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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