how to rotate a bitmap 90 degrees

Question

There is a statement in android canvas.drawBitmap(visiblePage, 0, 0, paint);

When I add canvas.rotate(90), there is no effect. But if I wri

Answer 1

In case your goal is to have a rotated image in an imageView or file you can use Exif to achieve that. The support library now offers that: https://android-developers.googleblog.com/2016/12/introducing-the-exifinterface-support-library.html

Below is its usage but to achieve your goal you have to check the library api documentation for that. I just wanted to give a hint that rotating the bitmap isn't always the best way.

Uri uri; // the URI you've received from the other app
InputStream in;
try {
  in = getContentResolver().openInputStream(uri);
  ExifInterface exifInterface = new ExifInterface(in);
  // Now you can extract any Exif tag you want
  // Assuming the image is a JPEG or supported raw format
} catch (IOException e) {
  // Handle any errors
} finally {
  if (in != null) {
    try {
      in.close();
    } catch (IOException ignored) {}
  }
}

int rotation = 0;
int orientation = exifInterface.getAttributeInt(
    ExifInterface.TAG_ORIENTATION,
    ExifInterface.ORIENTATION_NORMAL);
switch (orientation) {
  case ExifInterface.ORIENTATION_ROTATE_90:
    rotation = 90;
    break;
  case ExifInterface.ORIENTATION_ROTATE_180:
    rotation = 180;
    break;
  case ExifInterface.ORIENTATION_ROTATE_270:
    rotation = 270;
    break;
}

dependency

compile "com.android.support:exifinterface:25.1.0"