Programmatic AutoLayout Constraints Basics for Xamarin

  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 …
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Animating the stroke color of a CAShapeLayer with Xamarin

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 …

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GameplayKit path-finding in iOS 9 with Xamarin.iOS

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 …

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FizzBuzz with iOS 9 GameplayKit Expert System in C# with Xam.iOS

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 …

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

# 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 …

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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.


[code lang="csharp"]
interface IFoo


static class IFoo_Extensions
public static void …

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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):


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

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Natively Recognize Barcodes/QR Codes in iOS 7 with Xamarin.iOS

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 …

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My Favorite iOS 7 APIs Part 3 : CoreMotion (iPhone 5S only)

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

[code lang="csharp"]
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)

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My Favorite iOS 7 APIs: Multipeer Connectivity

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 …

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