在Java中序列化和反序列化android.graphics.Bitmap

Question

我开始开发我的第一个Android应用程序，并且已经构建了一个处理具有多个图层的图像的应用程序。我能够将项目文件导出为PNG格式的平面版本，但我希望能够保存分层图像以便以后进行编辑（包括应用于某些图层的任何选项，例如基于文本的图层）。

无论如何，我已确保需要写入文件的类是“可序列化”的，但由于android.graphics.Bitmap不可序列化，我遇到了一个障碍。以下代码将Bitmap作为PNG输出到ByteArray，并应在“readObject”中读取它。然而，当代码运行时-我可以验证“imageByteArrayLength”变量与输出的变量相同-但“Bitmap image”始终为空。

非常感谢您的帮助。谢谢阅读。

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);
    }
}   

- John Wordsworth

Answer 1

花了一些时间，但我已经找到了一个干净的解决方法。我创建了一个自定义对象（BitmapDataObject），它实现了Serializable接口并具有存储原始位图中PNG数据的byte[]。使用这个对象，数据可以正确地存储在ObjectOutputStream / ObjectInputStream中，从而通过将其存储为PNG格式的byte[]数组放入自定义对象中，可以序列化和反序列化位图对象。以下代码解决了我的问题。

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);
}

- John Wordsworth

---

我认为这段代码并没有正确地展示如何使用序列化。 - Justin Meiners

Answer 2

这是一个可序列化的对象示例，可以包装位图。

public class BitmapDataObject implements Serializable {

    private Bitmap currentImage;

    public BitmapDataObject(Bitmap bitmap)
    {
        currentImage = bitmap;
    }

    private void writeObject(java.io.ObjectOutputStream out) throws IOException {

        ByteArrayOutputStream stream = new ByteArrayOutputStream();
        currentImage.compress(Bitmap.CompressFormat.PNG, 100, stream);

        byte[] byteArray = stream.toByteArray();

        out.writeInt(byteArray.length);
        out.write(byteArray);

    }

    private void readObject(java.io.ObjectInputStream in) throws IOException, ClassNotFoundException {


        int bufferLength = in.readInt();

        byte[] byteArray = new byte[bufferLength];

        int pos = 0;
        do {
            int read = in.read(byteArray, pos, bufferLength - pos);

            if (read != -1) {
                pos += read;
            } else {
                break;
            }

        } while (pos < bufferLength);

        currentImage = BitmapFactory.decodeByteArray(byteArray, 0, bufferLength);

    }
}

- Justin Meiners

Answer 3

只需使用此代码创建一个名为BitmapDataObject的类。使用getter和setter在Bitmap和BitmapDataObject类之间切换。

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.Serializable;

public class BitmapDataObject implements Serializable {

    private Bitmap currentImage;

    public Bitmap getCurrentImage() {
        return currentImage;
    }

    public void setCurrentImage(Bitmap currentImage) {
        this.currentImage = currentImage;
    }

    public BitmapDataObject(Bitmap bitmap)
    {
        currentImage = bitmap;
    }

    private void writeObject(java.io.ObjectOutputStream out) throws IOException {
        ByteArrayOutputStream stream = new ByteArrayOutputStream();
        currentImage.compress(Bitmap.CompressFormat.PNG, 100, stream);
        byte[] byteArray = stream.toByteArray();
        out.writeInt(byteArray.length);
        out.write(byteArray);
    }

    private void readObject(java.io.ObjectInputStream in) throws IOException, ClassNotFoundException {
        int bufferLength = in.readInt();
        byte[] byteArray = new byte[bufferLength];
        int pos = 0;
        do {
            int read = in.read(byteArray, pos, bufferLength - pos);

            if (read != -1) {
                pos += read;
            } else {
                break;
            }
        } while (pos < bufferLength);
        currentImage = BitmapFactory.decodeByteArray(byteArray, 0, bufferLength);
    }

}

- Muhammad Aasharib Nawshad