如何解决PowerPoint Interop：如何检测用户何时关闭PowerPoint而又不保存更改？？

我有一个WPF应用程序，可将PowerPoint文件存储在sql Server数据库中。该应用程序具有一个编辑按钮，可以打开给定的PowerPoint文件进行编辑。由于PowerPoint是基于文件的应用程序，因此我必须使用临时文件来加载和保存PowerPoint。

为此目的我编写的帮助程序类具有绑定到编辑按钮的IsEnabled属性的属性；我们在编辑过程中禁用该按钮。编辑过程中，有一个ManualResetEvent会在此帮助程序类中挂起Edit方法。我钩上Presentation.Saved事件以检测用户何时将更改保存到PowerPoint中。不用说，这都是精心策划的。

在测试过程中，我们发现，如果用户在不保存更改的情况下关闭PowerPoint，然后对随后出现的“您希望保存更改”对话框回答“是”，则Presentation.Saved不会触发直到Presentation.CloseFinal事件已经执行之后，对我们而言，对此做任何事情都为时已晚。 Presentation.CloseFinal是我们从磁盘检索保存的文件并将其存储到数据库的地方。如果用户单击PowerPoint中的“保存”按钮，则会立即触发Presentation.Saved。

为了解决该问题，我钩住了PresentationClose事件并编写了以下代码。

// Detects when the user closes the PowerPoint after changes have been made.
private void Application_PresentationClose(Presentation presentation)
{
    // If the user has edited the presentation before closing PowerPoint,// this event fires twice.  The first time it fires,presentationSaved
    // is msoFalse.  That''s how we kNow the user has edited the PowerPoint.
    if (presentation.Saved == MsoTriState.msoFalse)
        IsDirty = true;
}

然后我检查IsDirty中的Presentation.CloseFinal属性，并将PowerPoint保存到数据库（如果将其设置为true）。

不幸的是，出现了无法预料的皱纹；似乎没有可靠的方法来确定用户是否放弃了更改。第二次触发此事件时，无论用户对“保存更改吗？”的回答如何，Presentation.Saved属性始终设置为MsoTriState.msoTrue。对话框。

如果用户放弃了所做的更改，PowerPoint Interop中是否有一种方法可以避免承担将未更改的文件保存到数据库的费用？

作为参考，以下是整个帮助器类：

using Microsoft.Office.Core;
using Microsoft.Office.Interop.PowerPoint;
using System;
using System.IO;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Xps.Packaging;
using PropertyChanged;  // PropertyChanged.Fody 

namespace Helpers
{
    /// <summary>
    /// Helper class for PowerPoint file handling
    /// </summary>
    [AddINotifyPropertyChangedInterface]
    public sealed class PowerPointApplication : Idisposable
    {
        private Application _application;
        private Presentation _presentation;
        private string _tempFolder;
        private string _pptPath;
        private string _extension;

        /// <summary>
        /// Used to block the Edit method until the PowerPoint presentation is closed.
        /// </summary>
        private ManualResetEvent manualResetEvent = new ManualResetEvent(false);

        public byte[] PptData { get; private set; }
        public byte[] PptxData { get; private set; }
        public byte[] JpgData { get; private set; }

        /// <summary>
        /// Indicates whether any instance of PowerPointApplication is in an edit state.
        /// Used to disable Edit PowerPoint buttons.
        /// </summary>
        public static bool IsEditing { get; private set; }

        /// <summary>
        /// Indicates if the PowerPoint file has been saved after changes were made to it.
        /// </summary>
        public bool IsSaved { get; set; }

        /// <summary>
        /// Indicates if the PowerPoint file has been changed but not saved.
        /// </summary>
        public bool IsDirty { get; set; }

        public PowerPointApplication()
        {
            _tempFolder = Path.GetTempPath();

            if (!Directory.Exists(_tempFolder))
                Directory.CreateDirectory(_tempFolder);

            _application = new Application();
            _application.PresentationSave += Application_PresentationSave;
            _application.PresentationClose += Application_PresentationClose;
            _application.PresentationCloseFinal += Application_PresentationCloseFinal;
        }

        // Detects when the user presses the "Save" button in PowerPoint
        private void Application_PresentationSave(Presentation presentation)
        {
            IsSaved = true;
        }

        // Detects when the user closes the PowerPoint after changes have been made.
        private void Application_PresentationClose(Presentation presentation)
        {
            // If the user has edited the presentation before closing PowerPoint,presentationSaved
            // is msoFalse.  That''s how we kNow the user has edited the PowerPoint.
            // It fires again after the users has responded to the "save changes?" dialog.
            if (presentation.Saved == MsoTriState.msoFalse)
                IsDirty = true;
        }

        private void Application_PresentationCloseFinal(Presentation presentation)
        {
            if ((IsDirty || IsSaved) && File.Exists(_pptPath))
            {
                var data = File.ReadAllBytes(_pptPath);

                if (_extension == "pptx")
                {
                    PptxData = data;
                    PptData = GetPpt(presentation);
                }
                else
                {
                    PptData = data;
                    PptxData = GetPptx(presentation);
                }
                JpgData = GetJpg(presentation);

