QR Code image generation into AsyncTask to keep things snappy

Generating the QR Code image can take some time, so do it in an AsyncTask
which then updates the ImageView once the QRCode is complete.  This will be
used for the kerplapp repo swapping process.

refs #3204 https://dev.guardianproject.info/issues/3204
refs #3201 https://dev.guardianproject.info/issues/3201

src/org/fdroid/fdroid/QrGenAsyncTask.java

@@ -0,0 +1,73 @@
+
+package org.fdroid.fdroid;
+
+import android.annotation.TargetApi;
+import android.app.Activity;
+import android.graphics.Bitmap;
+import android.graphics.Point;
+import android.os.AsyncTask;
+import android.os.Build;
+import android.util.Log;
+import android.view.Display;
+import android.widget.ImageView;
+
+import com.google.zxing.BarcodeFormat;
+import com.google.zxing.WriterException;
+import com.google.zxing.encode.Contents;
+import com.google.zxing.encode.QRCodeEncoder;
+
+public class QrGenAsyncTask extends AsyncTask<String, Void, Void> {
+    private static final String TAG = "QrGenAsyncTask";
+
+    private Activity activity;
+    private int viewId;
+    private Bitmap qrBitmap;
+
+    public QrGenAsyncTask(Activity activity, int viewId) {
+        this.activity = activity;
+        this.viewId = viewId;
+    }
+
+    /*
+     * The method for getting screen dimens changed, so this uses both the
+     * deprecated one and the 13+ one, and supports all Android versions.
+     */
+    @SuppressWarnings("deprecation")
+    @TargetApi(13)
+    @Override
+    protected Void doInBackground(String... s) {
+        String qrData = s[0];
+        Display display = activity.getWindowManager().getDefaultDisplay();
+        Point outSize = new Point();
+        int x, y, qrCodeDimension;
+        /* lame, got to use both the new and old APIs here */
+        if (Build.VERSION.SDK_INT >= 13) {
+            display.getSize(outSize);
+            x = outSize.x;
+            y = outSize.y;
+        } else {
+            x = display.getWidth();
+            y = display.getHeight();
+        }
+        if (x < y)
+            qrCodeDimension = x;
+        else
+            qrCodeDimension = y;
+        Log.i(TAG, "generating QRCode Bitmap of " + qrCodeDimension + "x" + qrCodeDimension);
+        QRCodeEncoder qrCodeEncoder = new QRCodeEncoder(qrData, null,
+                Contents.Type.TEXT, BarcodeFormat.QR_CODE.toString(), qrCodeDimension);
+
+        try {
+            qrBitmap = qrCodeEncoder.encodeAsBitmap();
+        } catch (WriterException e) {
+            Log.e(TAG, e.getMessage());
+        }
+        return (Void) null;
+    }
+
+    @Override
+    protected void onPostExecute(Void v) {
+        ImageView qrCodeImageView = (ImageView) activity.findViewById(viewId);
+        qrCodeImageView.setImageBitmap(qrBitmap);
+    }
+}