I’m trying to see how far I can go in implementing a WPF application purely in F# (and I don’t mean that third party or framework libraries must be F#, just my code). The application isn’t going to be massive or probably very complex, I’m just interested in finding the “pain points” of using F# and WPF. <\/p>\n
In previous posts I’ve created the code to start-up an application and load the main window along with how I might assign a view model to the DataContext of the main window. <\/p>\n
I now want to take care of the usual mundane tasks such as binding to a view model, handling property change events on the INotifyPropertyChanged interface and implementing commands using the ICommand interface.<\/p>\n
Handling property changes and INotifyPropertyChanged<\/strong><\/p>\n In my C# WPF projects I use a extension methods that both assign values (if a property has changed) and raises PropertyChanged events using Expression objects as opposed to “magic strings”, i.e.<\/p>\n I wanted to have something similar in F#. Instead of extension methods, I went the base class route<\/p>\n Where the propertyName functions is defined elsewhere as <\/p>\n\r\npublic string Name\r\n{\r\n get { return name; }\r\n set { this.RaiseAndSetIfChanged(x => x.Name, ref name, value); }\r\n}\r\n<\/pre>\n\r\ntype ViewModelBase() =\r\n let propertyChanged = Event<_, _>()\r\n interface INotifyPropertyChanged with\r\n [<CLIEvent>]\r\n member this.PropertyChanged = propertyChanged.Publish\r\n\r\n member private this.OnPropertyChanged p = propertyChanged.Trigger(this, PropertyChangedEventArgs(p))\r\n \r\n member this.RaisePropertyChanged (p : obj) =\r\n match p with\r\n | :? string as s -> \r\n this.OnPropertyChanged s\r\n | :? Expr as e -> \r\n match propertyName e with\r\n | Some(pi) -> \r\n this.OnPropertyChanged pi\r\n | None -> ()\r\n | :? (string array) as a ->\r\n a\r\n |> Array.iter (fun propertyName -> this.RaisePropertyChanged propertyName) \r\n | :? (Expr array) as a ->\r\n a\r\n |> Array.iter (fun propertyExpression -> this.RaisePropertyChanged propertyExpression) \r\n | null ->\r\n this.OnPropertyChanged null\r\n | _ -> ()\r\n\r\n member this.RaiseAndSetIfChanged ((p : obj), (backingField : 'b byref), newValue) =\r\n assert (p <> null)\r\n\r\n match EqualityComparer.Default.Equals(backingField, newValue) with\r\n | true -> false\r\n | false -> \r\n backingField <- newValue\r\n this.RaisePropertyChanged p\r\n true\r\n\r\n<\/pre>\n
\r\nlet rec propertyName quotation =\r\n match quotation with\r\n | PropertyGet (_,propertyInfo,_) -> Some(propertyInfo.Name)\r\n | Lambda (_,expr) -> propertyName expr\r\n | _ -> None\r\n<\/pre>\n