Flutter ConstraintLayout: A super powerful Stack, build flexible layouts with constraints

by Flutter Awesome

Flutter ConstraintLayout

A super powerful Stack, build flexible layouts with constraints. Similar to ConstraintLayout for Android and AutoLayout for iOS.

No matter how complex the layout is and how deep the constraints are, it has almost the same performance as Flex and Stack. When facing complex layouts, it provides better performance, flexibility, and a very flat code hierarchy than Flex and Stack. Say no to ‘nesting hell’.

View Flutter Web Online Example

Flutter ConstraintLayout has extremely high layout performance. It does not require linear equations to solve. It is recommended to use ConstraintLayout at the top level. For extremely complex layout(One thousand child elements, two thousand constraints), layout and drawing total time within 5 milliseconds(debug mode on Windows 10，release mode take less time), the frame rate can be easily reached 200 fps.

If not necessary, try to be relative to the parent layout, so that you can define less id. Or use relative id.

Warning: For layout performance considerations, constraints are always one-way, and there should be no two child elements directly or indirectly restrain each other. Each constraint should describe exactly where the child elements are located. Although constraints can only be one-way, you can still better handle things that were previously (Android ConstraintLayout) two-way constraints, such as chains.

Anyone who sends you a harassing message, you can send him Flutter code and use nested hell to insult him.

Feature

  1. build flexible layouts with constraints
    1. leftToLeft
    2. leftToRight
    3. rightToLeft
    4. rightToRight
    5. topToTop
    6. topToBottom
    7. bottomToTop
    8. bottomToBottom
    9. baselineToTop
    10. baselineToBottom
    11. baselineToBaseline
  2. margin and goneMargin
  3. clickPadding (quickly expand the click area of child elements without changing their actual size. This means that the click area can be shared between child elements without increasing nesting. Sometimes it may be necessary to combine with e-index)
  4. visibility control
    1. visible
    2. invisible
    3. gone
  5. constraint integrity hint
  6. bias
  7. z-index(drawing order, default is child index)
  8. translate
  9. percentage layout
  10. guideline
  11. constraints and widgets separation
  12. barrier
  13. dimension ratio
  14. relative id
  15. wrapper constraints
    1. topLeftTo
    2. topCenterTo
    3. topRightTo
    4. centerLeftTo
    5. centerTo
    6. centerRightTo
    7. bottomLeftTo
    8. bottomCenterTo
    9. bottomRightTo
    10. centerHorizontalTo
    11. centerVerticalTo
    12. outTopLeftTo
    13. outTopCenterTo
    14. outTopRightTo
    15. outCenterLeftTo
    16. outCenterRightTo
    17. outBottomLeftTo
    18. outBottomCenterTo
    19. outBottomRightTo
    20. centerTopLeftTo
    21. centerTopCenterTo
    22. centerTopRightTo
    23. centerCenterLeftTo
    24. centerCenterRightTo
    25. centerBottomLeftTo
    26. centerBottomCenterTo
    27. centerBottomRightTo
  16. staggered grid、grid、list(list is a special staggered grid, grid is also a special staggered grid)
  17. circle position
  18. e-index(event dispatch order, default is z-index)

Coming soon:

  1. chain
  2. constraints visualization
  3. self wrapContent
  4. more…

Support platform:

  1. Android
  2. iOS
  3. Mac
  4. Windows
  5. Linux
  6. Web

Import

Null-safety

dependencies:
  flutter_constraintlayout:
    git:
      url: 'https://github.com/hackware1993/Flutter-ConstraintLayout.git'
      ref: 'v0.9.27-stable'

dependencies:
  flutter_constraintlayout: ^0.9.27-stable
import 'package:flutter_constraintlayout/flutter_constraintlayout.dart';

Example Flutter Web Online Example

class ExampleState extends State<Example> {
  double x = 0;
  double y = 0;

  ConstraintId box0 = ConstraintId('box0');
  ConstraintId box1 = ConstraintId('box1');
  ConstraintId box2 = ConstraintId('box2');
  ConstraintId box3 = ConstraintId('box3');
  ConstraintId box4 = ConstraintId('box4');
  ConstraintId box5 = ConstraintId('box5');
  ConstraintId box6 = ConstraintId('box6');
  ConstraintId box7 = ConstraintId('box7');
  ConstraintId box8 = ConstraintId('box8');
  ConstraintId box9 = ConstraintId('box9');
  ConstraintId box10 = ConstraintId('box10');
  ConstraintId box11 = ConstraintId('box11');

