1 /* 2 * Copyright (C) 2015 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 package android.support.car.ui; 17 18 import android.content.Context; 19 import android.graphics.PointF; 20 import android.support.v7.widget.LinearLayoutManager; 21 import android.support.v7.widget.LinearSmoothScroller; 22 import android.support.v7.widget.RecyclerView; 23 import android.util.Log; 24 import android.view.View; 25 import android.view.animation.AnimationUtils; 26 import android.view.animation.Interpolator; 27 28 /** 29 * An extension of {@link LinearLayoutManager} that adds some helper methods for paging 30 * such as whether or not it is at the top or bottom of a list and layout param checking. 31 * @hide 32 */ 33 public class PagedLayoutManager extends LinearLayoutManager { 34 private static final String TAG = PagedLayoutManager.class.getSimpleName(); 35 36 private final LinearSmoothScroller mSmoothScrollerForDrag; 37 private final LinearSmoothScroller mSmoothScrollerForNonDrag; 38 39 private int mLastScrollPosition = 0; 40 private boolean mScrollingEnabled = true; 41 public Runnable mItemsChangedRunnable; 42 PagedLayoutManager(Context context)43 public PagedLayoutManager(Context context) { 44 super(context, VERTICAL, false); 45 mSmoothScrollerForDrag = new SnapToStartSmoothScroller(context, true); 46 mSmoothScrollerForNonDrag = new SnapToStartSmoothScroller(context, true); 47 } 48 setItemsChangedListener(Runnable runnable)49 public void setItemsChangedListener(Runnable runnable) { 50 mItemsChangedRunnable = runnable; 51 } 52 53 @Override onItemsChanged(RecyclerView recyclerView)54 public void onItemsChanged(RecyclerView recyclerView) { 55 super.onItemsChanged(recyclerView); 56 if (mItemsChangedRunnable != null) { 57 mItemsChangedRunnable.run(); 58 } 59 } 60 61 @Override getExtraLayoutSpace(RecyclerView.State state)62 protected int getExtraLayoutSpace(RecyclerView.State state) { 63 return getHeight() - getPaddingTop() - getPaddingBottom(); 64 } 65 66 @Override smoothScrollToPosition(RecyclerView recyclerView, RecyclerView.State state, int position)67 public void smoothScrollToPosition(RecyclerView recyclerView, RecyclerView.State state, 68 int position) { 69 boolean forDrag = recyclerView.getScrollState() == RecyclerView.SCROLL_STATE_SETTLING; 70 LinearSmoothScroller ss; 71 if (forDrag) { 72 ss = mSmoothScrollerForDrag; 73 } else { 74 ss = mSmoothScrollerForNonDrag; 75 } 76 ss.setTargetPosition(position); 77 startSmoothScroll(ss); 78 } 79 getLastScrollPosition()80 public int getLastScrollPosition() { 81 return mLastScrollPosition; 82 } 83 84 @Override scrollToPosition(int position)85 public void scrollToPosition(int position) { 86 super.scrollToPosition(position); 87 mLastScrollPosition = position; 88 } 89 90 @Override scrollVerticallyBy(int dy, RecyclerView.Recycler r, RecyclerView.State s)91 public int scrollVerticallyBy(int dy, RecyclerView.Recycler r, RecyclerView.State s) { 92 // Our isAtBottom will return true if the view is on screen the the margin extends below 93 // the bottom. This will make it so that you can't scroll if only the margin is hanging 94 // off the bottom. 95 if (isAtBottom() && dy > 0) { 96 return 0; 97 } 98 return super.scrollVerticallyBy(dy, r, s); 99 } 100 101 @Override canScrollVertically()102 public boolean canScrollVertically() { 103 return mScrollingEnabled; 104 } 105 setScrollingEnabled(boolean enabled)106 public void setScrollingEnabled(boolean enabled) { 107 mScrollingEnabled = enabled; 108 } 109 isAtTop()110 public boolean isAtTop() { 111 if (getChildCount() == 0 || getItemCount() == 0) { 112 return true; 113 } 114 return findFirstCompletelyVisibleItemPosition() < 1; 115 } 116 isAtBottom()117 public boolean isAtBottom() { 118 if (getChildCount() == 0 || getItemCount() == 0) { 119 return true; 120 } 121 return findLastCompletelyVisibleItemPosition() == getItemCount() - 1; 122 } 123 124 private class SnapToStartSmoothScroller extends LinearSmoothScroller { 125 private static final int DURATION_MS = 500; 126 private final Interpolator mInterpolator; 127 SnapToStartSmoothScroller(Context context, boolean forDrag)128 public SnapToStartSmoothScroller(Context context, boolean forDrag) { 129 super(context); 130 int interpolator = forDrag ? android.R.interpolator.decelerate_quint : 131 android.R.interpolator.fast_out_slow_in; 132 mInterpolator = AnimationUtils.loadInterpolator(context, interpolator); 133 } 134 135 @Override onTargetFound(View targetView, RecyclerView.State state, Action action)136 protected void onTargetFound(View targetView, RecyclerView.State state, Action action) { 137 int dy = calculateDyToMakeVisible(targetView, SNAP_TO_START); 138 if (dy == 0) { 139 Log.w(TAG, "Scroll distance is 0."); 140 return; 141 } 142 143 action.update(0, -dy, DURATION_MS, mInterpolator); 144 } 145 146 @Override computeScrollVectorForPosition(int targetPosition)147 public PointF computeScrollVectorForPosition(int targetPosition) { 148 return PagedLayoutManager.this 149 .computeScrollVectorForPosition(targetPosition); 150 } 151 } 152 } 153