Shape Marker Pointer in Flutter Linear Gauge (SfLinearGauge)

3 Sep 202114 minutes to read

The LinearShapePointer in SfLinearGauge have the following pre-defined shapes to mark a specific value. The default shape pointer is invertedTriangle.

1. Triangle
2. Inverted Triangle
3. Circle
4. Diamond
5. Rectangle

The following is the default appearance of default shape pointer.

DART

@override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: Center(
          child: SfLinearGauge(
            markerPointers: [LinearShapePointer(value: 50)]
          ),
        ),
      ),
    );
  }

Change the size

The size of the marker pointer can be changed by the height and width properties of LinearShapePointer. The following code sample demonstrates how to change the size of a shape pointer.

DART

@override
  Widget build(BuildContext context) {
    return MaterialApp(
      color: Colors.white,
      home: Scaffold(
        body: Center(
          child: SfLinearGauge(markerPointers: [
            LinearShapePointer(value: 50, height: 25, width: 25)
          ]),
        ),
      ),
    );
  }

Customize color

The color of the shape pointer can be changed by the color property. The following code example demonstrates the same.

DART

@override
  Widget build(BuildContext context) {
    return MaterialApp(
      color: Colors.white,
      home: Scaffold(
        body: Center(
          child: SfLinearGauge(markerPointers: [
            LinearShapePointer(value: 50, color: Colors.redAccent)
          ]),
        ),
      ),
    );

Customize the border

The border can be customized by the borderColor and borderWidth properties of the LinearShapePointer.

DART

@override
  Widget build(BuildContext context) {
    return MaterialApp(
      color: Colors.white,
      home: Scaffold(
        body: Center(
          child: SfLinearGauge(markerPointers: [
            LinearShapePointer(
                value: 50, borderColor: Colors.redAccent, borderWidth: 2)
          ]),
        ),
      ),
    );
  }

Customize the elevation

The elevation can be customized by the elevation and elevationColor properties.

DART

@override
  Widget build(BuildContext context) {
    return MaterialApp(
      color: Colors.white,
      home: Scaffold(
        body: Center(
          child: Container(
            color: Colors.white,
            child: SfLinearGauge(markerPointers: [
              LinearShapePointer(
                  value: 50,
                  shapeType: LinearShapePointerType.circle,
                  elevation: 5,
                  elevationColor: Colors.blueGrey)
            ]),
          ),
        ),
      ),
    );
  }

Change marker alignment

The marker pointer alignment can be changed by the markerAlignment property of LinearShapePointer.The available marker pointer alignments are start, end, and center.

DART

@override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: Center(
          child: SfLinearGauge(axisTrackExtent: 30, markerPointers: [
            LinearShapePointer(
                value: 0, markerAlignment: LinearMarkerAlignment.start)
          ]),
        ),
      ),
    );
  }

Customize position

By default, the shape pointer is positioned outside the axis. This position can be changed by the position property of a LinearShapePointer. It is possible to position the shape pointer inside, cross, or outside the axis. The following code sample demonstrates how to change the shape pointer position to inside the axis.

DART

@override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: Center(
          child: SfLinearGauge(markerPointers: [
            LinearShapePointer(
                value: 55,
                shapeType: LinearShapePointerType.triangle,
                position: LinearElementPosition.inside)
          ]),
        ),
      ),
    );
  }

Customize offset

In addition to position the shape pointer, it is also possible to change the offset of the shape pointer. The offset is the distance from the axis and it cannot be negative and The cross positioned elements will not get affected by the offset value. The following code sample demonstrates how to change the offset value of the shape pointer.

DART

@override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: Center(
          child: SfLinearGauge(markerPointers: [
            LinearShapePointer(
                value: 50,
                offset: 25,
                shapeType: LinearShapePointerType.triangle,
                position: LinearElementPosition.inside)
          ]),
        ),
      ),
    );
  }

Drag behavior

You can drag the pointers freely to any position when adding multiple pointers by setting the dragBehavior property to LinearMarkerDragBehavior.free.

The LinearMarkerDragBehavior.constrained can be used to limit the active pointer dragging beyond the other pointers.

Free

DART

double _firstPointer = 30;
double _secondPointer = 70;

@override
Widget build(BuildContext context) {
  return Scaffold(
    body: SfLinearGauge(
      markerPointers: [
        LinearShapePointer(
          value: _firstPointer,
          height: 25,
          width: 25,
          shapeType: LinearShapePointerType.invertedTriangle,
          dragBehavior: LinearMarkerDragBehavior.free,
          onChanged: (double newValue) {
            setState(() {
              _firstPointer = newValue;
            });
          },
        ),
        LinearShapePointer(
          value: _secondPointer,
          height: 25,
          width: 25,
          shapeType: LinearShapePointerType.invertedTriangle,
          dragBehavior: LinearMarkerDragBehavior.free,
          onChanged: (double newValue) {
            setState(() {
              _secondPointer = newValue;
            });
          },
        ),
      ],
    ),
  );
}

Constrained

DART

double _firstPointer = 30;
double _secondPointer = 70;

@override
Widget build(BuildContext context) {
  return Scaffold(
    body: SfLinearGauge(
      markerPointers: [
        LinearShapePointer(
          value: _firstPointer,
          height: 25,
          width: 25,
          shapeType: LinearShapePointerType.invertedTriangle,
          dragBehavior: LinearMarkerDragBehavior.constrained,
          onChanged: (double newValue) {
            setState(() {
              _firstPointer = newValue;
            });
          },
        ),
        LinearShapePointer(
          value: _secondPointer,
          height: 25,
          width: 25,
          shapeType: LinearShapePointerType.invertedTriangle,
          dragBehavior: LinearMarkerDragBehavior.constrained,
          onChanged: (double newValue) {
            setState(() {
              _secondPointer = newValue;
            });
          },
        ),
      ],
    ),
  );
}

Handle onChangeStart, onChanged, and onChangeEnd callbacks

The LinearShapePointer provides the onChangeStart, onChanged, and onChangeEnd callbacks. The onChangeStart callback will be called when the user start dragging the pointer, the onChanged callback will be called when dragging the pointer and the onChangeEnd callback will be called when the user stops the pointer dragging.

DART

double _value = 50;

@override
Widget build(BuildContext context) {
  return Scaffold(
    body: SfLinearGauge(
      markerPointers: [
        LinearShapePointer(
          value: _value,
          onChangeStart: (double newValue) {
            _value = newValue;
          },
          onChanged: (double newValue) {
            setState(() {
              _value = newValue;
            });
          },
          onChangeEnd: (double newValue) {
            _value = newValue;
          },
          shapeType: LinearShapePointerType.invertedTriangle,
        ),
      ],
    ),
  );
}