Interaction in Flutter Linear Gauge (SfLinearGauge)

25 Aug 202112 minutes to read

The shape and widget marker pointers in a Linear Gauge can be moved from one value to another by swiping or drag gestures.

Interaction with marker pointers

The onChanged callback is used to change the value of the marker pointer at run-time.

The following code sample demonstrates how to update simple marker pointer value based on swipe or drag gestures.

DART

double shapePointerValue = 25;
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: Center(
          child: SfLinearGauge(
            markerPointers: [
              LinearShapePointer(
                  value: shapePointerValue,
                  //Changes the value of shape pointer based on interaction
                  onChanged: (value) {
                    setState(() {
                      shapePointerValue = value;
                    });
                  },
                  color: Colors.blue[800]),
            ],
          ),
        ),
      ),
    );
  }

The following code sample demonstrates how to update multiple marker pointer values based on swipe or drag gesture.

DART

double shapePointerValue = 85;
  double barPointerValue = 85;
  double widgetPointerValue = 26;
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
        home: Scaffold(
            body: Center(
			child: Column(
			children: [
			SfLinearGauge(
            barPointers: [LinearBarPointer(value: shapePointerValue)],
            markerPointers: [
              LinearShapePointer(
                value: shapePointerValue,
                onChanged: (value) {
                  setState(() {
                    shapePointerValue = value;
                  });
                },
                color: Colors.blue[800]
              ),
            ],
          ),
		  
          SizedBox(height: 30),
          SfLinearGauge(
            barPointers: [LinearBarPointer(value: barPointerValue)],
            markerPointers: [
              LinearWidgetPointer(
			  position: LinearElementPosition.outside,
			  value: barPointerValue,
			  onChanged: (value) {
                  setState(() {
                    barPointerValue = value;
                  });
                },
                child: Container(
                  height: 20,
                  width: 20,
                  decoration: BoxDecoration(
                      color: Colors.orange[500], shape: BoxShape.circle)
                ),
              ),
            ],
          ),
          SizedBox(height: 25),
          SfLinearGauge(
            axisTrackStyle: LinearAxisTrackStyle(
              thickness: 10
            ),
            markerPointers: [
              LinearShapePointer(
                value: widgetPointerValue,
                shapeType: LinearShapePointerType.invertedTriangle,
                position: LinearElementPosition.cross,
                onChanged: (value) {
                  setState(() {
                    widgetPointerValue = value;
                  });
                },
                color: widgetPointerValue < 40
                    ? Colors.green
                    : widgetPointerValue < 80
                        ? Colors.orange
                        : Colors.red
              ),
              LinearWidgetPointer(
                value: widgetPointerValue,
                onChanged: (value) {
                  setState(() {
                    widgetPointerValue = value;
                  });
                },
                child: Container(
                  width: 55,
                  height: 45,
                  child: Center(
                    child: Text(
                      widgetPointerValue.toStringAsFixed(0),
                      style: TextStyle(
                        fontWeight: FontWeight.w500,
                        fontSize: 20,
                        color: widgetPointerValue < 40
                            ? Colors.green
                            : widgetPointerValue < 80
                                ? Colors.orange
                                : Colors.red
                      ),
                    ),
                  ),
                ),
                position: LinearElementPosition.outside,
              ),
            ],
            ranges: [
              LinearGaugeRange(
                  endValue: widgetPointerValue,
                  color: widgetPointerValue < 40
                      ? Colors.green
                      : widgetPointerValue < 80
                          ? Colors.orange
                          : Colors.red,
                  position: LinearElementPosition.cross)
            ],
          ),
        ],
        mainAxisAlignment: MainAxisAlignment.center
    )),    
	)
);