Make header optional in PaginatedDataTable (#69610)

packages/flutter/lib/src/material/paginated_data_table.dart

@@ -37,8 +37,7 @@ import 'theme.dart';
 class PaginatedDataTable extends StatefulWidget {
   /// Creates a widget describing a paginated [DataTable] on a [Card].
   ///
-  /// The [header] should give the card's header, typically a [Text] widget. It
-  /// must not be null.
+  /// The [header] should give the card's header, typically a [Text] widget.
   ///
   /// The [columns] argument must be a list of as many [DataColumn] objects as
   /// the table is to have columns, ignoring the leading checkbox column if any.
@@ -64,7 +63,7 @@ class PaginatedDataTable extends StatefulWidget {
   /// both have defaults, though, so don't have to be specified).
   PaginatedDataTable({
     Key? key,
-    required this.header,
+    this.header,
     this.actions,
     required this.columns,
     this.sortColumnIndex,
@@ -82,7 +81,7 @@ class PaginatedDataTable extends StatefulWidget {
     this.onRowsPerPageChanged,
     this.dragStartBehavior = DragStartBehavior.start,
     required this.source,
-  }) : assert(header != null),
+  }) : assert(actions == null || (actions != null && header != null)),
        assert(columns != null),
        assert(dragStartBehavior != null),
        assert(columns.isNotEmpty),
@@ -103,17 +102,19 @@ class PaginatedDataTable extends StatefulWidget {
        assert(source != null),
        super(key: key);
 
-  /// The table card's header.
+  /// The table card's optional header.
   ///
-  /// This is typically a [Text] widget, but can also be a [ButtonBar] with
-  /// [TextButton]s. Suitable defaults are automatically provided for the font,
-  /// button color, button padding, and so forth.
+  /// This is typically a [Text] widget, but can also be a [Row] of
+  /// [TextButton]s. To show icon buttons at the top end side of the table with
+  /// a header, set the [actions] property.
   ///
   /// If items in the table are selectable, then, when the selection is not
-  /// empty, the header is replaced by a count of the selected items.
-  final Widget header;
+  /// empty, the header is replaced by a count of the selected items. The
+  /// [actions] are still visible when items are selected.
+  final Widget? header;
 
-  /// Icon buttons to show at the top right of the table.
+  /// Icon buttons to show at the top end side of the table. The [header] must
+  /// not be null to show the actions.
   ///
   /// Typically, the exact actions included in this list will vary based on
   /// whether any rows are selected or not.
@@ -337,8 +338,8 @@ class PaginatedDataTableState extends State<PaginatedDataTable> {
     // HEADER
     final List<Widget> headerWidgets = <Widget>[];
     double startPadding = 24.0;
-    if (_selectedRowCount == 0) {
-      headerWidgets.add(Expanded(child: widget.header));
+    if (_selectedRowCount == 0 && widget.header != null) {
+      headerWidgets.add(Expanded(child: widget.header!));
       if (widget.header is ButtonBar) {
         // We adjust the padding when a button bar is present, because the
         // ButtonBar introduces 2 pixels of outside padding, plus 2 pixels
@@ -347,7 +348,7 @@ class PaginatedDataTableState extends State<PaginatedDataTable> {
         // inside of the button to line up with the 24.0 left inset.
         startPadding = 12.0;
       }
-    } else {
+    } else if (widget.header != null) {
       headerWidgets.add(Expanded(
         child: Text(localizations.selectedRowCountTitle(_selectedRowCount)),
       ));
@@ -432,6 +433,7 @@ class PaginatedDataTableState extends State<PaginatedDataTable> {
           child: Column(
             crossAxisAlignment: CrossAxisAlignment.stretch,
             children: <Widget>[
+              if (headerWidgets.isNotEmpty)
                 Semantics(
                   container: true,
                   child: DefaultTextStyle(

packages/flutter/test/material/paginated_data_table_test.dart

@@ -229,6 +229,43 @@ void main() {
     expect(tester.getTopRight(find.text('8')).dx, tester.getTopRight(find.text('Rows per page:')).dx + 40.0); // per spec
   });
 
+  testWidgets('PaginatedDataTable with and without header and actions', (WidgetTester tester) async {
+    await binding.setSurfaceSize(const Size(800, 800));
+    const String headerText = 'HEADER';
+    final List<Widget> actions = <Widget>[
+      IconButton(onPressed: () {}, icon: const Icon(Icons.add)),
+    ];
+    Widget buildTable({String? header, List<Widget>? actions}) => MaterialApp(
+      home: PaginatedDataTable(
+        header: header != null ? Text(header) : null,
+        actions: actions,
+        source: TestDataSource(onSelectChanged: (bool? value) {}),
+        showCheckboxColumn: true,
+        columns: const <DataColumn>[
+          DataColumn(label: Text('Name')),
+          DataColumn(label: Text('Calories'), numeric: true),
+          DataColumn(label: Text('Generation')),
+        ],
+      ),
+    );
+
+    await tester.pumpWidget(buildTable(header: headerText));
+    expect(find.text(headerText), findsOneWidget);
+    expect(find.byIcon(Icons.add), findsNothing);
+
+    await tester.pumpWidget(buildTable(header: headerText, actions: actions));
+    expect(find.text(headerText), findsOneWidget);
+    expect(find.byIcon(Icons.add), findsOneWidget);
+
+    await tester.pumpWidget(buildTable());
+    expect(find.text(headerText), findsNothing);
+    expect(find.byIcon(Icons.add), findsNothing);
+
+    expect(() => buildTable(actions: actions), throwsAssertionError);
+
+    await binding.setSurfaceSize(null);
+  });
+
   testWidgets('PaginatedDataTable with large text', (WidgetTester tester) async {
     final TestDataSource source = TestDataSource();
     await tester.pumpWidget(MaterialApp(