【初心者でも安心】Androidアプリ開発で役立つDrawableからByte配列への変換ガイド

AndroidでDrawableをByte配列に変換する方法

必要なもの

• サンプル画像
• Android Studio

手順

1. DrawableをBitmapに変換する

   DrawableをByte配列に変換するには、まずBitmapに変換する必要があります。以下のコード例のように、drawableToBitmap() 関数を使用して変換できます。

   public static Bitmap drawableToBitmap(Drawable drawable) {
       if (drawable instanceof BitmapDrawable) {
           return ((BitmapDrawable) drawable).getBitmap();
       }
   
       Bitmap bitmap = Bitmap.createBitmap(drawable.getIntrinsicWidth(), drawable.getIntrinsicHeight(), Bitmap.Config.ARGB_8888);
       Canvas canvas = new Canvas(bitmap);
       drawable.setBounds(0, 0, drawable.getIntrinsicWidth(), drawable.getIntrinsicHeight());
       drawable.draw(canvas);
       return bitmap;
   }
   

2. BitmapをByte配列に変換する

   BitmapをByte配列に変換するには、ByteArrayOutputStreamとcompress() メソッドを使用します。以下のコード例のように記述します。

   public static byte[] bitmapToByteArray(Bitmap bitmap) {
       ByteArrayOutputStream stream = new ByteArrayOutputStream();
       bitmap.compress(Bitmap.CompressFormat.PNG, 100, stream); // PNG形式に圧縮
       return stream.toByteArray();
   }
   

3. 上記1、2の手順を組み合わせることで、DrawableをByte配列に変換できます。

   public static byte[] drawableToByteArray(Drawable drawable) {
       Bitmap bitmap = drawableToBitmap(drawable);
       return bitmapToByteArray(bitmap);
   }
   

ImageView imageView = findViewById(R.id.imageView);
Drawable drawable = imageView.getDrawable();
byte[] byteArray = drawableToByteArray(drawable);
Log.d("TAG", "Byte array: " + Arrays.toString(byteArray));

注意点

• 大容量の画像を扱う場合は、メモリ使用量に注意する必要があります。
• 上記のコードはあくまで一例であり、状況に応じて圧縮形式や画質などを調整する必要があります。

• Drawable to byte[] - android - Stack Overflow

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.drawable.Drawable;
import android.util.Base64;

import java.io.ByteArrayOutputStream;

public class DrawableToByteArray {

    public static byte[] drawableToByteArray(Drawable drawable) {
        if (drawable instanceof BitmapDrawable) {
            Bitmap bitmap = ((BitmapDrawable) drawable).getBitmap();
            return bitmapToByteArray(bitmap);
        }

        Bitmap bitmap = Bitmap.createBitmap(drawable.getIntrinsicWidth(), drawable.getIntrinsicHeight(), Bitmap.Config.ARGB_8888);
        Canvas canvas = new Canvas(bitmap);
        drawable.setBounds(0, 0, drawable.getIntrinsicWidth(), drawable.getIntrinsicHeight());
        drawable.draw(canvas);
        return bitmapToByteArray(bitmap);
    }

    public static byte[] bitmapToByteArray(Bitmap bitmap) {
        ByteArrayOutputStream stream = new ByteArrayOutputStream();
        bitmap.compress(Bitmap.CompressFormat.PNG, 100, stream);
        byte[] byteArray = stream.toByteArray();
        return byteArray;
    }

    public static String drawableToBase64String(Drawable drawable) {
        byte[] byteArray = drawableToByteArray(drawable);
        return Base64.encodeToString(byteArray, Base64.DEFAULT);
    }

    public static Bitmap base64StringToBitmap(String base64String) {
        byte[] byteArray = Base64.decode(base64String, Base64.DEFAULT);
        return BitmapFactory.decodeByteArray(byteArray, 0, byteArray.length);
    }
}

To use this code, you can first get a reference to the Drawable you want to convert. For example, if you have an ImageView with an image in it, you can get the Drawable like this:

ImageView imageView = findViewById(R.id.imageView);
Drawable drawable = imageView.getDrawable();

Once you have the Drawable, you can call the drawableToByteArray() method to convert it to a byte array. For example:

byte[] byteArray = DrawableToByteArray.drawableToByteArray(drawable);

You can also convert the Drawable to a Base64 string using the drawableToBase64String() method:

String base64String = DrawableToByteArray.drawableToBase64String(drawable);

To convert a Base64 string back to a Bitmap, you can use the base64StringToBitmap() method:

Bitmap bitmap = DrawableToByteArray.base64StringToBitmap(base64String);

The getPixelArray() method can be used to get the pixel data of a Drawable as an array of integers. This data can then be converted to a byte array using the Arrays.toString() method.

public static byte[] drawableToByteArrayUsingPixelArray(Drawable drawable) {
    int width = drawable.getIntrinsicWidth();
    int height = drawable.getIntrinsicHeight();
    int[] pixels = new int[width * height];
    drawable.getPixelArray(pixels, 0, width);
    String pixelString = Arrays.toString(pixels);
    return pixelString.getBytes();
}

Using the NinePatchChunk class

The NinePatchChunk class can be used to decode a Nine-Patch image from a Drawable. The NinePatchChunk class has a getBitmap() method that can be used to get the Bitmap representation of the Nine-Patch image. This Bitmap can then be converted to a byte array using the bitmapToByteArray() method described above.

public static byte[] drawableToByteArrayUsingNinePatchChunk(Drawable drawable) {
    if (!(drawable instanceof NinePatchDrawable)) {
        return null;
    }

    NinePatchDrawable ninePatchDrawable = (NinePatchDrawable) drawable;
    NinePatchChunk ninePatchChunk = ninePatchDrawable.getNinePatchChunk();
    Bitmap bitmap = ninePatchChunk.getBitmap();
    return bitmapToByteArray(bitmap);
}

Using a third-party library

There are a number of third-party libraries available that can be used to convert Drawables to byte arrays. One popular library is Glide. Glide has a toBytes() method that can be used to convert a Drawable to a byte array.

import com.bumptech.glide.Glide;
import com.bumptech.glide.request.target.Target;

public static byte[] drawableToByteArrayUsingGlide(Drawable drawable) {
    try {
        return Glide.with(context)
                .load(drawable)
                .asBitmap()
                .into(new Target<Bitmap>() {
                    @Override
                    public void onResourceReady(@NonNull Bitmap resource, @Nullable Target<Bitmap> glideTarget) {
                        ByteArrayOutputStream stream = new ByteArrayOutputStream();
                        resource.compress(Bitmap.CompressFormat.PNG, 100, stream);
                        byte[] byteArray = stream.toByteArray();
                    }

                    @Override
                    public void onLoadFailed(@Nullable Drawable errorDrawable) {
                        // Handle error
                    }

                    @Override
                    public void onCleared() {
                        // Cleanup
                    }
                })
                .get();
    } catch (Exception e) {
        e.printStackTrace();
        return null;
    }
}