Material DataTable: added support of setting table row border thickness (#49692)

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

@@ -331,6 +331,7 @@ class DataTable extends StatelessWidget {
     this.horizontalMargin = 24.0,
     this.columnSpacing = 56.0,
     this.showCheckboxColumn = true,
+    this.dividerThickness = 1.0,
     @required this.rows,
   }) : assert(columns != null),
        assert(columns.isNotEmpty),
@@ -343,6 +344,7 @@ class DataTable extends StatelessWidget {
        assert(showCheckboxColumn != null),
        assert(rows != null),
        assert(!rows.any((DataRow row) => row.cells.length != columns.length)),
+       assert(dividerThickness != null && dividerThickness >= 0),
        _onlyTextColumn = _initOnlyTextColumn(columns),
        super(key: key);
 
@@ -467,6 +469,12 @@ class DataTable extends StatelessWidget {
   static const Color _grey100Opacity = Color(0x0A000000); // Grey 100 as opacity instead of solid color
   static const Color _grey300Opacity = Color(0x1E000000); // Dark theme variant is just a guess.
 
+  /// The width of the divider that appears between [TableRow]s.
+  ///
+  /// Must be non-null and greater than or equal to zero.
+  /// This value defaults to 1.0.
+  final double dividerThickness;
+
   Widget _buildCheckbox({
     Color color,
     bool checked,
@@ -613,12 +621,12 @@ class DataTable extends StatelessWidget {
 
     final ThemeData theme = Theme.of(context);
     final BoxDecoration _kSelectedDecoration = BoxDecoration(
-      border: Border(bottom: Divider.createBorderSide(context, width: 1.0)),
+      border: Border(bottom: Divider.createBorderSide(context, width:  dividerThickness)),
       // The backgroundColor has to be transparent so you can see the ink on the material
       color: (Theme.of(context).brightness == Brightness.light) ? _grey100Opacity : _grey300Opacity,
     );
     final BoxDecoration _kUnselectedDecoration = BoxDecoration(
-      border: Border(bottom: Divider.createBorderSide(context, width: 1.0)),
+      border: Border(bottom: Divider.createBorderSide(context, width: dividerThickness)),
     );
 
     final bool displayCheckboxColumn = showCheckboxColumn && rows.any((DataRow row) => row.onSelectChanged != null);

packages/flutter/test/material/data_table_test.dart

@@ -866,4 +866,56 @@ void main() {
       _customHorizontalMargin,
     );
   });
+
+  testWidgets('DataTable set border width test', (WidgetTester tester) async {
+    const List<DataColumn> columns = <DataColumn>[
+      DataColumn(label: Text('column1')),
+      DataColumn(label: Text('column2')),
+    ];
+
+    const List<DataCell> cells = <DataCell>[
+      DataCell(Text('cell1')),
+      DataCell(Text('cell2')),
+    ];
+
+    const List<DataRow> rows = <DataRow>[
+      DataRow(cells: cells),
+      DataRow(cells: cells),
+    ];
+
+    // no thickness provided - border should be default: i.e "1.0" as it
+    // set in DataTable constructor
+    await tester.pumpWidget(
+      MaterialApp(
+        home: Material(
+          child: DataTable(
+            columns: columns,
+            rows: rows,
+          ),
+        ),
+      ),
+    );
+
+    Table table = tester.widget(find.byType(Table));
+    TableRow tableRow = table.children.first;
+    BoxDecoration boxDecoration = tableRow.decoration as BoxDecoration;
+    expect(boxDecoration.border.bottom.width, 1.0);
+
+    const double thickness =  4.2;
+    await tester.pumpWidget(
+      MaterialApp(
+        home: Material(
+          child: DataTable(
+            dividerThickness: thickness,
+            columns: columns,
+            rows: rows,
+          ),
+        ),
+      ),
+    );
+    table = tester.widget(find.byType(Table));
+    tableRow = table.children.first;
+    boxDecoration = tableRow.decoration as BoxDecoration;
+    expect(boxDecoration.border.bottom.width, thickness);
+  });
 }