Java tutorial
/* * Copyright (C) 2006 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.view; import android.annotation.NonNull; import android.graphics.Rect; import android.os.Bundle; import android.view.accessibility.AccessibilityEvent; /** * Defines the responsibilities for a class that will be a parent of a View. * This is the API that a view sees when it wants to interact with its parent. * */ public interface ViewParent { /** * Called when something has changed which has invalidated the layout of a * child of this view parent. This will schedule a layout pass of the view * tree. */ public void requestLayout(); /** * Indicates whether layout was requested on this view parent. * * @return true if layout was requested, false otherwise */ public boolean isLayoutRequested(); /** * Called when a child wants the view hierarchy to gather and report * transparent regions to the window compositor. Views that "punch" holes in * the view hierarchy, such as SurfaceView can use this API to improve * performance of the system. When no such a view is present in the * hierarchy, this optimization in unnecessary and might slightly reduce the * view hierarchy performance. * * @param child the view requesting the transparent region computation * */ public void requestTransparentRegion(View child); /** * The target View has been invalidated, or has had a drawing property changed that * requires the hierarchy to re-render. * * This method is called by the View hierarchy to signal ancestors that a View either needs to * re-record its drawing commands, or drawing properties have changed. This is how Views * schedule a drawing traversal. * * This signal is generally only dispatched for attached Views, since only they need to draw. * * @param child Direct child of this ViewParent containing target * @param target The view that needs to redraw */ default void onDescendantInvalidated(@NonNull View child, @NonNull View target) { if (getParent() != null) { // Note: should pass 'this' as default, but can't since we may not be a View getParent().onDescendantInvalidated(child, target); } } /** * All or part of a child is dirty and needs to be redrawn. * * @param child The child which is dirty * @param r The area within the child that is invalid * * @deprecated Use {@link #onDescendantInvalidated(View, View)} instead. */ @Deprecated public void invalidateChild(View child, Rect r); /** * All or part of a child is dirty and needs to be redrawn. * * <p>The location array is an array of two int values which respectively * define the left and the top position of the dirty child.</p> * * <p>This method must return the parent of this ViewParent if the specified * rectangle must be invalidated in the parent. If the specified rectangle * does not require invalidation in the parent or if the parent does not * exist, this method must return null.</p> * * <p>When this method returns a non-null value, the location array must * have been updated with the left and top coordinates of this ViewParent.</p> * * @param location An array of 2 ints containing the left and top * coordinates of the child to invalidate * @param r The area within the child that is invalid * * @return the parent of this ViewParent or null * * @deprecated Use {@link #onDescendantInvalidated(View, View)} instead. */ @Deprecated public ViewParent invalidateChildInParent(int[] location, Rect r); /** * Returns the parent if it exists, or null. * * @return a ViewParent or null if this ViewParent does not have a parent */ public ViewParent getParent(); /** * Called when a child of this parent wants focus * * @param child The child of this ViewParent that wants focus. This view * will contain the focused view. It is not necessarily the view that * actually has focus. * @param focused The view that is a descendant of child that actually has * focus */ public void requestChildFocus(View child, View focused); /** * Tell view hierarchy that the global view attributes need to be * re-evaluated. * * @param child View whose attributes have changed. */ public void recomputeViewAttributes(View child); /** * Called when a child of this parent is giving up focus * * @param child The view that is giving up focus */ public void clearChildFocus(View child); /** * Compute the visible part of a rectangular region defined in terms of a child view's * coordinates. * * <p>Returns the clipped visible part of the rectangle <code>r</code>, defined in the * <code>child</code>'s local coordinate system. <code>r</code> is modified by this method to * contain the result, expressed in the global (root) coordinate system.</p> * * <p>The resulting rectangle is always axis aligned. If a rotation is applied to a node in the * View hierarchy, the result is the axis-aligned bounding box of the visible rectangle.