My talk “let awesome = App |> Seq.map F#” available…

Video from my Xamarin Evolve talk on using F# for programming mobile apps, in which I argue that functional and object-oriented programming are two great paradigms that pair great together.

Xamarin.Forms Programming in F#

Things are kind of busy what with Evolve being only 40 days away and iOS 8 coming down the pipe, but I thought I’d share the easy hack that allows you to program Xamarin.Forms with F#.

(Of course, Xamarin loves F# and official support and templates and documentation and all that sort of stuff is forthcoming. This is just something you can do for the moment to begin exploring Xamarin.Forms with F#.)

tl;dr: Use the beta PCL 78 F# Core and link to the facade assemblies for monotouch

OK, so assuming that was a bit too brief…

In Xamarin.Studio create a “New solution…” of type F#/iOS/iPhone/Empty Project…

Open the “References” folder and delete the existing reference to Fsharp.core.dll.

Right-click the solution and select “Add Packages…”

Screenshot 2014-08-27 15.42.39

 

In the NuGet dialog, select “Show pre-release packages” and type FSharp.Core into the search box. This should allow you to add the “FSharp.Core Mono delay signed” package.

Screenshot 2014-08-27 15.25.05Also, add the Xamarin.Forms package:

Screenshot 2014-08-27 15.46.26

And now the tricky part!  You have to add references to the System.ObjectModel.dll and System.Runtime.dlls from the monotouch facade assemblies by hand.

Right-click on the References folder, Select “Edit…”, and select “.NET Assembly”. Add references to System.ObjectModel.dll and System.Runtime.dll from, in my case:

/Library/Frameworks/Mono.framework/Versions/Current/lib/mono/4.5/Facades/

Your path may be a little different.

Write a Xamarin.Forms app in 36 lines of code :


namespace FSXF1

open System
open MonoTouch.UIKit
open MonoTouch.Foundation
open Xamarin.Forms

type App = class
 static member GetMainPage =
   let lbl = new Label()
   lbl.Text <- "Hello, F# Xam.Forms!"
   lbl.VerticalOptions <- LayoutOptions.CenterAndExpand
   lbl.HorizontalOptions <- LayoutOptions.CenterAndExpand

   let cp = new ContentPage()
   cp.Content <- lbl
   cp
end

[<Register("AppDelegate")>]
type AppDelegate() =
 inherit UIApplicationDelegate()

 member val Window = null with get, set

// This method is invoked when the application is ready to run.
 override this.FinishedLaunching(app, options) =
   this.Window <- new UIWindow(UIScreen.MainScreen.Bounds)
   Forms.Init()
   this.Window.RootViewController <- App.GetMainPage.CreateViewController()
   this.Window.MakeKeyAndVisible()
   true

module Main =
   [<EntryPoint>]
   let main args =
     UIApplication.Main(args, null, "AppDelegate")
     0

And you’re good to go!

Screenshot 2014-08-25 10.16.14

 

P.S. If it helps: https://github.com/lobrien/HelloXamarinFormsFSharp

Exploring HealthKit With Xamarin: Provisioning and Permissions Illustrated Walkthrough

One of the more interesting frameworks in iOS 8 is Health Kit, system-wide persistent storage for health-related information. I’m just beginning to explore the namespace myself, but thought I’d walk through the steps you need to manipulate Health Kit with Xamarin.

Because health-related information is so sensitive, developing for Health Kit requires:

  1. The app be developed using an “Explicit App ID” with Health Kit Services explicitly enabled (see below);
  2. The Entitlements.plist must have a com.apple.developer.healthkit key set to true; and
  3. At initial runtime, the user must grant access via a detailed permissions dialog

Additionally, it’s worth emphasizing the importance of checking error codes in Health Kit API function calls. If a user does not grant permission or if for any other reason the app makes a call to a non-permitted API, this does not raise an exception. Rather, a null or otherwise empty result will be returned and typically an out NSError or closure-parameter will be set.

