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.ViewParent;
22
23/**
24 * Helper class for implementing nested scrolling child views compatible with Android platform
25 * versions earlier than Android 5.0 Lollipop (API 21).
26 *
27 * <p>{@link android.view.View View} subclasses should instantiate a final instance of this
28 * class as a field at construction. For each <code>View</code> method that has a matching
29 * method signature in this class, delegate the operation to the helper instance in an overriden
30 * method implementation. This implements the standard framework policy for nested scrolling.</p>
31 *
32 * <p>Views invoking nested scrolling functionality should always do so from the relevant
33 * {@link ViewCompat}, {@link ViewGroupCompat} or {@link ViewParentCompat} compatibility
34 * shim static methods. This ensures interoperability with nested scrolling views on Android
35 * 5.0 Lollipop and newer.</p>
36 */
37public class NestedScrollingChildHelper {
38    private final View mView;
39    private ViewParent mNestedScrollingParent;
40    private boolean mIsNestedScrollingEnabled;
41    private int[] mTempNestedScrollConsumed;
42
43    /**
44     * Construct a new helper for a given view.
45     */
46    public NestedScrollingChildHelper(View view) {
47        mView = view;
48    }
49
50    /**
51     * Enable nested scrolling.
52     *
53     * <p>This is a delegate method. Call it from your {@link android.view.View View} subclass
54     * method/{@link NestedScrollingChild} interface method with the same signature to implement
55     * the standard policy.</p>
56     *
57     * @param enabled true to enable nested scrolling dispatch from this view, false otherwise
58     */
59    public void setNestedScrollingEnabled(boolean enabled) {
60        if (mIsNestedScrollingEnabled) {
61            ViewCompat.stopNestedScroll(mView);
62        }
63        mIsNestedScrollingEnabled = enabled;
64    }
65
66    /**
67     * Check if nested scrolling is enabled for this view.
68     *
69     * <p>This is a delegate method. Call it from your {@link android.view.View View} subclass
70     * method/{@link NestedScrollingChild} interface method with the same signature to implement
71     * the standard policy.</p>
72     *
73     * @return true if nested scrolling is enabled for this view
74     */
75    public boolean isNestedScrollingEnabled() {
76        return mIsNestedScrollingEnabled;
77    }
78
79    /**
80     * Check if this view has a nested scrolling parent view currently receiving events for
81     * a nested scroll in progress.
82     *
83     * <p>This is a delegate method. Call it from your {@link android.view.View View} subclass
84     * method/{@link NestedScrollingChild} interface method with the same signature to implement
85     * the standard policy.</p>
86     *
87     * @return true if this view has a nested scrolling parent, false otherwise
88     */
89    public boolean hasNestedScrollingParent() {
90        return mNestedScrollingParent != null;
91    }
92
93    /**
94     * Start a new nested scroll for this view.
95     *
96     * <p>This is a delegate method. Call it from your {@link android.view.View View} subclass
97     * method/{@link NestedScrollingChild} interface method with the same signature to implement
98     * the standard policy.</p>
99     *
100     * @param axes Supported nested scroll axes.
101     *             See {@link NestedScrollingChild#startNestedScroll(int)}.
102     * @return true if a cooperating parent view was found and nested scrolling started successfully
103     */
104    public boolean startNestedScroll(int axes) {
105        if (hasNestedScrollingParent()) {
106            // Already in progress
107            return true;
108        }
109        if (isNestedScrollingEnabled()) {
110            ViewParent p = mView.getParent();
111            View child = mView;
112            while (p != null) {
113                if (ViewParentCompat.onStartNestedScroll(p, child, mView, axes)) {
114                    mNestedScrollingParent = p;
115                    ViewParentCompat.onNestedScrollAccepted(p, child, mView, axes);
116                    return true;
117                }
118                if (p instanceof View) {
119                    child = (View) p;
120                }
121                p = p.getParent();
122            }
123        }
124        return false;
125    }
126
127    /**
128     * Stop a nested scroll in progress.
129     *
130     * <p>This is a delegate method. Call it from your {@link android.view.View View} subclass
131     * method/{@link NestedScrollingChild} interface method with the same signature to implement
132     * the standard policy.</p>
133     */
134    public void stopNestedScroll() {
135        if (mNestedScrollingParent != null) {
136            ViewParentCompat.onStopNestedScroll(mNestedScrollingParent, mView);
137            mNestedScrollingParent = null;
138        }
139    }
140
141    /**
142     * Dispatch one step of a nested scrolling operation to the current nested scrolling parent.
