MSDN Magazine - December 2008 - (Page 66)

Figure 5 Overloaded SaveAs Methods public static void SaveAs(this Document doc) { SaveAs(doc, (string) null); } public static void SaveAs(this Document doc, string fileName) { SaveAs(doc, fileName, null); } public static void SaveAs(this Document doc, string fileName, WdSaveFormat? fileFormat) { SaveAs(doc, new DocumentSaveAsArgs { FileName = fileName, FileFormat = fileFormat }); } public static void SaveAs(this Document doc, DocumentSaveAsArgs args) { doc.SaveAs( ref args.FileNameInternal, ref args.FileFormatInternal, ref args.LockCommentsInternal, ref args.PasswordInternal, ref args.AddToRecentFilesInternal, ref args.WritePasswordInternal, ref args.ReadOnlyRecommendedInternal, ref args.EmbedTrueTypeFontsInternal, ref args.SaveNativePictureFormatInternal, ref args.SaveFormsDataInternal, ref args.SaveAsAOCELetterInternal, ref args.EncodingInternal, ref args.InsertLineBreaksInternal, ref args.AllowSubstitutionsInternal, ref args.LineEndingInternal, ref args.AddBiDiMarksInternal); } which simply performs string and DateTime operations, and does not use the Office object models—this method is not listed here, but you can find it in the accompanying source-code download). Using the extensions, we can dispense with the string query and instead perform the same search using a LINQ query, which will bring all the benefits of design-time IntelliSense and compile-time type and syntax-checking—very different from the DASL string query experience. Note one limitation: the extensions do not expose the Outlook item’s Size property, so we use the Length of the Body property instead (this is another case where extending the extensions would make sense): var filteredItems = ( from item in folder.Items.AsQueryable () where item.MessageClass.StartsWith("IPM.Note") && item.Subject.StartsWith("RE:") && item.DateReceived >= DateTime.Now.ToUniversalTime() - new TimeSpan(30, 0, 0, 0) select item).ToList(); StringBuilder builder = new StringBuilder(); foreach (Mail item in filteredItems) { builder.AppendLine(String.Format("{0},{1},{2}", item.Date, item.DateReceived, item.Body.Length)); } CalculateElapsedTime(builder.ToString()); which are even more easily mistyped. Clearly, these query strings can rapidly become complex and difficult both to construct and to parse, slowing down productivity, increasing test cost, and making code maintenance difficult. In our example, we set up a DASL filter, shown in Figure 4, to find all Inbox items that are e-mail messages (that is, their Message- The extensions library itself supports a certain degree of extensibility. Class is based on IPM.Note), where the subject starts with “RE:” and were received in the last 30 days. We use Windows Desktop Search (WDS) if it is available, because this provides faster searching. WDS is installed by default on Windows Vista, but is optional on Windows XP and Windows Server 2003. Note that DASL queries always perform date-time comparisons in Coordinated Universal Time (officially abbreviated as UTC), so if you use a date literal in a comparison string, you must use its UTC value for the comparison. Once we have retrieved all the items of interest, we will compose a string for each item that consists of the time taken to send the e-mail and the size of the e-mail (using a custom method, CalculateElapsedTime, Figure 6 IntelliSense for an Extension Method in Visual Studio 66 msdn magazine Now that we’ve seen how much simpler and more error-free the developer’s coding experience is with the extensions, let’s look at how this simplicity and robustness are achieved under the covers. Consider first the Document.SaveAs method in Word. This takes 16 optional parameters, and in most cases you only need to specify a very small number of these parameters (or, in some cases, none). To write an extension method, you simply write a static method that takes the object you want to extend as its first (or only) parameter. So, to provide a strongly typed SaveAs method for the Document object, you can write a method called SaveAs that takes a Document object as its first parameter. You can also provide overloads for your extension methods so that each overload is used to simplify the developer’s coding experience, but the real functionality is ultimately invoked on the underlying PIA Document object itself. This is how the extensions are implemented, as shown in the code listings for the SaveAs method in Figure 5. At design-time in Visual Studio, the extension methods appear to the developer to be methods of the object that they extend, and are available through IntelliSense and autocomplete. IntelliSense will flag extension methods with “(extension),” as shown in Figure 6. You can also take advantage of the nullable types feature of C#, where a strongly typed parameter can be passed as null (note that this is not the same as passing a loosely typed object with the System.Type.Missing value). In the third overload SaveAs method Extension Internals VSTO Power Tools

Table of Contents Feed for the Digital Edition of MSDN Magazine - December 2008

MSDN Magazine - December 2008 Contents Toolbox CLR Inside Out Advanced Basics Cutting Edge Patterns In Practice Team System Real-World WF Visual Studio OBA Tools SOA Data Access Geneva Framework Test Run Foundations Windows With C++ Going Places End Bracket

MSDN Magazine - December 2008

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