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 import android.view.ViewParent; 23 24 import androidx.annotation.Nullable; 25 import androidx.core.view.ViewCompat.NestedScrollType; 26 import androidx.core.view.ViewCompat.ScrollAxis; 27 28 /** 29 * This interface should be implemented by {@link View View} subclasses that wish 30 * to support dispatching nested scrolling operations to a cooperating parent 31 * {@link android.view.ViewGroup ViewGroup}. 32 * 33 * <p>Classes implementing this interface should create a final instance of a 34 * {@link NestedScrollingChildHelper} as a field and delegate any View methods to the 35 * <code>NestedScrollingChildHelper</code> methods of the same signature.</p> 36 * 37 * <p>Views invoking nested scrolling functionality should always do so from the relevant 38 * {@link ViewCompat}, {@link ViewGroupCompat} or {@link ViewParentCompat} compatibility 39 * shim static methods. This ensures interoperability with nested scrolling views on all versions 40 * of Android.</p> 41 */ 42 public interface NestedScrollingChild2 extends NestedScrollingChild { 43 44 /** 45 * Begin a nestable scroll operation along the given axes, for the given input type. 46 * 47 * <p>A view starting a nested scroll promises to abide by the following contract:</p> 48 * 49 * <p>The view will call startNestedScroll upon initiating a scroll operation. In the case 50 * of a touch scroll type this corresponds to the initial {@link MotionEvent#ACTION_DOWN}. 51 * In the case of touch scrolling the nested scroll will be terminated automatically in 52 * the same manner as {@link ViewParent#requestDisallowInterceptTouchEvent(boolean)}. 53 * In the event of programmatic scrolling the caller must explicitly call 54 * {@link #stopNestedScroll(int)} to indicate the end of the nested scroll.</p> 55 * 56 * <p>If <code>startNestedScroll</code> returns true, a cooperative parent was found. 57 * If it returns false the caller may ignore the rest of this contract until the next scroll. 58 * Calling startNestedScroll while a nested scroll is already in progress will return true.</p> 59 * 60 * <p>At each incremental step of the scroll the caller should invoke 61 * {@link #dispatchNestedPreScroll(int, int, int[], int[], int) dispatchNestedPreScroll} 62 * once it has calculated the requested scrolling delta. If it returns true the nested scrolling 63 * parent at least partially consumed the scroll and the caller should adjust the amount it 64 * scrolls by.</p> 65 * 66 * <p>After applying the remainder of the scroll delta the caller should invoke 67 * {@link #dispatchNestedScroll(int, int, int, int, int[], int) dispatchNestedScroll}, passing 68 * both the delta consumed and the delta unconsumed. A nested scrolling parent may treat 69 * these values differently. See 70 * {@link NestedScrollingParent2#onNestedScroll(View, int, int, int, int, int)}. 71 * </p> 72 * 73 * @param axes Flags consisting of a combination of {@link ViewCompat#SCROLL_AXIS_HORIZONTAL} 74 * and/or {@link ViewCompat#SCROLL_AXIS_VERTICAL}. 75 * @param type the type of input which cause this scroll event 76 * @return true if a cooperative parent was found and nested scrolling has been enabled for 77 * the current gesture. 78 * 79 * @see #stopNestedScroll(int) 80 * @see #dispatchNestedPreScroll(int, int, int[], int[], int) 81 * @see #dispatchNestedScroll(int, int, int, int, int[], int) 82 */ 83 boolean startNestedScroll(@ScrollAxis int axes, @NestedScrollType int type); 84 85 /** 86 * Stop a nested scroll in progress for the given input type. 87 * 88 * <p>Calling this method when a nested scroll is not currently in progress is harmless.</p> 89 * 90 * @param type the type of input which cause this scroll event 91 * @see #startNestedScroll(int, int) 92 */ 93 void stopNestedScroll(@NestedScrollType int type); 94 95 /** 96 * Returns true if this view has a nested scrolling parent for the given input type. 97 * 98 * <p>The presence of a nested scrolling parent indicates that this view has initiated 99 * a nested scroll and it was accepted by an ancestor view further up the view hierarchy.</p> 100 * 101 * @param type the type of input which cause this scroll event 102 * 103 * @return whether this view has a nested scrolling parent 104 */ 105 boolean hasNestedScrollingParent(@NestedScrollType int type); 106 107 /** 108 * Dispatch one step of a nested scroll in progress. 109 * 110 * <p>Implementations of views that support nested scrolling should call this to report 111 * info about a scroll in progress to the current nested scrolling parent. If a nested scroll 112 * is not currently in progress or nested scrolling is not 113 * {@link #isNestedScrollingEnabled() enabled} for this view this method does nothing.</p> 114 * 115 * <p>Compatible View implementations should also call 116 * {@link #dispatchNestedPreScroll(int, int, int[], int[], int) dispatchNestedPreScroll} before 117 * consuming a component of the scroll event themselves.</p> 118 * 119 * @param dxConsumed Horizontal distance in pixels consumed by this view during this scroll step 120 * @param dyConsumed Vertical distance in pixels consumed by this view during this scroll step 121 * @param dxUnconsumed Horizontal scroll distance in pixels not consumed by this view 122 * @param dyUnconsumed Horizontal scroll distance in pixels not consumed by this view 123 * @param offsetInWindow Optional. If not null, on return this will contain the offset 124 * in local view coordinates of this view from before this operation 125 * to after it completes. View implementations may use this to adjust 126 * expected input coordinate tracking. 127 * @param type the type of input which cause this scroll event 128 * @return true if the event was dispatched, false if it could not be dispatched. 129 * @see #dispatchNestedPreScroll(int, int, int[], int[], int) 130 */ 131 boolean dispatchNestedScroll(int dxConsumed, int dyConsumed, 132 int dxUnconsumed, int dyUnconsumed, @Nullable int[] offsetInWindow, 133 @NestedScrollType int type); 134 135 /** 136 * Dispatch one step of a nested scroll in progress before this view consumes any portion of it. 137 * 138 * <p>Nested pre-scroll events are to nested scroll events what touch intercept is to touch. 139 * <code>dispatchNestedPreScroll</code> offers an opportunity for the parent view in a nested 140 * scrolling operation to consume some or all of the scroll operation before the child view 141 * consumes it.</p> 142 * 143 * @param dx Horizontal scroll distance in pixels 144 * @param dy Vertical scroll distance in pixels 145 * @param consumed Output. If not null, consumed[0] will contain the consumed component of dx 146 * and consumed[1] the consumed dy. 147 * @param offsetInWindow Optional. If not null, on return this will contain the offset 148 * in local view coordinates of this view from before this operation 149 * to after it completes. View implementations may use this to adjust 150 * expected input coordinate tracking. 151 * @param type the type of input which cause this scroll event 152 * @return true if the parent consumed some or all of the scroll delta 153 * @see #dispatchNestedScroll(int, int, int, int, int[], int) 154 */ 155 boolean dispatchNestedPreScroll(int dx, int dy, @Nullable int[] consumed, 156 @Nullable int[] offsetInWindow, @NestedScrollType int type); 157 } 158
