Calling method from another window (Class) issue

Question

In code behind file of the main window of WPF application I have a method quering a database with LINQ to SQL and writing results to an ObservableCollection:

Answer 1

1) Most importantly you shouldn't be calling db logic from you windows / forms. You should abstract it out into another class. Then you could have your method return a observable collection.

However in your case I am assuming that you are trying to use the secondary form to reload / load the collection and you want it used on your primary form. The problem with this is you are creating a new instance of the form so your collection is being populated but not on your main form but a copy.

There are a couple ways you can try to get around that.

1) Make the method static and your observable collection static so that it updates a single instance.

2) Pass an instance handle of your primary form into your secondary form so that you re-use the instance you already have. This would be preferable so that you are not creating new instances all over the place.

In the constructor of the second form you could pass in the instance of your primary window so then you can use it directly. This should solve your problem.

UPDATE: Here is some code samples. Basically there are many ways to pass a reference.

You could do it like this with a constructor:

// This is the constructor for your second window
private Window _parentHandle;

public SecondWindow(Window obj)
{
    this._parentHandle = obj;
}

Then from your primary form that has the method you would open that window like this.

SecondWindow w = new SecondWindow(this);
w.Show();

Now your second window has a direct handle to your first window so you can call your method on that variable and it will update.

Another way is to have a public Setter method on your second window as well.

public Window ParentContext
{
   get { return this._parentHandle; }
   set { this._parentHandle = value; }
}

Then you could create your form instance like this:

SecondWindow w = new SecondWindow();  // so just like normal
w.ParentContext = this; // set the instance to the calling form
w.Show();

That is the basics. This type of scenario works in just about any scenario where you need to pass a reference.

Hope that helps.