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// 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/rendering.dart';
import 'basic.dart';
import 'framework.dart';
/// Spacer creates an adjustable, empty spacer that can be used to tune the
/// spacing between widgets in a [Flex] container, like [Row] or [Column].
///
/// The [Spacer] widget will take up any available space, so setting the
/// [Flex.mainAxisAlignment] on a flex container that contains a [Spacer] to
/// [MainAxisAlignment.spaceAround], [MainAxisAlignment.spaceBetween], or
/// [MainAxisAlignment.spaceEvenly] will not have any visible effect: the
/// [Spacer] has taken up all of the additional space, therefore there is none
/// left to redistribute.
///
/// {@tool sample}
///
/// ```dart
/// Row(
/// children: <Widget>[
/// Text('Begin'),
/// Spacer(), // Defaults to a flex of one.
/// Text('Middle'),
/// // Gives twice the space between Middle and End than Begin and Middle.
/// Spacer(flex: 2),
/// Text('End'),
/// ],
/// )
/// ```
/// {@end-tool}
///
/// {@youtube 560 315 https://www.youtube.com/watch?v=7FJgd7QN1zI}
///
/// See also:
///
/// * [Row] and [Column], which are the most common containers to use a Spacer
/// in.
/// * [SizedBox], to create a box with a specific size and an optional child.
class Spacer extends StatelessWidget {
/// Creates a flexible space to insert into a [Flexible] widget.
///
/// The [flex] parameter may not be null or less than one.
const Spacer({Key key, this.flex = 1})
: assert(flex != null),
assert(flex > 0),
super(key: key);
/// The flex factor to use in determining how much space to take up.
///
/// The amount of space the [Spacer] can occupy in the main axis is determined
/// by dividing the free space proportionately, after placing the inflexible
/// children, according to the flex factors of the flexible children.
///
/// Defaults to one.
final int flex;
@override
Widget build(BuildContext context) {
return Expanded(
flex: flex,
child: const SizedBox.shrink(),
);
}
}