                IsSaved = true;
                IsDirty = false;
            }
            manualResetEvent.Set();
            IsEditing = false;

            Task.Run(() => DeleteFileDelayed(_pptPath));
        }

        /// <summary>
        /// Waits for PowerPoint to close,and then makes a best effort to delete the temp file.
        /// </summary>
        private static void DeleteFileDelayed(string path)
        {
            if (path == null) return;
            var file = new FileInfo(path);

            Thread.Sleep(5000);
            try
            {
                file.Delete();
            }
            catch { }
        }

        /// <summary>
        /// Opens the provided PowerPoint byte array in PowerPoint and displays it.
        /// </summary>
        public void Edit(byte[] data,string ext = "xml")
        {
            _extension = ext;
            _pptPath = GetTempFile(_extension);

            if (data == null)
            {
                // Open a blank presentation and establish a save path.
                _presentation = _application.Presentations.Add(MsoTriState.msoTrue);
                _presentation.SaveAs(_pptPath,PpSaveAsFileType.ppSaveAsXMLPresentation);
                IsSaved = false;
            }
            else
            {
                // Save the data to a file and open it.
                File.WriteallBytes(_pptPath,data);
                _presentation = _application.Presentations.Open(_pptPath);
                IsEditing = true;
            }

            // Make sure IsEnabled state of WPF buttons is properly set.
            ApplicationHelper.DoEvents();
            Thread.Sleep(100);
            ApplicationHelper.DoEvents();

            // Wait for PowerPoint to exit.
            manualResetEvent.WaitOne();
        }

        /// <summary>
        /// Opens the provided PowerPoint byte array in PowerPoint without displaying it.
        /// </summary>
        public void Open(byte[] data,string ext = "xml")
        {
            _extension = ext;
            _pptPath = GetTempFile(ext);
            File.WriteallBytes(_pptPath,data);
            _presentation = _application.Presentations.Open(_pptPath,WithWindow: MsoTriState.msoFalse);
            IsEditing = true;
        }

        public void Close()
        {
            _presentation.Close();
        }

        public byte[] GetJpg() { return GetJpg(_presentation); }
        /// <summary>
        /// Returns a byte array containing a JPEG image of the first slide in the PowerPoint.
        /// </summary>
        public byte[] GetJpg(Presentation presentation)
        {
            presentation.SavecopyAs(_tempFolder,PpSaveAsFileType.ppSaveAsJPG,MsoTriState.msoFalse);
            byte[] result = File.ReadAllBytes(Path.Combine(_tempFolder,"Slide1.jpg"));
            File.Delete(Path.Combine(_tempFolder,"Slide1.jpg"));
            return result;
        }

        public byte[] GetPptx() { return GetPptx(_presentation); }

        public byte[] GetPptx(Presentation presentation)
        {
            var path = Path.ChangeExtension(_pptPath,"pptx");
            presentation.SavecopyAs(path,PpSaveAsFileType.ppSaveAsOpenXMLPresentation,MsoTriState.msoFalse);
            byte[] result = File.ReadAllBytes(path);
            return result;
        }

        public byte[] GetPpt(Presentation presentation)
        {
            var path = Path.ChangeExtension(_pptPath,"ppt");
            presentation.SavecopyAs(path,PpSaveAsFileType.ppSaveAsPresentation,MsoTriState.msoFalse);
            byte[] result = File.ReadAllBytes(path);
            return result;
        }

        /// <summary>
        /// Returns an XPS document of the presentation.
        /// </summary>
        public XpsDocument ToXps(string pptFilename,string xpsFilename)
        {
            var presentation = _application.Presentations.Open(pptFilename,MsoTriState.msoTrue,MsoTriState.msoFalse,MsoTriState.msoFalse);
            presentation.ExportAsFixedFormat(xpsFilename,PpFixedFormatType.ppFixedFormatTypeXPS);
            return new XpsDocument(xpsFilename,FileAccess.Read);
        }

        /// <summary>
        /// Returns a path to a temporary working file having the specified extension.
        /// </summary>
        private string GetTempFile(string extension)
        {
            return Path.Combine(_tempFolder,Guid.NewGuid() + "." + extension);
        }

        #region Idisposable implementation
        public void dispose()
        {
            _application.PresentationSave -= Application_PresentationSave;
            _application.PresentationClose -= Application_PresentationClose;
            _application.PresentationCloseFinal -= Application_PresentationCloseFinal;

            IsEditing = false;
        }
        #endregion
    }
}

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