編輯

共用方式為

Open a presentation document for read-only access

  • 發行項

This topic describes how to use the classes in the Open XML SDK for Office to programmatically open a presentation document for read-only access.

How to Open a File for Read-Only Access

You may want to open a presentation document to read the slides. You might want to extract information from a slide, copy a slide to a slide library, or list the titles of the slides. In such cases you want to do so in a way that ensures the document remains unchanged. You can do that by opening the document for read-only access. This How-To topic discusses several ways to programmatically open a read-only presentation document.

Create an Instance of the PresentationDocument Class

In the Open XML SDK, the PresentationDocument class represents a presentation document package. To work with a presentation document, first create an instance of the PresentationDocument class, and then work with that instance. To create the class instance from the document call one of the Open methods. Several Open methods are provided, each with a different signature. The following table contains a subset of the overloads for the Open method that you can use to open the package.

Name Description
Open(String, Boolean) Create a new instance of the PresentationDocument class from the specified file.
Open(Stream, Boolean) Create a new instance of the PresentationDocument class from the I/O stream.
Open(Package) Create a new instance of the PresentationDocument class from the specified package.

The previous table includes two Open methods that accept a Boolean value as the second parameter to specify whether a document is editable. To open a document for read-only access, specify the value false for this parameter.

For example, you can open the presentation file as read-only and assign it to a PresentationDocument object as shown in the following using statement. In this code, the presentationFile parameter is a string that represents the path of the file from which you want to open the document.

    using (PresentationDocument presentationDocument = PresentationDocument.Open(presentationFile, false))
    {
        // Insert other code here.
    }

You can also use the second overload of the Open method, in the table above, to create an instance of the PresentationDocument class based on an I/O stream. You might use this approach if you have a Microsoft SharePoint Foundation 2010 application that uses stream I/O and you want to use the Open XML SDK to work with a document. The following code segment opens a document based on a stream.

    Stream stream = File.Open(strDoc, FileMode.Open);
    using (PresentationDocument presentationDocument =
        PresentationDocument.Open(stream, false)) 
    {
        // Place other code here.
    }

Suppose you have an application that employs the Open XML support in the System.IO.Packaging namespace of the .NET Framework Class Library, and you want to use the Open XML SDK to work with a package read-only. The Open XML SDK includes a method overload that accepts a Package as the only parameter. There is no Boolean parameter to indicate whether the document should be opened for editing. The recommended approach is to open the package as read-only prior to creating the instance of the PresentationDocument class. The following code segment performs this operation.

    Package presentationPackage = Package.Open(filepath, FileMode.Open, FileAccess.Read);
    using (PresentationDocument presentationDocument =
        PresentationDocument.Open(presentationPackage))
    {
        // Other code goes here.
    }

Basic Presentation Document Structure

The basic document structure of a PresentationML document consists of a number of parts, among which is the main part that contains the presentation definition. The following text from the ISO/IEC 29500 specification introduces the overall form of a PresentationML package.

The main part of a PresentationML package starts with a presentation root element. That element contains a presentation, which, in turn, refers to a slide list, a slide master list, a notes master list, and a handout master list. The slide list refers to all of the slides in the presentation; the slide master list refers to the entire slide masters used in the presentation; the notes master contains information about the formatting of notes pages; and the handout master describes how a handout looks.

A handout is a printed set of slides that can be provided to an audience.

As well as text and graphics, each slide can contain comments and notes, can have a layout, and can be part of one or more custom presentations. A comment is an annotation intended for the person maintaining the presentation slide deck. A note is a reminder or piece of text intended for the presenter or the audience.

Other features that a PresentationML document can include the following: animation, audio, video, and transitions between slides.

A PresentationML document is not stored as one large body in a single part. Instead, the elements that implement certain groupings of functionality are stored in separate parts. For example, all comments in a document are stored in one comment part while each slide has its own part.

© ISO/IEC29500: 2008.

The following XML code example represents a presentation that contains two slides denoted by the IDs 267 and 256.

    <p:presentation xmlns:p="…" … > 
       <p:sldMasterIdLst>
          <p:sldMasterId
             xmlns:rel="https://…/relationships" rel:id="rId1"/>
       </p:sldMasterIdLst>
       <p:notesMasterIdLst>
          <p:notesMasterId
             xmlns:rel="https://…/relationships" rel:id="rId4"/>
       </p:notesMasterIdLst>
       <p:handoutMasterIdLst>
          <p:handoutMasterId
             xmlns:rel="https://…/relationships" rel:id="rId5"/>
       </p:handoutMasterIdLst>
       <p:sldIdLst>
          <p:sldId id="267"
             xmlns:rel="https://…/relationships" rel:id="rId2"/>
          <p:sldId id="256"
             xmlns:rel="https://…/relationships" rel:id="rId3"/>
       </p:sldIdLst>
           <p:sldSz cx="9144000" cy="6858000"/>
       <p:notesSz cx="6858000" cy="9144000"/>
    </p:presentation>

Using the Open XML SDK, you can create document structure and content using strongly-typed classes that correspond to PresentationML elements. You can find these classes in the DocumentFormat.OpenXml.Presentation namespace. The following table lists the class names of the classes that correspond to the sld, sldLayout, sldMaster, and notesMaster elements.

