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基于Flutter实现按位置大小比例布局的控件

作者:CodeOfCC

做视频监控项目时需要需要展示多分屏,比如2x2、3x3、414等等,所以本文为大家介绍了如何基于Flutter实现按位置大小比例布局的控件,需要的可以参考一下

前言

做视频监控项目时需要需要展示多分屏,比如2x2、3x3、414等等,如果每一种分屏都单独实现会很麻烦,而且不能支持用户定制。最好的方式还是实现一个通用的分屏容器,而且采样比例计算位置大小,可以适配任意尺寸。

一、如何实现

最直观的实现方式是获取控件宽高然后按比例计算,但是flutter在build的时候无法获取位置宽高信息,只有绘制之后才能获取,所以这种方式并不容易实现,比较简单的方式应该是使用Row、Column结合Flexible。

1、数值转成分数

需要转换的数值

 final Rect rect; //子控件位置大小,比例值范围0-1

定义一个分数对象

//分数
class Rational {
  int den = 1; //分母
  int num = 0; //分子
  Rational(this.num, this.den);
  //通过double构造,accuracy小数点后精度
  factory Rational.fromDouble(double d, {int accuracy = 5}) {
    int den = 1;
    while (d > d.toInt() && accuracy-- > 0) {
      d *= 10;
      den *= 10;
    }
    return Rational(d.toInt(), den);
  }
}

转成分数并对齐分母

    //将位置大小转成分数
    final width = Rational.fromDouble(rect.width);
    final x = Rational.fromDouble(rect.left);
    final height = Rational.fromDouble(rect.height);
    final y = Rational.fromDouble(rect.top);
    //对齐分母
    if (width.den != x.den) {
      final den = width.den;
      width.den *= x.den;
      width.num *= x.den;
      x.den *= den;
      x.num *= den;
    }
    //对齐分母
    if (height.den != y.den) {
      final den = height.den;
      height.den *= y.den;
      height.num *= y.den;
      y.den *= den;
      y.num *= den;
    }

2、Row+Flexible布局横向

我们利用Row的自动布局,以及Flexible的比例布局的特性,根据上面的分数计算出控件比例的位置大小对应的flex值即可。

 Row(
      children: [
        Flexible(
          flex: x.num,
          child: Container(),
        ),
        Flexible(
          flex: width.num,
          child: child/*子控件,加上纵向布局则是Column*/
        ),
        Flexible(flex: width.den - width.num - x.num, child: Container()),
      ],
    );
  }

3、Column+Flexible布局纵向

我们利用Column的自动布局,以及Flexible的比例布局的特性,根据上面的分数计算出控件比例的位置大小对应的flex值即可。

Column(
            children: [
              Flexible(
                flex: y.num,
                child: Container(),
              ),
              Flexible(flex: height.num, child: child/*子控件*/),
              Flexible(
                flex: height.den - height.num - y.num,
                child: Container(),
              ),
            ],
          )

二、完整代码

proportion.dart

import 'package:flutter/material.dart';
//比例布局控件,
class Proportion extends StatelessWidget {
  final Rect rect; //位置大小,比例值范围0-1
  final Widget child;
  const Proportion({
    super.key,
    this.rect = const Rect.fromLTWH(0, 0, 1, 1),
    required this.child,
  });
  @override
  Widget build(BuildContext context) {
    //实现按比例显示布局
    final width = Rational.fromDouble(rect.width);
    final x = Rational.fromDouble(rect.left);
    final height = Rational.fromDouble(rect.height);
    final y = Rational.fromDouble(rect.top);
    if (width.den != x.den) {
      final den = width.den;
      width.den *= x.den;
      width.num *= x.den;
      x.den *= den;
      x.num *= den;
    }
    if (height.den != y.den) {
      final den = height.den;
      height.den *= y.den;
      height.num *= y.den;
      y.den *= den;
      y.num *= den;
    }
    return Row(
      children: [
        Flexible(
          flex: x.num,
          child: Container(),
        ),
        Flexible(
          flex: width.num,
          child: Column(
            children: [
              Flexible(
                flex: y.num,
                child: Container(),
              ),
              Flexible(flex: height.num, child: child),
              Flexible(
                flex: height.den - height.num - y.num,
                child: Container(),
              ),
            ],
          ),
        ),
        Flexible(flex: width.den - width.num - x.num, child: Container()),
      ],
    );
  }
}
//分数
class Rational {
  int den = 1; //分母
  int num = 0; //分子
  Rational(this.num, this.den);
  //通过double构造,accuracy小数点后精度
  factory Rational.fromDouble(double d, {int accuracy = 5}) {
    int den = 1;
    while (d > d.toInt() && accuracy-- > 0) {
      d *= 10;
      den *= 10;
    }
    return Rational(d.toInt(), den);
  }
}

