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Introduce a vertical/horizontal split layout (#1261)
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// Copyright 2019 The Chromium Authors. All rights reserved. | ||
// Use of this source code is governed by a BSD-style license that can be | ||
// found in the LICENSE file. | ||
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import 'dart:math'; | ||
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import 'package:flutter/material.dart'; | ||
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/// A widget that takes two children, lays them out along [axis], and allows | ||
/// the user to resize them. | ||
/// | ||
/// The user can customize the amount of space allocated to each child by | ||
/// dragging a divider between them. | ||
/// | ||
/// [initialFirstFraction] defines how much space to give the [firstChild] | ||
/// when first building this widget. [secondChild] will take the remaining | ||
/// space. | ||
/// | ||
/// The user can drag the widget with key [dividerKey] to change | ||
/// the space allocated between [firstChild] and [secondChild]. | ||
// TODO(djshuckerow): introduce support for a minimum fraction a child is allowed. | ||
class Split extends StatefulWidget { | ||
/// Builds a split oriented along [axis]. | ||
const Split({ | ||
Key key, | ||
@required this.axis, | ||
@required this.firstChild, | ||
@required this.secondChild, | ||
double initialFirstFraction, | ||
}) : initialFirstFraction = initialFirstFraction ?? 0.5, | ||
assert(axis != null), | ||
assert(firstChild != null), | ||
assert(secondChild != null), | ||
super(key: key); | ||
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/// The main axis the children will lay out on. | ||
/// | ||
/// If [Axis.horizontal], the children will be placed in a [Row] | ||
/// and they will be horizontally resizable. | ||
/// | ||
/// If [Axis.vertical], the children will be placed in a [Column] | ||
/// and they will be vertically resizable. | ||
/// | ||
/// Cannot be null. | ||
final Axis axis; | ||
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/// The child that will be laid out first along [axis]. | ||
final Widget firstChild; | ||
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/// The child that will be laid out last along [axis]. | ||
final Widget secondChild; | ||
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/// The fraction of the layout to allocate to [firstChild]. | ||
/// | ||
/// [secondChild] will receive a fraction of `1 - initialFirstFraction`. | ||
final double initialFirstFraction; | ||
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/// The key passed to the divider between [firstChild] and [secondChild]. | ||
/// | ||
/// Visible to grab it in tests. | ||
@visibleForTesting | ||
Key get dividerKey => Key('$this dividerKey'); | ||
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/// The size of the divider between [firstChild] and [secondChild] in | ||
/// logical pixels (dp, not px). | ||
static const double dividerMainAxisSize = 10.0; | ||
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@override | ||
State<StatefulWidget> createState() => _SplitState(); | ||
} | ||
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class _SplitState extends State<Split> { | ||
double firstFraction; | ||
double get secondFraction => 1 - firstFraction; | ||
bool get isHorizontal => widget.axis == Axis.horizontal; | ||
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@override | ||
void initState() { | ||
super.initState(); | ||
firstFraction = widget.initialFirstFraction; | ||
} | ||
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@override | ||
Widget build(BuildContext context) { | ||
return LayoutBuilder(builder: _buildLayout); | ||
} | ||
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Widget _buildLayout(BuildContext context, BoxConstraints constraints) { | ||
final width = constraints.maxWidth; | ||
final height = constraints.maxHeight; | ||
final axisSize = isHorizontal ? width : height; | ||
final crossAxisSize = isHorizontal ? height : width; | ||
const halfDivider = Split.dividerMainAxisSize / 2.0; | ||
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// Determine what fraction to give each child, including enough space to | ||
// display the divider. | ||
double firstSize = axisSize * firstFraction; | ||
double secondSize = axisSize * secondFraction; | ||
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// Clamp the sizes to be sure there is enough space for the dividers. | ||
firstSize = firstSize.clamp(halfDivider, axisSize - halfDivider); | ||
secondSize = secondSize.clamp(halfDivider, axisSize - halfDivider); | ||
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// Remove space from each child to place the divider in the middle. | ||
firstSize = firstSize - halfDivider; | ||
secondSize = secondSize - halfDivider; | ||
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void updateSpacing(DragUpdateDetails dragDetails) { | ||
final delta = isHorizontal ? dragDetails.delta.dx : dragDetails.delta.dy; | ||
final fractionalDelta = delta / axisSize; | ||
setState(() { | ||
// Update the fraction of space consumed by the children, | ||
// being sure not to allocate any negative space. | ||
firstFraction += fractionalDelta; | ||
firstFraction = firstFraction.clamp(0.0, 1.0); | ||
}); | ||
} | ||
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// TODO(https://github.com/flutter/flutter/issues/43747): use an icon. | ||
// The material icon for a drag handle is not currently available. | ||
// For now, draw an indicator that is 3 lines running in the direction | ||
// of the main axis, like a hamburger menu. | ||
// TODO(https://github.com/flutter/devtools/issues/1265): update mouse | ||
// to indicate that this is resizable. | ||
final dragIndicator = Flex( | ||
direction: isHorizontal ? Axis.vertical : Axis.horizontal, | ||
mainAxisSize: MainAxisSize.min, | ||
children: [ | ||
for (var i = 0; i < min(crossAxisSize / 6.0, 3).floor(); i++) | ||
Padding( | ||
padding: EdgeInsets.symmetric( | ||
vertical: isHorizontal ? 2.0 : 0.0, | ||
horizontal: isHorizontal ? 0.0 : 2.0, | ||
), | ||
child: DecoratedBox( | ||
decoration: BoxDecoration( | ||
color: Theme.of(context).indicatorColor, | ||
borderRadius: BorderRadius.circular(Split.dividerMainAxisSize), | ||
), | ||
child: SizedBox( | ||
height: isHorizontal ? 2.0 : Split.dividerMainAxisSize - 2.0, | ||
width: isHorizontal ? Split.dividerMainAxisSize - 2.0 : 2.0, | ||
), | ||
), | ||
), | ||
], | ||
); | ||
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final children = [ | ||
SizedBox( | ||
width: isHorizontal ? firstSize : width, | ||
height: isHorizontal ? height : firstSize, | ||
child: widget.firstChild, | ||
), | ||
GestureDetector( | ||
key: widget.dividerKey, | ||
behavior: HitTestBehavior.translucent, | ||
onHorizontalDragUpdate: isHorizontal ? updateSpacing : null, | ||
onVerticalDragUpdate: isHorizontal ? null : updateSpacing, | ||
child: SizedBox( | ||
width: isHorizontal ? Split.dividerMainAxisSize : width, | ||
height: isHorizontal ? height : Split.dividerMainAxisSize, | ||
child: Center( | ||
child: dragIndicator, | ||
), | ||
), | ||
), | ||
SizedBox( | ||
width: isHorizontal ? secondSize : width, | ||
height: isHorizontal ? height : secondSize, | ||
child: widget.secondChild, | ||
), | ||
]; | ||
return Flex(direction: widget.axis, children: children); | ||
} | ||
} |
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