1/*
2 * Copyright (C) 2017 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.Nullable;
21import android.support.v4.view.ViewCompat.NestedScrollType;
22import android.support.v4.view.ViewCompat.ScrollAxis;
23import android.view.MotionEvent;
24import android.view.View;
25import android.view.ViewParent;
26
27/**
28 * This interface should be implemented by {@link View View} subclasses that wish
29 * to support dispatching nested scrolling operations to a cooperating parent
30 * {@link android.view.ViewGroup ViewGroup}.
31 *
32 * <p>Classes implementing this interface should create a final instance of a
33 * {@link NestedScrollingChildHelper} as a field and delegate any View methods to the
34 * <code>NestedScrollingChildHelper</code> methods of the same signature.</p>
35 *
36 * <p>Views invoking nested scrolling functionality should always do so from the relevant
37 * {@link ViewCompat}, {@link ViewGroupCompat} or {@link ViewParentCompat} compatibility
38 * shim static methods. This ensures interoperability with nested scrolling views on all versions
39 * of Android.</p>
40 */
41public interface NestedScrollingChild2 extends NestedScrollingChild {
42
43    /**
44     * Begin a nestable scroll operation along the given axes, for the given input type.
45     *
46     * <p>A view starting a nested scroll promises to abide by the following contract:</p>
47     *
48     * <p>The view will call startNestedScroll upon initiating a scroll operation. In the case
49     * of a touch scroll type this corresponds to the initial {@link MotionEvent#ACTION_DOWN}.
50     * In the case of touch scrolling the nested scroll will be terminated automatically in
51     * the same manner as {@link ViewParent#requestDisallowInterceptTouchEvent(boolean)}.
52     * In the event of programmatic scrolling the caller must explicitly call
53     * {@link #stopNestedScroll(int)} to indicate the end of the nested scroll.</p>
54     *
55     * <p>If <code>startNestedScroll</code> returns true, a cooperative parent was found.
56     * If it returns false the caller may ignore the rest of this contract until the next scroll.
57     * Calling startNestedScroll while a nested scroll is already in progress will return true.</p>
58     *
59     * <p>At each incremental step of the scroll the caller should invoke
60     * {@link #dispatchNestedPreScroll(int, int, int[], int[], int) dispatchNestedPreScroll}
61     * once it has calculated the requested scrolling delta. If it returns true the nested scrolling
62     * parent at least partially consumed the scroll and the caller should adjust the amount it
63     * scrolls by.</p>
64     *
65     * <p>After applying the remainder of the scroll delta the caller should invoke
66     * {@link #dispatchNestedScroll(int, int, int, int, int[], int) dispatchNestedScroll}, passing
67     * both the delta consumed and the delta unconsumed. A nested scrolling parent may treat
68     * these values differently. See
69     * {@link NestedScrollingParent2#onNestedScroll(View, int, int, int, int, int)}.
70     * </p>
71     *
72     * @param axes Flags consisting of a combination of {@link ViewCompat#SCROLL_AXIS_HORIZONTAL}
73     *             and/or {@link ViewCompat#SCROLL_AXIS_VERTICAL}.
74     * @param type the type of input which cause this scroll event
75     * @return true if a cooperative parent was found and nested scrolling has been enabled for
76     *         the current gesture.
77     *
78     * @see #stopNestedScroll(int)
79     * @see #dispatchNestedPreScroll(int, int, int[], int[], int)
80     * @see #dispatchNestedScroll(int, int, int, int, int[], int)
81     */
82    boolean startNestedScroll(@ScrollAxis int axes, @NestedScrollType int type);
83
84    /**
85     * Stop a nested scroll in progress for the given input type.
86     *
87     * <p>Calling this method when a nested scroll is not currently in progress is harmless.</p>
88     *
89     * @param type the type of input which cause this scroll event
90     * @see #startNestedScroll(int, int)
91     */
92    void stopNestedScroll(@NestedScrollType int type);
93
94    /**
95     * Returns true if this view has a nested scrolling parent for the given input type.
96     *
97     * <p>The presence of a nested scrolling parent indicates that this view has initiated
98     * a nested scroll and it was accepted by an ancestor view further up the view hierarchy.</p>
99     *
100     * @param type the type of input which cause this scroll event
101     *
102     * @return whether this view has a nested scrolling parent
103     */
104    boolean hasNestedScrollingParent(@NestedScrollType int type);
105
106    /**
107     * Dispatch one step of a nested scroll in progress.
108     *
109     * <p>Implementations of views that support nested scrolling should call this to report
110     * info about a scroll in progress to the current nested scrolling parent. If a nested scroll
111     * is not currently in progress or nested scrolling is not
112     * {@link #isNestedScrollingEnabled() enabled} for this view this method does nothing.</p>
113     *
114     * <p>Compatible View implementations should also call
115     * {@link #dispatchNestedPreScroll(int, int, int[], int[], int) dispatchNestedPreScroll} before
116     * consuming a component of the scroll event themselves.</p>
117     *
118     * @param dxConsumed Horizontal distance in pixels consumed by this view during this scroll step
119     * @param dyConsumed Vertical distance in pixels consumed by this view during this scroll step
120     * @param dxUnconsumed Horizontal scroll distance in pixels not consumed by this view
121     * @param dyUnconsumed Horizontal scroll distance in pixels not consumed by this view
122     * @param offsetInWindow Optional. If not null, on return this will contain the offset
123     *                       in local view coordinates of this view from before this operation
124     *                       to after it completes. View implementations may use this to adjust
125     *                       expected input coordinate tracking.
126     * @param type the type of input which cause this scroll event
127     * @return true if the event was dispatched, false if it could not be dispatched.
128     * @see #dispatchNestedPreScroll(int, int, int[], int[], int)
129     */
130    boolean dispatchNestedScroll(int dxConsumed, int dyConsumed,
131            int dxUnconsumed, int dyUnconsumed, @Nullable int[] offsetInWindow,
132            @NestedScrollType int type);
133
134    /**
135     * Dispatch one step of a nested scroll in progress before this view consumes any portion of it.
136     *
137     * <p>Nested pre-scroll events are to nested scroll events what touch intercept is to touch.
138     * <code>dispatchNestedPreScroll</code> offers an opportunity for the parent view in a nested
139     * scrolling operation to consume some or all of the scroll operation before the child view
140     * consumes it.</p>
141     *
142     * @param dx Horizontal scroll distance in pixels
143     * @param dy Vertical scroll distance in pixels
144     * @param consumed Output. If not null, consumed[0] will contain the consumed component of dx
145     *                 and consumed[1] the consumed dy.
146     * @param offsetInWindow Optional. If not null, on return this will contain the offset
147     *                       in local view coordinates of this view from before this operation
148     *                       to after it completes. View implementations may use this to adjust
149     *                       expected input coordinate tracking.
150     * @param type the type of input which cause this scroll event
151     * @return true if the parent consumed some or all of the scroll delta
152     * @see #dispatchNestedScroll(int, int, int, int, int[], int)
153     */
154    boolean dispatchNestedPreScroll(int dx, int dy, @Nullable int[] consumed,
155            @Nullable int[] offsetInWindow, @NestedScrollType int type);
156}
157