PresentationML Element Open XML SDK Class Description
sld Slide Presentation Slide. It is the root element of SlidePart.
sldLayout SlideLayout Slide Layout. It is the root element of SlideLayoutPart.
sldMaster SlideMaster Slide Master. It is the root element of SlideMasterPart.
notesMaster NotesMaster Notes Master (or handoutMaster). It is the root element of NotesMasterPart.

How the Sample Code Works

In the sample code, after you open the presentation document in the using statement for read-only access, instantiate the PresentationPart, and open the slide list. Then you get the relationship ID of the first slide.

    // Get the relationship ID of the first slide.
    PresentationPart part = ppt.PresentationPart;
    OpenXmlElementList slideIds = part.Presentation.SlideIdList.ChildElements;
    string relId = (slideIds[index] as SlideId).RelationshipId;

From the relationship ID, relId, you get the slide part, and then the inner text of the slide by building a text string using StringBuilder.

    // Get the slide part from the relationship ID.
    SlidePart slide = (SlidePart)part.GetPartById(relId);

    // Build a StringBuilder object.
    StringBuilder paragraphText = new StringBuilder();

    // Get the inner text of the slide.
    IEnumerable<A.Text> texts = slide.Slide.Descendants<A.Text>();
    foreach (A.Text text in texts)
    {
        paragraphText.Append(text.Text);
    }
    sldText = paragraphText.ToString();

The inner text of the slide, which is an out parameter of the GetSlideIdAndText method, is passed back to the main method to be displayed.

Important

This example displays only the text in the presentation file. Non-text parts, such as shapes or graphics, are not displayed.

Sample Code

The following example opens a presentation file for read-only access and gets the inner text of a slide at a specified index. To call the method GetSlideIdAndText pass in the full path of the presentation document. Also pass in the out parameter sldText, which will be assigned a value in the method itself, and then you can display its value in the main program. For example, the following call to the GetSlideIdAndText method gets the inner text in the second slide in a presentation file named "Myppt13.pptx".

Tip

The most expected exception in this program is the ArgumentOutOfRangeException exception. It could be thrown if, for example, you have a file with two slides, and you wanted to display the text in slide number 4. Therefore, it is best to use a try block when you call the GetSlideIdAndText method as shown in the following example.

    string file = @"C:\Users\Public\Documents\Myppt13.pptx";
    string slideText;
    int index = 1;
    try
    {
        GetSlideIdAndText(out slideText, file, index);
        Console.WriteLine("The text in the slide #{0} is: {1}", index + 1, slideText);
    }
    catch (ArgumentOutOfRangeException exp)
    {
        Console.WriteLine(exp.Message);
    }

The following is the complete code listing in C# and Visual Basic.


using DocumentFormat.OpenXml;
using DocumentFormat.OpenXml.Packaging;
using DocumentFormat.OpenXml.Presentation;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using A = DocumentFormat.OpenXml.Drawing;

GetSlideIdAndText(out string text, args[0], int.Parse(args[1]));

static void GetSlideIdAndText(out string sldText, string docName, int index)
{
    using (PresentationDocument ppt = PresentationDocument.Open(docName, false))
    {
        // Get the relationship ID of the first slide.
        PresentationPart? part = ppt.PresentationPart;
        OpenXmlElementList slideIds = part?.Presentation?.SlideIdList?.ChildElements ?? default;

        // If there are no slide IDs then there are no slides.
        if (slideIds.Count == 0)
        {
            sldText = "";
            return;
        }

        string? relId = (slideIds[index] as SlideId)?.RelationshipId;

        if (relId is null)
        {
            sldText = "";
            return;
        }

        // Get the slide part from the relationship ID.
        SlidePart slide = (SlidePart)part!.GetPartById(relId);

        // Build a StringBuilder object.
        StringBuilder paragraphText = new StringBuilder();

        // Get the inner text of the slide:
        IEnumerable<A.Text> texts = slide.Slide.Descendants<A.Text>();
        foreach (A.Text text in texts)
        {
            paragraphText.Append(text.Text);
        }
        sldText = paragraphText.ToString();
    }
}