Flutter实现搜索框中文占位提示文字

class SearchBarDelegate extends SearchDelegate<String>{

  @override
  String get searchFieldLabel => '搜索内容';
  ...
}

class SearchBarDelegate extends SearchDelegate<String>{
  SearchBarDelegate({
    String hintText,
  }) : super(
    searchFieldLabel: hintText,
    keyboardType: TextInputType.text,
    textInputAction: TextInputAction.search,
  );
  ...
}

     showSearch(context: context, 
                  delegate: SearchBarDelegate(hintText: '搜索')
      );