AlertDialog.java

private void showOpenWith(File file) {

 if (getContext() == null) {
  return;
 }

 String extension = getFileExtension(file);

 Uri uri = null;
 if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {

  uri = FileProvider.getUriForFile(getContext(), "dynamic.school.fileprovider", file);
 } else {

  uri = Uri.fromFile(file);
 }

 Log.i("BQ7CH72", "File uri :: " + uri);

 try {
  MimeTypeMap mime = MimeTypeMap.getSingleton();
  Intent intent = new Intent(Intent.ACTION_VIEW);
  intent.setFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION);
  intent.setDataAndType(uri, mime.getMimeTypeFromExtension(extension));
  startActivityForResult(intent, ACTIVITY_VIEW_ATTACHMENT);
 } catch (ActivityNotFoundException e) {

  Toast.makeText(getContext(), "This file cannot be viewed on this device." +
   " Application not found for opening this type of file.", Toast.LENGTH_LONG).show();
 }
}

private String getFileExtension(File file) {
    String[] files = file.getAbsolutePath().split("\\\\");
    files = files[files.length - 1].split("\\.");
    return files[files.length - 1];
}

AndroidManifest.xml

<provider
    android:name="android.support.v4.content.FileProvider"
    android:authorities="my.domain.fileprovider"
    android:exported="false"
    android:grantUriPermissions="true">
    <meta-data
        android:name="android.support.FILE_PROVIDER_PATHS"
        android:resource="@xml/file_paths" />
</provider>

file_paths.xml

<?xml version="1.0" encoding="utf-8"?>
<paths>
    <external-path
        name="my_images"
        path="Android/data/dynamic.school/files/Pictures" />
    <external-path
        name="external_files"
        path="/" />
    <external-files-path
        name="external_files"
        path="/" />
    <root-path
        name="sdcard1"
        path="/" />
    <cache-path
        name="cache"
        path="/" />
    <files-path
        name="files"
        path="/" />
</paths>