57 58 @Override 59 public boolean canTargetScrollVertically(int direction) { 60 final ListView target = mTarget; 61 final int itemCount = target.getCount(); 62 final int childCount = target.getChildCount(); 63 final int firstPosition = target.getFirstVisiblePosition(); 64 final int lastPosition = firstPosition + childCount; 65 66 if (direction > 0) { 67 // Are we already showing the entire last item? 68 if (lastPosition >= itemCount) { 69 final View lastView = target.getChildAt(childCount - 1); 70 if (lastView.getBottom() <= target.getHeight()) { 71 return false; 72 } 73 } 74 } else if (direction < 0) { 75 // Are we already showing the entire first item? 76 if (firstPosition <= 0) { 77 final View firstView = target.getChildAt(0); 78 if (firstView.getTop() >= 0) { 79 return false; 80 } 81 } 82 } else { 83 // The behavior for direction 0 is undefined and we can return 84 // whatever we want. 85 return false; 86 } 87 88 return true; 89 } 90} 91