|
| 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.slidingmenu.lib.menu; |
| 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 | +} |
0 commit comments