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， 两个变量
final List _points = []; //承载对应的点
final StreamController _controller = StreamController(); //数据通信
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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
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void _clear() { _points.clear(); _controller.add(null); } |
dispose时释放StreamController
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@override void dispose() { _controller.close(); super.dispose(); } |
画笔Painter
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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; } |
