@Override
        public void onFinish(@NonNull CameraPickerHelper helper) {
            AbsBoxingViewFragment fragment = mWr.get();
            if (fragment == null) {
                return;
            }
            File file = new File(helper.getSourceFilePath());

            if (!file.exists()) {
                onError(helper);
                return;
            }
            ImageMedia cameraMedia = new ImageMedia(file);
            cameraMedia.saveMediaStore(fragment.getAppCr());
            fragment.onCameraFinish(cameraMedia);
        }
start camera to take a photo.

@param activity      the caller activity.
@param fragment      the caller fragment, may be null.
@param subFolderPath the folder name in "DCIM/bili/boxing/"
boxing/src/main/java/com/bilibili/boxing/AbsBoxingViewFragment.java