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.graphics.Canvas; import android.graphics.Rect; /** * Abstract interface to someone holding a display surface. Allows you to * control the surface size and format, edit the pixels in the surface, and * monitor changes to the surface. This interface is typically available * through the {@link SurfaceView} class. * * <p>When using this interface from a thread other than the one running * its {@link SurfaceView}, you will want to carefully read the * methods * {@link #lockCanvas} and {@link Callback#surfaceCreated Callback.surfaceCreated()}. */ public interface SurfaceHolder { /** @deprecated this is ignored, this value is set automatically when needed. */ @Deprecated public static final int SURFACE_TYPE_NORMAL = 0; /** @deprecated this is ignored, this value is set automatically when needed. */ @Deprecated public static final int SURFACE_TYPE_HARDWARE = 1; /** @deprecated this is ignored, this value is set automatically when needed. */ @Deprecated public static final int SURFACE_TYPE_GPU = 2; /** @deprecated this is ignored, this value is set automatically when needed. */ @Deprecated public static final int SURFACE_TYPE_PUSH_BUFFERS = 3; /** * Exception that is thrown from {@link #lockCanvas} when called on a Surface * whose type is SURFACE_TYPE_PUSH_BUFFERS. */ public static class BadSurfaceTypeException extends RuntimeException { public BadSurfaceTypeException() { } public BadSurfaceTypeException(String name) { super(name); } } /** * A client may implement this interface to receive information about * changes to the surface. When used with a {@link SurfaceView}, the * Surface being held is only available between calls to * {@link #surfaceCreated(SurfaceHolder)} and * {@link #surfaceDestroyed(SurfaceHolder)}. The Callback is set with * {@link SurfaceHolder#addCallback SurfaceHolder.addCallback} method. */ public interface Callback { /** * This is called immediately after the surface is first created. * Implementations of this should start up whatever rendering code * they desire. Note that only one thread can ever draw into * a {@link Surface}, so you should not draw into the Surface here * if your normal rendering will be in another thread. * * @param holder The SurfaceHolder whose surface is being created. */ public void surfaceCreated(SurfaceHolder holder); /** * This is called immediately after any structural changes (format or * size) have been made to the surface. You should at this point update * the imagery in the surface. This method is always called at least * once, after {@link #surfaceCreated}. * * @param holder The SurfaceHolder whose surface has changed. * @param format The new PixelFormat of the surface. * @param width The new width of the surface. * @param height The new height of the surface. */ public void surfaceChanged(SurfaceHolder holder, int format, int width, int height); /** * This is called immediately before a surface is being destroyed. After * returning from this call, you should no longer try to access this * surface. If you have a rendering thread that directly accesses * the surface, you must ensure that thread is no longer touching the * Surface before returning from this function. * * @param holder The SurfaceHolder whose surface is being destroyed. */ public void surfaceDestroyed(SurfaceHolder holder); } /** * Additional callbacks that can be received for {@link Callback}. */ public interface Callback2 extends Callback { /** * Called when the application needs to redraw the content of its * surface, after it is resized or for some other reason. By not * returning from here until the redraw is complete, you can ensure that * the user will not see your surface in a bad state (at its new * size before it has been correctly drawn that way). This will * typically be preceeded by a call to {@link #surfaceChanged}. * * As of O, {@link #surfaceRedrawNeededAsync} may be implemented * to provide a non-blocking implementation. If {@link #surfaceRedrawNeededAsync} * is not implemented, then this will be called instead. * * @param holder The SurfaceHolder whose surface has changed. */ void surfaceRedrawNeeded(SurfaceHolder holder); /** * An alternative to surfaceRedrawNeeded where it is not required to block * until the redraw is complete. You should initiate the redraw, and return, * later invoking drawingFinished when your redraw is complete. * * This can be useful to avoid blocking your main application thread on rendering. * * As of O, if this is implemented {@link #surfaceRedrawNeeded} will not be called. * However it is still recommended to implement {@link #surfaceRedrawNeeded} for * compatibility with older versions of the platform. * * @param holder The SurfaceHolder which needs redrawing. * @param drawingFinished A runnable to signal completion. This may be invoked * from any thread. * */ default void surfaceRedrawNeededAsync(SurfaceHolder holder, Runnable drawingFinished) { surfaceRedrawNeeded(holder); drawingFinished.run(); } } /** * Add a Callback interface for this holder. There can several Callback * interfaces associated with a holder. * * @param callback The new Callback interface. */ public void addCallback(Callback callback); /** * Removes a previously added Callback interface from this holder. * * @param callback The Callback interface to remove. */ public void removeCallback(Callback callback); /** * Use this method to find out if the surface is in the process of being * created from Callback methods. This is intended to be used with * {@link Callback#surfaceChanged}. * * @return true if the surface is in the process of being created. */ public boolean isCreating(); /** * Sets the surface's