How to: Apply a theme to a presentation (Open XML SDK)

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 the Open(String, Boolean) method that uses a file path, and 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. To open a document for read/write access, specify the value true for this parameter. In the following using statement, two presentation files are opened, the target presentation, to which to apply a theme, and the source presentation, which already has that theme applied. The source presentation file is opened for read-only access, and the target presentation file is opened for read/write access. In this code, the themePresentation parameter is a string that represents the path for the source presentation document, and the presentationFile parameter is a string that represents the path for the target presentation document.

The using statement provides a recommended alternative to the typical .Open, .Save, .Close sequence. It ensures that the Dispose method (internal method used by the Open XML SDK to clean up resources) is automatically called when the closing brace is reached. The block that follows the using statement establishes a scope for the object that is created or named in the using statement, in this case themeDocument and presentationDocument.

The basic document structure of a PresentationML document consists of 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 following XML code segment represents a presentation that contains two slides denoted by the ID 267 and 256.

<p:presentation xmlns:p="…" … > 
   <p:sldMasterIdLst>
      <p:sldMasterId
         xmlns:rel="http://…/relationships" rel:id="rId1"/>
   </p:sldMasterIdLst>
   <p:notesMasterIdLst>
      <p:notesMasterId
         xmlns:rel="http://…/relationships" rel:id="rId4"/>
   </p:notesMasterIdLst>
   <p:handoutMasterIdLst>
      <p:handoutMasterId
         xmlns:rel="http://…/relationships" rel:id="rId5"/>
   </p:handoutMasterIdLst>
   <p:sldIdLst>
      <p:sldId id="267"
         xmlns:rel="http://…/relationships" rel:id="rId2"/>
      <p:sldId id="256"
         xmlns:rel="http://…/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 2.5, 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.

The following information from the ISO/IEC 29500 specification can be useful when working with this element.

The following table lists the possible child types of the Theme class.

The following XML Schema fragment defines the four parts of the theme element. The themeElements element is the piece that holds the main formatting defined within the theme. The other parts provide overrides, defaults, and additions to the information contained in themeElements. The complex type defining a theme, CT_OfficeStyleSheet, is defined in the following manner.

<complexType name="CT_OfficeStyleSheet">
   <sequence>
       <element name="themeElements" type="CT_BaseStyles" minOccurs="1" maxOccurs="1"/>
       <element name="objectDefaults" type="CT_ObjectStyleDefaults" minOccurs="0" maxOccurs="1"/>
       <element name="extraClrSchemeLst" type="CT_ColorSchemeList" minOccurs="0" maxOccurs="1"/>
       <element name="custClrLst" type="CT_CustomColorList" minOccurs="0" maxOccurs="1"/>
       <element name="extLst" type="CT_OfficeArtExtensionList" minOccurs="0" maxOccurs="1"/>
   </sequence>
   <attribute name="name" type="xsd:string" use="optional" default=""/>
</complexType>

This complex type also holds a CT_OfficeArtExtensionList, which is used for future extensibility of this complex type.

The sample code consists of two overloads of the method ApplyThemeToPresentation, and the GetSlideLayoutType method. The following code segment shows the first overloaded method, in which the two presentation files, themePresentation and presentationFile, are opened and passed to the second overloaded method as parameters.

In the second overloaded method, the code starts by checking whether any of the presentation files is empty, in which case it throws an exception. The code then gets the presentation part of the presentation document by declaring a PresentationPart object and setting it equal to the presentation part of the target PresentationDocument object passed in. It then gets the slide master parts from the presentation parts of both objects passed in, and gets the relationship ID of the slide master part of the target presentation.

The code then removes the existing theme part and the slide master part from the target presentation. By reusing the old relationship ID, it adds the new slide master part from the source presentation to the target presentation. It also adds the theme part to the target presentation.

The code iterates through all the slide layout parts in the slide master part and adds them to the list of new slide layouts. It specifies the default layout type. For this example, the code for the default layout type is "Title and Content".

The code iterates through all the slide parts in the target presentation and removes the slide layout relationship on all slides. It uses the GetSlideLayoutType method to find the layout type of the slide layout part. For any slide with an existing slide layout part, it adds a new slide layout part of the same type it had previously. For any slide without an existing slide layout part, it adds a new slide layout part of the default type.

// Remove the slide layout relationship on all slides. 
foreach (var slidePart in presentationPart.SlideParts)
{
    layoutType = null;

    if (slidePart.SlideLayoutPart != null)
    {
        // Determine the slide layout type for each slide.
        layoutType = GetSlideLayoutType(slidePart.SlideLayoutPart);

        // Delete the old layout part.
        slidePart.DeletePart(slidePart.SlideLayoutPart);
    }

    if (layoutType != null && newSlideLayouts.TryGetValue(layoutType, out newLayoutPart))
    {
        // Apply the new layout part.
        slidePart.AddPart(newLayoutPart);
    }
    else
    {
        newLayoutPart = newSlideLayouts[defaultLayoutType];

        // Apply the new default layout part.
        slidePart.AddPart(newLayoutPart);
    }
}

' Remove the slide layout relationship on all slides. 
For Each slidePart In presentationPart.SlideParts
    layoutType = Nothing

    If slidePart.SlideLayoutPart IsNot Nothing Then
        ' Determine the slide layout type for each slide.
        layoutType = GetSlideLayoutType(slidePart.SlideLayoutPart)

        ' Delete the old layout part.
        slidePart.DeletePart(slidePart.SlideLayoutPart)
    End If

    If layoutType IsNot Nothing AndAlso newSlideLayouts.TryGetValue(layoutType, newLayoutPart) Then
        ' Apply the new layout part.
        slidePart.AddPart(newLayoutPart)
    Else
        newLayoutPart = newSlideLayouts(defaultLayoutType)

        ' Apply the new default layout part.
        slidePart.AddPart(newLayoutPart)
    End If
Next slidePart

To get the type of the slide layout, the code uses the GetSlideLayoutType method that takes the slide layout part as a parameter, and returns to the second overloaded ApplyThemeToPresentation method a string that represents the name of the slide layout type

The following is the complete sample code to copy a theme from one presentation to another. To use the program, you must create two presentations, a source presentation with the theme you would like to copy, for example, Myppt9-theme.pptx, and the other one is the target presentation, for example, Myppt9.pptx. You can use the following call in your program to perform the copying.

After performing that call you can inspect the file Myppt2.pptx, and you would see the same theme of the file Myppt9-theme.pptx.

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