Flutter 中通過 Container 實現時間軸效果

時間軸是前端UI經常用的，先看下效果圖:

時間軸的特點 1、在列表中的高度不確定，高度取決於右側 item 的高度 2、時間軸通常在第一個 item 中的樣式和其他 item 中不同。

實現

一、藉助 Container 中 decoration 屬性，設定左側的 border，可以實現時間軸高度隨著 item 變化效果

      Center(
          child: Container(
        width: 100,
        height: 100,
        decoration: BoxDecoration(
          border: Border(left: BorderSide(color: Colors.red)),
          color: Color(0x11000000),
        ),
      ))
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效果 :

二、重寫 BorderDirectional 中 paint 方法

BorderDirectional 中原來的 paint 方法，可以看出，設定不同的屬性，會呼叫不同的繪製方法實現不同的效果，這裡重新 paint 方法，實現時間軸的效果

paint 方法中引數 canvas ： 這個就是畫布了，藉助這個 canvas 可以隨意實現各種效果 rect : Container 的範圍大小

我們的 paint 方法實現，按照 UI 設計圖，對應的位置畫上圓和線就可以了

  @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());
    }
  }
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最終效果

三、完整程式碼

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;
  }
}
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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)),
          ]),
        ));
  }
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