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.support.annotation.NonNull;
21import android.support.v4.view.ViewCompat.NestedScrollType;
22import android.support.v4.view.ViewCompat.ScrollAxis;
23import android.view.View;
24import android.view.ViewGroup;
25
26/**
27 * Helper class for implementing nested scrolling parent views compatible with Android platform
28 * versions earlier than Android 5.0 Lollipop (API 21).
29 *
30 * <p>{@link android.view.ViewGroup ViewGroup} subclasses should instantiate a final instance
31 * of this class as a field at construction. For each <code>ViewGroup</code> method that has
32 * a matching method signature in this class, delegate the operation to the helper instance
33 * in an overridden method implementation. This implements the standard framework policy
34 * for nested scrolling.</p>
35 *
36 * <p>Views invoking nested scrolling functionality should always do so from the relevant
37 * {@link android.support.v4.view.ViewCompat}, {@link android.support.v4.view.ViewGroupCompat} or
38 * {@link android.support.v4.view.ViewParentCompat} compatibility
39 * shim static methods. This ensures interoperability with nested scrolling views on Android
40 * 5.0 Lollipop and newer.</p>
41 */
42public class NestedScrollingParentHelper {
43    private final ViewGroup mViewGroup;
44    private int mNestedScrollAxes;
45
46    /**
47     * Construct a new helper for a given ViewGroup
48     */
49    public NestedScrollingParentHelper(@NonNull ViewGroup viewGroup) {
50        mViewGroup = viewGroup;
51    }
52
53    /**
54     * Called when a nested scrolling operation initiated by a descendant view is accepted
55     * by this ViewGroup.
56     *
57     * <p>This is a delegate method. Call it from your {@link android.view.ViewGroup ViewGroup}
58     * subclass method/{@link android.support.v4.view.NestedScrollingParent} interface method with
59     * the same signature to implement the standard policy.</p>
60     */
61    public void onNestedScrollAccepted(@NonNull View child, @NonNull View target,
62            @ScrollAxis int axes) {
63        onNestedScrollAccepted(child, target, axes, ViewCompat.TYPE_TOUCH);
64    }
65
66    /**
67     * Called when a nested scrolling operation initiated by a descendant view is accepted
68     * by this ViewGroup.
69     *
70     * <p>This is a delegate method. Call it from your {@link android.view.ViewGroup ViewGroup}
71     * subclass method/{@link android.support.v4.view.NestedScrollingParent2} interface method with
72     * the same signature to implement the standard policy.</p>
73     */
74    public void onNestedScrollAccepted(@NonNull View child, @NonNull View target,
75            @ScrollAxis int axes, @NestedScrollType int type) {
76        mNestedScrollAxes = axes;
77    }
78
79    /**
80     * Return the current axes of nested scrolling for this ViewGroup.
81     *
82     * <p>This is a delegate method. Call it from your {@link android.view.ViewGroup ViewGroup}
83     * subclass method/{@link android.support.v4.view.NestedScrollingParent} interface method with
84     * the same signature to implement the standard policy.</p>
85     */
86    @ScrollAxis
87    public int getNestedScrollAxes() {
88        return mNestedScrollAxes;
89    }
90
91    /**
92     * React to a nested scroll operation ending.
93     *
94     * <p>This is a delegate method. Call it from your {@link android.view.ViewGroup ViewGroup}
95     * subclass method/{@link android.support.v4.view.NestedScrollingParent} interface method with
96     * the same signature to implement the standard policy.</p>
97     */
98    public void onStopNestedScroll(@NonNull View target) {
99        onStopNestedScroll(target, ViewCompat.TYPE_TOUCH);
100    }
101
102    /**
103     * React to a nested scroll operation ending.
104     *
105     * <p>This is a delegate method. Call it from your {@link android.view.ViewGroup ViewGroup}
106     * subclass method/{@link android.support.v4.view.NestedScrollingParent2} interface method with
107     * the same signature to implement the standard policy.</p>
108     */
109    public void onStopNestedScroll(@NonNull View target, @NestedScrollType int type) {
110        mNestedScrollAxes = 0;
111    }
112}
113