Provisioning and Permissions

Xamarin has a great article on device provisioning, but just to hit the highlights for Health Kit:

You need to set an “Explicit App ID” and explicitly enable “Health Kit” as an app service. Here, I’m created an ID for an app whose ID is “{PREFIX}.com.xamarin.HKWork”:

Screen-Shot-2014-07-11-at-7.49.46-AM

Screen Shot 2014-07-11 at 7.51.14 AM

After you do that, you’ll have to create a new provisioning profile for this App ID:

Screen Shot 2014-07-11 at 7.59.17 AM

Once you’ve awaited the generation of the profile, download it and double-click to install it on your development system:

Screen Shot 2014-07-11 at 8.05.17 AM

Now, in your Xamarin Studio project, open your Info.plist and set the Bundle Identifier to your explicit App ID (without the team prefix):

Screen Shot 2014-07-11 at 8.56.35 AM

And set your project’s Bundle Signing options so that you are using your new provisioning profile:

Screen Shot 2014-07-11 at 8.14.07 AM

(Now that I’ve written that, I suspect that you can probably leave it as “Automatic”, since the App ID is explicitly the same as that in the custom provisioning profile: that’s how the two are matched by the system. But still, I’m going to leave the step just to be clear what’s happening. And I don’t think there’s any harm in setting the provisioning profile explicitly.)

You’ve taken care of Info.plist, so now open Entitlements.plist. (Some project templates don’t automatically generate an Entitlements.plist file. If your project doesn’t have one, use File/New File…/iOS and choose Entitlements.plist.) Click on “Source” and add a new key com.apple.developer.HealthKit of type Boolean with a value of Yes (== true):

Screen Shot 2014-07-11 at 9.14.53 AM

Write code to request permission from the app user

To use Health Kit, the user must grant your app access. This involves these API calls:

var temperatureKey = HKQuantityTypeIdentifierKey.BodyTemperature;
var tempQuantityType = HKObjectType.GetQuantityType (temperatureKey);

var hks = new HKHealthStore ();
hks.RequestAuthorizationToShare (new NSSet (new [] { tempQuantityType }), new NSSet (), (success, error) => {
	Console.WriteLine ("Authorized:" + success);
	if (error != null) {
		Console.WriteLine ("Authorization error: " + error);
	}
});

Here, we are requesting authorization to share body temperature data (i.e., “share data generated by my app with the HealthStore database”). When this app is run, the user will be presented with the Health Kit permissions dialog, which will give the user fine-grained control over the requested types of data you’ll share. In this case, for instance, the dialog inside the Health app looks like this:

IMG_1314

Write a brilliant app

I have no insight into how to do that.

… that has some health-related information

Oh good, I can help with that.

Creating and storing data in the shared HealthKit store involves these API calls:

var temperatureKey = HKQuantityTypeIdentifierKey.BodyTemperature;
var tempQuantityType = HKObjectType.GetQuantityType (temperatureKey);
var myCurrentTemp = HKQuantity.FromQuantity (HKUnit.DegreeFahrenheit, 98.6);
var meta = NSDictionary.FromObjectAndKey (new NSNumber (4), HKMetadataKey.BodyTemperatureSensorLocation);
var tempSample = HKQuantitySample.FromType (tempQuantityType, myCurrentTemp, new NSDate (), new NSDate (), meta);

hks.SaveObject(tempSample, (success, error) => {
	Console.WriteLine("Write succeeded: " + success);
	if(error != null)
	{
		Console.WriteLine(error);
	}
});

I trust it’s obvious that the types of data you attempt to store must match those you’ve requested permission from the end-user and that your error-handling should be considerably more sophisticated (since it’s incredibly possible that app users are going to be very cautious about allowing access to their medical data, even if it’s clearly central to the app’s value).

The resulting shared data (assuming that permissions are granted) looks like this in the Health app:

image1

Notice that although I created the data using Fahrenheit, in this case it’s being displayed as Celsius (which I imagine is the opposite of the likely use-case!). Units of measure and conversions are built in to Health Kit, which I’ll cover in a later post. For now, though: Happy Healthing!

