Apidemo学习 PurgeableBitmap

/**
 * PurgeableBitmap demonstrates the effects of setting Bitmaps as being
 * purgeable.
 *
 * In the NonPurgeable case, an encoded bitstream is decoded to a different
 * Bitmap over and over again up to 200 times until out-of-memory occurs.
 * In contrast, the Purgeable case shows that the system can complete decoding
 * the encoded bitstream 200 times without hitting the out-of-memory case.
 * 
 * BitmapFactory.Option 由一个属性public boolean inPurgeable

    如果inPurgeable 设为True的话表示使用BitmapFactory创建的Bitmap用于存储Pixel的内存空间在系统内存不足时可以被回收， 
    在应用需要再次访问Bitmap的Pixel时（如绘制Bitmap或是调用getPixel），系统会再次调用BitmapFactory decoder重新生成Bitmap的Pixel数组。
    为了能够重新解码图像，bitmap要能够访问存储Bitmap的原始数据。
   本例显示了inPurgeable设为True和False的两种情况，不停的创建一个bitmap
   mOptions 为BitmapFactory.Option类型，mOptions.isPurgable可以为true和false。 在isPurgeable为false时表示创建的Bitmap的Pixel内存空间不能被回收，
   这样BitmapFactory在不停decodeByteArray创建新的Bitmap对象，不同设备的内存不同，因此能够同时创建的Bitmap个数可能有所不同，200个bitmap足以使大部分的设备重新OutOfMemory错误。

当isPurgable设为true时，系统中内存不足时，可以回收部分Bitmap占据的内存空间，这时一般不会出现OutOfMemory 错误。

本例有两个例子NonPurgeable 和 Purgeable，其定义的代码是同样的类PurgeableBitmap和PurgeableBitmapView，
 但它们在Android的Launcher都有自己的启动图标。这是因为在AndroidManifest.xml中使用了activity-alias定义。

activity-alias定义可以为同一个Activty指定别名，指定不同的IntentFilter或其它配置，从而使得同一个Activity可以有不同的属性，
图标等。 activity-alias 和activity支持的属性基本一致，在功能上和Activity基本一致。

 */
public class 
PurgeableBitmap 

extends GraphicsActivity { private PurgeableBitmapView mView; private final RefreshHandler mRedrawHandler = new RefreshHandler(); class RefreshHandler extends Handler { @Override public void handleMessage(Message msg) { int index = mView.update(this); if (index > 0) { showAlertDialog(getDialogMessage(true, index)); } else if (index < 0){ mView.invalidate(); showAlertDialog(getDialogMessage(false, -index)); } else { mView.invalidate(); } } public void sleep(long delayMillis) { this.removeMessages(0); sendMessageDelayed(obtainMessage(0), delayMillis); } } @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); mView = new PurgeableBitmapView(this, detectIfPurgeableRequest()); mRedrawHandler.sleep(0); setContentView(mView); } private boolean detectIfPurgeableRequest() { PackageManager pm = getPackageManager(); CharSequence labelSeq = null; try { ActivityInfo info = pm.getActivityInfo(this.getComponentName(), PackageManager.GET_META_DATA); labelSeq = info.loadLabel(pm); } catch (NameNotFoundException e) { e.printStackTrace(); return false; } String[] components = labelSeq.toString().split("/"); if (components[components.length - 1].equals("Purgeable")) { return true; } else { return false; } } private String getDialogMessage(boolean isOutOfMemory, int index) { StringBuilder sb = new StringBuilder(); if (isOutOfMemory) { sb.append("Out of memery occurs when the "); sb.append(index); sb.append("th Bitmap is decoded."); } else { sb.append("Complete decoding ") .append(index) .append(" bitmaps without running out of memory."); } return sb.toString(); } private void showAlertDialog(String message) { AlertDialog.Builder builder = new AlertDialog.Builder(this); builder.setMessage(message) .setCancelable(false) .setPositiveButton("Yes", new DialogInterface.OnClickListener() { public void onClick(DialogInterface dialog, int id) { } }); AlertDialog alert = builder.create(); alert.show(); }}

/**
 * PurgeableBitmapView works with PurgeableBitmap to demonstrate the effects of setting
 * Bitmaps as being purgeable.
 *
 * PurgeableBitmapView decodes an encoded bitstream to a Bitmap each time update()
 * is invoked(), and its onDraw() draws the Bitmap and a number to screen.
 * The number is used to indicate the number of Bitmaps that has been decoded.
 */
public class PurgeableBitmapView extends View {
    private final byte[] bitstream;

    private Bitmap mBitmap;
    private final int mArraySize = 200;
    private final Bitmap[] mBitmapArray = new Bitmap [mArraySize];
    private final Options mOptions = new Options();
    private static final int WIDTH = 150;
    private static final int HEIGHT = 450;
    private static final int STRIDE = 320;   // must be >= WIDTH
    private int mDecodingCount = 0;
    private final Paint mPaint = new Paint();
    private final int textSize = 32;
    private static int delay = 100;

    public PurgeableBitmapView(Context context, boolean isPurgeable) {
        super(context);
        setFocusable(true);
        mOptions.inPurgeable = isPurgeable;

        int[] colors = createColors();
        Bitmap src = Bitmap.createBitmap(colors, 0, STRIDE, WIDTH, HEIGHT,
                Bitmap.Config.ARGB_8888);
        bitstream = generateBitstream(src, Bitmap.CompressFormat.JPEG, 80);

        mPaint.setTextSize(textSize);
        mPaint.setColor(Color.GRAY);
    }

    private int[] createColors() {//颜色变化
        int[] colors = new int[STRIDE * HEIGHT];
        for (int y = 0; y < HEIGHT; y++) {
            for (int x = 0; x < WIDTH; x++) {
                int r = x * 255 / (WIDTH - 1);
                int g = y * 255 / (HEIGHT - 1);
                int b = 255 - Math.min(r, g);
                int a = Math.max(r, g);
                colors[y * STRIDE + x] = (a << 24) | (r << 16) | (g << 8) | b;
            }
        }
        return colors;
    }

    public int update(PurgeableBitmap.RefreshHandler handler) {
        try {
            mBitmapArray[mDecodingCount] = BitmapFactory.decodeByteArray(
                bitstream, 0, bitstream.length, mOptions);
            mBitmap = mBitmapArray[mDecodingCount];
            mDecodingCount++;
            if (mDecodingCount < mArraySize) {
                handler.sleep(delay);
                return 0;
            } else {
                return -mDecodingCount;
            }

        } catch (OutOfMemoryError error) {
            for (int i = 0; i < mDecodingCount; i++) {
                mBitmapArray[i].recycle();
            }
            return mDecodingCount + 1;
        }
    }

    @Override protected void onDraw(Canvas canvas) {
        canvas.drawColor(Color.WHITE);
        canvas.drawBitmap(mBitmap, 0, 0, null);
        canvas.drawText(String.valueOf(mDecodingCount), WIDTH / 2 - 20,
            HEIGHT / 2, mPaint);
    }

    private byte[] generateBitstream(Bitmap src, Bitmap.CompressFormat format,
            int quality) {
        ByteArrayOutputStream os = new ByteArrayOutputStream();
        src.compress(format, quality, os);
        return os.toByteArray();
    }

}