Android FileProvider cannot find file

Question

I am relatively new to Android programming and followed several different tutorials. The target was to copy a pdf-file from the assets folder to the external storage and then open an Intent when a button is pressed to open a PDF-Viewer. I tried to adjust my code to the latest Android version using FileProvider as described here: https://inthecheesefactory.com/blog/how-to-share-access-to-file-with-fileprovider-on-android-nougat/en

Opening the file on older Android versions worked so I know that the whole copying process is working, the thing is I just can't figure out where the error in my code is.

 File file = new File(Environment.getExternalStorageDirectory() + "/" + "index.pdf");
    Intent intent = new Intent(Intent.ACTION_VIEW);
    //old version
    Uri fileURI = Uri.fromFile(file);
    //new version
    Uri fileUri = FileProvider.getUriForFile(MainActivity.this,
            BuildConfig.APPLICATION_ID + ".provider", file);

    getApplicationContext().grantUriPermission(PACKAGE_NAME, fileUri, Intent.FLAG_GRANT_READ_URI_PERMISSION);
    intent.setDataAndType(fileUri,"application/pdf");
    intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
    intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);

I set up my FileProvider as described in the above link.

<provider
        android:name="android.support.v4.content.FileProvider"
        android:authorities="${applicationId}.provider"
        android:exported="false"
        android:grantUriPermissions="true">
        <meta-data
            android:name="android.support.FILE_PROVIDER_PATHS"
            android:resource="@xml/provider_paths"/>
    </provider>

using the following xml

<?xml version="1.0" encoding="utf-8"?>
<paths xmlns:android="http://schemas.android.com/apk/res/android">
<external-path name="external_files" path="."/>
</paths>

I would be really glad if someone could explain me my error.

Answer 1

From the comments: I had to add intent.addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION); also.