Generate barcode in an AsyncTask

This change moves the generation of the barcode into its
own async task. In addition, the size of the ImageView is
used to determine the barcode size to use.

There will be cases when the size of the ImageView will not
be known when the barcode generation starts. This will be resolved
in a future commit.

app/src/main/java/protect/card_locker/BarcodeImageWriterTask.java

@@ -0,0 +1,91 @@
+package protect.card_locker;
+
+import android.graphics.Bitmap;
+import android.os.AsyncTask;
+import android.util.Log;
+import android.widget.ImageView;
+
+import com.google.zxing.BarcodeFormat;
+import com.google.zxing.MultiFormatWriter;
+import com.google.zxing.WriterException;
+import com.google.zxing.common.BitMatrix;
+
+import java.lang.ref.WeakReference;
+
+/**
+ * This task will generate a barcode and load it into an ImageView.
+ * Only a weak reference of the ImageView is kept, so this class will not
+ * prevent the ImageView from being garbage collected.
+ */
+class BarcodeImageWriterTask extends AsyncTask<Void, Void, Bitmap>
+{
+    private static final String TAG = "LoyaltyCardLocker";
+
+    private final WeakReference<ImageView> imageViewReference;
+    private final String cardId;
+    private final BarcodeFormat format;
+    private final int imageHeight;
+    private final int imageWidth;
+
+    public BarcodeImageWriterTask(ImageView imageView, String cardIdString,
+                                  BarcodeFormat barcodeFormat)
+    {
+        // Use a WeakReference to ensure the ImageView can be garbage collected
+        imageViewReference = new WeakReference<>(imageView);
+
+        cardId = cardIdString;
+        format = barcodeFormat;
+        imageHeight = imageView.getHeight();
+        imageWidth = imageView.getWidth();
+    }
+
+    public Bitmap doInBackground(Void... params)
+    {
+        MultiFormatWriter writer = new MultiFormatWriter();
+        BitMatrix bitMatrix;
+        try
+        {
+            bitMatrix = writer.encode(cardId, format, imageWidth, imageHeight, null);
+
+            final int WHITE = 0xFFFFFFFF;
+            final int BLACK = 0xFF000000;
+
+            int bitMatrixWidth = bitMatrix.getWidth();
+            int bitMatrixHeight = bitMatrix.getHeight();
+
+            int[] pixels = new int[bitMatrixWidth * bitMatrixHeight];
+
+            for (int y = 0; y < bitMatrixHeight; y++)
+            {
+                int offset = y * bitMatrixWidth;
+                for (int x = 0; x < bitMatrixWidth; x++)
+                {
+                    int color = bitMatrix.get(x, y) ? BLACK : WHITE;
+                    pixels[offset + x] = color;
+                }
+            }
+            Bitmap bitmap = Bitmap.createBitmap(bitMatrixWidth, bitMatrixHeight,
+                    Bitmap.Config.ARGB_8888);
+            bitmap.setPixels(pixels, 0, bitMatrixWidth, 0, 0, bitMatrixWidth, bitMatrixHeight);
+            return bitmap;
+        }
+        catch (WriterException | IllegalArgumentException e)
+        {
+            Log.e(TAG, "Failed to generate barcode", e);
+        }
+
+        return null;
+    }
+
+    protected void onPostExecute(Bitmap result)
+    {
+        ImageView imageView = imageViewReference.get();
+        if(imageView == null)
+        {
+            // The ImageView no longer exists, nothing to do
+            return;
+        }
+
+        imageView.setImageBitmap(result);
+    }
+}