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
17
18package android.support.v4.view;
19
20import android.view.View;
21import android.view.ViewGroup;
22
23/**
24 * Helper class for implementing nested scrolling parent views compatible with Android platform
25 * versions earlier than Android 5.0 Lollipop (API 21).
26 *
27 * <p>{@link android.view.ViewGroup ViewGroup} subclasses should instantiate a final instance
28 * of this class as a field at construction. For each <code>ViewGroup</code> method that has
29 * a matching method signature in this class, delegate the operation to the helper instance
30 * in an overridden method implementation. This implements the standard framework policy
31 * for nested scrolling.</p>
32 *
33 * <p>Views invoking nested scrolling functionality should always do so from the relevant
34 * {@link android.support.v4.view.ViewCompat}, {@link android.support.v4.view.ViewGroupCompat} or
35 * {@link android.support.v4.view.ViewParentCompat} compatibility
36 * shim static methods. This ensures interoperability with nested scrolling views on Android
37 * 5.0 Lollipop and newer.</p>
38 */
39public class NestedScrollingParentHelper {
40    private final ViewGroup mViewGroup;
41    private int mNestedScrollAxes;
42
43    /**
44     * Construct a new helper for a given ViewGroup
45     */
46    public NestedScrollingParentHelper(ViewGroup viewGroup) {
47        mViewGroup = viewGroup;
48    }
49
50    /**
51     * Called when a nested scrolling operation initiated by a descendant view is accepted
52     * by this ViewGroup.
53     *
54     * <p>This is a delegate method. Call it from your {@link android.view.ViewGroup ViewGroup}
55     * subclass method/{@link android.support.v4.view.NestedScrollingParent} interface method with
56     * the same signature to implement the standard policy.</p>
57     */
58    public void onNestedScrollAccepted(View child, View target, int axes) {
59        mNestedScrollAxes = axes;
60    }
61
62    /**
63     * Return the current axes of nested scrolling for this ViewGroup.
64     *
65     * <p>This is a delegate method. Call it from your {@link android.view.ViewGroup ViewGroup}
66     * subclass method/{@link android.support.v4.view.NestedScrollingParent} interface method with
67     * the same signature to implement the standard policy.</p>
68     */
69    public int getNestedScrollAxes() {
70        return mNestedScrollAxes;
71    }
72
73    /**
74     * React to a nested scroll operation ending.
75     *
76     * <p>This is a delegate method. Call it from your {@link android.view.ViewGroup ViewGroup}
77     * subclass method/{@link android.support.v4.view.NestedScrollingParent} interface method with
78     * the same signature to implement the standard policy.</p>
79     *
80     * @param target View that initiated the nested scroll
81     */
82    public void onStopNestedScroll(View target) {
83        mNestedScrollAxes = 0;
84    }
85}
86