Unmodified, your sample still does some pretty weird things.
Run it, open the file dialog and position it so it's over the active part of the radial slider. Double click a file. If the click is over the active area, as the file dialog closes you will see the marker on the radial slider flicker from the set position to ... somewhere else, I'd assume the click point, and then flick back to the correct setting. It's a little easier to replicate if you stretch out the control to cover a larger area of screen, for a larger target.
Another strange thing that happens with your example is that all other controls on the form are only partially rendered until the cursor is moved out of the rectangle owned by the radial slider. Not sure if this image will get through to the forum, but here goes:

This happens with both Default and Frame SliderStyles.
Another manifestation occurs when I change the code to set the textbox from the slider. The code you provided sets slider value to text box value when the slider is changed (?!), so I commented out the first line and un-commented the second as follows:
private void radialSlider1_ValueChanged(object sender,
Syncfusion.Windows.Forms.Tools.RadialSlider.ValueChangedEventArgs args)
{
//this.radialSlider1.Value = Double.Parse(this.textBoxExt1.Text);
this.textBoxExt1.Text = this.radialSlider1.Value.ToString();
this.radialSlider1.Refresh();
}
Now it resets the textbox value correctly - but ONLY once the cursor is moved out of the active area of the radial slider.
As to my specific problems, the retrieval and restoration of a value from the registry is still an issue. With this code:
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
SaveSetting("MP3_Randomizer", "Saved Settings", "Volume", RadialSlider1.Value.ToString)
End Sub
Public Sub New()
' This call is required by the designer.
InitializeComponent()
' Add any initialization after the InitializeComponent() call.
RadialSlider1.Value = CDbl(GetSetting("MP3_Randomizer", "Saved Settings", "Volume", ""))
MsgBox("Value = " & RadialSlider1.Value)
End Sub
the value is set, but the display is not updated. Try it yourself by adding
this.textBoxExt1.Text = "7";
at line 17, so the code reads:
public Form1()
{
InitializeComponent();
// this.radialSlider1.Refresh();
this.textBoxExt1.Text = "7";
this.radialSlider1.Update();
this.radialSlider1.Value = Double.Parse(this.textBoxExt1.Text);
this.radialSlider1.Update();
}
I have attached a simple example in VB that sets and restores slider values to and from the registry. Try it out, please, and let me know why the slider is not updated on initialization.