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        backgroundColor: Colors.black,
        body: ConstraintLayout(
          // Constraints can be separated from widgets
          childConstraints: [
            Constraint(
              id: box0,
              width: 200,
              height: 200,
              bottomLeftTo: parent,
              zIndex: 20,
            )
          ],
          children: [
            Container(
              color: Colors.redAccent,
              alignment: Alignment.center,
              child: const Text('box0'),
            ).applyConstraintId(
              id: box0, // Constraints can be separated from widgets
            ),
            Container(
              color: Colors.redAccent,
              alignment: Alignment.center,
              child: const Text('box1'),
            ).apply(
              constraint: Constraint(
                // Constraints set with widgets
                id: box1,
                width: 200,
                height: 100,
                topRightTo: parent,
              ),
            ),
            Container(
              color: Colors.blue,
              alignment: Alignment.center,
              child: const Text('box2'),
            ).applyConstraint(
              // Constraints set with widgets easy way
              id: box2,
              width: matchConstraint,
              height: matchConstraint,
              centerHorizontalTo: box3,
              top: box3.bottom,
              bottom: parent.bottom,
            ),
            Container(
              color: Colors.orange,
              width: 200,
              height: 150,
              alignment: Alignment.center,
              child: const Text('box3'),
            ).applyConstraint(
              id: box3,
              width: wrapContent,
              height: wrapContent,
              right: box1.left,
              top: box1.bottom,
            ),
            Container(
              color: Colors.redAccent,
              alignment: Alignment.center,
              child: const Text('box4'),
            ).applyConstraint(
              id: box4,
              width: 50,
              height: 50,
              bottomRightTo: parent,
            ),
            GestureDetector(
              child: Container(
                color: Colors.pink,
                alignment: Alignment.center,
                child: const Text('box5 draggable'),
              ),
              onPanUpdate: (details) {
                setState(() {
                  x += details.delta.dx;
                  y += details.delta.dy;
                });
              },
            ).applyConstraint(
              id: box5,
              width: 120,
              height: 100,
              centerTo: parent,
              zIndex: 100,
              translate: Offset(x, y),
              translateConstraint: true,
            ),
            Container(
              color: Colors.lightGreen,
              alignment: Alignment.center,
              child: const Text('box6'),
            ).applyConstraint(
              id: box6,
              width: 120,
              height: 120,
              centerVerticalTo: box2,
              verticalBias: 0.8,
              left: box3.right,
              right: parent.right,
            ),
            Container(
              color: Colors.lightGreen,
              alignment: Alignment.center,
              child: const Text('box7'),
            ).applyConstraint(
              id: box7,
              width: matchConstraint,
              height: matchConstraint,
              left: parent.left,
              right: box3.left,
              centerVerticalTo: parent,
              margin: const EdgeInsets.all(50),
            ),
            Container(
              color: Colors.cyan,
              alignment: Alignment.center,
              child: const Text('child[7] pinned to the top right'),
            ).applyConstraint(
              width: 200,
              height: 100,
              left: box5.right,
              bottom: box5.top,
            ),
            const Text(
              'box9 baseline to box7',
              style: TextStyle(
                color: Colors.white,
              ),
            ).applyConstraint(
              id: box9,
              width: wrapContent,
              height: wrapContent,
              baseline: box7.baseline,
              left: box7.left,
            ),
            ...horizontalChain(
              centerHorizontalTo: parent,
              hChainList: [
                Container(
                  color: Colors.redAccent,
                  alignment: Alignment.center,
                  child: const Text('chain item 1'),
                ).applyConstraint(
                  id: box10,
                  width: matchConstraint,
                  height: 200,
                  top: parent.top,
                ),
                Container(
                  color: Colors.redAccent,
                  alignment: Alignment.center,
                  child: const Text('chain item 2'),
                ).applyConstraint(
                  id: box11,
                  width: matchConstraint,
                  height: 200,
                  top: parent.top,
                ),
              ],
            ),
            Container(
              color: Colors.yellow,
              alignment: Alignment.bottomCenter,
              child: const Text(
                  'percentage layout\nwidth: 50% of parent\nheight: 30% of parent'),
            ).applyConstraint(
              width: matchConstraint,
              height: matchConstraint,
              widthPercent: 0.5,
              heightPercent: 0.3,
              horizontalBias: 0,
              verticalBias: 0,
              centerTo: parent,
            ),
          ],
        ),
      ),
    );
  }
}

