public partial class RadForm1 : Telerik.WinControls.UI.RadForm
{
    public RadForm1()
    {
        InitializeComponent();
        this.radDataEntry1.EditorInitializing += RadDataEntry1_EditorInitializing;
        List<TestClass> list = new List<TestClass>();
        this.bindingSource1.DataSource = list;
        this.radDataEntry1.DataSource = this.bindingSource1;
        this.radBindingNavigator1.BindingSource = this.bindingSource1;
        this.radBindingNavigator1.BindingNavigatorElement.DeleteButton.MouseDown += DeleteButton_MouseDown;
        this.radBindingNavigator1.BindingNavigatorElement.AddNewButton.MouseDown += AddNewButton_MouseDown;

    }

    private void AddNewButton_MouseDown(object sender, MouseEventArgs e)
    {
        if ((this.bindingSource1.DataSource as List<TestClass>).Count == 0)
        {
                editor.Minimum = 1;
        }
    }

    private void DeleteButton_MouseDown(object sender, MouseEventArgs e)
    {
        if ((this.bindingSource1.DataSource as List<TestClass>).Count == 1)
        {
            editor.Minimum = 0;
        }
    }
    RadSpinEditor editor = new RadSpinEditor();
    private void RadDataEntry1_EditorInitializing(object sender, EditorInitializingEventArgs e)
    {
        if (e.Editor is RadSpinEditor spinEditor)
        {
                editor = spinEditor;
        }
    }
}

internal class TestClass
{
    [RadRange(1, 8000)]
    public int PacketSize { get; set; } = 512;
}