How to enable/disable validation of your custom Options Tab

csharp

How to enable/disable validation of your custom Options Tab?                         By Philippe Leefsma
In those following posts Kean is showing how to add your own custom tab to the AutoCAD Options dialog:
Adding a custom tab to AutoCAD's options dialog using .NET - Part 1
Adding a custom tab to AutoCAD's options dialog using .NET - Part 2
What those samples aren’t showing, is how you can enable/disable the OK button, so the user will only be able to validate the dialog if his choices are matching your logic.
In order to achieve such a feature, a little hack relying on a couple of Win32 P/Invoked APIs is likely to be needed:
In the sample below, I am using FindWindowEx and EnableWindow to control the OK button, depending on the value provided in a textbox.

public partial class OptionsTabControl : UserControl

{

    private IntPtr _hWndOkBtn;

    [DllImport("user32.dll", SetLastError = true

    private static extern IntPtr FindWindowEx(

        IntPtr parentHandle,

        IntPtr childAfter,

        string className,

        string windowTitle);

    [DllImport("user32.dll"

    [return: MarshalAs(UnmanagedType

    static extern bool EnableWindow(

        IntPtr hWnd,

        bool bEnable);

    public OptionsTabControl()

    {

        InitializeComponent();

        // Finds Options dialog

        IntPtr hWnd = FindWindowEx(IntPtr.Zero,

            IntPtr.Zero,

            "#32770",

            "Options");

        // Finds Ok button

        _hWndOkBtn = FindWindowEx(hWnd,

            IntPtr.Zero,

            "Button",

            "Ok");

        EnableWindow(_hWndOkBtn, false);

        tbValidation.Text = "Validate me ...";

    }

    private void tbValidation_TextChanged(

        object sender,

        EventArgs e)

    {

        if (tbValidation.Text.Length == 0)

            EnableWindow(_hWndOkBtn, false);

        else

        {

            bool enabled =

                (tbValidation.Text == "ADN rules!");

            EnableWindow(_hWndOkBtn, enabled);

        }

    }

}

Complete sample also attached.

AcadOptionsDlg.zip