Question

After a hiatus from my Silverlight / F# application, i am starting back into it and am running into an issue I cannot seem to get my head around. I have a member variable of my usercontrol that is a list ref, on button clicks I want to add records to it – but it never updates. I am pretty sure it has to do with being a member but I havent figured it out.

Thanks in advance to those who take the time to view and reply.

the problem lines:

.
.
.
member this.brokers = ref List.empty
.
.
.
// this line doesn't seem to work
this.brokers := candidate :: (!this.brokers)
.
.
.

the class:

type Page() as this =    
    inherit UriUserControl("/xyz;component/page.xaml", "page")
    do
        this.firm.ItemsSource <- RpcXYZ.getFirms()
        this.email.Background <- SolidColorBrush(Colors.Red)
        this.addBtn.IsEnabled <- false
        ()

    // instance data
    member this.brokers = ref List.empty

    // bound controls for add candidate
    member this.FE : FrameworkElement = (this.Content :?> FrameworkElement)
    member this.fname : TextBox = this.FE ? fname
    member this.lname : TextBox = this.FE ? lname
    member this.email : TextBox = this.FE ? email
    member this.firm : RadComboBox = this.FE ? firms
    member this.addBtn : RadButton = this.FE ? addBtn

    member this.addCadidate_Click (sender : obj) (args : RoutedEventArgs)  = 
        let inline findFirm (f : RpcXYZ.firm) =
            f.id = Int32.Parse(this.firm.SelectedValue.ToString())

        let candidate : SalesRep = {
            id = -1 ; 
            fname =  this.fname.Text ;
            lname = this.lname.Text ;
            email = this.email.Text ;
            phone = "" ;
            firm = List.find findFirm <| RpcXYZ.getFirms();
            score = None ;
        }

        // this line is fine t is a list of 1 item after 1 click
        let t = candidate :: (!this.brokers)

        // this line doesn't seem to work
        this.brokers := candidate :: (!this.brokers)

        ChildWindow().Show()  |> ignore ;

    member this.email_Changed (o : obj) (arg : TextChangedEventArgs) = 
        let txtBox = (o :?> TextBox)
        let emailRegex = Regex("(\w[-._\w]*\w@\w[-._\w]*\w\.\w{2,3})")
        if emailRegex.IsMatch(txtBox.Text) = false then
            txtBox.Background <- SolidColorBrush(Colors.Red)
            this.addBtn.IsEnabled <- false
        else
            txtBox.Background <- new SolidColorBrush(Colors.White)
            this.addBtn.IsEnabled <- true

Answer 1

This

member this.brokers = ref List.Empty

defines a property getter. Every time you touch .brokers, it re-runs the code on the right hand side. That’s the issue.

The fix would be to define an instance variable, and return that:

let brokers = ref List.Empty
member this.Brokers = brokers

Then a single ref is allocated when an instance of the class is constructed, and you keep accessing that same ref object via the member property.