Advanced usage

  1. guideline Flutter Web Online Example

class GuidelineExample extends StatelessWidget {
  const GuidelineExample({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    ConstraintId guideline = ConstraintId('guideline');
    return MaterialApp(
      home: Scaffold(
        body: ConstraintLayout(
          children: [
            Container(
              color: const Color(0xFF005BBB),
            ).applyConstraint(
              width: matchParent,
              height: matchConstraint,
              top: parent.top,
              bottom: guideline.top,
            ),
            Guideline(
              id: guideline,
              horizontal: true,
              guidelinePercent: 0.5,
            ),
            Container(
              color: const Color(0xFFFFD500),
            ).applyConstraint(
              width: matchParent,
              height: matchConstraint,
              top: guideline.bottom,
              bottom: parent.bottom,
            ),
            const Text(
              'Stand with the people of Ukraine',
              style: TextStyle(
                fontSize: 40,
                color: Colors.white,
              ),
            ).applyConstraint(
              width: wrapContent,
              height: wrapContent,
              centerHorizontalTo: parent,
              bottom: guideline.bottom,
            )
          ],
        ),
      ),
    );
  }
}
  1. barrier Flutter Web Online Example

class BarrierExample extends StatelessWidget {
  const BarrierExample({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    ConstraintId leftChild = ConstraintId('leftChild');
    ConstraintId rightChild = ConstraintId('rightChild');
    ConstraintId barrier = ConstraintId('barrier');
    return MaterialApp(
      home: Scaffold(
        body: ConstraintLayout(
          debugShowGuideline: true,
          children: [
            Container(
              color: const Color(0xFF005BBB),
            ).applyConstraint(
              id: leftChild,
              width: 200,
              height: 200,
              top: parent.top,
              left: parent.left,
            ),
            Container(
              color: const Color(0xFFFFD500),
            ).applyConstraint(
              id: rightChild,
              width: 200,
              height: matchConstraint,
              right: parent.right,
              top: parent.top,
              bottom: parent.bottom,
              heightPercent: 0.5,
              verticalBias: 0,
            ),
            Barrier(
              id: barrier,
              direction: BarrierDirection.bottom,
              referencedIds: [leftChild, rightChild],
            ),
            const Text(
              'Align to barrier',
              style: TextStyle(
                fontSize: 40,
                color: Colors.blue,
              ),
            ).applyConstraint(
              width: wrapContent,
              height: wrapContent,
              centerHorizontalTo: parent,
              top: barrier.bottom,
              goneMargin: const EdgeInsets.only(top: 20),
            )
          ],
        ),
      ),
    );
  }
}
  1. badge Flutter Web Online Example

class BadgeExample extends StatelessWidget {
  const BadgeExample({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    ConstraintId anchor = ConstraintId('anchor');
    return Scaffold(
      body: ConstraintLayout(
        children: [
          Container(
            color: Colors.yellow,
          ).applyConstraint(
            width: 200,
            height: 200,
            centerTo: parent,
            id: anchor,
          ),
          Container(
            color: Colors.green,
            child: const Text(
              'Indeterminate badge size',
              style: TextStyle(
                color: Colors.black,
                fontSize: 20,
              ),
            ),
          ).applyConstraint(
            left: anchor.right,
            bottom: anchor.top,
            translate: const Offset(-0.5, 0.5),
            percentageTranslate: true,
          ),
          Container(
            color: Colors.green,
          ).applyConstraint(
            width: 100,
            height: 100,
            left: anchor.right,
            right: anchor.right,
            top: anchor.bottom,
            bottom: anchor.bottom,
          )
        ],
      ),
    );
  }
}
  1. grid Flutter Web Online Example

class GridExample extends StatelessWidget {
  const GridExample({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    List<Color> colors = [
      Colors.redAccent,
      Colors.greenAccent,
      Colors.blueAccent,
      Colors.orangeAccent,
      Colors.yellow,
      Colors.pink,
      Colors.lightBlueAccent
    ];
    return Scaffold(
      body: ConstraintLayout(
        children: [
          ...constraintGrid(
              id: ConstraintId('grid'),
              left: parent.left,
              top: parent.top,
              itemCount: 50,
              columnCount: 8,
              itemWidth: 50,
              itemHeight: 50,
              itemBuilder: (index) {
                return Container(
                  color: colors[index % colors.length],
                );
              },
              itemMarginBuilder: (index) {
                return const EdgeInsets.only(
                  left: 10,
                  top: 10,
                );
              })
        ],
      ),
    );
  }
}
  1. staggered grid Flutter Web Online Example

