100 lines
4.1 KiB
Java
100 lines
4.1 KiB
Java
/*
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* Copyright (C) 2017 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.android.internal.widget;
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import android.view.View;
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/**
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* A helper class to do scroll offset calculations.
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*/
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class ScrollbarHelper {
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/**
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* @param startChild View closest to start of the list. (top or left)
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* @param endChild View closest to end of the list (bottom or right)
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*/
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static int computeScrollOffset(RecyclerView.State state, OrientationHelper orientation,
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View startChild, View endChild, RecyclerView.LayoutManager lm,
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boolean smoothScrollbarEnabled, boolean reverseLayout) {
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if (lm.getChildCount() == 0 || state.getItemCount() == 0 || startChild == null
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|| endChild == null) {
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return 0;
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}
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final int minPosition = Math.min(lm.getPosition(startChild),
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lm.getPosition(endChild));
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final int maxPosition = Math.max(lm.getPosition(startChild),
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lm.getPosition(endChild));
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final int itemsBefore = reverseLayout
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? Math.max(0, state.getItemCount() - maxPosition - 1)
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: Math.max(0, minPosition);
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if (!smoothScrollbarEnabled) {
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return itemsBefore;
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}
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final int laidOutArea = Math.abs(orientation.getDecoratedEnd(endChild)
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- orientation.getDecoratedStart(startChild));
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final int itemRange = Math.abs(lm.getPosition(startChild)
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- lm.getPosition(endChild)) + 1;
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final float avgSizePerRow = (float) laidOutArea / itemRange;
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return Math.round(itemsBefore * avgSizePerRow + (orientation.getStartAfterPadding()
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- orientation.getDecoratedStart(startChild)));
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}
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/**
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* @param startChild View closest to start of the list. (top or left)
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* @param endChild View closest to end of the list (bottom or right)
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*/
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static int computeScrollExtent(RecyclerView.State state, OrientationHelper orientation,
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View startChild, View endChild, RecyclerView.LayoutManager lm,
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boolean smoothScrollbarEnabled) {
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if (lm.getChildCount() == 0 || state.getItemCount() == 0 || startChild == null
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|| endChild == null) {
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return 0;
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}
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if (!smoothScrollbarEnabled) {
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return Math.abs(lm.getPosition(startChild) - lm.getPosition(endChild)) + 1;
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}
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final int extend = orientation.getDecoratedEnd(endChild)
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- orientation.getDecoratedStart(startChild);
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return Math.min(orientation.getTotalSpace(), extend);
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}
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/**
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* @param startChild View closest to start of the list. (top or left)
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* @param endChild View closest to end of the list (bottom or right)
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*/
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static int computeScrollRange(RecyclerView.State state, OrientationHelper orientation,
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View startChild, View endChild, RecyclerView.LayoutManager lm,
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boolean smoothScrollbarEnabled) {
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if (lm.getChildCount() == 0 || state.getItemCount() == 0 || startChild == null
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|| endChild == null) {
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return 0;
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}
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if (!smoothScrollbarEnabled) {
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return state.getItemCount();
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}
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// smooth scrollbar enabled. try to estimate better.
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final int laidOutArea = orientation.getDecoratedEnd(endChild)
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- orientation.getDecoratedStart(startChild);
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final int laidOutRange = Math.abs(lm.getPosition(startChild)
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- lm.getPosition(endChild))
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+ 1;
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// estimate a size for full list.
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return (int) ((float) laidOutArea / laidOutRange * state.getItemCount());
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}
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}
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