Android中Bitmap, Drawable, Byte之间的转化

 1.  Bitmap 转化为 byte
 ByteArrayOutputStream out = new ByteArrayOutputStream();
 bitmap.compress(Bitmap.CompressFormat.PNG, 100, out);
 byte[] array= out.toByteArray();

 2. byte转化为bitmap
 final ContentResolver contentResolver = context.getContentResolver();
 final PackageManager manager = context.getPackageManager();
 final Cursor c = contentResolver.query(uri, null, null, null, null);
 final int icon3DIndex = c.getColumnIndexOrThrow(ColumnName);
 byte[] data = c.getBlob(icon3DIndex);
 Bitmap bitmap = BitmapFactory.decodeByteArray(data, 0, data.length);

 3. bitmap转化为Drawable
 Drawable drawable = new FastBitmapDrawable(bitmap);
 ...

 4. Drawable转化为bitmap
  a. BitmapDrawable, FastBitmapDrawable直接用getBitmap
  b. 其他类型的Drawable用Canvas画到一个bitmap上
       Canvas canvas = new Canvas(bitmap)
       drawable.draw(canvas);