StreamControllerCustomPainter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
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();
}
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;
}
