C# Knob Control using Windows Forms

• Download KnobControlProject - 1 MB
• Download KnobControl - 641.3 KB

Introduction

This code was originally written by Jigar Desai a long time ago as a proof of concept. (The original article for this control can be found on C-SharpCorner.com.)

I needed a knob control in C#, with full functionalities for my personal projects and decided to improve it by making its output type a class library and adding as many properties as possible to be a full and flexible control.

• The control accepts now graduations with text and sub graduations.
• The text of the graduations can be drawn inside or outside the knob.
• The "start angle" and the "end angle" of the graduations are adjustable.
  C#

  // "start angle" and "end angle" possible values:
  
  // 90 = bottom (minimum value for "start angle")
  // 180 = left
  // 270 = top
  // 360 = right
  // 450 = bottom again (maximum value for "end angle")
  
  // So the couple (90, 450) will give an entire circle 
  // and the couple (180, 360) will give half a circle.

• The MouseWheel event is now managed.

Tip: You might have noticed that a UserControl doesn't show the MouseWheel event in the Properties window. Hint of trouble there. The WM_MOUSEWHEEL message bubbles. If the control that has the focus doesn't handle it, then Windows passes it on to its Parent. Repeatedly, until it finds a parent window that wants to handle it.

HandledMouseEventArgs lets you stop the bubbling.

protected override void OnMouseWheel(MouseEventArgs e)
{           
    base.OnMouseWheel(e);

    if ( isFocused && isKnobRotating && 
    Utility.isPointinRectangle(new Point(e.X, e.Y), rKnob))
    {                
        // the Delta value is always 120, as explained in MSDN
        int v = (e.Delta / 120) * (_maximum - _minimum) / _mouseWheelBarPartitions;
        SetProperValue(Value + v);

        // Avoid to send MouseWheel event to the parent container
        ((HandledMouseEventArgs)e).Handled = true;
    }
}

Properties

The single event managed by this control is the ValueChanged event.

private void knobControl1_ValueChanged(object Sender)
{
     label1.Text = knobControl1.Value.ToString();
}

This project was developed with Visual Studio version 2017.

The code is not difficult to understand and to modify to suit your needs. The main difficulty is that you need some Math skills to understand how all is displayed (not so much in fact: sinus and cosinus level required :-)).

You can download the demo project to see the KnobControl in action or simply the source of the KnobControl.

History

• 11^th December, 2019: Initial version