Paulo Morgado

The application I'm currently working on has a rather complex UI. It's something like two tabbed work spaces and an outlook-like work space, that make one workspace by itself, that can have several instances inside another tabbed workspace, that can have several instances inside another tabbed workspace. Imagine something like Visual Studio, inside a tab.

Each work space is controlled by its own work item and the same goes to every smart part.

With a UI like this, the work item activation service supplied by the CAB is of no use for me because I need to know what is the active work item at various levels.

What I came up with to solve my problem is the following implementation of the work item activation service:

public class HierarchicalWorkItemActivationService : IWorkItemActivationService
{
    private object syncroot = new object();
    private WorkItem activeWorkItem;
    private WorkItem hostingWorkItem;

    public HierarchicalWorkItemActivationService()
    {
    }

    [ServiceDependency]
    public WorkItem HostingWorkItem
    {
        set
        {
            Debug.Assert(value != null);
            if (value == null)
            {
                throw new ArgumentNullException("value");
            }
            Debug.Assert(this.hostingWorkItem == null);
            if (this.hostingWorkItem != null)
            {
                throw new InvalidOperationException("HostingWorkItem already set.");
            }
            this.hostingWorkItem = value;
        }
    }

    public void ChangeStatus(WorkItem item)
    {
        lock (syncroot)
        {
            if (item == this.hostingWorkItem)
            {
                WorkItem hostingParentWorkItem = this.hostingWorkItem.Parent;
                if (hostingParentWorkItem != null)
                {
                    IWorkItemActivationService parentWorkItemActivationService = hostingParentWorkItem.Services.Get<IWorkItemActivationService>();
                    if (parentWorkItemActivationService != null)
                    {
                        parentWorkItemActivationService.ChangeStatus(this.hostingWorkItem);
                    }
                }
            }
            else
            {
                if (item.Status == WorkItemStatus.Active)
                {
                    if (item != this.activeWorkItem)
                    {
                        if (this.activeWorkItem != null && this.activeWorkItem.Status != WorkItemStatus.Terminated)
                        {
                            this.activeWorkItem.Deactivate();

                            // If the activeWorkItem is still active deactivates the item and aborts.
                            if (this.activeWorkItem.Status == WorkItemStatus.Active)
                            {
                                item.Deactivate();
                                return;
                            }
                        }
                        this.activeWorkItem = item;
                    }
                }
            }
        }
    }
}

For those who like to unit test their software and are developing CAB applications, the SCSF comes with sample applications with unit tests. These unit tests are built on top of an useful set of testable classes which one of them is the TestableRootWorkItem.

As I understand it, the MVP (Model/View/Presenter) design pattern states that all presentation decisions are the Presenter's responsibility.

In the CAB world, this should include the Smart Part Info.

But the IWorkspace interface only allows you to provide the Smart Part Info (a class that implements the ISmartPartInfo interface and each work space uses a specific one), or the the smart part (the View in the MVP design pattern) should know what information to provide to the work space it lives in by implementing the ISmartPartInfoProvider interface.

To enable the presenter to provide the smart part info changes need to be made to the IWorkspace interface and its implementations. New Show and ApplySmartPartInfo methods need to be added:

/// <summary>
/// Applies the smartPartInfo to the smartPart.

/// </summary>
void ApplySmartPartInfo(object smartPart, ISmartPartInfoProvider smartPartInfoProvider);
/// <summary>
/// Shows SmartPart using the given SmartPartInfo
/// </summary>
/// <param name="smartPart">Smart part to show.</param>
/// <param name="smartPartInfoProvider"></param>
void Show(object smartPart, ISmartPartInfoProvider smartPartInfoProvider);

And it should be implemented in all the classes that implement IWorkspace:

/// <summary>
/// Applies the smartPartInfo to the smartPart.
/// </summary>
public void ApplySmartPartInfo(object smartPart, ISmartPartInfoProvider smartPartInfoProvider)
{
    Microsoft.Practices.CompositeUI.Utility.Guard.ArgumentNotNull(smartPart, "smartPart");
    Microsoft.Practices.CompositeUI.Utility.Guard.ArgumentNotNull(smartPartInfoProvider, "smartPartInfoProvider");
    ThrowIfUnsupportedSP(smartPart);
    ThrowIfSmartPartNotShownPreviously((TSmartPart)smartPart);

    TSmartPart typedSmartPart = (TSmartPart)smartPart;
    TSmartPartInfo typedSmartPartInfo = GetSupportedSPI(smartPartInfoProvider.GetSmartPartInfo(typeof(TSmartPartInfo)));
    Microsoft.Practices.CompositeUI.Utility.Guard.ArgumentNotNull(typedSmartPartInfo, "typedSmartPartInfo");

    OnApplySmartPartInfo(typedSmartPart, typedSmartPartInfo);
}

/// <summary>
/// Shows SmartPart using the given SmartPartInfo
/// </summary>
/// <param name="smartPart">Smart part to show.</param>
/// <param name="smartPartInfoProvider"></param>
public void Show(object smartPart, ISmartPartInfoProvider smartPartInfoProvider)
{
    Microsoft.Practices.CompositeUI.Utility.Guard.ArgumentNotNull(smartPart, "smartPart");
    Microsoft.Practices.CompositeUI.Utility.Guard.ArgumentNotNull(smartPartInfoProvider, "smartPartInfoProvider");
    ThrowIfUnsupportedSP(smartPart);
       
    TSmartPart typedSmartPart = (TSmartPart)smartPart;

    if (smartParts.Contains(typedSmartPart))
    {
        ApplySmartPartInfo(typedSmartPart, smartPartInfoProvider);
        Activate(typedSmartPart);
    }
    else
    {
        TSmartPartInfo typedSmartPartInfo = GetSupportedSPI(smartPartInfoProvider.GetSmartPartInfo(typeof(TSmartPartInfo)));
        Microsoft.Practices.CompositeUI.Utility.Guard.ArgumentNotNull(typedSmartPartInfo, "typedSmartPartInfo");
        smartParts.Add(typedSmartPart);
        OnShow(typedSmartPart, typedSmartPartInfo);
    }
}

For those who don't know, the ManagedObjectCollection registers its elements using the objects running type as part of the key.

