Shell Services
A shell service creates and interacts with shell objects, and is the main customization point for interfacing with a file system such as the Windows shell.
All shell services implement the IShellService interface, which defines the members needed to drive the user interface and behavior functionality in UI controls like ShellTreeListBox.
Built-In Windows Shell Service
The Shell Object Framework comes with a pre-built WindowsShellService class for the Windows operating system shell. This shell service wraps up all the native Win32 API and COM calls needed to interface with the full Windows shell. This functionality provides much more than what you can achieve with standard .NET System.IO namespace features, including full access to virtual folders/objects and libraries in the shell, system icons, etc.
An instance of the WindowsShellService class is set as the default shell service for the ShellTreeListBox and ShellListView controls. This allows those UI controls to support working with the Windows shell out of the box.
All of the methods on WindowsShellService are virtual, allowing you to override and customize their results as appropriate.
Using Independently of UI
While shell services are harnessed to drive the user interface of the shell controls, they and the related shell objects can be used completely independently of any user interfaces.
They fully support calls to any of their members, allowing you to programmatically examine shell folder and file hierarchies, or properties of shell objects. This is especially useful for working with the WindowsShellService, since its implementation provides shell data not available in the System.IO namespace.
Creating an Object's Children
The CreateObjectChildren method creates the collection of child shell objects for the specified parent shell object.
This method is invoked when the ShellObjectBase.Children property is first accessed, which often occurs as the parent shell object is being expanded in a tree control, or is set as the root shell folder of a list control. The method's results are used to construct the collection returned by that property.
Only shell folders (not files or links) should ever return children.
Creating an Object for a Parsing Name
The CreateObjectForParsingName method creates an IShellObject based on the specified full parsing name.
A full parsing name is a unique string that can identify a shell object, often the same as a file system path. See the Shell Objects topic for more information on parsing names.
The AreNamesCaseSensitive property returns whether shell object names like parsing names are case-sensitive. The WindowsShellService implementation returns false for this property.
Getting an Object's Full Path
The Grids tree controls like TreeListBox have their own concept of "paths." Those tree controls provide the foundation of several shell UI controls and thus inherit that "path" concept, which can be different from a shell file system path.
First, a tree control "path" segment is returned for each item in the tree. These paths can be combined with a path separator delimiter (often "\") to construct what is called a "full path." Thus, a "full path" becomes a delimited string where each "path" segment in it, can be examined to walk down the tree hierarchy.
The Shell Objects topic has more information on paths. In general though, the IShellObject.RelativeParsingName is what is returned as the path segment for each shell object, used to build up a "full path."
Creating an Object's Properties
The CreateProperties method creates a collection of IShellProperty objects for the specified shell objects.
A ShellPropertyRequestKind enum value is also passed, specifying the kind of properties to return. These values are supported:
DefaultColumns- Return the properties that should show in a ShellListView control.AllColumns- Isn't really used in UI but allows you to examine all available properties.
The IShellProperty interface defines a property, such as its key, canonical name (non-localized name), display name, default column width, column sort direction, column horizontal alignment, etc. The column-related properties are specifically for use within a ShellListView control.
If you wish to supply your own shell property results, make a class that implements the IShellProperty interface and return instances of that.
The most common properties returned for file system folders have these canonical names:
"System.ItemNameDisplay""System.DateModified""System.ItemType""System.Size"
Getting an Object's Property Value
The GetPropertyValue method examines an IShellObject to return a value for the specified IShellProperty.
This method is called when getting values to insert into ShellListView control cells.
Comparing Objects Using a Property
The CompareObjectsUsingProperty method compares two IShellObject instances using the specified IShellProperty.
This method is called when sorting a ShellListView control by a column, since each column represents an IShellProperty. The integer result from numerous calls to the method for various shell object pairs is used to determine their final sort order.