我有一个将 PowerPoint 文件存储在 SQL Server 数据库中的 WPF 应用程序。该应用程序有一个编辑按钮，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，我必须使用临时文件来加载和保存 PowerPoint。
我为此目的编写的辅助类有一个绑定到编辑按钮属性的IsEnabled属性；我们在编辑过程中禁用按钮。在编辑过程中，有一个ManualResetEvent暂停Edit此帮助程序类中的方法。我挂钩 Presentation.Saved 事件以检测用户何时将更改保存到其 PowerPoint。不用说，这一切都是精心策划的。
在测试过程中，我们发现，如果用户在没有保存更改的情况下关闭 PowerPoint，然后对随后的“是否要保存更改”对话框回答“是”， 则在事件执行Presentation.Saved后才会触发，Presentation.CloseFinal我们对此无能为力，为时已晚。 Presentation.CloseFinal是我们从磁盘中检索保存的文件并将其存储到数据库的地方。 Presentation.Saved如果用户单击 PowerPoint 中的“保存”按钮，则立即触发。
为了解决这个问题，我挂钩了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，我检查我的IsDirty属性Presentation.CloseFinal并将 PowerPoint 保存到数据库中（如果设置为true.
不幸的是，有一个无法预料的皱纹；似乎没有可靠的方法来确定用户是否放弃了他们的更改。此事件第二次触发时，无论用户对“保存您的更改吗？”的回答如何，该Presentation.Saved属性始终设置为。MsoTriState.msoTrue对话。
如果用户放弃更改，PowerPoint Interop 中是否有办法避免将未更改的文件保存到数据库的成本？
作为参考，这里是辅助类的全部内容：
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,
// this event fires twice. The first time it fires, 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
}
}