textChanged

main.dart

  void _textChanged(String text) {
    if(text.isEmpty) {
      setState((){_isLoading = false;});
      _clearList();
      return;
    }
    setState((){_isLoading = true;});
    _clearList();
    http.get("https://www.googleapis.com/books/v1/volumes?q=$text")
        .then((response) => response.body)
        .then(JSON.decode)
        .then((map) => map["items"])
        .then((list) {list.forEach(_addBook);})
        .catchError(_onError)
        .then((e){setState((){_isLoading = false;});});
  }

  void _onError(dynamic d) {
    setState(() {
      _isLoading = false;
    });
  }

  void _clearList() {
    setState(() {
      _items.clear();
    });
  }