</p> * * @param child A child View, whose rectangular visible region we want to compute * @param r The input rectangle, defined in the child coordinate system. Will be overwritten to * contain the resulting visible rectangle, expressed in global (root) coordinates * @param offset The input coordinates of a point, defined in the child coordinate system. * As with the <code>r</code> parameter, this will be overwritten to contain the global (root) * coordinates of that point. * A <code>null</code> value is valid (in case you are not interested in this result) * @return true if the resulting rectangle is not empty, false otherwise */ public boolean getChildVisibleRect(View child, Rect r, android.graphics.Point offset); /** * Find the nearest view in the specified direction that wants to take focus * * @param v The view that currently has focus * @param direction One of FOCUS_UP, FOCUS_DOWN, FOCUS_LEFT, and FOCUS_RIGHT */ public View focusSearch(View v, int direction); /** * Find the nearest keyboard navigation cluster in the specified direction. * This does not actually give focus to that cluster. * * @param currentCluster The starting point of the search. Null means the current cluster is not * found yet * @param direction Direction to look * * @return The nearest keyboard navigation cluster in the specified direction, or null if none * can be found */ View keyboardNavigationClusterSearch(View currentCluster, int direction); /** * Change the z order of the child so it's on top of all other children. * This ordering change may affect layout, if this container * uses an order-dependent layout scheme (e.g., LinearLayout). Prior * to {@link android.os.Build.VERSION_CODES#KITKAT} this * method should be followed by calls to {@link #requestLayout()} and * {@link View#invalidate()} on this parent to force the parent to redraw * with the new child ordering. * * @param child The child to bring to the top of the z order */ public void bringChildToFront(View child); /** * Tells the parent that a new focusable view has become available. This is * to handle transitions from the case where there are no focusable views to * the case where the first focusable view appears. * * @param v The view that has become newly focusable */ public void focusableViewAvailable(View v); /** * Shows the context menu for the specified view or its ancestors. * <p> * In most cases, a subclass does not need to override this. However, if * the subclass is added directly to the window manager (for example, * {@link ViewManager#addView(View, android.view.ViewGroup.LayoutParams)}) * then it should override this and show the context menu. * * @param originalView the source view where the context menu was first * invoked * @return {@code true} if the context menu was shown, {@code false} * otherwise * @see #showContextMenuForChild(View, float, float) */ public boolean showContextMenuForChild(View originalView); /** * Shows the context menu for the specified view or its ancestors anchored * to the specified view-relative coordinate. * <p> * In most cases, a subclass does not need to override this. However, if * the subclass is added directly to the window manager (for example, * {@link ViewManager#addView(View, android.view.ViewGroup.LayoutParams)}) * then it should override this and show the context menu. * <p> * If a subclass overrides this method it should also override * {@link #showContextMenuForChild(View)}. * * @param originalView the source view where the context menu was first * invoked * @param x the X coordinate in pixels relative to the original view to * which the menu should be anchored, or {@link Float#NaN} to * disable anchoring * @param y the Y coordinate in pixels relative to the original view to * which the menu should be anchored, or {@link Float#NaN} to * disable anchoring * @return {@code true} if the context menu was shown, {@code false} * otherwise */ boolean showContextMenuForChild(View originalView, float x, float y); /** * Have the parent populate the specified context menu if it has anything to * add (and then recurse on its parent). * * @param menu The menu to populate */ public void createContextMenu(ContextMenu menu); /** * Start an action mode for the specified view with the default type * {@link ActionMode#TYPE_PRIMARY}. * * <p>In most cases, a subclass does not need to override this. However, if the * subclass is added directly to the window manager (for example, * {@link ViewManager#addView(View, android.view.ViewGroup.LayoutParams)}) * then it should override this and start the action mode.</p> * * @param originalView The source view where the action mode was first invoked * @param callback The callback that will handle lifecycle events for the action mode * @return The new action mode if it was started, null otherwise * * @see #startActionModeForChild(View, android.view.ActionMode.Callback, int) */ public ActionMode startActionModeForChild(View originalView, ActionMode.Callback callback); /** * Start an action mode of a specific type for the specified view. * * <p>In most cases, a subclass does not need to override this. However, if the * subclass is added directly to the window manager (for example, * {@link ViewManager#addView(View, android.view.ViewGroup.LayoutParams)}) * then it should override this and start the action mode.