Azure, Web & Mobile

How to fix the IPv4 loopback interface: port already in use error.

Super quick post here. Sometimes when debugging your .NET Core application on Mac, you’ll find the port won’t free up, and thus you can’t redeploy without getting the following fatal error:

Unable to start Kestrel. System.IO.IOException: Failed to bind to address http://localhost:5000 on the IPv4 loopback interface: port already in use.

To fix this, you’ll need to fire up Terminal and enter the following:

sudo lsof -i :5000

In my case, this outputted the following:

Screen Shot 2017-10-20 at 18.54.54.png

I know the error is referencing the IPv4 Type which allows me to quickly find the PID number, which I’ll use to kill the connection. I do this with the following command

kill -9 18057

With that done, I can now get back to debugging my .Core web API on macOS.

Auto Layout, Beer Drinkin, iOS, Uncategorized

Stretchy UITableView Headers with Xamarin

The Yahoo News Digest app includes a couple of interesting user interface elements that I wanted to use within my own apps. The feature that I was most keen to recreate was the stretching UITableViewHeader. Its an effect seen in lots of iOS (sometimes referred to as a parallax header). As Beer Drinkin is going to support multi-tasking on iOS, I needed to ensure my implementation continues to support Storyboards and Auto Layout. Fortunately it proved very simple to get everything setup. In this blog post I’ll be sharing how I went about implementing it


Setting up the Storyboard

Adding a header view

To get started I opened my existing Storyboard and selected the UIViewController that requires the tableview header. In my case the scene (or view controller) isn’t a UITableViewController because I require a floating ‘Check in’ button to be visible at all times. Its worth noting that all the steps in the tutorial work with both UITableViewControllers and UIViewControllers.

Screen Shot 2016-02-01 at 11.36.06

Once I had the storyboard loaded, I dragged a UIView from the toolbox and made sure to insert it above the UITableViewCells as a the header view for the table. I then added a UIImageView to the new UIView and set its constraints to be 0,0,0,0. This way when the parent view (the UIView) resizes, the UIImageView will resize as well. I also made sure to set the UIImageView view mode property to Aspect Fit, which makes sure the image looks great no matter what size the view.

Screen Shot 2016-02-01 at 11.39.13

Adding some C#

Adding the resize code

If I were to have run this now, the table header would be displayed but wouldn’t resize with scroll events. To add scaling, I needed to add a code into my ViewController to setup the stretchy goodness that I wanted.

Because I use the header views height in a number of locations throughout the beer description view controller, I went ahead and created a variable rather than scattering magic numbers over my class.

private nfloat headerViewHeight = 200;

Managing the header view

To allow me to manage the table header, I needed to remove it from the UITableView and keep it as a variable for use later. To do this I created a variable in the beer description view controller.

private UIView headerView;

When we load the view controller, we’ll want to set our headerView variable and then set the UITableViews header property to null. This means the tableview has no header view to manage anymore, instead I’ve taken control of the view which allows me to ensure it resizes correctly as the table view scrolls.Despite having just removed the header view from the UITableView, I actually want to go ahead and add it to the table view hierarchy (but not as the header view property of the UITableView)

 headerView = tableView.TableHeaderView;
 tableView.TableHeaderView = null;
 tableView.AddSubview (headerView);
 tableView.ContentInset = new UIEdgeInsets (headerViewHeight, 0, 0, 0);
 tableView.BackgroundColor = UIColor.Clear;

Listening to TableViewDidScroll

In order to successfully respond to the DidScroll event of the UITableViewSource, I’ll need to create an event in the table views delegate. This is because of an issue with the UITableView DidScroll event not firing when a delegate has been set.

public override void Scrolled (UIScrollView scrollView)
    DidScroll ();

public event DidScrollEventHandler DidScroll;

We can now hook up the table DidScroll event with a small piece of logic for resizing the view.