The Protocol Pattern

In C# (and F#), one can define extension methods on interfaces. These extension methods can have implementations, which can be used as default implementations for implementors of the extension. I haven’t heard a name for this technique.

Example:

interface IFoo
{

}

static class IFoo_Extensions 
{
	public static void Foo(this IFoo self) { Console.WriteLine("Foo"); }
}

class ImplementingClass : IFoo
{

}


class MainClass
{
	public static void Main (string[] args)
	{
		var aFoo = new ImplementingClass ();
		aFoo.Foo (); //Prints "Foo" from extension default implementation

	}
}

Xamarin uses this pattern extensively when binding Objective-C Protocols, which are essentially interfaces with optional methods. For instance, if you have an interface where some methods must be implemented by the library user but some aren’t, you can do this:

interface IFoo
{
	//Methods defined here, as always, must be implemented
	void Necessary ();
}

static class IFoo_Extensions
{
	//"Optional" methods defined here with default implementations
	public static void Optional (this IFoo self)
	{
	}
}

class ImplementingClass : IFoo
{
	public void Necessary ()
	{
		Console.WriteLine ("Necessary");
	}

//    public void Optional()
//    {
//        Console.WriteLine("Overridden");
//    }

}

Obviously, it’s not exactly the same to have a default implementation defined in an extension method as it is to have an optional method that simply does not exist. But conceptually it’s close enough that I’ve started referring to this technique as the “Protocol Pattern.”

Thoughts?

Local Notifications in iOS 8 With Xamarin

As of iOS 8, the user has to provide explicit permission for apps to respond to local notifications. This means that now, the first time the program is run, you need to run code such as:

//F#
UIUserNotificationSettings.GetSettingsForTypes(
    UIUserNotificationType.Alert
    ||| UIUserNotificationType.Badge
    ||| UIUserNotificationType.Sound,
    new NSSet())
|> UIApplication.SharedApplication.RegisterUserNotificationSettings

or

//C#
var settings = UIUserNotificationSettings.GetSettingsForTypes(
    UIUserNotificationType.Alert
    | UIUserNotificationType.Badge
    | UIUserNotificationType.Sound,
    new NSSet());
UIApplication.SharedApplication.RegisterUserNotificationSettings(settings);

Which will present a user dialog. When they complete that dialog, the system will call the UIAppDelegate.DidRegisterUserNotificationSettings method. You can check the status using UIApplication.CurrentUserNotificationSettings.

If you try to send a notification without these settings being allowed, you will get a runtime error of the form:

Attempting to schedule a local notification {...} with an alert but haven't received permission from the user to display alerts
Attempting to schedule a local notification {...} with a sound but haven't received permission from the user to play sounds
Attempting to schedule a local notification {...} with a badge number but haven't received permission from the user to badge the application

F# For Scripting

It’s F# Week at Xamarin. Also, in the US, it’s only a 4-day work-week. F# saves 20% of your time. QED.

Anyway, I don’t have any actually interesting F# to share, but I recommend:

But what I thought I could quickly contribute is that:

  • F# is an awesome scripting language; and
  • Scripting may be the best way to learn F#

Scripting tasks often involve transforming a stream of text by repeatedly Filtering, Assigning, Reducing, Transforming, and Slicing it (“a sequence of FARTS“) and this is an area where the functional approach is pretty clearly easier to work with than the OOP approach of a network of cooperating objects.

And since scripting tasks are often private or semi-private low-complexity chores, they’re an excellent domain for regularly exercising your knowledge of a new language. It’s all well and good to carve out a couple weekends and work through a book but nothing beats regular exposure.

(While I’m on the subject, these are currently my favorite F# books. Initial exploration:

Deeper dives:

)

F# scripts are F# files with the .fsx extension. On OS X with mono, they can be run with fsharpi script.fsx or:

#if run_with_bin_sh
  exec fsharpi --exec $0 $*
#endif
printfn "%A" fsi.CommandLineArgs

To add references, use #r:

#if run_with_bin_sh
  exec fsharpi --exec $0 $*
#endif

#r "System.Core.dll"
#r "System.Xml"

open System
open System.Xml.Linq
open System.IO

//...etc...

