setting 'ref'

very nice job, loved this package

my question is setting refs

```
ref={(ref) => this.listView = ref} // how we do in in other components but doesnt work here
ref='listView' // works
```

is there any preference in doing the second method ?

No file or test is named. Start by reproducing the callback-ref and string-ref examples from the issue, then inspect how the list view handles refs; done means establishing and documenting which ref form is supported, or confirming the callback form works.

Written by the indexing model from the issue text.