title: File cant be assigned with ImagePicker Flutter
body: <p>i am learning imagepicker from <a href="https://pub.dev/packages/image_picker" rel="nofollow noreferrer">https://pub.dev/packages/image_picker</a> ,
  but i don't why i got an error when i have use the way step by step.</p>
  
  <p>this is the problem :</p>
  
  <p>first, i declare a File variable </p>
  
  <pre><code>File _imageFile ;
  </code></pre>
  
  <p>then i use it in a method,</p>
  
  <pre><code>_getimg() async{
  var _img = await ImagePicker(source: ImageSource.gallery);
  setState(() {
        _imageFile = _img ;
      });
  }
  </code></pre>
  
  <p>and then i got this error :</p>
  
  <blockquote>
    <p>A value of type 'File (where File is defined in
    D:\Flutter\flutter\bin\cache\pkg\sky_engine\lib\io\file.dart)' can't
    be assigned to a variable of type 'File (where File is defined in
    D:\Flutter\flutter\bin\cache\pkg\sky_engine\lib\html\html_dart2js.dart)'.</p>
  </blockquote>