Vertical divider (#22377)

* Add vertical divider option.

* added vertical divider

* restored hello world

* final changes

* a few changes

* comment fixes

* added VerticalDivider

* few changes

* comment changes:

* ultra nits

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

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 import 'package:flutter/widgets.dart';
+import 'package:flutter/painting.dart';
 
 import 'theme.dart';
 
@@ -12,11 +13,12 @@ import 'theme.dart';
 /// In the material design language, this represents a divider.
 ///
 /// Dividers can be used in lists, [Drawer]s, and elsewhere to separate content
-/// vertically. To create a one-pixel divider between items in a list, consider
-/// using [ListTile.divideTiles], which is optimized for this case.
+/// vertically or horizontally depending on the value of the [axis] enum.
+/// To create a one-pixel divider between items in a list, consider using
+/// [ListTile.divideTiles], which is optimized for this case.
 ///
-/// The box's total height is controlled by [height]. The appropriate padding is
-/// automatically computed from the height.
+/// The box's total height is controlled by [height]. The appropriate
+/// padding is automatically computed from the width or height.
 ///
 /// See also:
 ///
@@ -35,13 +37,14 @@ class Divider extends StatelessWidget {
   }) : assert(height >= 0.0),
        super(key: key);
 
-  /// The divider's vertical extent.
+
+  /// The divider's height extent.
   ///
   /// The divider itself is always drawn as one device pixel thick horizontal
   /// line that is centered within the height specified by this value.
   ///
-  /// A divider with a height of 0.0 is always drawn as a line with a height of
-  /// exactly one device pixel, without any padding around it.
+  /// A divider with a [height] of 0.0 is always drawn as a line with a height
+  /// of exactly one device pixel, without any padding around it.
   final double height;
 
   /// The amount of empty space to the left of the divider.
@@ -111,3 +114,109 @@ class Divider extends StatelessWidget {
     );
   }
 }
+
+/// A one device pixel thick vertical line, with padding on either
+/// side.
+///
+/// In the material design language, this represents a divider.
+///
+/// Dividers can be used in lists, [Drawer]s, and elsewhere to separate content
+/// horizontally. To create a one-pixel divider between items in a list,
+/// consider using [ListTile.divideTiles], which is optimized for this case.
+///
+/// The box's total width is controlled by [width]. The appropriate
+/// padding is automatically computed from the width.
+///
+/// See also:
+///
+///  * [PopupMenuDivider], which is the equivalent but for popup menus.
+///  * [ListTile.divideTiles], another approach to dividing widgets in a list.
+///  * <https://material.google.com/components/dividers.html>
+class VerticalDivider extends StatelessWidget {
+  /// Creates a material design divider.
+  ///
+  /// The width must be positive.
+  const VerticalDivider({
+    Key key,
+    this.width = 16.0,
+    this.indent = 0.0,
+    this.color
+  }) : assert(width >= 0.0),
+       super(key: key);
+
+  /// The divider's width.
+  ///
+  /// The divider itself is always drawn as one device pixel thick
+  /// line that is centered within the width specified by this value.
+  ///
+  /// A divider with a [width] of 0.0 is always drawn as a line with a width
+  /// of exactly one device pixel, without any padding around it.
+  final double width;
+
+  /// The amount of empty space to the left of the divider.
+  final double indent;
+
+  /// The color to use when painting the line.
+  ///
+  /// Defaults to the current theme's divider color, given by
+  /// [ThemeData.dividerColor].
+  ///
+  /// ## Sample code
+  ///
+  /// ```dart
+  /// Divider(
+  ///   color: Colors.deepOrange,
+  /// )
+  /// ```
+  final Color color;
+
+  /// Computes the [BorderSide] that represents a divider of the specified
+  /// color, or, if there is no specified color, of the default
+  /// [ThemeData.dividerColor] specified in the ambient [Theme].
+  ///
+  /// The `width` argument can be used to override the default width of the
+  /// divider border, which is usually 0.0 (a hairline border).
+  ///
+  /// ## Sample code
+  ///
+  /// This example uses this method to create a box that has a divider above and
+  /// below it. This is sometimes useful with lists, for instance, to separate a
+  /// scrollable section from the rest of the interface.
+  ///
+  /// ```dart
+  /// DecoratedBox(
+  ///   decoration: BoxDecoration(
+  ///     border: Border(
+  ///       top: Divider.createBorderSide(context),
+  ///       bottom: Divider.createBorderSide(context),
+  ///     ),
+  ///   ),
+  ///   // child: ...
+  /// )
+  /// ```
+  static BorderSide createBorderSide(BuildContext context, { Color color, double width = 0.0 }) {
+    assert(width != null);
+    return BorderSide(
+      color: color ?? Theme.of(context).dividerColor,
+      width: width,
+    );
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return SizedBox(
+      width: width,
+      child: Center(
+        child: Container(
+          height: 0.0,
+          margin: EdgeInsetsDirectional.only(start: indent),
+          decoration: BoxDecoration(
+            border: Border(
+              left: createBorderSide(context, color: color),
+            ),
+          ),
+        ),
+      ),
+    );
+  }
+}

packages/flutter/test/material/divider_test.dart

@@ -4,6 +4,7 @@
 
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
+import 'package:flutter/painting.dart';
 import '../rendering/mock_canvas.dart';
 
 void main() {
@@ -20,4 +21,18 @@ void main() {
     expect(box.size.height, 16.0);
     expect(find.byType(Divider), paints..path(strokeWidth: 0.0));
   });
+
+  testWidgets('Vertical Divider Test', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      const Directionality(
+        textDirection: TextDirection.ltr,
+        child: Center(
+          child: VerticalDivider(),
+        ),
+      ),
+    );
+    final RenderBox box = tester.firstRenderObject(find.byType(VerticalDivider));
+    expect(box.size.width, 16.0);
+    expect(find.byType(VerticalDivider), paints..path(strokeWidth: 0.0));
+  });
 }