//Update Tableview
tableView.Source = new BeerDescriptionDataSource(ref cells);
var deleg = new DescriptionDelegate (ref cells);
deleg.DidScroll += UpdateHeaderView;
tableView.Delegate = deleg;

tableView.ReloadData ();
View.SetNeedsDisplay ();
void UpdateHeaderView ()
    var headerRect = new CGRect (0, -headerViewHeight, tableView.Frame.Width, headerViewHeight);
    if (tableView.ContentOffset.Y < -headerViewHeight)
        headerRect.Location = new CGPoint (headerRect.Location.X, tableView.ContentOffset.Y);
        headerRect.Size = new CGSize (headerRect.Size.Width, -tableView.ContentOffset.Y);
    headerView.Frame = headerRect;


Its very easy to use this approach to add resizing animations to any number of controls within your UITableView. My favourite part of this solution is that it works perfectly across all iOS devices and doesn’t force me to drop support of Autolayout.


Find your users gender without asking

The app I’m working on in my spare time (BeerDrinkin) requires a modest amount of user data to in the future provide the best possible suggestions for new beers the user might like to try. Part of building a great model of my users is knowing thier gender.

When a user authenticates within BeerDrinkin using Facebook, I can simply parse the returned information and add the users gender to my database. Unfortunately, not all social authentication providers were born equal. With the recent addition of Google Auth, which I added to allow my father (who isn’t even sure what Facebook is) to use my app, I was unable to get the users gender.

Its for this reason that I’ve created a library that allows me to query Genderize. Genderize is a restful service which allows me to determine the gender of a user based on only a first name. It offers a free tier which includes the ability to query 1000 names a day which is more than enough for my requirements. If I find myself hitting the limit I’ll firstly buy a bottle of champagne to celebrate high user adoption and to drink away the thoughts of my Azure bill. On a serious note, Genderize provide the option to upgrade the account plan for a nominal fee to 100,000 users a month.

Given that BeerDrinkin does some sneaky UX to make a Facebook auth more likely (I delay showing the Google sign-in button for a few seconds so the user intially is confronted with only 1 option. Its very subtle but seems to help push Facebook as the prefered option), the free teir should be perfect for me.

Creating a PCL to interact with Genderize

To get started I headed over to the Genderize’s documentation to see what response I should expect back when querying the service. It’s actually increbily easy to use this service so much so that the entire PCL consists of no more than 100 lines of code.

Sample JSON response


Corresponding C# model

public class Response
    private string gender { get; set; }

    public string Name { get; set; }

    public Gender Gender { get; set; }

    public string Probability { get; set; }

    public int Count { get; set; }

public enum Gender

One thing to note is that I’m using Json.NET’s JsonConverter to deal with converting from a string gender to an enum. This is just one of the many featuress of Json.NET that make it a pleasure to use.

Genderize Client Code

public class Client
    public Client()

    public async Task GenderizeSingleName(string name)
        if (_client == null)
            _client = new HttpClient();

        Response model;

        var url = string.Format("{0}", name);
        var response = await _client.GetAsync(url);

        var jsonString = response.Content.ReadAsStringAsync();
        model = JsonConvert.DeserializeObject(jsonString.Result);

        return model;

    HttpClient _client;

As always, its open source

If you want to use the library, you can go ahead and grab a copy from my GitHub page. Once I get home from Australia I’ll add more features and publish to Nuget.



Cross-Platform Desktop UIs with C#


I’ve spent the last 4 weeks traveling Europe for the Xamarin European roadshow, and have had the opportunity to meet a few thousand C# developers who share a passion for cross-platform development.

In almost every city, I’ve been asked to recommend a Xamarin.Forms style library for developing desktop applications. In this blog post I’m going to give an overview of the different options available to desktop developers who wish to target Windows, Mac and Linux.

