1) В Android есть системная функциональность для выбора картинки из галереи ... и эта системная функциональность возвращает Uri
 
2) В Android есть системная функция ImageView.setImageURI(uri) для отображения картинки по uri

Мой вывод: Android много где использует функциональность с URI и мало где использует функциональность с file path

context.getExternalFilesDir
Returns the absolute path to the directory on the primary shared/external storage device where the application can place persistent files it owns. These files are internal to the applications, and not typically visible to the user as media.

This is like getFilesDir() in that these files will be deleted when the application is uninstalled, however there are some important differences:
Shared storage may not always be available, since removable media can be ejected by the user. Media state can be checked using Environment#getExternalStorageState(File) .

There is no security enforced with these files. For example, any application holding Manifest.permission.WRITE_EXTERNAL_STORAGE can write to these files.

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Return a content URI for a given File. Specific temporary permissions for the content URI can be set with Context.grantUriPermission(String, Uri, int), or added to an Intent by calling setData() and then setFlags(); in both cases, the applicable flags are Intent.FLAG_GRANT_READ_URI_PERMISSION and Intent.FLAG_GRANT_WRITE_URI_PERMISSION. A FileProvider can only return a content Uri for file paths defined in their meta-data element.