| /* |
| * Copyright (C) 2015 The Android Open Source Project |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| |
| package android.support.v4.view; |
| |
| import android.support.annotation.NonNull; |
| import android.support.v4.view.ViewCompat.ScrollAxis; |
| import android.view.MotionEvent; |
| import android.view.VelocityTracker; |
| import android.view.View; |
| import android.view.ViewConfiguration; |
| |
| /** |
| * This interface should be implemented by {@link android.view.ViewGroup ViewGroup} subclasses |
| * that wish to support scrolling operations delegated by a nested child view. |
| * |
| * <p>Classes implementing this interface should create a final instance of a |
| * {@link NestedScrollingParentHelper} as a field and delegate any View or ViewGroup methods |
| * to the <code>NestedScrollingParentHelper</code> methods of the same signature.</p> |
| * |
| * <p>Views invoking nested scrolling functionality should always do so from the relevant |
| * {@link ViewCompat}, {@link ViewGroupCompat} or {@link ViewParentCompat} compatibility |
| * shim static methods. This ensures interoperability with nested scrolling views on Android |
| * 5.0 Lollipop and newer.</p> |
| */ |
| public interface NestedScrollingParent { |
| /** |
| * React to a descendant view initiating a nestable scroll operation, claiming the |
| * nested scroll operation if appropriate. |
| * |
| * <p>This method will be called in response to a descendant view invoking |
| * {@link ViewCompat#startNestedScroll(View, int)}. Each parent up the view hierarchy will be |
| * given an opportunity to respond and claim the nested scrolling operation by returning |
| * <code>true</code>.</p> |
| * |
| * <p>This method may be overridden by ViewParent implementations to indicate when the view |
| * is willing to support a nested scrolling operation that is about to begin. If it returns |
| * true, this ViewParent will become the target view's nested scrolling parent for the duration |
| * of the scroll operation in progress. When the nested scroll is finished this ViewParent |
| * will receive a call to {@link #onStopNestedScroll(View)}. |
| * </p> |
| * |
| * @param child Direct child of this ViewParent containing target |
| * @param target View that initiated the nested scroll |
| * @param axes Flags consisting of {@link ViewCompat#SCROLL_AXIS_HORIZONTAL}, |
| * {@link ViewCompat#SCROLL_AXIS_VERTICAL} or both |
| * @return true if this ViewParent accepts the nested scroll operation |
| */ |
| boolean onStartNestedScroll(@NonNull View child, @NonNull View target, @ScrollAxis int axes); |
| |
| /** |
| * React to the successful claiming of a nested scroll operation. |
| * |
| * <p>This method will be called after |
| * {@link #onStartNestedScroll(View, View, int) onStartNestedScroll} returns true. It offers |
| * an opportunity for the view and its superclasses to perform initial configuration |
| * for the nested scroll. Implementations of this method should always call their superclass's |
| * implementation of this method if one is present.</p> |
| * |
| * @param child Direct child of this ViewParent containing target |
| * @param target View that initiated the nested scroll |
| * @param axes Flags consisting of {@link ViewCompat#SCROLL_AXIS_HORIZONTAL}, |
| * {@link ViewCompat#SCROLL_AXIS_VERTICAL} or both |
| * @see #onStartNestedScroll(View, View, int) |
| * @see #onStopNestedScroll(View) |
| */ |
| void onNestedScrollAccepted(@NonNull View child, @NonNull View target, @ScrollAxis int axes); |
| |
| /** |
| * React to a nested scroll operation ending. |
| * |
| * <p>Perform cleanup after a nested scrolling operation. |
| * This method will be called when a nested scroll stops, for example when a nested touch |
| * scroll ends with a {@link MotionEvent#ACTION_UP} or {@link MotionEvent#ACTION_CANCEL} event. |
| * Implementations of this method should always call their superclass's implementation of this |
| * method if one is present.</p> |
| * |
| * @param target View that initiated the nested scroll |
| */ |
| void onStopNestedScroll(@NonNull View target); |
| |
| /** |
| * React to a nested scroll in progress. |
| * |
| * <p>This method will be called when the ViewParent's current nested scrolling child view |
| * dispatches a nested scroll event. To receive calls to this method the ViewParent must have |
| * previously returned <code>true</code> for a call to |
| * {@link #onStartNestedScroll(View, View, int)}.</p> |
| * |
| * <p>Both the consumed and unconsumed portions of the scroll distance are reported to the |
| * ViewParent. An implementation may choose to use the consumed portion to match or chase scroll |
| * position of multiple child elements, for example. The unconsumed portion may be used to |
| * allow continuous dragging of multiple scrolling or draggable elements, such as scrolling |
| * a list within a vertical drawer where the drawer begins dragging once the edge of inner |