class StaggeredGridExample extends StatelessWidget {
  const StaggeredGridExample({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    List<Color> colors = [
      Colors.redAccent,
      Colors.greenAccent,
      Colors.blueAccent,
      Colors.orangeAccent,
      Colors.yellow,
      Colors.pink,
      Colors.lightBlueAccent
    ];
    const double smallestSize = 40;
    const int columnCount = 8;
    Random random = Random();
    return Scaffold(
      body: ConstraintLayout(
        children: [
          TextButton(
            onPressed: () {
              (context as Element).markNeedsBuild();
            },
            child: const Text(
              'Upset',
              style: TextStyle(
                fontSize: 32,
                height: 1.5,
              ),
            ),
          ).applyConstraint(
            left: ConstraintId('horizontalList').right,
            top: ConstraintId('horizontalList').top,
          ),
          ...constraintGrid(
              id: ConstraintId('horizontalList'),
              left: parent.left,
              top: parent.top,
              margin: const EdgeInsets.only(
                left: 100,
              ),
              itemCount: 50,
              columnCount: columnCount,
              itemBuilder: (index) {
                return Container(
                  color: colors[index % colors.length],
                  alignment: Alignment.center,
                  child: Text('$index'),
                );
              },
              itemSizeBuilder: (index) {
                if (index == 0) {
                  return const Size(
                      smallestSize * columnCount + 35, smallestSize);
                }
                if (index == 6) {
                  return const Size(smallestSize * 2 + 5, smallestSize);
                }
                if (index == 7) {
                  return const Size(smallestSize * 6 + 25, smallestSize);
                }
                if (index == 19) {
                  return const Size(smallestSize * 2 + 5, smallestSize);
                }
                if (index == 29) {
                  return const Size(smallestSize * 3 + 10, smallestSize);
                }
                return Size(
                    smallestSize, (2 + random.nextInt(4)) * smallestSize);
              },
              itemSpanBuilder: (index) {
                if (index == 0) {
                  return columnCount;
                }
                if (index == 6) {
                  return 2;
                }
                if (index == 7) {
                  return 6;
                }
                if (index == 19) {
                  return 2;
                }
                if (index == 29) {
                  return 3;
                }
                return 1;
              },
              itemMarginBuilder: (index) {
                return const EdgeInsets.only(
                  left: 5,
                  top: 5,
                );
              })
        ],
      ),
    );
  }
}
  1. circle position Flutter Web Online Example

class CirclePositionExampleState extends State<CirclePositionExample> {
  late Timer timer;
  late int hour;
  late int minute;
  late int second;

  double centerTranslateX = 0;
  double centerTranslateY = 0;

  @override
  void initState() {
    super.initState();
    calculateClockAngle();
    timer = Timer.periodic(const Duration(seconds: 1), (_) {
      calculateClockAngle();
    });
  }

  void calculateClockAngle() {
    setState(() {
      DateTime now = DateTime.now();
      hour = now.hour;
      minute = now.minute;
      second = now.second;
    });
  }

