Flutter-自定义折叠流布局实现-阿里云开发者社区

需求

在 Flutter 开发中，常常需要实现自定义布局以满足不同的需求。本文将介绍如何通过自定义组件实现一个折叠流布局，该组件能够显示一系列标签，并且在内容超出一定行数时，可以展开和收起。

效果

该折叠流布局可以显示一组标签，并在标签数量超过指定行数时提供展开和收起功能。初始状态下只显示限定行数的标签，并在最后一个位置显示展开按钮。点击展开按钮可以显示全部标签，再次点击展开按钮可以收起标签。

效果图如下：

实现思路

实现一个自定义的折叠流布局组件需要以下几个步骤：

创建一个 TagFlowWidget 组件，接受标签数据、最大行数和样式等参数。
在 TagFlowWidget 组件中使用 Flow 布局，并实现自定义的 FlowDelegate 来处理标签布局和展开收起逻辑。
在 FlowDelegate 中计算当前显示的行数，根据行数决定是否显示展开或收起按钮。

具体实现包括以下关键部分：

TagFlowWidget 组件的构建逻辑
自定义 FlowDelegate 的布局和绘制逻辑
展开和收起状态的管理

实现代码

下面是完整的实现代码，包括 TagFlowWidget 组件和 TagFlowDelegate 代理类。

import 'package:flutter/material.dart';

class TagFlowWidget extends StatefulWidget {
  final List<String> items;
  final int maxRows;
  final double spaceHorizontal;
  final double spaceVertical;
  final double itemHeight;
  final Color? itemBgColor;
  final BorderRadiusGeometry? borderRadius;
  final double? horizontalPadding;
  final TextStyle? itemStyle;

  const TagFlowWidget({
    Key? key,
    required this.items,
    required this.maxRows,
    required this.itemHeight,
    this.borderRadius,
    this.horizontalPadding,
    this.spaceHorizontal = 0,
    this.spaceVertical = 0,
    this.itemBgColor,
    this.itemStyle,
  }) : super(key: key);

  @override
  TagFlowWidgetState createState() => TagFlowWidgetState();
}

class TagFlowWidgetState extends State<TagFlowWidget> {
  bool isExpanded = false;

  @override
  Widget build(BuildContext context) {
    return LayoutBuilder(
      builder: (BuildContext context, BoxConstraints constraints) {
        final maxWidth = constraints.maxWidth;
        return Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          mainAxisSize: MainAxisSize.max,
          children: [
            Flow(
              delegate: TagFlowDelegate(
                maxRows: widget.maxRows,
                isExpanded: isExpanded,
                maxWidth: maxWidth,
                itemHeight: widget.itemHeight,
                spaceHorizontal: widget.spaceHorizontal,
                spaceVertical: widget.spaceVertical,
                itemCount: widget.items.length,
              ),
              children: [
                ...widget.items.map((item) {
                  return Container(
                      padding: EdgeInsets.symmetric(
                        horizontal: widget.horizontalPadding ?? 0,
                      ),
                      height: widget.itemHeight,
                      decoration: BoxDecoration(
                        color: widget.itemBgColor,
                        borderRadius: widget.borderRadius,
                      ),
                      child: Column(
                        mainAxisSize: MainAxisSize.max,
                        crossAxisAlignment: CrossAxisAlignment.center,
                        mainAxisAlignment: MainAxisAlignment.center,
                        children: [
                          Text(
                            item,
                            style: widget.itemStyle,

                          ),
                        ],
                      ));
                }).toList(),
                GestureDetector(
                  behavior: HitTestBehavior.opaque,
                  onTap: () {
                    setState(() {
                      isExpanded = !isExpanded;
                    });
                  },
                  child: Container(
                    padding: EdgeInsets.symmetric(
                      horizontal: widget.horizontalPadding ?? 0,
                    ),
                    height: widget.itemHeight,
                    decoration: BoxDecoration(
                      color: widget.itemBgColor,
                      borderRadius: widget.borderRadius,
                    ),
                    child: Icon(
                      isExpanded
                          ? Icons.keyboard_arrow_up
                          : Icons.keyboard_arrow_down,
                    ),
                  ),
                ),
              ],
            ),
          ],
        );
      },
    );
  }
}

class TagFlowET {
  static int maxRowCount = 0;
}

class TagFlowDelegate extends FlowDelegate {
  final double maxWidth;
  final double spaceHorizontal;
  final double spaceVertical;
  int maxRows;
  final bool isExpanded;
  double height = 0;
  final double itemHeight;
  final int itemCount;

