SearchDelegate<T> constructor Null safety

SearchDelegate<T>(
  1. {String? searchFieldLabel,
  2. TextStyle? searchFieldStyle,
  3. InputDecorationTheme? searchFieldDecorationTheme,
  4. TextInputType? keyboardType,
  5. TextInputAction textInputAction: TextInputAction.search}
)

Constructor to be called by subclasses which may specify searchFieldLabel, either searchFieldStyle or searchFieldDecorationTheme, keyboardType and/or textInputAction. Only one of searchFieldLabel and searchFieldDecorationTheme may be non-null.

link 
class CustomSearchHintDelegate extends SearchDelegate {
  CustomSearchHintDelegate({
    required String hintText,
  }) : super(
    searchFieldLabel: hintText,
    keyboardType: TextInputType.text,
    textInputAction: TextInputAction.search,
  );

  @override
  Widget buildLeading(BuildContext context) => Text("leading");

  PreferredSizeWidget buildBottom(BuildContext context) {
    return PreferredSize(
       preferredSize: Size.fromHeight(56.0),
       child: Text("bottom"));
  }

  @override
  Widget buildSuggestions(BuildContext context) => Text("suggestions");

  @override
  Widget buildResults(BuildContext context) => Text('results');

  @override
  List<Widget> buildActions(BuildContext context) => [];
}

Implementation

SearchDelegate({
  this.searchFieldLabel,
  this.searchFieldStyle,
  this.searchFieldDecorationTheme,
  this.keyboardType,
  this.textInputAction = TextInputAction.search,
}) : assert(searchFieldStyle == null || searchFieldDecorationTheme == null);