MSDN Magazine - December 2008 - (Page 67)

shown in Figure 5, the WdSaveFormat parameter is specified as nullable (declared using the ? syntax), which allows us to invoke this method and pass null for this parameter. The real work of saving the document is ultimately done in the overload that takes a DocumentSaveAsArgs object. As we have seen, this uses object initializers, to allow the developer to provide values for the interesting parameters by name and to omit any that can be defaulted. The DocumentSaveAsArgs class is derived from the SaveAsArgs extensions class. The argument values themselves are stored within internal fields of the class, such as FileNameInternal, and these are used directly by the extension methods. The developer uses the public properties, such as FileName, rather than the internal fields. This design arises because of the requirement in most methods in the Word object model to pass parameters by reference. The argument classes in the extensions library for the other Office applications do not use this extra layer: public abstract class SaveAsArgs : ExtensionArgs { internal object FileNameInternal = Type.Missing; public string FileName { get { return ToReference (FileNameInternal); } set { FileNameInternal = ToObject(value); } } // code omitted for brevity. } } // code omitted for brevity. (Expression expression) { MethodCallExpression call = expression as MethodCallExpression; switch (call.Method.Name) { case "Where": return new OutlookItemSourceWhereHandler ( this, expression, _builder, _search); case "Select": return new OutlookItemSourceSelectHandler ( this, expression); } The OutlookItemSource class uses other internal extensions classes to build a DASL query string from the LINQ query. For example, the ParseMethodCallExpression method converts LINQ expressions such as Contains to DASL query sub-strings such as (LIKE ‘%’): private static void ParseMethodCallExpression(MethodCallExpression call) { if (call.Method.DeclaringType == typeof(string)) { string format = null; switch (call.Method.Name) { case "Contains": format = @"({0} LIKE '%{1}%')"; break; case "StartsWith": format = @"({0} LIKE '{1}%')"; break; case "EndsWith": format = @"({0} LIKE '%{1}')"; break; } // code omitted for brevity. } } } SaveAsArgs is, in turn, derived from ExtensionArgs, which includes code to convert between real types and their boxed equivalents and includes logic for handling System.Type.Missing: protected T ToReference (object obj) where T : class { return (obj != null && obj != Type.Missing) ? (T) obj : null; } The OutlookItemProperty attribute provides a mapping between DASL properties and properties on the Outlook item interfaces. This attribute is used on the public properties exposed from the OutlookItem class, and this is how the extensions allow the developer to avoid the use of the obscure URN/hex tag strings to specify target properties: public class OutlookItem : IOutlookItemWrapper { [OutlookItemProperty( "http://schemas.microsoft.com/mapi/proptag/0x001a001e")] public virtual string MessageClass { get { return GetProperty("MessageClass") as string; } } // code omitted for brevity. } Parameterized properties are also handled by overloaded extension methods in the extensions library—as before, these use the underlying PIA objects for the ultimate functionality. For example, the Excel.Range extensions provide three overloads that use the get_Range property method under the covers: public static Range Range(this Worksheet worksheet, string name) { return worksheet.get_Range(name, Type.Missing); } public static Range Range(this Worksheet worksheet, string name1, string name2) { return worksheet.get_Range(name1, name2); } public static Range Range(this Worksheet worksheet, string range1, Range range2) { return worksheet.get_Range(range1, range2); } Figure 7 Extending the Excel Methods public static class RangeExtensions { public static Excel.Range Offset( this Excel.Range cells, int rowOffset, int columnOffset) { return cells.get_Offset(rowOffset, columnOffset) as Excel.Range; } } public static class ShapesExtensions { public static Excel.Shape AddChart( this Excel.Shapes shapes, Excel.XlChartType chartType) { return shapes.AddChart(chartType, Type.Missing, Type.Missing, Type.Missing, Type.Missing); } } public static class ShapeExtensions { public static void Select(this Excel.Shape shape) { shape.Select(Type.Missing); } } public static class ChartExtensions { public static void SetSourceData(this Excel.Chart chart, Excel.Range range) { chart.SetSourceData(range, Type.Missing); } } To support LINQ-to-DASL queries in Outlook, the extensions library provides an abstract base class to represent the data source for the query: OutlookItemSource. This class implements the IQueryable and IQueryProvider interfaces used by LINQ. The extensions also provide derived classes ItemsSource and ApplicationSource for performing queries on the Items collection of a single folder and queries across multiple folders, respectively: public abstract class OutlookItemSource : IQueryProvider, IQueryable { public IQueryable CreateQuery msdnmagazine.com December 2008 67 http://www.msdnmagazine.com

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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