I’ve been using F# for scripting for more than a year now and I can honestly say that it’s displaced Ruby as my scripting language of choice.

Give it a shot!

iOS 8, Scene Kit @ 60FPS, programmed in F#, using Xamarin.iOS

I have the best job in the world:

namespace SceneKitFSharp

open System
open MonoTouch.UIKit
open MonoTouch.Foundation
open MonoTouch.SceneKit
open MonoTouch.CoreAnimation

type MySceneKitController () =
    inherit UIViewController()

    override this.ViewDidLoad () =
        let scene = new SCNScene ()

        //Positions everyone!
        let boxNode = new SCNNode ()
        boxNode.Geometry <- new SCNBox(
            Width = 1.0F, 
            Height = 1.0F, 
            Length = 1.0F, 
            ChamferRadius = 0.02f
        )
        scene.RootNode.AddChildNode (boxNode)

        let material = new SCNMaterial ()
        material.Diffuse.Contents <- UIImage.FromFile ("textureX.png")
        material.Specular.Contents <- UIColor.Gray
        material.LocksAmbientWithDiffuse <- true
        boxNode.Geometry.FirstMaterial <- material

        //Lights!
        let lightNode = new SCNNode()
        lightNode.Light <- new SCNLight ()
        lightNode.Light.LightType <- SCNLightType.Omni
        lightNode.Position <- new SCNVector3 (0.0F, 10.0F, 10.0F)
        scene.RootNode.AddChildNode (lightNode)

        let ambientLightNode = new SCNNode ()
        ambientLightNode.Light <- new SCNLight ()
        ambientLightNode.Light.LightType <- SCNLightType.Ambient
        ambientLightNode.Light.Color <- UIColor.DarkGray
        scene.RootNode.AddChildNode (ambientLightNode)

        //Camera!
        let cameraNode = new SCNNode ()
        cameraNode.Camera <- new SCNCamera ()
        scene.RootNode.AddChildNode (cameraNode)
        cameraNode.Position <- new SCNVector3 (0.0F, 0.0F, 3.0F)


        // Action!
        let animation = new CABasicAnimation(
            KeyPath = "rotation"
        )
        let t = new SCNVector4 (1.0F, 1.0F, 0.0F, float32 (Math.PI * 2.0))
        animation.To <- NSValue.FromVector (t)

        animation.Duration <- float 5.0F
        animation.RepeatCount <- float32 Double.MaxValue //repeat forever
        boxNode.AddAnimation(animation,new NSString("rotation"))

        let scnView = new SCNView(UIScreen.MainScreen.Bounds)
        scnView.Scene <- scene
        scnView.AllowsCameraControl <- true
        scnView.ShowsStatistics <- true
        scnView.BackgroundColor <- UIColor.Black

        this.View <- scnView
       

[<Register ("AppDelegate")>]
type AppDelegate () =
    inherit UIApplicationDelegate ()

    // This method is invoked when the application is ready to run.
    override this.FinishedLaunching (app, options) =
        let window = new UIWindow (UIScreen.MainScreen.Bounds)
        window.RootViewController <- new MySceneKitController()
        window.MakeKeyAndVisible ()
        true

module Main =
    [<EntryPoint>]
    let main args =
        UIApplication.Main (args, null, "AppDelegate")
        0

IMG_0272

photo

Using Xamarin.Forms.Maps: You have to Init() first!

