How to call a function when a static property changes or is re-bound

Question

What is the easiest way to fire a callback/handler function when a list of strings changes but also when it's re-bound.

I tried switching from List to ObservableCollection and using CollectionChanged it does work on Add/Remove, but I also need it to work like this when I re-bind the list using "= new".

static class GlobalProperties
{
    private static ObservableCollection<string> _mylist = new ObservableCollection<string>();

    public static ObservableCollection<string> MyList
    {
        get
        {
            return _mylist ;
        }
        set
        {
            _mylist = value;
        }
    }
}

class Program
{
    static void Main(string[] args)
    {
        Globals.MyList.CollectionChanged += HandleChange;
    }

    public static void HandleChange(object sender, NotifyCollectionChangedEventArgs e)
    {
        Console.WriteLine("test");
    }
}

I need to be able to attach a handler/callback function to - also when setting the property, and not just when adding or removing. This needs to be possible from the main function of the console application.

where are you stuck? you seem to be on the right track. you an just add your function to your `set { }` and as a listener to the `_mylist` — Neville Nazerane, Jan 17 '18 at 23:38
I have these 2 files. The Program.cs with the main function and this GlobalProperties.cs which has a bunch of static properties. The handler function needs to be outside the GlobalProperties (right now in Program.cs, main function), so wouldnt it create a circular dependency to refer a function in Program.cs from GlobalProperties.cs when Program.cs already uses GlobalProperties.cs? — Dac0d3r, Jan 17 '18 at 23:41
Why not add a `CollectionChanged` event to the `GlobalProperties` class, and call it in the setter `if (_mylist != value)`? — Rufus L, Jan 17 '18 at 23:47
Well I might end up doing just that, but ideally I'd prefer to keep only the observable global properties there. Also the handler function might need to be in another context/scope with variables and logic which is not accessible from within the GlobalProperties class. — Dac0d3r, Jan 17 '18 at 23:52

Neville Nazerane · Accepted Answer · 2018-01-18T00:08:36.990

2

You could use this:

static class GlobalProperties
{
    private static ObservableCollection<string> _mylist = new ObservableCollection<string>();

    public static ObservableCollection<string> MyList
    {
        get
        {
            return _mylist;
        }
        set
        {
            if (_mylist == value) return; // suggested on comment. Relocate if you still need to run GotUpdated()
            _mylist = value;
            GotUpdated();
            _mylist.CollectionChanged += (sender, e) => GotUpdated();
        }
    }


    public static Action GotUpdated { private get; set; }

}

edited Jan 18 '18 at 00:08

answered Jan 17 '18 at 23:45

Neville Nazerane

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check this if you want to make it as an event https://stackoverflow.com/questions/623451/how-can-i-make-my-own-event-in-c – Neville Nazerane Jan 17 '18 at 23:49
1

Won't this add a duplicate event delegate on every set? – Jonathon Chase Jan 17 '18 at 23:54
no, it is done after the new _mylist object is assigned. Unless the same object is being reassigned, in which case we can `=+` first – Neville Nazerane Jan 17 '18 at 23:55
Thanks. A question to your code. How would I define the handler function outside GlobalProperties - eg. in Program.cs -> main function? I cannot do this: "Globals.GotUpdated = HandleChange;" Getting the error: No Overload for 'HandleChange' matches delegate 'Action' – Dac0d3r Jan 18 '18 at 00:00
1

Or in the setter you can just add the first line: `if (_mylist == value) return;` – Rufus L Jan 18 '18 at 00:04
Well if you want to use it as an event, you can check the link in my first comment on how to make an event instead of `Action GotUpdated`. Else if you don't need the parameters in your `HandleChange` function, you can use `Globals.GotUpdated = () => HandleChange()` – Neville Nazerane Jan 18 '18 at 00:05
@RufusL yes, that if statement can be added in any line according to the OPs requirement. For instance if he still needs to run the `GotUpdated()` – Neville Nazerane Jan 18 '18 at 00:07
It would be sweet to be able to do: Globals.GotUpdated = `(myParam) => HandleChange(myParam);`, but then I'd need to go the events route? – Dac0d3r Jan 18 '18 at 00:10
1

no you can do `Action – Neville Nazerane Jan 18 '18 at 00:42

How to call a function when a static property changes or is re-bound

1 Answers1