  @override
  void dispose() {
    super.dispose();
    timer.cancel();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: ConstraintLayout(
        children: [
          GestureDetector(
            child: Container(
              decoration: const BoxDecoration(
                color: Colors.red,
                borderRadius: BorderRadius.all(
                  Radius.circular(1000),
                ),
              ),
            ),
            onPanUpdate: (details) {
              setState(() {
                centerTranslateX += details.delta.dx;
                centerTranslateY += details.delta.dy;
              });
            },
          ).applyConstraint(
            width: 20,
            height: 20,
            centerTo: parent,
            zIndex: 100,
            translate: Offset(centerTranslateX, centerTranslateY),
            translateConstraint: true,
          ),
          for (int i = 0; i < 12; i++)
            Text(
              '${i + 1}',
              style: const TextStyle(
                fontWeight: FontWeight.bold,
                fontSize: 25,
              ),
            ).applyConstraint(
              centerTo: rId(0),
              translate: circleTranslate(
                radius: 205,
                angle: (i + 1) * 30,
              ),
            ),
          for (int i = 0; i < 60; i++)
            if (i % 5 != 0)
              Transform.rotate(
                angle: pi + pi * (i * 6 / 180),
                child: Container(
                  color: Colors.grey,
                  margin: const EdgeInsets.only(
                    top: 405,
                  ),
                ),
              ).applyConstraint(
                width: 1,
                height: 415,
                centerTo: rId(0),
              ),
          Transform.rotate(
            angle: pi + pi * (hour * 30 / 180),
            alignment: Alignment.topCenter,
            child: Container(
              color: Colors.green,
            ),
          ).applyConstraint(
            width: 5,
            height: 80,
            centerTo: rId(0),
            translate: const Offset(0, 0.5),
            percentageTranslate: true,
          ),
          Transform.rotate(
            angle: pi + pi * (minute * 6 / 180),
            alignment: Alignment.topCenter,
            child: Container(
              color: Colors.pink,
            ),
          ).applyConstraint(
            width: 5,
            height: 120,
            centerTo: rId(0),
            translate: const Offset(0, 0.5),
            percentageTranslate: true,
          ),
          Transform.rotate(
            angle: pi + pi * (second * 6 / 180),
            alignment: Alignment.topCenter,
            child: Container(
              color: Colors.blue,
            ),
          ).applyConstraint(
            width: 5,
            height: 180,
            centerTo: rId(0),
            translate: const Offset(0, 0.5),
            percentageTranslate: true,
          ),
          Text(
            '$hour:$minute:$second',
            style: const TextStyle(
              fontSize: 40,
            ),
          ).applyConstraint(
            outTopCenterTo: rId(0),
            margin: const EdgeInsets.only(
              bottom: 250,
            ),
          )
        ],
      ),
    );
  }
}

Performance optimization

  1. When the layout is complex, if the child elements need to be repainted frequently, it is recommended to use RepaintBoundary to improve performance.

class OffPaintExample extends StatelessWidget {
  const OffPaintExample({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: ConstraintLayout(
          children: [
            Container(
              color: Colors.orangeAccent,
            ).offPaint().applyConstraint(
              width: 200,
              height: 200,
              topRightTo: parent,
            )
          ],
        ),
      ),
    );
  }
}
  1. Try to use const Widget. If you can’t declare a child element as const and it won’t change, you can use OffBuildWidget to avoid the rebuilding of the child element.

class OffBuildExample extends StatelessWidget {
  const OffBuildExample({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: ConstraintLayout(
          children: [

            /// subtrees that do not change
            Container(
              color: Colors.orangeAccent,
            ).offBuild(id: 'id').applyConstraint(
              width: 200,
              height: 200,
              topRightTo: parent,
            )
          ],
        ),
      ),
    );
  }
}

  1. Child elements will automatically become RelayoutBoundary unless width or height is wrapContent. The use of wrapContent can be reasonably reduced, because after the size of ConstraintLayout changes (usually the size of the window changes), all child elements whose width or height is wrapContent will be re-layout. And since the constraints passed to other child elements won’t change, no real re-layout will be triggered.

  2. If you use Guideline or Barrier in the children list, Element and RenderObject will inevitably be generated for them, which will be laid out but not drawn. At this point you can use GuidelineDefine or BarrierDefine to optimize it, no Element and RenderObject will be generated anymore:

class BarrierExample extends StatelessWidget {
  const BarrierExample({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    ConstraintId leftChild = ConstraintId('leftChild');
    ConstraintId rightChild = ConstraintId('rightChild');
    ConstraintId barrier = ConstraintId('barrier');
    return Scaffold(
      body: ConstraintLayout(
        childConstraints: [
          BarrierDefine(
            id: barrier,
            direction: BarrierDirection.bottom,
            referencedIds: [leftChild, rightChild],
          ),
        ],
        children: [
          Container(
            color: const Color(0xFF005BBB),
          ).applyConstraint(
            id: leftChild,
            width: 200,
            height: 200,
            topLeftTo: parent,
          ),
          Container(
            color: const Color(0xFFFFD500),
          ).applyConstraint(
            id: rightChild,
            width: 200,
            height: matchConstraint,
            centerRightTo: parent,
            heightPercent: 0.5,
            verticalBias: 0,
          ),
          const Text(
            'Align to barrier',
            style: TextStyle(
              fontSize: 40,
              color: Colors.blue,
            ),
          ).applyConstraint(
            centerHorizontalTo: parent,
            top: barrier.bottom,
          )
        ],
      ),
    );
  }
}

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Contact

hackware1993@gmail.com

License

MIT License

Copyright (c) 2022 hackware1993

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and
associated documentation files (the "Software"), to deal in the Software without restriction,
including without limitation the rights to use, copy, modify, merge, publish, distribute,
sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial
portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT
NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES
OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

GitHub

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