The first time I wrote a Xamarin.Forms.Maps program, I couldn’t figure out why my map wasn’t appearing. And then I put a call to Xamarin.FormsMaps.Init() into the AppDelegate (iOS) and MainActivity (Android):

Shared:

    public class App
	{
		public static Page GetMainPage ()
		{	
			return new ContentPage { 
				Content = new StackLayout {
					Children = {
						new BoxView { BackgroundColor = Color.Green },
						new Map(MapSpan.FromCenterAndRadius(new Position(37,-122), Distance.FromMiles(10))){
							VerticalOptions = LayoutOptions.FillAndExpand,
							HeightRequest = 100,
							WidthRequest = 960,
							BackgroundColor = Color.Blue
						},
						new BoxView { BackgroundColor = Color.Red }
					}
				}
			};
		}
	}

iOS:

    namespace HelloMap.iOS
	{
		[Register ("AppDelegate")]
		public partial class AppDelegate : UIApplicationDelegate
		{
			UIWindow window;

			public override bool FinishedLaunching (UIApplication app, NSDictionary options)
			{
				Forms.Init ();
				FormsMaps.Init ();

				window = new UIWindow (UIScreen.MainScreen.Bounds);
				
				window.RootViewController = App.GetMainPage ().CreateViewController ();
				window.MakeKeyAndVisible ();
				
				return true;
			}
		}
	}

Android:

    namespace HelloMap.Android
	{
		[Activity (Label = "HelloMap.Android.Android", MainLauncher = true)]
		public class MainActivity : AndroidActivity
		{
			protected override void OnCreate (Bundle bundle)
			{
				base.OnCreate (bundle);

				Xamarin.Forms.Forms.Init (this, bundle);
				FormsMaps.Init(this, bundle);

				SetPage (App.GetMainPage ());
			}
		}
	}

Happy Cross-Platform Coding!

Screen Shot 2014-05-30 at 1.52.09 PM

50 PRINT “HAPPY BIRTHDAY”

I think BASIC’s greatest strength may be that it was something that many people — not just those with a particular background — could learn. There was no gatekeeper, either literally or figuratively: you didn’t have to push punchcards under a bank-teller window nor did you have to learn recursion before learning recursion. In the 80s, virtually every machine ran BASIC and learning how to login and start the interpreter was generally the hardest part of beginning to “program an X machine.”

People get drop-through imperative programming: either the line-by-line flexibility of BASIC or the blocks of FORTRAN and Flash (I didn’t understand Flash until I realized that it’s just FORTRAN with worse numerics and better graphics). You don’t have to be a born programmer to understand:

 10 PRINT "HELP! I AM CAUGHT IN A PROGRAM LOOP!"
 20 GOTO 10

I imagine that 95% of the people who got a passing grade in their BASIC programming class or typed in a few games from the back of COMPUTE! magazine never wrote themselves another program. But the 5% who did found that personal computers could help them in their job. And the 1-in-100 or 1-in-1000 who went beyond that found themselves in a community where only drive and talent mattered and credentials meant nothing.

I’m a college dropout and never took a CS course in my life. At 25 I was hired as Technical Editor for a magazine that specialized in Artificial Intelligence and for Computer Language, the best programming magazine of all time (as far as size or circulation goes, we were the “We Try Harder” Avis to Dr. Dobb’s Journal‘s Hertz).

Today, the design of programming languages is discussed at sites like Lambda the Ultimate and while I can muddle through even some of the more arcane papers, and while I understand the value of a dense, high signal-to-noise ratio on certain topics, it seems to me that there’s not nearly enough reflection on the market triumphs of popular languages. I’m not advocating a return to the line-numbered BASIC interpreters (single-threaded, as if that had to be mentioned!) of my youth, but I am saying that 50 years ago, Kemeny, Kurtz, and colleagues captured lightning in a bottle. So did Dan Bricklin, inventor of the computerized spreadsheet, another tool for manipulating data and calculations that empowered an audience vastly larger than that emerging from the bottleneck of “Computer Science courses at good universities.”

I’m not suggesting that marketshare is the only, or even dominant, factor in assessing a language’s quality. In the case of JavaScript, for instance, I see an example of the contingent nature of history, as discussed in Steven Jay Gould’s classic Wonderful Life. JavaScript is a market triumph, it behooves all professional programmers to master it, but I think it’s fair to say that it has some flaws as a programming language.

Nor am I saying that there’s not a lot of discussion of “beginner’s languages.” I volunteer at a local school and am tremendously impressed by Scratch, for instance. Because Scratch is accessible at such a young age, it may generate the same kind of nostalgia that some of us share for BASIC. But I don’t suspect that it will have the truly broad, industry-expanding impact of BASIC or Flash.

