F# version of QuickText.cs example for Continuous app

quick_text.fsx

//
// Quick Text Example
//
// Enables you to text quickly by defining standard messages.
//
// 1. Add the ability to delete messages
// 2. Add the most recent message at the top
//

open System
open System.Collections.ObjectModel
open System.Linq

open Foundation
open UIKit
open Xamarin.Forms

//
// Setup a "database" of quick messages stored in a text file.
//
let messages = ObservableCollection<string> ()

let ReadMessages () =
    try
        let lines = System.IO.File.ReadLines ("QuickTextMessages.txt")
        messages.Clear()
        
        for line in lines do
            //printfn "%s" line
            messages.Add(line)
    with
    | ex -> messages.Add("helli")
            //printfn "%s" ex.ToString()

let SaveMessages () =
    try
        System.IO.File.WriteAllLines ("QuickTextMessages.txt", messages)
    with
    | ex -> printfn "%s" ex.ToString()

ReadMessages ()

//
// Construct the UI
//
let lst = ListView()

lst.ItemsSource <- messages

let listPage = ContentPage (
    Content = lst,
    Title = "Quick Text"
)

let addItem = ToolbarItem (
    Text = "Add"
)

listPage.ToolbarItems.Add addItem

//put in separate function cuz the interpreter was not correctly reporting compile errors as a lambda in the function below (also a lambda).
let handleadd (itm : UIAlertView) =
    itm.Clicked.Add (fun (a : UIButtonEventArgs) ->
        if (a.ButtonIndex <> itm.CancelButtonIndex) then
            messages.Add itm.GetTextField(nint(0)).Text
            SaveMessages ()
    )    

//
// Add interaction
//
addItem.Clicked.Add (fun (a : EventArgs) ->
    // Create an add message UI
    let alert = new UIAlertView ("Add Message", "", null, "Cancel", "Add")
    alert.AlertViewStyle <- UIAlertViewStyle.PlainTextInput
    // Handle the user input
    handleadd alert
    alert.Show()
)

lst.ItemSelected.Add (fun (e : SelectedItemChangedEventArgs) ->

    match e.SelectedItem with
    | null -> ()
    | _ ->
      // Get the selected message
      let message = (string)e.SelectedItem;
      
      // Deselect the list cell
      lst.SelectedItem <- null
      
      // Create the activity UI
      let actItems = [|
          new NSString(message) :> NSObject
      |]
      let act = new UIActivityViewController (actItems, Array.empty<UIActivity>)
      
      // Display the activity UI
      let window = UIApplication.SharedApplication.KeyWindow
      act.PopoverPresentationController.SourceView <- window
      window.RootViewController.PresentViewController(act, true, null)
)

//
// Display
//
let Main = NavigationPage(listPage)