Revit api extension to close all or active UI documents.

UIDocumentCloseExtension.cs

using Autodesk.Revit.UI;
using System;
using UIFramework;

namespace RevitTest.UIDocument.Tests
{
    ///<summary>
    /// Provides extension methods for closing UI documents in the Revit application.
    /// </summary>
    public static class UIDocumentCloseExtension
    {
        /// <summary>
        /// Closes all open UI documents in the Revit application.
        /// </summary>
        /// <param name="uiapp">The UIApplication instance.</param>
        /// <param name="saveModified">Indicates whether to save modified documents.</param>
        public static void CloseAllUIDocument(this UIApplication uiapp, bool saveModified = false)
        {
            using (new DialogBoxShowingForceResultYesNo(uiapp, saveModified))
            {
                foreach (var frameControl in MainWindow.getMainWnd().getAllViews())
                {
                    frameControl.closeWindow();
                }
            }
        }

        /// <summary>
        /// Closes the active UI document in the Revit application.
        /// </summary>
        /// <param name="uiapp">The UIApplication instance.</param>
        /// <param name="saveModified">Indicates whether to save the modified document.</param>
        public static void CloseActiveUIDocument(this UIApplication uiapp, bool saveModified = false)
        {
            var frameManager = MainWindow.getMainWnd().frameManager;
            var activeFrameControl = frameManager.onGetActiveFrame();
            if (activeFrameControl is null) return;

            var activeFrameHost = activeFrameControl.Content as MFCMDIFrameHost;
            var activeDocument = activeFrameHost.document;

            var allViews = frameManager.getAllMDIFrames();
            using (new DialogBoxShowingForceResultYesNo(uiapp, saveModified))
            {
                foreach (var frameControl in allViews)
                {
                    var frameHost = frameControl.Content as MFCMDIFrameHost;
                    if (frameHost.document == activeDocument)
                    {
                        frameControl.closeWindow();
                    }
                }
            }
        }

        /// <summary>
        /// Helper class to force a specific result for dialog boxes shown in the Revit application.
        /// </summary>
        public class DialogBoxShowingForceResultYesNo : IDisposable
        {
            private readonly UIApplication uiapp;
            readonly private bool resultYes;

            /// <summary>
            /// Initializes a new instance of the <see cref="DialogBoxShowingForceResultYesNo"/> class.
            /// </summary>
            /// <param name="uiapp">The UIApplication instance.</param>
            /// <param name="resultYes">Indicates whether to force a 'Yes' result for dialog boxes.</param>
            public DialogBoxShowingForceResultYesNo(UIApplication uiapp, bool resultYes)
            {
                this.uiapp = uiapp;
                this.resultYes = resultYes;
                uiapp.DialogBoxShowing += OnDialogBoxShowing;
            }

            /// <summary>
            /// Event handler for the DialogBoxShowing event.
            /// </summary>
            /// <param name="sender">The event sender.</param>
            /// <param name="e">The event arguments.</param>
            void OnDialogBoxShowing(object sender, Autodesk.Revit.UI.Events.DialogBoxShowingEventArgs e)
            {
                var uiapp = sender as UIApplication;
                var result = resultYes ? TaskDialogResult.Yes : TaskDialogResult.No;
                e.OverrideResult((int)result);
            }

            /// <summary>
            /// Disposes the instance and unsubscribes from the DialogBoxShowing event.
            /// </summary>
            public void Dispose()
            {
                uiapp.DialogBoxShowing -= OnDialogBoxShowing;
            }
        }
    }
}

This code require UIFramework reference.

Included in the Revit_All_Main_Versions_API_x64 package.

<PackageReference Include="Revit_All_Main_Versions_API_x64" Version="$(RevitVersion).*" IncludeAssets="build; compile" PrivateAssets="All" />

or in the Nice3point.Revit.Api.UIFramework package.

<PackageReference Include="Nice3point.Revit.Api.UIFramework" Version="$(RevitVersion).*"/>

[Transaction(TransactionMode.Manual)]
public class CommandCloseActiveUIDocument : IExternalCommand
{
    public Result Execute(ExternalCommandData commandData, ref string message, ElementSet elementSet)
    {
        UIApplication uiapp = commandData.Application;

        uiapp.CloseActiveUIDocument();

        return Result.Succeeded;
    }
}