divider.dart

// Copyright 2014 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'package:flutter/widgets.dart';

import 'divider_theme.dart';
import 'theme.dart';

// Examples can assume:
// late BuildContext context;

/// A thin horizontal 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.
///
/// To create a divider between [ListTile] items, consider using
/// [ListTile.divideTiles], which is optimized for this case.
///
/// {@youtube 560 315 https://www.youtube.com/watch?v=_liUC641Nmk}
///
/// The box's total height is controlled by [height]. The appropriate
/// padding is automatically computed from the height.
///
/// {@tool dartpad}
/// This sample shows how to display a Divider between an orange and blue box
/// inside a column. The Divider is 20 logical pixels in height and contains a
/// vertically centered black line that is 5 logical pixels thick. The black
/// line is indented by 20 logical pixels.
///
/// ![](https://flutter.github.io/assets-for-api-docs/assets/material/divider.png)
///
/// ** See code in examples/api/lib/material/divider/divider.0.dart **
/// {@end-tool}
///
/// See also:
///
///  * [PopupMenuDivider], which is the equivalent but for popup menus.
///  * [ListTile.divideTiles], another approach to dividing widgets in a list.
///  * [VerticalDivider], which is the vertical analog of this widget.
///  * <https://material.io/design/components/dividers.html>
class Divider extends StatelessWidget {
  /// Creates a Material Design divider.
  ///
  /// The [height], [thickness], [indent], and [endIndent] must be null or
  /// non-negative.
  const Divider({
    super.key,
    this.height,
    this.thickness,
    this.indent,
    this.endIndent,
    this.color,
  }) : assert(height == null || height >= 0.0),
       assert(thickness == null || thickness >= 0.0),
       assert(indent == null || indent >= 0.0),
       assert(endIndent == null || endIndent >= 0.0);


  /// The divider's height extent.
  ///
  /// The divider itself is always drawn as a horizontal line that is centered
  /// within the height specified by this value.
  ///
  /// If this is null, then the [DividerThemeData.space] is used. If that is
  /// also null, then this defaults to 16.0.
  final double? height;

  /// The thickness of the line drawn within the divider.
  ///
  /// A divider with a [thickness] of 0.0 is always drawn as a line with a
  /// height of exactly one device pixel.
  ///
  /// If this is null, then the [DividerThemeData.thickness] is used. If
  /// that is also null, then this defaults to 0.0.
  final double? thickness;

  /// The amount of empty space to the leading edge of the divider.
  ///
  /// If this is null, then the [DividerThemeData.indent] is used. If that is
  /// also null, then this defaults to 0.0.
  final double? indent;

  /// The amount of empty space to the trailing edge of the divider.
  ///
  /// If this is null, then the [DividerThemeData.endIndent] is used. If that is
  /// also null, then this defaults to 0.0.
  final double? endIndent;

  /// The color to use when painting the line.
  ///
  /// If this is null, then the [DividerThemeData.color] is used. If that is
  /// also null, then [ThemeData.dividerColor] is used.
  ///
  /// {@tool snippet}
  ///
  /// ```dart
  /// const Divider(
  ///   color: Colors.deepOrange,
  /// )
  /// ```
  /// {@end-tool}
  final Color? color;

  /// Computes the [BorderSide] that represents a divider.
  ///
  /// If [color] is null, then [DividerThemeData.color] is used. If that is also
  /// null, then [ThemeData.dividerColor] is used.
  ///
  /// If [width] is null, then [DividerThemeData.thickness] is used. If that is
  /// also null, then this defaults to 0.0 (a hairline border).
  ///
  /// If [context] is null, the default color of [BorderSide] is used and the
  /// default width of 0.0 is used.
  ///
  /// {@tool snippet}
  ///
  /// 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: ...
  /// )
  /// ```
  /// {@end-tool}
  static BorderSide createBorderSide(BuildContext? context, { Color? color, double? width }) {
    final Color? effectiveColor = color
        ?? (context != null ? (DividerTheme.of(context).color ?? Theme.of(context).dividerColor) : null);
    final double effectiveWidth =  width
        ?? (context != null ? DividerTheme.of(context).thickness : null)
        ?? 0.0;

    // Prevent assertion since it is possible that context is null and no color
    // is specified.
    if (effectiveColor == null) {
      return BorderSide(
        width: effectiveWidth,
      );
    }
    return BorderSide(
      color: effectiveColor,
      width: effectiveWidth,
    );
  }

