TaskDialog Class

public sealed class TaskDialog : IWin32Window, 
	IDisposable

using System.Diagnostics;
using System.Windows.Forms;
using KGySoft.WinForms.Components;

// These aliases are needed if you target .NET 5.0+
using TaskDialog = KGySoft.WinForms.Components.TaskDialog;
using TaskDialogButton = KGySoft.WinForms.Components.TaskDialogButton; // if you use custom buttons
using TaskDialogRadioButton = KGySoft.WinForms.Components.TaskDialogRadioButton; // if you use radio buttons

void ShowSimpleTaskDialog(IWin32Window? owner = null)
{
    using var taskDialog = new TaskDialog
    {
        Caption = "Simple Dialog",
        Message = "Hello TaskDialog",
        StandardButtons = TaskDialogStandardButtons.OK | TaskDialogStandardButtons.Cancel,
        Buttons = { new TaskDialogButton("Custom Button 1"), new TaskDialogButton("Custom Button 2") },
    };

    taskDialog.Show(owner);

    // The selected standard button. Cancel, if you closed the dialog, or Custom if you pressed a custom button.
    Debug.WriteLine($"Dialog Result: {taskDialog.DialogResult}");

    // The selected custom button index. -1, if you closed the dialog or pressed a standard button.
    Debug.WriteLine($"Selected Custom Button: {taskDialog.SelectedButtonIndex}");
}

Application.EnableVisualStyles(); // tip: comment this out to see how it works without visual styles
Application.SetCompatibleTextRenderingDefault(false);
ShowSimpleTaskDialog();

// the updated body of the ShowSimpleTaskDialog method above:
using var taskDialog = new TaskDialog
{
    Caption = "Simple Dialog",
    Message = "Hello TaskDialog",
    StandardButtons = TaskDialogStandardButtons.OK | TaskDialogStandardButtons.Cancel,
    Buttons = { new TaskDialogButton("Custom Button 1"), new TaskDialogButton("Custom Button 2") },

    // update:
    RadioButtons = { new TaskDialogRadioButton("Option 1"), new TaskDialogRadioButton("Option 2") },
    CheckBoxText = "This is a checkbox",
    Options = TaskDialogOptions.UseCommandLinks // affects the appearance of Buttons
};

taskDialog.Show(owner);

Debug.WriteLine($"Dialog Result: {taskDialog.DialogResult}");
Debug.WriteLine($"Selected Custom Button: {taskDialog.SelectedButtonIndex}");
Debug.WriteLine($"Selected Radio Button: {taskDialog.SelectedRadioButtonIndex}");
Debug.WriteLine($"Checkbox is checked: {taskDialog.CheckBoxChecked}");

// Alternative way to get every result in a single line:
TaskDialogResult standardButton = taskDialog.Show(owner, out int customButton, out int radioButton, out bool isChecked);

// updated initialization:
using var taskDialog = new TaskDialog
{
    Caption = "Simple Dialog",
    Message = "Hello TaskDialog",
    StandardButtons = TaskDialogStandardButtons.OK | TaskDialogStandardButtons.Cancel,
    Buttons = { new TaskDialogButton("Custom Button 1"), new TaskDialogButton("Custom Button 2") },
    RadioButtons = { new TaskDialogRadioButton("Option 1"), new TaskDialogRadioButton("Option 2") },
    CheckBoxText = "This is a checkbox",
    // Options = TaskDialogOptions.UseCommandLinks,

    // update:
    Options = TaskDialogOptions.UseCommandLinks | TaskDialogOptions.DetailsExpanded,
    MainInstruction = "Some highlighted title",
    DetailsText = "An optionally long details text that can be concealed",
    ShowDetailsText = "Show details",
    HideDetailsText = "Hide details",
    FooterText = "Even more text in the footer",
    Icon = TaskDialogStandardIcon.Information,
    FooterIcon = TaskDialogStandardIcon.SecurityShield,
};
taskDialog.Buttons[0].Description = "Oh, and here I can place even more text";