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How to change radial gauge's value with the mouse/keyboard


Product RadRadialGauge for WinForms


This article demonstrates a sample approach how to change the value of RadRadialGauge by handling user's mouse/keyboard input.


We will detect when the user either moves the mouse, keeping pressed the left mouse button or presses the up/down arrow keys. The below gif file illustrates the achieved behavior:

radialgauge-value-changes 001

Changing the Value with the Mouse

Handle the MouseMove event and check whether the left mouse button is pressed. Then, calculate the new gauge's value considering the angle of the current mouse location to the center of the gauge.

protected override void OnLoad(EventArgs e)

    this.radRadialGauge1.MouseMove += radRadialGauge1_MouseMove; 
    this.radialGaugeNeedle1.BindValue = true;

private void radRadialGauge1_MouseMove(object sender, MouseEventArgs e)
    if (e.Button == System.Windows.Forms.MouseButtons.Left)

private void UpdateValue(Point pointLocation)
    float centerX = this.radRadialGauge1.GaugeElement.GaugeCenter.X + this.radialGaugeNeedle1.TotalTransform.DX;
    float centerY = this.radRadialGauge1.GaugeElement.GaugeCenter.Y + this.radialGaugeNeedle1.TotalTransform.DY;
    PointF center = new PointF(centerX, centerY);

    double radian = Math.Atan2(pointLocation.Y - center.Y, pointLocation.X - center.X);
    double angle = radian * (180 / Math.PI);
    if (angle < 0.0)
        angle += 360.0;

    float newValue = CalculateValueByAngle(angle, this.radRadialGauge1.RangeStart, this.radRadialGauge1.RangeEnd, this.radRadialGauge1.StartAngle, this.radRadialGauge1.SweepAngle);
    this.radRadialGauge1.Value = Math.Min(newValue, (float)this.radRadialGauge1.RangeEnd);

public float CalculateValueByAngle(double needleAngleDegree, double rangeStart, double rangeEnd, double startAngle, double sweepAngle)
    float value = 0;
    double angleDiff = needleAngleDegree - startAngle;
    if (angleDiff < 0)
        angleDiff += 360;
    double ratio = (angleDiff) / sweepAngle;
    value = (float)(ratio * Math.Abs(rangeEnd - rangeStart) + rangeStart);
    return value;

Private Sub radRadialGauge1_MouseMove(ByVal sender As Object, ByVal e As MouseEventArgs)
    If e.Button = System.Windows.Forms.MouseButtons.Left Then
    End If
End Sub
Private Sub UpdateValue(ByVal pointLocation As Point)
    Dim centerX As Single = Me.RadRadialGauge1.GaugeElement.GaugeCenter.X + Me.RadialGaugeNeedle1.TotalTransform.DX
    Dim centerY As Single = Me.RadRadialGauge1.GaugeElement.GaugeCenter.Y + Me.RadialGaugeNeedle1.TotalTransform.DY
    Dim center As PointF = New PointF(centerX, centerY)
    Dim radian As Double = Math.Atan2(pointLocation.Y - center.Y, pointLocation.X - center.X)
    Dim angle As Double = radian * (180 / Math.PI)
    If angle < 0.0 Then
        angle += 360.0
    End If
    Dim newValue As Single = CalculateValueByAngle(angle, Me.RadRadialGauge1.RangeStart, Me.RadRadialGauge1.RangeEnd, Me.RadRadialGauge1.StartAngle, Me.RadRadialGauge1.SweepAngle)
    Me.RadRadialGauge1.Value = Math.Min(newValue, CSng(Me.RadRadialGauge1.RangeEnd))
End Sub
Public Function CalculateValueByAngle(ByVal needleAngleDegree As Double, ByVal rangeStart As Double, ByVal rangeEnd As Double, ByVal startAngle As Double, ByVal sweepAngle As Double) As Single
    Dim value As Single = 0
    Dim angleDiff As Double = needleAngleDegree - startAngle
    If angleDiff < 0 Then
        angleDiff += 360
    End If
    Dim ratio As Double = (angleDiff) / sweepAngle
    value = CSng((ratio * Math.Abs(rangeEnd - rangeStart) + rangeStart))
    Return value
End Function

Changing the Value with the Keyboard

Add a timer to detect whether the up/down arrow key is pressed in order to adjust the value of RadRadialGauge. In the PreviewKeyDown event you can enable a flag to distinguish which arrow key is pressed. It is necessary to stop the timer when you release the mouse:

Private timer As Timer = New Timer()
Public Sub New()
    AddHandler Me.RadRadialGauge1.MouseMove, AddressOf radRadialGauge1_MouseMove
    Me.RadialGaugeNeedle1.BindValue = True
    AddHandler Me.RadRadialGauge1.PreviewKeyDown, AddressOf radRadialGauge1_PreviewKeyDown
    AddHandler Me.RadRadialGauge1.KeyUp, AddressOf radRadialGauge1_KeyUp
    AddHandler timer.Tick, AddressOf timer_Tick
    timer.Interval = 100
End Sub
Private Sub timer_Tick(ByVal sender As Object, ByVal e As EventArgs)
    Dim newValue As Single
    If isDownArrow Then
        newValue = Math.Max(0, Me.RadRadialGauge1.Value - 1)
        Me.RadRadialGauge1.Value = newValue
    ElseIf isUpArrow Then
        newValue = Math.Max(Me.RadRadialGauge1.Value + 1, CSng(Me.RadRadialGauge1.RangeEnd))
        Me.RadRadialGauge1.Value += 1
    End If
End Sub
Private Sub radRadialGauge1_KeyUp(ByVal sender As Object, ByVal e As KeyEventArgs)
    isDownArrow = False
    isUpArrow = False
End Sub
Private isDownArrow As Boolean = False
Private isUpArrow As Boolean = False
Private Sub radRadialGauge1_PreviewKeyDown(ByVal sender As Object, ByVal e As PreviewKeyDownEventArgs)
    If e.KeyData = Keys.Down Then
        isDownArrow = True
    ElseIf e.KeyData = Keys.Up Then
        isUpArrow = True
    End If
End Sub

A complete solution providing a C# and VB.NET project is available here.

See Also

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