Java tutorial
/* * Copyright (C) 2011 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.widget; import android.content.Context; import android.graphics.Canvas; import android.os.Build; /** * Helper for accessing {@link android.widget.EdgeEffect} introduced after * API level 4 in a backwards compatible fashion. * * This class is used to access {@link android.widget.EdgeEffect} on platform versions * that support it. When running on older platforms it will result in no-ops. It should * be used by views that wish to use the standard Android visual effects at the edges * of scrolling containers. */ public class EdgeEffectCompat { private Object mEdgeEffect; private static final EdgeEffectImpl IMPL; static { if (Build.VERSION.SDK_INT >= 14) { // ICS IMPL = new EdgeEffectIcsImpl(); } else { IMPL = new BaseEdgeEffectImpl(); } } interface EdgeEffectImpl { public Object newEdgeEffect(Context context); public void setSize(Object edgeEffect, int width, int height); public boolean isFinished(Object edgeEffect); public void finish(Object edgeEffect); public boolean onPull(Object edgeEffect, float deltaDistance); public boolean onRelease(Object edgeEffect); public boolean onAbsorb(Object edgeEffect, int velocity); public boolean draw(Object edgeEffect, Canvas canvas); } /** * Null implementation to use pre-ICS */ static class BaseEdgeEffectImpl implements EdgeEffectImpl { public Object newEdgeEffect(Context context) { return null; } public void setSize(Object edgeEffect, int width, int height) { } public boolean isFinished(Object edgeEffect) { return true; } public void finish(Object edgeEffect) { } public boolean onPull(Object edgeEffect, float deltaDistance) { return false; } public boolean onRelease(Object edgeEffect) { return false; } public boolean onAbsorb(Object edgeEffect, int velocity) { return false; } public boolean draw(Object edgeEffect, Canvas canvas) { return false; } } static class EdgeEffectIcsImpl implements EdgeEffectImpl { public Object newEdgeEffect(Context context) { return EdgeEffectCompatIcs.newEdgeEffect(context); } public void setSize(Object edgeEffect, int width, int height) { EdgeEffectCompatIcs.setSize(edgeEffect, width, height); } public boolean isFinished(Object edgeEffect) { return EdgeEffectCompatIcs.isFinished(edgeEffect); } public void finish(Object edgeEffect) { EdgeEffectCompatIcs.finish(edgeEffect); } public boolean onPull(Object edgeEffect, float deltaDistance) { return EdgeEffectCompatIcs.onPull(edgeEffect, deltaDistance); } public boolean onRelease(Object edgeEffect) { return EdgeEffectCompatIcs.onRelease(edgeEffect); } public boolean onAbsorb(Object edgeEffect, int velocity) { return EdgeEffectCompatIcs.onAbsorb(edgeEffect, velocity); } public boolean draw(Object edgeEffect, Canvas canvas) { return EdgeEffectCompatIcs.draw(edgeEffect, canvas); } } /** * Construct a new EdgeEffect themed using the given context. * * <p>Note: On platform versions that do not support EdgeEffect, all operations * on the newly constructed object will be mocked/no-ops.</p> * * @param context Context to use for theming the effect */ public EdgeEffectCompat(Context context) { mEdgeEffect = IMPL.newEdgeEffect(context); } /** * Set the size of this edge effect in pixels. * * @param width Effect width in pixels * @param height Effect height in pixels */ public void setSize(int width, int height) { IMPL.setSize(mEdgeEffect, width, height); } /** * Reports if this EdgeEffectCompat's animation is finished. If this method returns false * after a call to {@link #draw(Canvas)} the host widget should schedule another * drawing pass to continue the animation. * * @return true if animation is finished, false if drawing should continue on the next frame. */ public boolean isFinished() { return IMPL.isFinished(mEdgeEffect); } /** * Immediately finish the current animation. * After this call {@link #isFinished()} will return true. */ public void finish() { IMPL.finish(mEdgeEffect); } /** * A view should call this when content is pulled away from an edge by the user. * This will update the state of the current visual effect and its associated animation. * The host view should always {@link android.view.View#invalidate()} if this method * returns true and draw the results accordingly. * * @param deltaDistance Change in distance since the last call. Values may be 0 (no change) to * 1.f (full length of the view) or negative values to express change * back toward the edge reached to initiate the effect. * @return true if the host view should call invalidate, false if it should not. */ public boolean onPull(float deltaDistance) { return IMPL.onPull(mEdgeEffect, deltaDistance); } /** * Call when the object is released after being pulled. * This will begin the "decay" phase of the effect. After calling this method * the host view should {@link android.view.View#invalidate()} if this method * returns true and thereby draw the results accordingly. * * @return true if the host view should invalidate, false if it should not. */ public boolean onRelease() { return IMPL.onRelease(mEdgeEffect); } /** * Call when the effect absorbs an impact at the given velocity. * Used when a fling reaches the scroll boundary. * * <p>When using a {@link android.widget.Scroller} or {@link android.widget.OverScroller}, * the method <code>getCurrVelocity</code> will provide a reasonable approximation * to use here.</p> * * @param velocity Velocity at impact in pixels per second. * @return true if the host view should invalidate, false if it should not. */ public boolean onAbsorb(int velocity) { return IMPL.onAbsorb(mEdgeEffect, velocity); } /** * Draw into the provided canvas. Assumes that the canvas has been rotated * accordingly and the size has been set. The effect will be drawn the full * width of X=0 to X=width, beginning from Y=0 and extending to some factor < * 1.f of height. * * @param canvas Canvas to draw into * @return true if drawing should continue beyond this frame to continue the * animation */ public boolean draw(Canvas canvas) { return IMPL.draw(mEdgeEffect, canvas); } }