private Uri getFileUri(@NonNull Context context, @NonNull File file) {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
            return FileProvider.getUriForFile(context,
                    context.getApplicationContext().getPackageName() + ".file.provider", mOutputFile);
        } else {
            return Uri.fromFile(file);
        }
    }
start system camera to take a picture

@param activity      not null if fragment is null.
@param fragment      not null if activity is null.
@param subFolderPath a folder in external DCIM,must start with "/".
boxing/src/main/java/com/bilibili/boxing/utils/CameraPickerHelper.java