  @override
  Widget build(BuildContext context) {
    final DividerThemeData dividerTheme = DividerTheme.of(context);
    final double height = this.height ?? dividerTheme.space ?? 16.0;
    final double thickness = this.thickness ?? dividerTheme.thickness ?? 0.0;
    final double indent = this.indent ?? dividerTheme.indent ?? 0.0;
    final double endIndent = this.endIndent ?? dividerTheme.endIndent ?? 0.0;

    return SizedBox(
      height: height,
      child: Center(
        child: Container(
          height: thickness,
          margin: EdgeInsetsDirectional.only(start: indent, end: endIndent),
          decoration: BoxDecoration(
            border: Border(
              bottom: createBorderSide(context, color: color, width: thickness),
            ),
          ),
        ),
      ),
    );
  }
}

/// A thin vertical line, with padding on either side.
///
/// In the Material Design language, this represents a divider. Vertical
/// dividers can be used in horizontally scrolling lists, such as a
/// [ListView] with [ListView.scrollDirection] set to [Axis.horizontal].
///
/// The box's total width is controlled by [width]. The appropriate
/// padding is automatically computed from the width.
///
/// {@tool dartpad}
/// This sample shows how to display a [VerticalDivider] between a purple and orange box
/// inside a [Row]. The [VerticalDivider] is 20 logical pixels in width and contains a
/// horizontally centered black line that is 1 logical pixels thick. The grey
/// line is indented by 20 logical pixels.
///
/// ** See code in examples/api/lib/material/divider/vertical_divider.0.dart **
/// {@end-tool}
///
/// See also:
///
///  * [ListView.separated], which can be used to generate vertical dividers.
///  * [Divider], which is the horizontal analog of this widget.
///  * <https://material.io/design/components/dividers.html>
class VerticalDivider extends StatelessWidget {
  /// Creates a Material Design vertical divider.
  ///
  /// The [width], [thickness], [indent], and [endIndent] must be null or
  /// non-negative.
  const VerticalDivider({
    super.key,
    this.width,
    this.thickness,
    this.indent,
    this.endIndent,
    this.color,
  }) : assert(width == null || width >= 0.0),
       assert(thickness == null || thickness >= 0.0),
       assert(indent == null || indent >= 0.0),
       assert(endIndent == null || endIndent >= 0.0);

  /// The divider's width.
  ///
  /// The divider itself is always drawn as a vertical line that is centered
  /// within the width specified by this value.
  ///
  /// If this is null, then the [DividerThemeData.space] is used. If that is
  /// also null, then this defaults to 16.0.
  final double? width;

  /// The thickness of the line drawn within the divider.
  ///
  /// A divider with a [thickness] of 0.0 is always drawn as a line with a
  /// width of exactly one device pixel.
  ///
  /// If this is null, then the [DividerThemeData.thickness] is used which
  /// defaults to 0.0.
  final double? thickness;

  /// The amount of empty space on top of the divider.
  ///
  /// If this is null, then the [DividerThemeData.indent] is used. If that is
  /// also null, then this defaults to 0.0.
  final double? indent;

  /// The amount of empty space under the divider.
  ///
  /// If this is null, then the [DividerThemeData.endIndent] is used. If that is
  /// also null, then this defaults to 0.0.
  final double? endIndent;

  /// The color to use when painting the line.
  ///
  /// If this is null, then the [DividerThemeData.color] is used. If that is
  /// also null, then [ThemeData.dividerColor] is used.
  ///
  /// {@tool snippet}
  ///
  /// ```dart
  /// const Divider(
  ///   color: Colors.deepOrange,
  /// )
  /// ```
  /// {@end-tool}
  final Color? color;

  @override
  Widget build(BuildContext context) {
    final DividerThemeData dividerTheme = DividerTheme.of(context);
    final double width = this.width ?? dividerTheme.space ?? 16.0;
    final double thickness = this.thickness ?? dividerTheme.thickness ?? 0.0;
    final double indent = this.indent ?? dividerTheme.indent ?? 0.0;
    final double endIndent = this.endIndent ?? dividerTheme.endIndent ?? 0.0;

    return SizedBox(
      width: width,
      child: Center(
        child: Container(
          width: thickness,
          margin: EdgeInsetsDirectional.only(top: indent, bottom: endIndent),
          decoration: BoxDecoration(
            border: Border(
              left: Divider.createBorderSide(context, color: color, width: thickness),
            ),
          ),
        ),
      ),
    );
  }
}