Recently, I had the need to add and retrieve a component to the WorkItem's Items collection independently of its running. I only wanted to retrieve the component (using a ComponentDependency) with a specified name. Needless to say that I couldn't, because I was trying to retrieve an object, and that was not the running type of the object added to the WorkItem.

I started thinking of the ability of the ServiceCollection to add items registering them with a different type would be very helpfully to the ManagedObjectCollection. So, decided to add some changes.

To be able to build elements and register them with a different type, I had to change the Build method: 

private TItem Build(Type typeToBuild, Type typeToRegisterAs, string idToBuild, object item)
{
	if (idToBuild != null && Contains(idToBuild, SearchMode.Local, true))
		throw new ArgumentException(String.Format(CultureInfo.CurrentCulture,
			Properties.Resources.DuplicateID, idToBuild));

	if (item != null && Object.ReferenceEquals(item,
		locator.Get(new DependencyResolutionLocatorKey(typeof(WorkItem), null))))
		throw new ArgumentException(Properties.Resources.CannotAddWorkItemToItself, "item");

	if (item == null)
		item = BuildFirstTimeItem(typeToBuild, typeToRegisterAs, idToBuild, null);
	else if (!container.Contains(item))
		item = BuildFirstTimeItem(typeToBuild, typeToRegisterAs, idToBuild, item);
	else
		BuildRepeatedItem(typeToBuild, typeToRegisterAs, idToBuild, item);

	return (TItem)item;
}

private object BuildFirstTimeItem(Type typeToBuild, Type typeToRegisterAs, string idToBuild, object item)
{
    item = builder.BuildUp(locator, typeToBuild, NormalizeID(idToBuild), item);

    if (typeToRegisterAs != typeToBuild)
    {
        locator.Add(new DependencyResolutionLocatorKey(typeToRegisterAs, idToBuild), item);
        locator.Remove(new DependencyResolutionLocatorKey(typeToBuild, idToBuild));
    }

    return item;
}

private void BuildRepeatedItem(Type typeToBuild, Type typeToRegisterAs, string idToBuild, object item)
{
    locator.Add(new DependencyResolutionLocatorKey(typeToRegisterAs, NormalizeID(idToBuild)), item);
}

And, to assure compability with the existing methods:

private TItem Build(Type typeToBuild, string idToBuild, object item)
{
    return Build(typeToBuild, typeToBuild, idToBuild, item);
}

Now, all I needed was to add the new methods to add elements:

public void Add(Type typeToRegisterAs, TItem item)
{
    Add(typeToRegisterAs, item, null);
}

public void Add(Type typeToRegisterAs, TItem item, string id)
{
    Guard.ArgumentNotNull(item, "item");
    Guard.TypeIsAssignableFromType(typeof(TItem), typeToRegisterAs, "typeToBuild");

    Build(typeToRegisterAs, item.GetType(), id, item);
}

public void Add<TTypeToRegisterAs>(TTypeToRegisterAs item)
    where TTypeToRegisterAs : TItem
{
    Add<TTypeToRegisterAs>(item, null);
}

public void Add<TTypeToRegisterAs>(TTypeToRegisterAs item, string id)
    where TTypeToRegisterAs : TItem
{
    Guard.ArgumentNotNull(item, "item");

    Build(item.GetType(), typeof(TTypeToRegisterAs), id, item);
}

public TItem AddNew(Type typeToBuild, Type typeToRegisterAs)
{
    Guard.TypeIsAssignableFromType(typeToBuild, typeToRegisterAs, "typeToBuild");

    return AddNew(typeToBuild, typeToRegisterAs, null);
}

public TItem AddNew(Type typeToBuild, Type typeToRegisterAs, string id)
{
    Guard.TypeIsAssignableFromType(typeToBuild, typeof(TItem), "typeToBuild");
    Guard.TypeIsAssignableFromType(typeToBuild, typeToRegisterAs, "typeToRegisterAs");

    return Build(typeToBuild, typeToRegisterAs, id, null);
}

public TTypeToBuild AddNew<TTypeToBuild, TTypeToRegisterAs>()
    where TTypeToRegisterAs : TItem
    where TTypeToBuild : TTypeToRegisterAs
{
    return (TTypeToBuild)Build(typeof(TTypeToBuild), typeof(TTypeToRegisterAs), null, null);
}

public TTypeToBuild AddNew<TTypeToBuild, TTypeToRegisterAs>(string id)
    where TTypeToRegisterAs : TItem
    where TTypeToBuild : TTypeToRegisterAs
{
    return (TTypeToBuild)Build(typeof(TTypeToBuild), typeof(TTypeToRegisterAs), id, null);
}