Flutter通过Container实现时间轴效果

时间轴是前端UI经常用到的效果，先看下效果图:

时间轴的特点
1、在列表中的高度不确定，高度取决于右侧 item 的高度
2、时间轴通常在第一个 item 中的样式和其他 item 中不同。

实现

一、借助 Container 中 decoration 属性，设置左侧的 border，可以实现时间轴高度随着 item 变化效果

      Center(
          child: Container(
        width: 100,
        height: 100,
        decoration: BoxDecoration(
        // 设置 BoxDecoration 的 border, border  的高度就是 Container 的高度
          border: Border(left: BorderSide(color: Colors.red)),
          color: Color(0x11000000),
        ),
      ))

效果 (图中红线是 Container 左侧的 border，可以在这里扩展成 timeline) :

二、重写 BorderDirectional 中 paint 方法

BorderDirectional 中原来的 paint 方法，可以看出，设置不同的属性，会调用不同的绘制方法实现不同的效果，这里重新 paint 方法，实现时间轴的效果

paint 方法中参数
canvas ： 这个就是画布了，借助这个 canvas 可以随意实现各种效果
rect : Container 的范围大小

我们的 paint 方法实现，按照 UI 设计图，对应的位置画上圆和线就可以了

  @override
  void paint(Canvas canvas, Rect rect, {TextDirection? textDirection, BoxShape shape = BoxShape.rectangle, BorderRadius? borderRadius}) {
    if (position != 1) {
      canvas.drawLine(Offset(rect.left+margin + radius / 2, rect.top), Offset(rect.left +margin+ radius / 2, rect.bottom), _strokePaint());
      canvas.drawCircle(Offset(rect.left +margin+ radius / 2, rect.top + radius * 2), radius, _fillPaint());
      canvas.drawCircle(Offset(rect.left +margin+ radius / 2, rect.top + radius * 2), radius,_strokePaint());
    } else {
      canvas.drawLine(Offset(rect.left+margin + radius / 2, rect.top + radius * 2), Offset(rect.left+margin + radius / 2, rect.bottom), _strokePaint());
      canvas.drawCircle(Offset(rect.left+margin + radius / 2, rect.top + radius * 2), radius, _fillPaint());
      canvas.drawCircle(Offset(rect.left +margin+ radius / 2, rect.top + radius * 2), radius, _strokePaint());
      canvas.drawCircle(Offset(rect.left +margin+ radius / 2, rect.top + radius * 2), radius / 2, _strokePaint());
    }
  }

最终效果

三、完整代码

class BorderTimeLine extends BorderDirectional {
  int position;

  BorderTimeLine(this.position);

  double radius = 10;
  double margin= 20;
  Paint _paint = Paint()
    ..color = Color(0xFFDDDDDD)
    ..strokeWidth = 1;

  @override
  void paint(Canvas canvas, Rect rect, {TextDirection? textDirection, BoxShape shape = BoxShape.rectangle, BorderRadius? borderRadius}) {
    if (position != 0) {
      canvas.drawLine(Offset(rect.left+margin + radius / 2, rect.top), Offset(rect.left +margin+ radius / 2, rect.bottom), _strokePaint());
      canvas.drawCircle(Offset(rect.left +margin+ radius / 2, rect.top + radius * 2), radius, _fillPaint());
      canvas.drawCircle(Offset(rect.left +margin+ radius / 2, rect.top + radius * 2), radius,_strokePaint());
    } else {
      canvas.drawLine(Offset(rect.left+margin + radius / 2, rect.top + radius * 2), Offset(rect.left+margin + radius / 2, rect.bottom), _strokePaint());
      canvas.drawCircle(Offset(rect.left+margin + radius / 2, rect.top + radius * 2), radius, _fillPaint());
      canvas.drawCircle(Offset(rect.left +margin+ radius / 2, rect.top + radius * 2), radius, _strokePaint());
      canvas.drawCircle(Offset(rect.left +margin+ radius / 2, rect.top + radius * 2), radius / 2, _strokePaint());
    }
  }

  Paint _fillPaint(){
    _paint.color=Colors.white;
    _paint.style=PaintingStyle.fill;
    return _paint;
  }
  Paint _strokePaint(){
    _paint.color=Color(0xFFDDDDDD);
    _paint.style=PaintingStyle.stroke;
    return _paint;
  }
}

在 ListView 中的 item 中使用

  Widget _buildItem(BuildContext c, int i) {
    return Container(
        width: double.infinity,
        padding: EdgeInsets.symmetric(horizontal: 20),
        decoration: BoxDecoration(border: BorderTimeLine(i)),
        child: Padding(
          padding: const EdgeInsets.symmetric(horizontal: 20),
          child: Column(crossAxisAlignment: CrossAxisAlignment.start, mainAxisSize: MainAxisSize.min, children: [
            Padding(padding: EdgeInsets.symmetric(vertical: 10)),
            Divider(color: Colors.grey.shade300, thickness: 40),
            Text("$i" * 6, style: TextStyle(color: Colors.black, fontSize: 16)),
            Text("abc\n" * Random().nextInt(10)),
            Padding(padding: EdgeInsets.symmetric(vertical: 10)),
          ]),
        ));
  }

全部代码 github

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