CAB/SCSF: View Parameters

CAB/SCSF use the wellknown Model-View-Presenter design pattern for its views. There is, however, a design flaw in its implementation: you cannot pass parameters to the view constructor. As documenten in the SCSF knowledge base, the proven practice is to pass the parameters using the WorkItem State collection.

This proven practice can be improved using generics to become type-safe, while still adhering to the MVP design rules. Add the following new method to the WorkItemController base class in the Infrastructure.Interface project:

public virtual TView ShowViewInWorkspace<TView, TParams>(string viewId, string workspaceName, TParams viewParams)
where TParams : class
{
string stateKey = StateItemNames.PresenterConstructorParams + typeof(TView).FullName + ":" + typeof(TParams).FullName;
_workItem.State[stateKey] = viewParams;

TView view = ShowViewInWorkspace<TView>(viewId, workspaceName);
return view;
}

Then add the following new method to the Presenter base class in the Infrastructure.Interface project:

protected TParams ViewParameters<TParams>() where TParams : class
{
//NOTE: must use typeof(view instance) to get correct run-time type of generic view type
string stateKey = StateItemNames.PresenterConstructorParams + _view.GetType().FullName + ":" + typeof(TParams).FullName;
return (TParams)_workItem.State[stateKey];
}

Now you can simply pass the parameters from the module controller to the view using ShowViewInWorkspace and then get the parameters in the presenter's OnViewReady event:

_viewParameters = ViewParameters<ViewParameters>();
if (_viewParameters == null)
{
throw new ArgumentException("Required view parameter error", "ViewParameters", null);
}

This little design improvement hides the gory details of using the untyped object State collection, e.g. generating shared keys and type casting.