1 /* 2 * Copyright 2018 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 18 package androidx.core.view; 19 20 import android.view.MotionEvent; 21 import android.view.View; 22 23 import androidx.annotation.NonNull; 24 import androidx.core.view.ViewCompat.NestedScrollType; 25 import androidx.core.view.ViewCompat.ScrollAxis; 26 27 /** 28 * This interface should be implemented by {@link android.view.ViewGroup ViewGroup} subclasses 29 * that wish to support scrolling operations delegated by a nested child view. 30 * 31 * <p>Classes implementing this interface should create a final instance of a 32 * {@link NestedScrollingParentHelper} as a field and delegate any View or ViewGroup methods 33 * to the <code>NestedScrollingParentHelper</code> methods of the same signature.</p> 34 * 35 * <p>Views invoking nested scrolling functionality should always do so from the relevant 36 * {@link ViewCompat}, {@link ViewGroupCompat} or {@link ViewParentCompat} compatibility 37 * shim static methods. This ensures interoperability with nested scrolling views on all versions 38 * of Android.</p> 39 */ 40 public interface NestedScrollingParent2 extends NestedScrollingParent { 41 /** 42 * React to a descendant view initiating a nestable scroll operation, claiming the 43 * nested scroll operation if appropriate. 44 * 45 * <p>This method will be called in response to a descendant view invoking 46 * {@link ViewCompat#startNestedScroll(View, int)}. Each parent up the view hierarchy will be 47 * given an opportunity to respond and claim the nested scrolling operation by returning 48 * <code>true</code>.</p> 49 * 50 * <p>This method may be overridden by ViewParent implementations to indicate when the view 51 * is willing to support a nested scrolling operation that is about to begin. If it returns 52 * true, this ViewParent will become the target view's nested scrolling parent for the duration 53 * of the scroll operation in progress. When the nested scroll is finished this ViewParent 54 * will receive a call to {@link #onStopNestedScroll(View, int)}. 55 * </p> 56 * 57 * @param child Direct child of this ViewParent containing target 58 * @param target View that initiated the nested scroll 59 * @param axes Flags consisting of {@link ViewCompat#SCROLL_AXIS_HORIZONTAL}, 60 * {@link ViewCompat#SCROLL_AXIS_VERTICAL} or both 61 * @param type the type of input which cause this scroll event 62 * @return true if this ViewParent accepts the nested scroll operation 63 */ onStartNestedScroll(@onNull View child, @NonNull View target, @ScrollAxis int axes, @NestedScrollType int type)64 boolean onStartNestedScroll(@NonNull View child, @NonNull View target, @ScrollAxis int axes, 65 @NestedScrollType int type); 66 67 /** 68 * React to the successful claiming of a nested scroll operation. 69 * 70 * <p>This method will be called after 71 * {@link #onStartNestedScroll(View, View, int, int) onStartNestedScroll} returns true. It 72 * offers an opportunity for the view and its superclasses to perform initial configuration 73 * for the nested scroll. Implementations of this method should always call their superclass's 74 * implementation of this method if one is present.</p> 75 * 76 * @param child Direct child of this ViewParent containing target 77 * @param target View that initiated the nested scroll 78 * @param axes Flags consisting of {@link ViewCompat#SCROLL_AXIS_HORIZONTAL}, 79 * {@link ViewCompat#SCROLL_AXIS_VERTICAL} or both 80 * @param type the type of input which cause this scroll event 81 * @see #onStartNestedScroll(View, View, int, int) 82 * @see #onStopNestedScroll(View, int) 83 */ onNestedScrollAccepted(@onNull View child, @NonNull View target, @ScrollAxis int axes, @NestedScrollType int type)84 void onNestedScrollAccepted(@NonNull View child, @NonNull View target, @ScrollAxis int axes, 85 @NestedScrollType int type); 86 87 /** 88 * React to a nested scroll operation ending. 89 * 90 * <p>Perform cleanup after a nested scrolling operation. 91 * This method will be called when a nested scroll stops, for example when a nested touch 92 * scroll ends with a {@link MotionEvent#ACTION_UP} or {@link MotionEvent#ACTION_CANCEL} event. 93 * Implementations of this method should always call their superclass's implementation of this 94 * method if one is present.</p> 95 * 96 * @param target View that initiated the nested scroll 97 * @param type the type of input which cause this scroll event 98 */ onStopNestedScroll(@onNull View target, @NestedScrollType int type)99 void onStopNestedScroll(@NonNull View target, @NestedScrollType int type); 100 101 /** 102 * React to a nested scroll in progress. 103 * 104 * <p>This method will be called when the ViewParent's current nested scrolling child view 105 * dispatches a nested scroll event. To receive calls to this method the ViewParent must have 106 * previously returned <code>true</code> for a call to 107 * {@link #onStartNestedScroll(View, View, int, int)}.</p> 108 * 109 * <p>Both the consumed and unconsumed portions of the scroll distance are reported to the 110 * ViewParent. An implementation may choose to use the consumed portion to match or chase scroll 111 * position of multiple child elements, for example. The unconsumed portion may be used to 112 * allow continuous dragging of multiple scrolling or draggable elements, such as scrolling 113 * a list within a vertical drawer where the drawer begins dragging once the edge of inner 114 * scrolling content is reached.</p> 115 * 116 * @param target The descendent view controlling the nested scroll 117 * @param dxConsumed Horizontal scroll distance in pixels already consumed by target 118 * @param dyConsumed Vertical scroll distance in pixels already consumed by target 119 * @param dxUnconsumed Horizontal scroll distance in pixels not consumed by target 120 * @param dyUnconsumed Vertical scroll distance in pixels not consumed by target 121 * @param type the type of input which cause this scroll event 122 */ onNestedScroll(@onNull View target, int dxConsumed, int dyConsumed, int dxUnconsumed, int dyUnconsumed, @NestedScrollType int type)123 void onNestedScroll(@NonNull View target, int dxConsumed, int dyConsumed, 124 int dxUnconsumed, int dyUnconsumed, @NestedScrollType int type); 125 126 /** 127 * React to a nested scroll in progress before the target view consumes a portion of the scroll. 128 * 129 * <p>When working with nested scrolling often the parent view may want an opportunity 130 * to consume the scroll before the nested scrolling child does. An example of this is a 131 * drawer that contains a scrollable list. The user will want to be able to scroll the list 132 * fully into view before the list itself begins scrolling.</p> 133 * 134 * <p><code>onNestedPreScroll</code> is called when a nested scrolling child invokes 135 * {@link View#dispatchNestedPreScroll(int, int, int[], int[])}. The implementation should 136 * report how any pixels of the scroll reported by dx, dy were consumed in the 137 * <code>consumed</code> array. Index 0 corresponds to dx and index 1 corresponds to dy. 138 * This parameter will never be null. Initial values for consumed[0] and consumed[1] 139 * will always be 0.</p> 140 * 141 * @param target View that initiated the nested scroll 142 * @param dx Horizontal scroll distance in pixels 143 * @param dy Vertical scroll distance in pixels 144 * @param consumed Output. The horizontal and vertical scroll distance consumed by this parent 145 * @param type the type of input which cause this scroll event 146 */ onNestedPreScroll(@onNull View target, int dx, int dy, @NonNull int[] consumed, @NestedScrollType int type)147 void onNestedPreScroll(@NonNull View target, int dx, int dy, @NonNull int[] consumed, 148 @NestedScrollType int type); 149 150 } 151