Java tutorial
/* * Copyright (C) 2017 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.Nullable; import android.support.v4.view.ViewCompat.NestedScrollType; import android.support.v4.view.ViewCompat.ScrollAxis; import android.view.MotionEvent; import android.view.View; import android.view.ViewParent; /** * This interface should be implemented by {@link View View} subclasses that wish * to support dispatching nested scrolling operations to a cooperating parent * {@link android.view.ViewGroup ViewGroup}. * * <p>Classes implementing this interface should create a final instance of a * {@link NestedScrollingChildHelper} as a field and delegate any View methods to the * <code>NestedScrollingChildHelper</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 all versions * of Android.</p> */ public interface NestedScrollingChild2 extends NestedScrollingChild { /** * Begin a nestable scroll operation along the given axes, for the given input type. * * <p>A view starting a nested scroll promises to abide by the following contract:</p> * * <p>The view will call startNestedScroll upon initiating a scroll operation. In the case * of a touch scroll type this corresponds to the initial {@link MotionEvent#ACTION_DOWN}. * In the case of touch scrolling the nested scroll will be terminated automatically in * the same manner as {@link ViewParent#requestDisallowInterceptTouchEvent(boolean)}. * In the event of programmatic scrolling the caller must explicitly call * {@link #stopNestedScroll(int)} to indicate the end of the nested scroll.</p> * * <p>If <code>startNestedScroll</code> returns true, a cooperative parent was found. * If it returns false the caller may ignore the rest of this contract until the next scroll. * Calling startNestedScroll while a nested scroll is already in progress will return true.</p> * * <p>At each incremental step of the scroll the caller should invoke * {@link #dispatchNestedPreScroll(int, int, int[], int[], int) dispatchNestedPreScroll} * once it has calculated the requested scrolling delta. If it returns true the nested scrolling * parent at least partially consumed the scroll and the caller should adjust the amount it * scrolls by.</p> * * <p>After applying the remainder of the scroll delta the caller should invoke * {@link #dispatchNestedScroll(int, int, int, int, int[], int) dispatchNestedScroll}, passing * both the delta consumed and the delta unconsumed. A nested scrolling parent may treat * these values differently. See * {@link NestedScrollingParent2#onNestedScroll(View, int, int, int, int, int)}. * </p> * * @param axes Flags consisting of a combination of {@link ViewCompat#SCROLL_AXIS_HORIZONTAL} * and/or {@link ViewCompat#SCROLL_AXIS_VERTICAL}. * @param type the type of input which cause this scroll event * @return true if a cooperative parent was found and nested scrolling has been enabled for * the current gesture. * * @see #stopNestedScroll(int) * @see #dispatchNestedPreScroll(int, int, int[], int[], int) * @see #dispatchNestedScroll(int, int, int, int, int[], int) */ boolean startNestedScroll(@ScrollAxis int axes, @NestedScrollType int type); /** * Stop a nested scroll in progress for the given input type. * * <p>Calling this method when a nested scroll is not currently in progress is harmless.</p> * * @param type the type of input which cause this scroll event * @see #startNestedScroll(int, int) */ void stopNestedScroll(@NestedScrollType int type); /** * Returns true if this view has a nested scrolling parent for the given input type. * * <p>The presence of a nested scrolling parent indicates that this view has initiated * a nested scroll and it was accepted by an ancestor view further up the view hierarchy.</p> * * @param type the type of input which cause this scroll event * * @return whether this view has a nested scrolling parent */ boolean hasNestedScrollingParent(@NestedScrollType int type); /** * Dispatch one step of a nested scroll in progress. * * <p>Implementations of views that support nested scrolling should call this to report * info about a scroll in progress to the current nested scrolling parent. If a nested scroll * is not currently in progress or nested scrolling is not * {@link #isNestedScrollingEnabled() enabled} for this view this method does nothing.</p> * * <p>Compatible View implementations should also call * {@link #dispatchNestedPreScroll(int, int, int[], int[], int) dispatchNestedPreScroll} before * consuming a component of the scroll event themselves.</p> * * @param dxConsumed Horizontal distance in pixels consumed by this view during this scroll step * @param dyConsumed Vertical distance in pixels consumed by this view during this scroll step * @param dxUnconsumed Horizontal scroll distance in pixels not consumed by this view * @param dyUnconsumed Horizontal scroll distance in pixels not consumed by this view * @param offsetInWindow Optional. If not null, on return this will contain the offset * in local view coordinates of this view from before this operation * to after it completes. View implementations may use this to adjust * expected input coordinate tracking. * @param type the type of input which cause this scroll event * @return true if the event was dispatched, false if it could not be dispatched. * @see #dispatchNestedPreScroll(int, int, int[], int[], int) */ boolean dispatchNestedScroll(int dxConsumed, int dyConsumed, int dxUnconsumed, int dyUnconsumed, @Nullable int[] offsetInWindow, @NestedScrollType int type); /** * Dispatch one step of a nested scroll in progress before this view consumes any portion of it. * * <p>Nested pre-scroll events are to nested scroll events what touch intercept is to touch. * <code>dispatchNestedPreScroll</code> offers an opportunity for the parent view in a nested * scrolling operation to consume some or all of the scroll operation before the child view * consumes it.</p> * * @param dx Horizontal scroll distance in pixels * @param dy Vertical scroll distance in pixels * @param consumed Output. If not null, consumed[0] will contain the consumed component of dx * and consumed[1] the consumed dy. * @param offsetInWindow Optional. If not null, on return this will contain the offset * in local view coordinates of this view from before this operation * to after it completes. View implementations may use this to adjust * expected input coordinate tracking. * @param type the type of input which cause this scroll event * @return true if the parent consumed some or all of the scroll delta * @see #dispatchNestedScroll(int, int, int, int, int[], int) */ boolean dispatchNestedPreScroll(int dx, int dy, @Nullable int[] consumed, @Nullable int[] offsetInWindow, @NestedScrollType int type); }