C# 4 and .NET 4

768 ❘ ChaPTer 28 mAnAGed extensibility frAmewOrk
catalog.Changed += (sender, e) = >
{
var sb = new StringBuilder();
foreach (var definition in e.AddedDefinitions)
{
foreach (var metadata in definition.Metadata)
{
sb.AppendFormat(
"added definition with metadata - key: {0}, " +
"value: {1}\n", metadata.Key, metadata.Value);
}
}
foreach (var definition in e.RemovedDefinitions)
{
foreach (var metadata in definition.Metadata)
{
sb.AppendFormat(
"removed definition with metadata - key: {0}, " +
"value: {1}\n", metadata.Key, metadata.Value);
}
}
this.textStatus.Text += sb.ToString();
};
//...
code snippet WPFCalculator/MainWindow.xaml.cs
To get immediate notifi cation of new add-ins loaded to a directory, you can use the
System.IO.FileSystemWatcher to register for changes on the add-in directory, and
invoke the Refresh method of the DirectoryCatalog with the Changed event of the
FileSystemWatcher.
The CompositionContainer just needs a ComposablePartCatalog to fi nd parts. DirectoryCatalog
derives from ComposablePartCatalog . Other catalogs are AssemblyCatalog , TypeCatalog , and
AggregateCatalog . Let ’ s compare all these catalogs:
➤
➤
➤
➤
T h e DirectoryCatalog searches parts within a directory.
T h e AssemblyCatalog searches for parts directly within a referenced assembly. Contrary
to the DirectoryCatalog , where assemblies might change in the directory during runtime, the
AssemblyCatalog is immutable and parts cannot change.
T h e TypeCatalog searches for imports within a list of types. IEnumerable < Type > can be passed to
the constructor of this catalog.
T h e AggregateCatalog is a catalog of catalogs. This catalog can be created from multiple
ComposablePartCatalog objects and searches in all these catalogs. For example, you can create
an AssemblyCatalog to search for imports within an assembly, two DirectoryCatalog objects to
search in two different directories, and an AggregateCatalog that combines the three catalogs for
import searches.
When running the sample application (see Figure 28 - 4), the SimpleCalculator add - in is loaded, and you
can do some calculations with operations supported by the add - in. From the AddIns menu, you can start
add - ins that implement the interface ICalculatorExtender and see the user interface from these add -
ins in the tab control. Information about exports and changes in the directory catalog is shown with the
www.it-ebooks.info