| * scrolling content is reached.</p> |
| * |
| * @param target The descendent view controlling the nested scroll |
| * @param dxConsumed Horizontal scroll distance in pixels already consumed by target |
| * @param dyConsumed Vertical scroll distance in pixels already consumed by target |
| * @param dxUnconsumed Horizontal scroll distance in pixels not consumed by target |
| * @param dyUnconsumed Vertical scroll distance in pixels not consumed by target |
| */ |
| void onNestedScroll(@NonNull View target, int dxConsumed, int dyConsumed, |
| int dxUnconsumed, int dyUnconsumed); |
| |
| /** |
| * React to a nested scroll in progress before the target view consumes a portion of the scroll. |
| * |
| * <p>When working with nested scrolling often the parent view may want an opportunity |
| * to consume the scroll before the nested scrolling child does. An example of this is a |
| * drawer that contains a scrollable list. The user will want to be able to scroll the list |
| * fully into view before the list itself begins scrolling.</p> |
| * |
| * <p><code>onNestedPreScroll</code> is called when a nested scrolling child invokes |
| * {@link View#dispatchNestedPreScroll(int, int, int[], int[])}. The implementation should |
| * report how any pixels of the scroll reported by dx, dy were consumed in the |
| * <code>consumed</code> array. Index 0 corresponds to dx and index 1 corresponds to dy. |
| * This parameter will never be null. Initial values for consumed[0] and consumed[1] |
| * will always be 0.</p> |
| * |
| * @param target View that initiated the nested scroll |
| * @param dx Horizontal scroll distance in pixels |
| * @param dy Vertical scroll distance in pixels |
| * @param consumed Output. The horizontal and vertical scroll distance consumed by this parent |
| */ |
| void onNestedPreScroll(@NonNull View target, int dx, int dy, @NonNull int[] consumed); |
| |
| /** |
| * Request a fling from a nested scroll. |
| * |
| * <p>This method signifies that a nested scrolling child has detected suitable conditions |
| * for a fling. Generally this means that a touch scroll has ended with a |
| * {@link VelocityTracker velocity} in the direction of scrolling that meets or exceeds |
| * the {@link ViewConfiguration#getScaledMinimumFlingVelocity() minimum fling velocity} |
| * along a scrollable axis.</p> |
| * |
| * <p>If a nested scrolling child view would normally fling but it is at the edge of |
| * its own content, it can use this method to delegate the fling to its nested scrolling |
| * parent instead. The parent may optionally consume the fling or observe a child fling.</p> |
| * |
| * @param target View that initiated the nested scroll |
| * @param velocityX Horizontal velocity in pixels per second |
| * @param velocityY Vertical velocity in pixels per second |
| * @param consumed true if the child consumed the fling, false otherwise |
| * @return true if this parent consumed or otherwise reacted to the fling |
| */ |
| boolean onNestedFling(@NonNull View target, float velocityX, float velocityY, boolean consumed); |
| |
| /** |
| * React to a nested fling before the target view consumes it. |
| * |
| * <p>This method siginfies that a nested scrolling child has detected a fling with the given |
| * velocity along each axis. Generally this means that a touch scroll has ended with a |
| * {@link VelocityTracker velocity} in the direction of scrolling that meets or exceeds |
| * the {@link ViewConfiguration#getScaledMinimumFlingVelocity() minimum fling velocity} |
| * along a scrollable axis.</p> |
| * |
| * <p>If a nested scrolling parent is consuming motion as part of a |
| * {@link #onNestedPreScroll(View, int, int, int[]) pre-scroll}, it may be appropriate for |
| * it to also consume the pre-fling to complete that same motion. By returning |
| * <code>true</code> from this method, the parent indicates that the child should not |
| * fling its own internal content as well.</p> |
| * |
| * @param target View that initiated the nested scroll |
| * @param velocityX Horizontal velocity in pixels per second |
| * @param velocityY Vertical velocity in pixels per second |
| * @return true if this parent consumed the fling ahead of the target view |
| */ |
| boolean onNestedPreFling(@NonNull View target, float velocityX, float velocityY); |
| |
| /** |
| * Return the current axes of nested scrolling for this NestedScrollingParent. |
| * |
| * <p>A NestedScrollingParent returning something other than {@link ViewCompat#SCROLL_AXIS_NONE} |
| * is currently acting as a nested scrolling parent for one or more descendant views in |
| * the hierarchy.</p> |
| * |
| * @return Flags indicating the current axes of nested scrolling |
| * @see ViewCompat#SCROLL_AXIS_HORIZONTAL |
| * @see ViewCompat#SCROLL_AXIS_VERTICAL |
| * @see ViewCompat#SCROLL_AXIS_NONE |
| */ |
| @ScrollAxis |
| int getNestedScrollAxes(); |
| } |