Kiwi Ingenuity

Sometimes there is a requirement to temporarily store an object that can be later retrieved.  My particular problem at the time was that I wanted to share a View Model with a second view, but alas neither view knows about one another.

My first thought was to store the view model object temporarily in a Unity Container.  That way I could easily retrieve the object at a later time. This solution was not satisfactory however because this was only suppose to be a temporary storage solution and Unity does not support any unregister operation.  Not having the ability to remove (unregister) the object was not an option.

My solution was to create a Temporary Storage Service. The service I am demonstrating here allows for the Deposit and the Withdrawal of data (objects).  Some people may want to store the data for a little bit longer than straight in and straight out.  This solution could easily be modified to suit.

My Temporary Storage Service looks like this.

public class TemporaryStorageService : ITemporaryStorageService
{
    public void Deposit<T>(Object o, string key)
    {
        System.Windows.Application.Current.Properties[key] = o;
    } 

    public T Withdraw<T>(string key)
    {   T o = (T)System.Windows.Application.Current.Properties[key];
        System.Windows.Application.Current.Properties.Remove(key);
        return o;
    }
} 

The Interface

publicinterface ITemporaryStorageService
{
   void Deposit<T>(Object o, string key);
   T Withdraw<T>(string key);
}

Register the service with Unity

// Temporary Storage Service
ITemporaryStorageService temporaryStorageService = new TemporaryStorageService();
unityContainer.RegisterInstance<ITemporaryStorageService>(temporaryStorageService);

Now I can call my Service whenever I need to store any Objects temporarily.  As I said above my immediate need was to store a view model temporarily.  So this is what I did.

My first view creates a new view model and immediately puts it in temporary storage

public class SomeWindow : Window
{
    ITemporaryStorageService _temporaryStorageService; 

    public SomeWindow(ITemporaryStorageService temporaryStorageService)
    {
        this._temporaryStorageService = temporaryStorageService;
        InitializeComponent();
    } 

    [Dependency]
    public SharedViewModel VM
    {
        set
        {
            this.DataContext = value;


            // We will store the view model in the Application Properites
            this._temporaryStorageService.Deposit<SharedViewModel>(value, "SharedViewModel");
        }
    }
} 

Then when I initialise my second view I call upon the stored viewmodel.

[Dependency]
public CashBook.MVVM.Services.ITemporaryStorageService TemporaryStorageService
{
   set
   {
      this.DataContext = value.Withdraw<SharedViewModel>("SharedViewModel");
   }
}

Works like a charm!