Serializing and De-Serializing android.graphics.Bitmap in Java

Question

I have started work on an my first android application and have the basis of an application that handles an image with multiple layers. I am able to export a flat version of the project file as a PNG but I would like to be able to save the layered image for later editing (including any options applied to certain layers, such as text based layers).

Anyway, I have ensured that the classes that need to be written to a file are 'Serializable' but have run into a bit of a road block caused by the fact that android.graphics.Bitmap isn't serializable. The following code essentially outputs the Bitmap as a PNG into a ByteArray and should read it back in as part of 'readObject'. However, when the code runs - I can verify that the 'imageByteArrayLength' variable that is read in is the same as that which is output - but the 'Bitmap image' is always null.

Any help would be greatly appreciated. Thanks for reading.

private String title;
private int width;
private int height;
private Bitmap sourceImage;
private Canvas sourceCanvas;        
private Bitmap currentImage;
private Canvas currentCanvas;   
private Paint currentPaint; 

private void writeObject(ObjectOutputStream out) throws IOException{
    out.writeObject(title);
    out.writeInt(width);
    out.writeInt(height);

    ByteArrayOutputStream stream = new ByteArrayOutputStream();
    currentImage.compress(Bitmap.CompressFormat.PNG, 100, stream);
    byte[] imageByteArray = stream.toByteArray();

    int length = imageByteArray.length;
    out.writeInt(length);
    out.write(imageByteArray);          
}

private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException{
    this.title = (String)in.readObject();
    this.width = in.readInt();
    this.height = in.readInt();

    int imageByteArrayLength = in.readInt();
    byte[] imageByteArray = new byte[imageByteArrayLength];
    in.read(imageByteArray, 0, imageByteArrayLength);

    BitmapFactory.Options opt = new BitmapFactory.Options();
    opt.inPreferredConfig = Bitmap.Config.ARGB_8888;

    Bitmap image = BitmapFactory.decodeByteArray(imageByteArray, 0, imageByteArrayLength, opt);

    sourceImage = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
    currentImage = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);

    sourceCanvas = new Canvas(sourceImage);
    currentCanvas = new Canvas(currentImage);
    currentPaint = new Paint(Paint.ANTI_ALIAS_FLAG);

    if ( image != null ) {
        sourceCanvas.drawBitmap(image, 0, 0, currentPaint);
    }
}   

Answer 1

It took a while, but I have found a clean solution to this problem. I produced a custom object (BitmapDataObject) that implements Serializable and has a byte[] to store the PNG data from the original Bitmap. Using this, the data is stored correctly in the ObjectOutputStream / ObjectInputStream - which effectively allows one to Serialize and Deserialize a Bitmap object by storing it as a PNG in a byte[] in a custom object. The code below resolves my query.

private String title;
private int sourceWidth, currentWidth;
private int sourceHeight, currentHeight;
private Bitmap sourceImage;
private Canvas sourceCanvas;        
private Bitmap currentImage;
private Canvas currentCanvas;   
private Paint currentPaint; 

protected class BitmapDataObject implements Serializable {
    private static final long serialVersionUID = 111696345129311948L;
    public byte[] imageByteArray;
}

/** Included for serialization - write this layer to the output stream. */
private void writeObject(ObjectOutputStream out) throws IOException{
    out.writeObject(title);
    out.writeInt(currentWidth);
    out.writeInt(currentHeight);

    ByteArrayOutputStream stream = new ByteArrayOutputStream();
    currentImage.compress(Bitmap.CompressFormat.PNG, 100, stream);
    BitmapDataObject bitmapDataObject = new BitmapDataObject();     
    bitmapDataObject.imageByteArray = stream.toByteArray();

    out.writeObject(bitmapDataObject);
}

/** Included for serialization - read this object from the supplied input stream. */
private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException{
    title = (String)in.readObject();
    sourceWidth = currentWidth = in.readInt();
    sourceHeight = currentHeight = in.readInt();

    BitmapDataObject bitmapDataObject = (BitmapDataObject)in.readObject();
    Bitmap image = BitmapFactory.decodeByteArray(bitmapDataObject.imageByteArray, 0, bitmapDataObject.imageByteArray.length);

    sourceImage = Bitmap.createBitmap(sourceWidth, sourceHeight, Bitmap.Config.ARGB_8888);
    currentImage = Bitmap.createBitmap(sourceWidth, sourceHeight, Bitmap.Config.ARGB_8888);

    sourceCanvas = new Canvas(sourceImage);
    currentCanvas = new Canvas(currentImage);

    currentPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    thumbnailPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    thumbnailPaint.setARGB(255, 200, 200, 200);
    thumbnailPaint.setStyle(Paint.Style.FILL);
}