type. * * @deprecated this is ignored, this value is set automatically when needed. */ @Deprecated public void setType(int type); /** * Make the surface a fixed size. It will never change from this size. * When working with a {@link SurfaceView}, this must be called from the * same thread running the SurfaceView's window. * * @param width The surface's width. * @param height The surface's height. */ public void setFixedSize(int width, int height); /** * Allow the surface to resized based on layout of its container (this is * the default). When this is enabled, you should monitor * {@link Callback#surfaceChanged} for changes to the size of the surface. * When working with a {@link SurfaceView}, this must be called from the * same thread running the SurfaceView's window. */ public void setSizeFromLayout(); /** * Set the desired PixelFormat of the surface. The default is OPAQUE. * When working with a {@link SurfaceView}, this must be called from the * same thread running the SurfaceView's window. * * @param format A constant from PixelFormat. * * @see android.graphics.PixelFormat */ public void setFormat(int format); /** * Enable or disable option to keep the screen turned on while this * surface is displayed. The default is false, allowing it to turn off. * This is safe to call from any thread. * * @param screenOn Set to true to force the screen to stay on, false * to allow it to turn off. */ public void setKeepScreenOn(boolean screenOn); /** * Start editing the pixels in the surface. The returned Canvas can be used * to draw into the surface's bitmap. A null is returned if the surface has * not been created or otherwise cannot be edited. You will usually need * to implement {@link Callback#surfaceCreated Callback.surfaceCreated} * to find out when the Surface is available for use. * * <p>The content of the Surface is never preserved between unlockCanvas() and * lockCanvas(), for this reason, every pixel within the Surface area * must be written. The only exception to this rule is when a dirty * rectangle is specified, in which case, non-dirty pixels will be * preserved. * * <p>If you call this repeatedly when the Surface is not ready (before * {@link Callback#surfaceCreated Callback.surfaceCreated} or after * {@link Callback#surfaceDestroyed Callback.surfaceDestroyed}), your calls * will be throttled to a slow rate in order to avoid consuming CPU. * * <p>If null is not returned, this function internally holds a lock until * the corresponding {@link #unlockCanvasAndPost} call, preventing * {@link SurfaceView} from creating, destroying, or modifying the surface * while it is being drawn. This can be more convenient than accessing * the Surface directly, as you do not need to do special synchronization * with a drawing thread in {@link Callback#surfaceDestroyed * Callback.surfaceDestroyed}. * * @return Canvas Use to draw into the surface. */ public Canvas lockCanvas(); /** * Just like {@link #lockCanvas()} but allows specification of a dirty rectangle. * Every * pixel within that rectangle must be written; however pixels outside * the dirty rectangle will be preserved by the next call to lockCanvas(). * * @see android.view.SurfaceHolder#lockCanvas * * @param dirty Area of the Surface that will be modified. * @return Canvas Use to draw into the surface. */ public Canvas lockCanvas(Rect dirty); /** * <p>Just like {@link #lockCanvas()} but the returned canvas is hardware-accelerated. * * <p>See the <a href="{@docRoot}guide/topics/graphics/hardware-accel.html#unsupported"> * unsupported drawing operations</a> for a list of what is and isn't * supported in a hardware-accelerated canvas. * * @return Canvas Use to draw into the surface. * @throws IllegalStateException If the canvas cannot be locked. */ default Canvas lockHardwareCanvas() { throw new IllegalStateException("This SurfaceHolder doesn't support lockHardwareCanvas"); } /** * Finish editing pixels in the surface. After this call, the surface's * current pixels will be shown on the screen, but its content is lost, * in particular there is no guarantee that the content of the Surface * will remain unchanged when lockCanvas() is called again. * * @see #lockCanvas() * * @param canvas The Canvas previously returned by lockCanvas(). */ public void unlockCanvasAndPost(Canvas canvas); /** * Retrieve the current size of the surface. Note: do not modify the * returned Rect. This is only safe to call from the thread of * {@link SurfaceView}'s window, or while inside of * {@link #lockCanvas()}. * * @return Rect The surface's dimensions. The left and top are always 0. */ public Rect getSurfaceFrame(); /** * Direct access to the surface object. The Surface may not always be * available -- for example when using a {@link SurfaceView} the holder's * Surface is not created until the view has been attached to the window * manager and performed a layout in order to determine the dimensions * and screen position of the Surface. You will thus usually need * to implement {@link Callback#surfaceCreated Callback.surfaceCreated} * to find out when the Surface is available for use. * * <p>Note that if you directly access the Surface from another thread, * it is critical that you correctly implement * {@link Callback#surfaceCreated Callback.surfaceCreated} and * {@link Callback#surfaceDestroyed Callback.surfaceDestroyed} to ensure * that thread only accesses the Surface while it is valid, and that the * Surface does not get destroyed while the thread is using it. * * <p>This method is intended to be used by frameworks which often need * direct access to the Surface object (usually to pass it to native code). * * @return Surface The surface. */ public Surface getSurface(); }