Traditional Approach

The first approach is what we’ve named at Xamarin the ‘traditional’ approach. You’ve probably seen this approach, but for mobile. The general idea is that you should implement your user interface uniquely for each platform you wish to target. This means on Mac, you would use Cocoa (Xamarin.Mac), Windows would use WPF and Linux would use Gtk (Gtk#). This approach will guarantee that your desktop application looks and behaves as the platform users expect. It also means that your application looks great if Apple, Microsoft or the OpenSource community decide to update the look and feel of the underlying OS. It’s also worth noting that with this approach you gain 100% access to every UI control and API available in the UI libraries, and won’t be limited in your ability to create beautiful experiences for your users.

In case you’re in any doubt, this is the approach I recommend you take when developing your apps. This is actually the approach Xamarin has started to use for our new products. You can see this in action with our Profiler and Android Simulator; both of these use WPF on Windows, and Xamarin.Mac (Cocoa) on OS X.


Much like Xamarin.Forms, Xwt allows you to use one API that maps to the native widgets of the platform. This means your application when running on Windows will be using WPF widgets, on Mac its Cocoa, and Linux is Gtk. This results in a 100% native user interface on three platforms from one codebase. Much like Xamarin.Forms, because its aim is to create a unified API for all desktop platforms, it only maps to a subset of widgets and properties. It’s worth noting that with Xwt you still have the ability to implement a native widget which isn’t mapped as part of the API.

For all platforms you can use the native engine, or the Gtk engine. If you’re wondering what a Gtk app looks like on Windows and Mac, then I recommend downloading Xamarin Studio. This is primarily built using Gtk, and in areas actually uses Xwt. On Windows the native engine is WPF, on OS X its Cocoa, and on Linux it remains Gtk (using Gtk#).


One other option you might want to consider, is using a WebView for your user interface whilst maintaining a C# backend. This is the approach that Rdio has taken for their OS X client, and to a novice it’s difficult to spot that it’s not a native app. This approach can produce some great looking applications which can even run in the Cloud, but it would be difficult to claim you’ve created an application when the reality is you’ve packaged up a website.


Although this approach is not yet ready for consumption, I thought I would mention it as it’s a project on GitHub that excites me. Much like Xamarin.Mac is a binding to the Cocoa framework, a group of enterprising .Net developers are aiming to create a .Net binding to the Qt library. Having used Qt in a previous life, I can confirm that the UIs can often be a little hit or miss (because it’s a lowest common denominator approach). That said, if you’re developing an internal application, or willing to take the time to craft the UI for each platform (different layouts for each platform) then it can work really well.

The project is still in its infancy, and many developers have tried and failed at this approach. Its not ready for production as yet (it doesn’t appear to even be close) but its a great start. My fingers are crossed that the developers continue to invest their time in the project, and the .Net community gains access to one of the most widely used cross-platform user interfaces frameworks in existence.


Renaming your Xamarin.Mac App

Apple has a number of guidelines and rules for developers looking to publish their Apps to Apple’s app ecosystem. One of these rules relates to the name of your app. To give you a quick overview of how some developers can have issues with theses rules, I’ve gone ahead and listed a few of them below:

  • Apps with names, descriptions, screenshots, or previews that are not relevant to the content and functionality of the App will be rejected.
  • App names in iTunes Connect and as displayed on a device should be similar, so as to not cause confusion
  • Apps that misspell Apple product names in their App name (i.e., GPS for Iphone, iTunz) will be rejected.

If your App has any of the following issues then Apple will reject your binary and ask you to change the app name. In this tutorial, I will show you the properties you need to change your app name.

Menubar & About dialog

To update the name in the Finder menu bar and the About dialog, you will need to update the Bundle Name which can be found in your projects Info.plist (you will need to select the ‘Source’ tab).



To update the name displayed in the Dock (on hovering over the app icon), you will need to change the “Assembly name.” To do this, you will need to navigate to the project options (right click the project and select “Options”). You will find the Assembly name property under the “Output” tab.


Installer Package

If you’re producing an installer package for your App, you will need to edit the project name in order for the generated package to have your new name. To do this, simply right click on the project and select “Rename”.