</p> * * @param originalView The source view where the action mode was first invoked * @param callback The callback that will handle lifecycle events for the action mode * @param type One of {@link ActionMode#TYPE_PRIMARY} or {@link ActionMode#TYPE_FLOATING}. * @return The new action mode if it was started, null otherwise */ public ActionMode startActionModeForChild(View originalView, ActionMode.Callback callback, int type); /** * This method is called on the parent when a child's drawable state * has changed. * * @param child The child whose drawable state has changed. */ public void childDrawableStateChanged(View child); /** * Called when a child does not want this parent and its ancestors to * intercept touch events with * {@link ViewGroup#onInterceptTouchEvent(MotionEvent)}. * * <p>This parent should pass this call onto its parents. This parent must obey * this request for the duration of the touch (that is, only clear the flag * after this parent has received an up or a cancel.</p> * * @param disallowIntercept True if the child does not want the parent to * intercept touch events. */ public void requestDisallowInterceptTouchEvent(boolean disallowIntercept); /** * Called when a child of this group wants a particular rectangle to be * positioned onto the screen. {@link ViewGroup}s overriding this can trust * that: * <ul> * <li>child will be a direct child of this group</li> * <li>rectangle will be in the child's content coordinates</li> * </ul> * * <p>{@link ViewGroup}s overriding this should uphold the contract:</p> * <ul> * <li>nothing will change if the rectangle is already visible</li> * <li>the view port will be scrolled only just enough to make the * rectangle visible</li> * <ul> * * @param child The direct child making the request. * @param rectangle The rectangle in the child's coordinates the child * wishes to be on the screen. * @param immediate True to forbid animated or delayed scrolling, * false otherwise * @return Whether the group scrolled to handle the operation */ public boolean requestChildRectangleOnScreen(View child, Rect rectangle, boolean immediate); /** * Called by a child to request from its parent to send an {@link AccessibilityEvent}. * The child has already populated a record for itself in the event and is delegating * to its parent to send the event. The parent can optionally add a record for itself. * <p> * Note: An accessibility event is fired by an individual view which populates the * event with a record for its state and requests from its parent to perform * the sending. The parent can optionally add a record for itself before * dispatching the request to its parent. A parent can also choose not to * respect the request for sending the event. The accessibility event is sent * by the topmost view in the view tree.</p> * * @param child The child which requests sending the event. * @param event The event to be sent. * @return True if the event was sent. */ public boolean requestSendAccessibilityEvent(View child, AccessibilityEvent event); /** * Called when a child view now has or no longer is tracking transient state. * * <p>"Transient state" is any state that a View might hold that is not expected to * be reflected in the data model that the View currently presents. This state only * affects the presentation to the user within the View itself, such as the current * state of animations in progress or the state of a text selection operation.</p> * * <p>Transient state is useful for hinting to other components of the View system * that a particular view is tracking something complex but encapsulated. * A <code>ListView</code> for example may acknowledge that list item Views * with transient state should be preserved within their position or stable item ID * instead of treating that view as trivially replaceable by the backing adapter. * This allows adapter implementations to be simpler instead of needing to track * the state of item view animations in progress such that they could be restored * in the event of an unexpected recycling and rebinding of attached item views.</p> * * <p>This method is called on a parent view when a child view or a view within * its subtree begins or ends tracking of internal transient state.</p> * * @param child Child view whose state has changed * @param hasTransientState true if this child has transient state */ public void childHasTransientStateChanged(View child, boolean hasTransientState); /** * Ask that a new dispatch of {@link View#fitSystemWindows(Rect) * View.fitSystemWindows(Rect)} be performed. */ public void requestFitSystemWindows(); /** * Gets the parent of a given View for accessibility. Since some Views are not * exposed to the accessibility layer the parent for accessibility is not * necessarily the direct parent of the View, rather it is a predecessor. * * @return The parent or <code>null</code> if no such is found. */ public ViewParent getParentForAccessibility(); /** * Notifies a view parent that the accessibility state of one of its * descendants has changed and that the structure of the subtree is * different. * @param child The direct child whose subtree has changed. * @param source The descendant view that changed. May