143     *
144     * <p>This is a delegate method. Call it from your {@link android.view.View View} subclass
145     * method/{@link NestedScrollingChild} interface method with the same signature to implement
146     * the standard policy.</p>
147     *
148     * @return true if the parent consumed any of the nested scroll
149     */
150    public boolean dispatchNestedScroll(int dxConsumed, int dyConsumed,
151            int dxUnconsumed, int dyUnconsumed, int[] offsetInWindow) {
152        if (isNestedScrollingEnabled() && mNestedScrollingParent != null) {
153            if (dxConsumed != 0 || dyConsumed != 0 || dxUnconsumed != 0 || dyUnconsumed != 0) {
154                int startX = 0;
155                int startY = 0;
156                if (offsetInWindow != null) {
157                    mView.getLocationInWindow(offsetInWindow);
158                    startX = offsetInWindow[0];
159                    startY = offsetInWindow[1];
160                }
161
162                ViewParentCompat.onNestedScroll(mNestedScrollingParent, mView, dxConsumed,
163                        dyConsumed, dxUnconsumed, dyUnconsumed);
164
165                if (offsetInWindow != null) {
166                    mView.getLocationInWindow(offsetInWindow);
167                    offsetInWindow[0] -= startX;
168                    offsetInWindow[1] -= startY;
169                }
170                return true;
171            } else if (offsetInWindow != null) {
172                // No motion, no dispatch. Keep offsetInWindow up to date.
173                offsetInWindow[0] = 0;
174                offsetInWindow[1] = 0;
175            }
176        }
177        return false;
178    }
179
180    /**
181     * Dispatch one step of a nested pre-scrolling operation to the current nested scrolling parent.
182     *
183     * <p>This is a delegate method. Call it from your {@link android.view.View View} subclass
184     * method/{@link NestedScrollingChild} interface method with the same signature to implement
185     * the standard policy.</p>
186     *
187     * @return true if the parent consumed any of the nested scroll
188     */
189    public boolean dispatchNestedPreScroll(int dx, int dy, int[] consumed, int[] offsetInWindow) {
190        if (isNestedScrollingEnabled() && mNestedScrollingParent != null) {
191            if (dx != 0 || dy != 0) {
192                int startX = 0;
193                int startY = 0;
194                if (offsetInWindow != null) {
195                    mView.getLocationInWindow(offsetInWindow);
196                    startX = offsetInWindow[0];
197                    startY = offsetInWindow[1];
198                }
199
200                if (consumed == null) {
201                    if (mTempNestedScrollConsumed == null) {
202                        mTempNestedScrollConsumed = new int[2];
203                    }
204                    consumed = mTempNestedScrollConsumed;
205                }
206                consumed[0] = 0;
207                consumed[1] = 0;
208                ViewParentCompat.onNestedPreScroll(mNestedScrollingParent, mView, dx, dy, consumed);
209
210                if (offsetInWindow != null) {
211                    mView.getLocationInWindow(offsetInWindow);
212                    offsetInWindow[0] -= startX;
213                    offsetInWindow[1] -= startY;
214                }
215                return consumed[0] != 0 || consumed[1] != 0;
216            } else if (offsetInWindow != null) {
217                offsetInWindow[0] = 0;
218                offsetInWindow[1] = 0;
219            }
220        }
221        return false;
222    }
223
224    /**
225     * Dispatch a nested fling operation to the current nested scrolling parent.
226     *
227     * <p>This is a delegate method. Call it from your {@link android.view.View View} subclass
228     * method/{@link NestedScrollingChild} interface method with the same signature to implement
229     * the standard policy.</p>
230     *
231     * @return true if the parent consumed the nested fling
232     */
233    public boolean dispatchNestedFling(float velocityX, float velocityY, boolean consumed) {
234        if (isNestedScrollingEnabled() && mNestedScrollingParent != null) {
235            return ViewParentCompat.onNestedFling(mNestedScrollingParent, mView, velocityX,
236                    velocityY, consumed);
237        }
238        return false;
239    }
240
241    /**
242     * Dispatch a nested pre-fling operation to the current nested scrolling parent.
243     *
244     * <p>This is a delegate method. Call it from your {@link android.view.View View} subclass
245     * method/{@link NestedScrollingChild} interface method with the same signature to implement
246     * the standard policy.</p>
247     *
248     * @return true if the parent consumed the nested fling
249     */
250    public boolean dispatchNestedPreFling(float velocityX, float velocityY) {
251        if (isNestedScrollingEnabled() && mNestedScrollingParent != null) {
252            return ViewParentCompat.onNestedPreFling(mNestedScrollingParent, mView, velocityX,
253                    velocityY);
254        }
255        return false;
256    }
257
258    /**
259     * View subclasses should always call this method on their
260     * <code>NestedScrollingChildHelper</code> when detached from a window.
261     *
262     * <p>This is a delegate method. Call it from your {@link android.view.View View} subclass
263     * method/{@link NestedScrollingChild} interface method with the same signature to implement
264     * the standard policy.</p>
265     */
266    public void onDetachedFromWindow() {
267        ViewCompat.stopNestedScroll(mView);
268    }
269
270    /**
271     * Called when a nested scrolling child stops its current nested scroll operation.
272     *
273     * <p>This is a delegate method. Call it from your {@link android.view.View View} subclass
274     * method/{@link NestedScrollingChild} interface method with the same signature to implement
275     * the standard policy.</p>
276     *
277     * @param child Child view stopping its nested scroll. This may not be a direct child view.
278     */
279    public void onStopNestedScroll(View child) {
280        ViewCompat.stopNestedScroll(mView);
281    }
282}
283