UPDATE新增fieldViewBuilder，防止回车时选择。

要实现这一点，您可以使用optionsViewBuilder，如下所示：

Autocomplete<String>(
  fieldViewBuilder:
      (context, textEditingController, focusNode, onFieldSubmitted) {
    return TextFormField(
      controller: textEditingController,
      focusNode: focusNode,
    );
  },
  optionsBuilder: (TextEditingValue textEditingValue) {
    if (textEditingValue.text == '') {
      return const Iterable<String>.empty();
    }
    return _kOptions.where((String option) {
      return option.contains(textEditingValue.text.toLowerCase());
    });
  },
  optionsViewBuilder: (
    BuildContext context,
    AutocompleteOnSelected<String> onSelected,
    Iterable<String> options,
  ) {
    return Align(
      alignment: Alignment.topLeft,
      child: Material(
        elevation: 4.0,
        child: Container(
          constraints: const BoxConstraints(maxHeight: 200),
          child: ListView.builder(
            padding: const EdgeInsets.all(8.0),
            itemCount: options.length,
            shrinkWrap: true,
            itemBuilder: (BuildContext context, int index) {
              final String option = options.elementAt(index);
              return GestureDetector(
                onTap: () {
                  onSelected(option);
                },
                child: ListTile(
                  title: Text(option),
                ),
              );
            },
          ),
        ),
      ),
    );
  },
  onSelected: (String selection) {
    debugPrint('You just selected $selection');
  },
)

现在没有预选选项：