常用布局(可选)

proportions.dart

import 'package:flutter/material.dart';
import 'proportion.dart';
//常用布局,需配合stack作为父容器使用
class Proportions {
  Proportions._();
  //全屏
  static List<Proportion> fullScreen({
    required Widget child,
  }) =>
      [
        Proportion(
          rect: const Rect.fromLTWH(0, 0, 1, 1),
          child: child,
        )
      ];
  //二分屏
  static List<Proportion> halfScreen({
    required Widget left,
    required Widget right,
  }) =>
      [
        Proportion(
          rect: const Rect.fromLTWH(0, 0, 0.5, 1),
          child: left,
        ),
        Proportion(
          rect: const Rect.fromLTWH(0.5, 0, 0.5, 1),
          child: right,
        ),
      ];
  //四分屏
  static List<Proportion> quadScreen({
    required List<Widget> children,
  }) {
    return [
      Proportion(
        rect: const Rect.fromLTWH(0, 0, 0.5, 0.5),
        child: children[0],
      ), //左上
      Proportion(
        rect: const Rect.fromLTWH(0.5, 0, 0.5, 0.5),
        child: children[1],
      ), //右上
      Proportion(
        rect: const Rect.fromLTWH(0, 0.5, 0.5, 0.5),
        child: children[2],
      ), //左下
      Proportion(
        rect: const Rect.fromLTWH(0.5, 0.5, 0.5, 0.5),
        child: children[3],
      ), //右下
    ];
  }
  //6  分屏
  static List<Proportion> sixScreen({
    required List<Widget> children,
  }) {
    return [
      Proportion(
        rect: const Rect.fromLTWH(0, 0, 0.666, 0.666),
        child: children[0],
      ), //左上
      Proportion(
        rect: const Rect.fromLTWH(0.666, 0, 0.333, 0.333),
        child: children[1],
      ), //右上
      Proportion(
        rect: const Rect.fromLTWH(0.666, 0.333, 0.333, 0.333),
        child: children[2],
      ), //右中
      Proportion(
        rect: const Rect.fromLTWH(0.666, 0.666, 0.333, 0.333),
        child: children[3],
      ), //右下
      Proportion(
        rect: const Rect.fromLTWH(0.333, 0.666, 0.333, 0.333),
        child: children[4],
      ), //中下
      Proportion(
        rect: const Rect.fromLTWH(0, 0.666, 0.333, 0.333),
        child: children[5],
      ), //左下
    ];
  }
  //8  分屏
  static List<Proportion> eightScreen({
    required List<Widget> children,
  }) {
    return [
      Proportion(
        rect: const Rect.fromLTWH(0, 0, 0.75, 0.75),
        child: children[0],
      ), //左上
      Proportion(
        rect: const Rect.fromLTWH(0.75, 0, 0.25, 0.25),
        child: children[1],
      ), //右上
      Proportion(
        rect: const Rect.fromLTWH(0.75, 0.25, 0.25, 0.25),
        child: children[2],
      ), //右中1
      Proportion(
        rect: const Rect.fromLTWH(0.75, 0.5, 0.25, 0.25),
        child: children[3],
      ), //右中2
      Proportion(
        rect: const Rect.fromLTWH(0.75, 0.75, 0.25, 0.25),
        child: children[4],
      ), //右下
      Proportion(
        rect: const Rect.fromLTWH(0.5, 0.75, 0.25, 0.25),
        child: children[5],
      ), //中下2
      Proportion(
        rect: const Rect.fromLTWH(0.25, 0.75, 0.25, 0.25),
        child: children[6],
      ), //中下1
      Proportion(
        rect: const Rect.fromLTWH(0, 0.75, 0.25, 0.25),
        child: children[7],
      ), //左下
    ];
  }
  //9  分屏
  static List<Proportion> nightScreen({
    required List<Widget> children,
  }) {
    int n = 0;
    return [
      ...children.getRange(0, 9).map(
        (element) {
          final i = n++;
          return Proportion(
            rect: Rect.fromLTWH(
              (i % 3) * 0.333,
              (i ~/ 3) * 0.333,
              0.333,
              0.333,
            ),
            child: element,
          );
        },
      )
    ];
  }
  //16  分屏
  static List<Proportion> sixteenScreen({
    required List<Widget> children,
  }) {
    int n = 0;
    return [
      ...children.getRange(0, 16).map(
        (element) {
          final i = n++;
          return Proportion(
            rect: Rect.fromLTWH((i % 4) * 0.25, (i ~/ 4) * 0.25, 0.25, 0.25),
            child: element,
          );
        },
      )
    ];
  }
  //414分屏
  static List<Proportion> fourOneFourScreen({
    required List<Widget> children,
  }) {
    int n = 0;
    return [
      //左4
      ...children.getRange(0, 4).map(
        (element) {
          final i = n++;
          return Proportion(
            rect: Rect.fromLTWH((i ~/ 4) * 0.25, (i % 4) * 0.25, 0.25, 0.25),
            child: element,
          );
        },
      ),
      //中间
      Proportion(
        rect: const Rect.fromLTWH(0.25, 0, 0.5, 1),
        child: children[4],
      ),
      //右边4
      ...children.getRange(5, 9).map(
        (element) {
          final i = n++ + 8;
          return Proportion(
            rect: Rect.fromLTWH((i ~/ 4) * 0.25, (i % 4) * 0.25, 0.25, 0.25),
            child: element,
          );
        },
      )
    ];
  }
}

