title: Flutter: A problem when using FilePicker to pick files
body: <p>Some of my codes is as following:</p>
  <pre><code>File? _file;
    PlatformFile? _platformFile;
  
    selectFile() async {
      final file = await FilePicker.platform.pickFiles(
          type: FileType.custom,
          allowedExtensions: ['mp3', 'm4a']
      );
  
      if (file != null) {
        setState(() {
          _file = File(file.files.single.path!);
          _platformFile = file.files.first;
          print(&quot;Size: &quot;);
          print(_platformFile?.size);
        });
      }
  
      loadingController.forward();
    }
  </code></pre>
  <p>When calling <code>selectFile</code>, there should be a list full of <code>.mp3</code> and <code>.m4a</code> files. However, there is no files shown in the list. The picture is as following.<a href="https://i.stack.imgur.com/y9ir7.jpg" rel="nofollow noreferrer">enter image description here</a></p>
  <p>I wondered that if it is beacuse that some varibles have not be set? Or some other details I have not noticed?</p>
  <p>Thanks for your help.</p>