如何使用Flutter实现手写签名效果

目录

思路

需要监听用户触摸的起始点和结束点，并记录途经点，这里我使用了StreamController将途经点从起始位置到结束位置绘制出来，这里用到CustomPainter

绘制流程

获取触摸点作为画笔的起始点手机途经点绘制途径路线结束触摸点重置画笔

具体实现

需要一个Listener用来监听用户行为，并将这些行为的点添加到StreamController中，>

final List _points = []; //承载对应的点
final StreamController _controller = StreamController(); //数据通信

Widget _buildWriteWidget() {
  return Stack(
    children: [
      Listener( //用来监听用户的触摸行为
        child: Container(
          color: Colors.transparent,
        ),
        onPointerDown: (PointerDownEvent event) {
          _points.add(event.localPosition);
          _controller.sink.add([_points]);  //起始点的记录
        },
        onPointerMove: (PointerMoveEvent event) {
          _points.add(event.localPosition);
          _controller.sink.add([_points]);  //添加途经点
        },
        onPointerUp: (PointerUpEvent event) {
          _points.add(Offset.zero); //结束的标记
        },
      ),
      StreamBuilder(
          stream: _controller.stream,
          builder: (BuildContext context, AsyncSnapshot snapshot) {
            return snapshot.hasData
                ? CustomPaint(painter: LinePainter(snapshot.data))  //关联数据到Painter
                : const SizedBox();
          }),
      Positioned(
          bottom: 50,
          right: 50,
          child: FloatingActionButton(
            onPressed: () {
              _clear();
            },
            child: const Icon(Icons.cleaning_services),
          ))
    ],
  );
}

清除StreamController的内容，重置数据

void _clear() {
  _points.clear();
  _controller.add(null);
}

dispose时释放StreamController

@override
void dispose() {
  _controller.close();
  super.dispose();
}

画笔Painter

class LinePainter extends CustomPainter {
  final List<List<Offset>> lines;
  final Color paintColor = Colors.black;
  final Paint _paint = Paint();

  LinePainter(this.lines);

  @override
  void paint(Canvas canvas, Size size) {
    _paint.strokeCap = StrokeCap.round;
    _paint.strokeWidth = 5.0;
    if (lines.isEmpty) {
      canvas.drawPoints(PointMode.polygon, [Offset.zero, Offset.zero], _paint);
    } else {
      for (int i = 0; i < lines.length; i++) {
        for (int j = 0; j < lines[i].length - 1; j++) {
          if (lines[i][j] != Offset.zero && lines[i][j + 1] != Offset.zero) {
            canvas.drawLine(lines[i][j], lines[i][j + 1], _paint);  //绘制相应的点
          }
        }
      }
    }
  }

  @override
  bool shouldRepaint(covariant CustomPainter oldDelegate) => true;
}

总结

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