三、使用示例

1、基本用法

设置子控件位置大小。一般配合stack作为父容器使用

    Proportion(
      rect: Rect.fromLTRB(0, 0, 0.5, 0.5), //子控件位置大小,(0, 0, 0.5, 0.5)表示左上1/4的区域
      child: ColoredBox(color: Colors.red), //子控件
    );

2、四分屏

final List<int> _nums = [1, 2, 3, 4, 5, 6, 7, 8, 9];
 Stack(
            children: Proportions.quadScreen(children: [
          ..._nums.map((e) => Container(
                constraints: const BoxConstraints.expand(),
                decoration: BoxDecoration(
                    border: Border.all(color: Colors.deepPurple.shade300)),
                child: Center(child: Text("video $e")),
              ))

3、六分屏

final List<int> _nums = [1, 2, 3, 4, 5, 6, 7, 8, 9];
 Stack(
            children: Proportions.sixScreen(children: [
          ..._nums.map((e) => Container(
                constraints: const BoxConstraints.expand(),
                decoration: BoxDecoration(
                    border: Border.all(color: Colors.deepPurple.shade300)),
                child: Center(child: Text("video $e")),
              ))

4、八分屏

final List<int> _nums = [1, 2, 3, 4, 5, 6, 7, 8, 9];
 Stack(
            children: Proportions.eightScreen(children: [
          ..._nums.map((e) => Container(
                constraints: const BoxConstraints.expand(),
                decoration: BoxDecoration(
                    border: Border.all(color: Colors.deepPurple.shade300)),
                child: Center(child: Text("video $e")),
              ))

5、九分屏

final List<int> _nums = [1, 2, 3, 4, 5, 6, 7, 8, 9];
 Stack(
            children: Proportions.nightScreen(children: [
          ..._nums.map((e) => Container(
                constraints: const BoxConstraints.expand(),
                decoration: BoxDecoration(
                    border: Border.all(color: Colors.deepPurple.shade300)),
                child: Center(child: Text("video $e")),
              ))

6、414分屏

final List<int> _nums = [1, 2, 3, 4, 5, 6, 7, 8, 9];
 Stack(
            children: Proportions.fourOneFourScreen(children: [
          ..._nums.map((e) => Container(
                constraints: const BoxConstraints.expand(),
                decoration: BoxDecoration(
                    border: Border.all(color: Colors.deepPurple.shade300)),
                child: Center(child: Text("video $e")),
              ))

始终保持比例

总结

以上就是今天要讲的内容,本文用的是比较简单的方式实现了比例布局控件,其主要特点是可以灵活使用,尤其是方便视频分屏预览的实现。本质上也是对一类布局规则的总结得出的一个通用的控件,因为考虑到2x2、3x3还是可以写死的,但是到了4x4、5x5写死则需要16、25个参数,那就必须改用数组,也就意味着需要根据规则计算位置,那和本文一样了。所以本文的控件是有实际使用意义的。

到此这篇关于基于Flutter实现按位置大小比例布局的控件的文章就介绍到这了,更多相关Flutter布局控件内容请搜索脚本之家以前的文章或继续浏览下面的相关文章希望大家以后多多支持脚本之家!

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