drawable 转换为Bitmap:

   private Bitmap drawableToBitmap(Drawable drawable, int width, int height) {
         Bitmap bitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
 
         Canvas canvas = new Canvas(bitmap);
         drawable.setBounds(0, 0, width, height);
         drawable.draw(canvas);
         return bitmap;
     }

保存Bitmap，格式可以是png， jpg等：

      public enum CompressFormat {
          JPEG    (0),
          PNG     (1),
          WEBP    (2);
      }

  public File saveBitmap(Bitmap bitmap, File directory, String filename, CompressFormat format) {
     if (directory == null) {
         directory = context.getCacheDir();
     } else {
     // Check if the given directory exists or try to create it.
         if (!directory.isDirectory() && !directory.mkdirs()) {
           return null;   
         }   
    }     
    File file = null;
    OutputStream os = null;
    try {
        filename = (format == CompressFormat.PNG) ? filename + ".png" : filename + ".jpg";
        file = new File(directory, filename);   
        os = new FileOutputStream(file);
        bitmap.compress(format, DEFAULT_COMPRESS_QUALITY, os);
   } catch (FileNotFoundException e) {
       e.printStackTrace();
   } finally {
       closeStream(os);
   }   
   return file;
}

简单的保存为png code：

//Context.getFilesDir()，该方法返回/data/data/package name/files的File对象。

try {
    File  file = new File(mContext.getFilesDir(), name+".png");
    FileOutputStream fos = new FileOutputStream(file);
    bitmap.compress(Bitmap.CompressFormat.PNG, 90, fos);
    fos.close();
} catch (IOException e) {
    Log.i(TAG, "failed to write PNG", e);
}

Bitmap--------> Drawable:

Drawable drawable = new BitmapDrawable(bitmap);