  TagFlowDelegate({
    required this.maxWidth,
    required this.itemCount,
    required this.spaceHorizontal,
    required this.spaceVertical,
    required this.maxRows,
    required this.isExpanded,
    required this.itemHeight,
  }) {
    if (!isExpanded) {
      TagFlowET.maxRowCount = maxRows;
    }
  }

  @override
  void paintChildren(FlowPaintingContext context) {
    TagFlowET.maxRowCount = _getMaxRowCount(context);
    if (maxRows >= TagFlowET.maxRowCount) {
      maxRows = TagFlowET.maxRowCount;
    }
    double x = 0;
    double y = 0;
    double rowHeight = 0;
    int rowCount = 1;
    for (int i = 0; i < context.childCount; i++) {
      final childSize = context.getChildSize(i)!;
      final arrowBtnSize = context.getChildSize(context.childCount - 1)!;

      if (rowCount >= maxRows &&
          !isExpanded &&
          (x + childSize.width + arrowBtnSize.width) >= maxWidth) {
        context.paintChild(
          context.childCount - 1,
          transform: Matrix4.translationValues(x, y, 0),
        );
        break;
      }

      if (x + childSize.width > maxWidth) {
        x = 0;
        y += rowHeight + spaceVertical;
        rowHeight = 0;
        rowCount++;
      }

      if (!(i == context.childCount - 1 && isExpanded && rowCount <= maxRows)) {
        context.paintChild(
          i,
          transform: Matrix4.translationValues(x, y, 0),
        );
      }

      x += childSize.width + spaceHorizontal;
      rowHeight = childSize.height;
    }
  }

  int _getMaxRowCount(FlowPaintingContext context) {
    double x = 0;
    var rowCount = 1;
    for (int i = 0; i < context.childCount; i++) {
      final childSize = context.getChildSize(i)!;
      final arrowSize = context.getChildSize(context.childCount - 1)!;
      if (x + childSize.width > maxWidth) {
        x = 0;
        rowCount++;
      }
      if (i == context.childCount - 1 &&
          (x + childSize.width + arrowSize.width) > maxWidth) {
        rowCount++;
      }
      x += childSize.width + spaceHorizontal;
    }
    return rowCount;
  }

  @override
  Size getSize(BoxConstraints constraints) {
    final height = (itemHeight * TagFlowET.maxRowCount) +
        (spaceVertical * (TagFlowET.maxRowCount - 1));
    return Size(constraints.maxWidth, height);
  }

  @override
  bool shouldRelayout(covariant FlowDelegate oldDelegate) {
    return oldDelegate != this ||
        (oldDelegate as TagFlowDelegate).isExpanded != isExpanded;
  }

  @override
  bool shouldRepaint(covariant FlowDelegate oldDelegate) {
    return oldDelegate != this ||
        (oldDelegate as TagFlowDelegate).isExpanded != isExpanded;
  }
}

具体使用

import 'package:flutter/material.dart';
import 'package:flutter_xy/widgets/xy_app_bar.dart';
import 'package:flutter_xy/xydemo/flow/tag_flow_view.dart';

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

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: XYAppBar(
            title: '折叠标签',
            onBack: () {
              Navigator.pop(context);
            }),
        body: Container(
            padding: const EdgeInsets.all(16.0),
            child: Column(
              children: [
                TagFlowWidget(
                  items: const [
                    '衣服',
                    'T恤宽松男',
                    '男鞋',
                    '香蕉苹果',
                    '休闲裤',
                    '牛仔裤',
                    '红薯',
                    '红薯',
                    '红薯',
                    '红薯',
                    '西红柿',
                    '更多商品',
                    '热销商品',
                    '最新商品',
                    '特价商品',
                    '限时特价商品',
                    '限时商品',
                    '热门商品',
                  ],
                  maxRows: 3,
                  spaceHorizontal: 8,
                  spaceVertical: 8,
                  itemHeight: 30,
                  horizontalPadding: 8,
                  itemBgColor: Colors.lightBlue.withAlpha(30),
                  itemStyle: const TextStyle(height: 1.1),
                  borderRadius: const BorderRadius.all(Radius.circular(8)),
                ),
              ],
            )),
      ),
    );
  }
}

通过上述代码，我们实现了一个自定义的折叠流布局组件 TagFlowWidget，并通过 TagFlowDelegate 来控制标签的布局和展开收起的逻辑。希望这篇文章对你在 Flutter 开发中的自定义布局实现有所帮助。

详情见：github.com/yixiaolunhui/flutter_xy

Flutter-自定义折叠流布局实现

需求

效果

实现思路

实现代码

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