1. Create element without an explicit Frame.
2. Set TranslatesAutoresizingMaskIntroConstraints = false
3. Create an array of NSLayoutConstraints
4. Work top-to-bottom, left-to-right, or vice versa. Do this consistently throughout program
5. Use Layout Anchors
6. Use the top-level UIViews SafeAreaLayoutGuide to position relative to the Window / screen
7. For each dimension, set its location (LeadingAnchor / TopAnchor or …

I wanted to indicate the most recent move in an AI-on-AI game of TicTacToe, so I wanted to have the most recent move be highlighted. The Xs and Os are CAShapeLayer objects.

Here's the code to do it, ~~featuring a very ugly hack to cast an IntPtr to an NSObject …

Easy-peasy, lemon-squeazy:

[code lang="csharp"]
var a = GKGraphNode2D.FromPoint (new Vector2 (0, 5));
var b = GKGraphNode2D.FromPoint (new Vector2 (3, 0));
var c = GKGraphNode2D.FromPoint (new Vector2 (2, 6));
var d = GKGraphNode2D.FromPoint (new Vector2 (4, 6));
var e = GKGraphNode2D.FromPoint (new Vector2 (6, 5));
var f = GKGraphNode2D.FromPoint (new …

OK, so this is silly, but:

[code lang="csharp"]
var clearRule = GKRule.FromPredicate ((rules) => reset, rules => {
output = "";
reset = false;
});
clearRule.Salience = 1;

var fizzRule = GKRule.FromPredicate (mod (3), rules => {
output += "fizz";
});
fizzRule.Salience = 2;
var buzzRule = GKRule.FromPredicate (mod (5), rules => {
output += "buzz";
});
buzzRule.Salience = 2;

var outputRule = GKRule.FromPredicate …

# How to: Handoff to a Xamarin iPhone app from Apple Watch

There are two ways to activate the parent (aka container) app from an Apple Watch app. You can either directly activate the container app using WKInterfaceController.OpenParentApplication or you can use Handoff.

Using Handoff is a little more complex …

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:

[code lang="csharp"]
interface IFoo
{

}

static class IFoo_Extensions
{
public static void …

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:

[code lang="csharp"]
public class App
{
public static Page GetMainPage ()
{
return new ContentPage …

There have been great barcode-reading libraries available for Xamarin for some time, but iOS 7 has built-in barcode-recognition support.

There's only one tricky bit: you have to tell the AVCaptureMetadataOutput what types of barcodes you're interested in after you've added it to the AVCaptureSession. (I suppose what happens behind the …

The new M7 coprocessor in the iPhone 5S makes pedometer apps trivial:

[code lang="csharp"]
if(CMStepCounter.IsStepCountingAvailable)
{
var counter = new CMStepCounter();
//Last 8 hours
counter.QueryStepCount(NSDate.FromTimeIntervalSinceNow(-8 * 60 * 60), NSDate.Now, NSOperationQueue.CurrentQueue, StepQueryHandler);
}

void StepQueryHandler(int nssteps, NSError error)
{
Console.WriteLine(nssteps);
}
[/code]

Multipeer Connectivity allows you to discover and share data with other iOS devices within Bluetooth radio range or on the same WiFi subnet. It is much easier to use than Bonjour.

I wrote a simple MPC chat program in Xamarin.iOS.

There's necessarily a few hundred lines of code, but …