Question

Suppose I have 3 classes to handle all database related requests:

public class DB_A{}
public class DB_B{}
public class DB_C{}

and I got 2 windows to interact with user:

window1.xaml;window1.xaml.cs;
window2.xaml;window2.xaml.cs

as window1 & window2 need to interact with database, they need to use functions from previous 3 classes, I created a class DataHandler:

public class DataHandler
{
    public DB_A a;
    public DB_B b;
    public DB_C c;

    public DataHandler()
    {
        a = new DB_A();
        b = new DB_B();
        c = new DB_C();
    }

    //some functions... ...
}

now the class DataHandler can handle all database related request, and now i need to pass a instant of DataHandler to both window1 and window2.

I tried to re-write the constructor for both window1 and window2 with parameter, but it does not allow me to do that. After google i know that WPF window form does not allow constructor with parameter.

Is there any way to pass my DataHandler to the two window form classes?

Answer 1

Make DataHandler a singleton, and let the window classes access it.

public class DataHandler
{
    //singleton instance
    static DataHandler _instance = new DataHandler ();

    public DataHandler Instance
    {
          get { return _instance; }
    }
};

Then,

public partial class Window1 : Window
{
   DataHandler _dataHandler;

   public Window1()
   {
        InitializeComponent();

        _dataHandler = DataHandler.Instance;
   }
}

Similarly, write other Window class.

Or even better is, apply some variant of MVP pattern, most likely, MVVM. Read these articles:

• Composite Guidance for WPF : MVVM vs MVP
• WPF patterns : MVC, MVP or MVVM or…?
• Model-View-Presenter Pattern
• Model View Presenter