Today, there’s some talk of functional programming sweeping over the industry in the same way that object-orientation did in the early 1990s. I am not a functional programming True Believer, but I truly believe that functional programming has advantages. And it seems to me that languages such as F# on the CLR and Scala on the JVM have a “you can have it all” aspect (no-hassle availability of libraries, the ability to integrate with legacy code, object-functional hybrid type-systems) that at the very least make them appealing to some teams.

But, although perhaps not as broadly accessible as line numbers and GOTO, OOP has something of BASIC’s “learnability.” We can teach OOP to a lot of people, without a lot of preliminaries. And some will struggle through, and some will have a comfortable understanding, and some will have taken a step towards design and architecting large systems. With Functional Programming, it’s not as clear to me that there’s that same “muddle through” path. It’s hard for me to imagine a better introduction to functional ideas than the early chapters of Structure and Interpretation of Computer Programs, but I think of that as a text that weeds out, not one that expands the base. If you’re a natural-born programmer with a semester in front of you SICP is a great book. But if you “just” have potential or are a working developer with a “where does this help my day-to-day problems?” pragmatism, I don’t know what you should read.

Goto 10

BASIC was the first programming language for most of those in my generation. We sat in front of green- and amber-texted monitors or machines that spooled seemingly infinite reams of paper. We typed on chiclet keys and teletypes, punched papertape and cards and threaded magnetic reels. Compared to today’s machines we had indistinguishable-from-0 working memory or horsepower.

You have no idea how fun it was.

Reviewing Values for iOS UIViewContentMode with Xamarin and F#

Who can remember the scaling behavior of UIView.ContentMode? Not me!

So I wrote this quick little F# program to review them:

    namespace Simple
     
    open System
    open MonoTouch.UIKit
    open MonoTouch.Foundation
    open System.Drawing
     
    type ContentView ( color : UIColor ) as self = 
        inherit UIView ()
        do
            self.BackgroundColor < - color

    type ContentModeModel  () = 
         inherit UIPickerViewModel ()

         let T = typedefof<UIViewContentMode>

         let selectionChanged = Event<_>()

         member this.SelectionChanged = selectionChanged.Publish 

         override this.GetRowsInComponent(_, _) = Enum.GetNames(T).Length
           
         override this.GetTitle(_, row : int, _) = Enum.GetName(T, row)

         override this.GetComponentCount(_) = 1

         override this.Selected(_, row : int, _) = selectionChanged.Trigger(enum<UIViewContentMode>(row))
       
     
    type SimpleController ( ) =
        inherit UIViewController ()
     
        override this.ViewDidLoad () = 
            this.View < - new ContentView(UIColor.Blue)

            let imgView = new UIImageView(new RectangleF(20.0F, 80.0F, UIScreen.MainScreen.Bounds.Width - 40.0F, 100.0F))
            imgView.Image <- UIImage.FromFile("flower.png")
            imgView.ClipsToBounds <- true
            this.View.AddSubview(imgView)

            let picker = new UIPickerView(new RectangleF(20.0F, UIScreen.MainScreen.Bounds.Height - 180.0F, 250.0F, 140.0F))
            let model = new ContentModeModel()
            picker.Model <- model 

            model.SelectionChanged.Add <| fun newMode -> imgView.ContentMode < - newMode

            this.View.AddSubview(picker)
     
    [<Register ("AppDelegate")>]
    type AppDelegate () =
        inherit UIApplicationDelegate ()
     
        let window = new UIWindow (UIScreen.MainScreen.Bounds)
     
        // This method is invoked when the application is ready to run.
        override this.FinishedLaunching (app, options) =
            let viewController = new SimpleController()
            window.RootViewController < - viewController
            window.MakeKeyAndVisible ()
            true
     
    module Main =
        [<EntryPoint>]
        let main args =
            UIApplication.Main (args, null, "AppDelegate")
            0

No real interesting techniques, but another nice quick iOS app in Xamarin using F#.

contentview

div>