not be {@code null}. * @param changeType A bit mask of the types of changes that occurred. One * or more of: * <ul> * <li>{@link AccessibilityEvent#CONTENT_CHANGE_TYPE_CONTENT_DESCRIPTION} * <li>{@link AccessibilityEvent#CONTENT_CHANGE_TYPE_SUBTREE} * <li>{@link AccessibilityEvent#CONTENT_CHANGE_TYPE_TEXT} * <li>{@link AccessibilityEvent#CONTENT_CHANGE_TYPE_UNDEFINED} * </ul> */ public void notifySubtreeAccessibilityStateChanged(View child, @NonNull View source, int changeType); /** * Tells if this view parent can resolve the layout direction. * See {@link View#setLayoutDirection(int)} * * @return True if this view parent can resolve the layout direction. */ public boolean canResolveLayoutDirection(); /** * Tells if this view parent layout direction is resolved. * See {@link View#setLayoutDirection(int)} * * @return True if this view parent layout direction is resolved. */ public boolean isLayoutDirectionResolved(); /** * Return this view parent layout direction. See {@link View#getLayoutDirection()} * * @return {@link View#LAYOUT_DIRECTION_RTL} if the layout direction is RTL or returns * {@link View#LAYOUT_DIRECTION_LTR} if the layout direction is not RTL. */ public int getLayoutDirection(); /** * Tells if this view parent can resolve the text direction. * See {@link View#setTextDirection(int)} * * @return True if this view parent can resolve the text direction. */ public boolean canResolveTextDirection(); /** * Tells if this view parent text direction is resolved. * See {@link View#setTextDirection(int)} * * @return True if this view parent text direction is resolved. */ public boolean isTextDirectionResolved(); /** * Return this view parent text direction. See {@link View#getTextDirection()} * * @return the resolved text direction. Returns one of: * * {@link View#TEXT_DIRECTION_FIRST_STRONG} * {@link View#TEXT_DIRECTION_ANY_RTL}, * {@link View#TEXT_DIRECTION_LTR}, * {@link View#TEXT_DIRECTION_RTL}, * {@link View#TEXT_DIRECTION_LOCALE} */ public int getTextDirection(); /** * Tells if this view parent can resolve the text alignment. * See {@link View#setTextAlignment(int)} * * @return True if this view parent can resolve the text alignment. */ public boolean canResolveTextAlignment(); /** * Tells if this view parent text alignment is resolved. * See {@link View#setTextAlignment(int)} * * @return True if this view parent text alignment is resolved. */ public boolean isTextAlignmentResolved(); /** * Return this view parent text alignment. See {@link android.view.View#getTextAlignment()} * * @return the resolved text alignment. Returns one of: * * {@link View#TEXT_ALIGNMENT_GRAVITY}, * {@link View#TEXT_ALIGNMENT_CENTER}, * {@link View#TEXT_ALIGNMENT_TEXT_START}, * {@link View#TEXT_ALIGNMENT_TEXT_END}, * {@link View#TEXT_ALIGNMENT_VIEW_START}, * {@link View#TEXT_ALIGNMENT_VIEW_END} */ public int getTextAlignment(); /** * 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 View#startNestedScroll(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 nestedScrollAxes Flags consisting of {@link View#SCROLL_AXIS_HORIZONTAL}, * {@link View#SCROLL_AXIS_VERTICAL} or both * @return true if this ViewParent accepts the nested scroll operation */ public boolean onStartNestedScroll(View child, View target, int nestedScrollAxes); /** * 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 nestedScrollAxes Flags consisting of {@link View#SCROLL_AXIS_HORIZONTAL}, * {@link View#SCROLL_AXIS_VERTICAL} or both * @see #onStartNestedScroll(View, View, int) * @see #onStopNestedScroll(View) */ public void onNestedScrollAccepted(View child, View target, int nestedScrollAxes); /** * 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 */ public void onStopNestedScroll(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 */ public void onNestedScroll(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 */ public void onNestedPreScroll(View target, int dx, int dy, 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 */ public boolean onNestedFling(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 */ public boolean onNestedPreFling(View target, float velocityX, float velocityY); /** * React to an accessibility action delegated by a target descendant view before the target * processes it. * * <p>This method may be called by a target descendant view if the target wishes to give * a view in its parent chain a chance to react to the event before normal processing occurs. * Most commonly this will be a scroll event such as * {@link android.view.accessibility.AccessibilityNodeInfo#ACTION_SCROLL_FORWARD}. * A ViewParent that supports acting as a nested scrolling parent should override this * method and act accordingly to implement scrolling via accesibility systems.</p> * * @param target The target view dispatching this action * @param action Action being performed; see * {@link android.view.accessibility.AccessibilityNodeInfo} * @param arguments Optional action arguments * @return true if the action was consumed by this ViewParent */ public boolean onNestedPrePerformAccessibilityAction(View target, int action, Bundle arguments); }