Monday, October 30, 2017

3 Steps to implementing Azure Blob Storage with adhoc SAS Tokens and Xamarin

I couldn't find a cohesive and updated example on how to use azure blob storage, so I created a working example. Well, mostly working. There are a few issues.

What you'll find there is an example that
  • runs against the local storage emulator (using the UWP client)
    • If someone has the time to find out how to connect the android emulator to the local storage emulator, kindly answer here
    • to connect to the local storage emulator from an android emulator, use the following connection string: "UseDevelopmentStorage=true;DevelopmentStorageProxyUri="
  • runs against the azure cloud storage
  • uses connection string with shared keys
  • uses an ad-hoc Shared Access Signature (SAS) token to provide limited time access to storage containers
  • bonus: generate and view pdf documents using Syncfusion packages.
For mobile clients (web or mobile apps), you're going to want to steer clear of using shared keys as a means of authenticating with azure storage. Unfortunately this is the mechanism that most of the samples are using.
The recommended way to connect to your azure storage account is by retrieving a temporary SAS Token from a secure service, and then using that token to send and receive blobs from azure storage.


So lets get started.

Step 1: Understand how blob storage accounts work. You can simulate azure storage using the local emulator (although with the SAS Token scenario this currently isn't viable due to the lack of https support), or create an azure storage account and containers.

Step 2: Create a secure server endpoint to serve temporary SAS Tokens. You'll find a ASP.NET Core example in the linked github repo. See the this implementation for generating and returning a SAS Token. More documentation on SAS Tokens can be found here.
The example stores the shared key connection strings in the appsettings.json file. You can provide different appsetings.[ASPNETCORE_ENVIRONMENT].json files, and toggle which one to use in the Properties/launchSettings.json file. 

Step 3: Create a client that retrieves the SAS Token, and uses that to create a container which is used to upload and download blob content. In the code example, the AzureBlobStorageService class is responsible for all the heavy lifting. The create container method will analyze the storage settings, preferring SAS Token connections over connection strings that contain shared keys.

To switch between different kinds of usage, you can toggle the implementation of ICloudBlobStorageSettingsProvider in App.cs , or create your own implementation.

When using the local storage emulator, make sure to read through the documentation on getting the emulator service started and using the storage explorer to analyse storage content.

Chances are pretty good I may have missed something in the code, so if you spot it, be sure to log an issue or better yet, submit a pull request ;)

Happy Coding.

Daily Links 30 Oct 2017

Time zone conversion in Xamarin Forms XAML using NodaTime

Azure Tips and Tricks Part 33 - Prevent Changes to Resources in Azure App Service

Using Azure Storage in ASP.NET Core

An Elasticsearch Tutorial for .NET Developers

Reducing apk size : A quick hack!

Visual Studio 2017 Update 4 makes it easy to modernize your desktop application and make it store ready

Get Fluent with the XAML Controls Gallery

Get Started with Azure IoT Technical Training for Developers

Transient Fault Handling in Xamarin.Forms using Polly

Validating User Input in Xamarin.Forms IV

Best Practices for Designing a Pragmatic RESTful API

Android Studio 3.0

5 Things to Love about GraphQL

Exploring GraphQL and creating a GraphQL endpoint in ASP.NET Core

Tuesday, October 17, 2017

Mobile App On-boarding with Xamarin Forms and Syncfusion

In my previous post, I talked about how awesome xamarin is for creating cross-platform mobile apps. I’ve been thinking a lot about customer on-boarding recently, so I thought I’d do another proof of concept app to illustrate it using xamarin.
As before, I prefer using real companies to illustrate the point. I’m a big fan of Highrise, and how they build product, so I thought they’d make a good candidate this time around, especially since they’re pretty transparent about their processes and value proposition, so it was pretty easy to generate content.
Here’s a quick walk-through the result:

So I’m not going to go into too much technical details here — if you want to check out the source code, check out the github repo. Instead I’m going to break down the app page by page:

The Splash Page

There’s nothing great about the android splash screen, except to note that it’s a 9-patch image, which scales and stretches no matter what orientation or screen size the device is.

The Welcome Page

This page is really the main point of doing the proof of concept. It’s the first thing potentially new customers will see, so it really needs to sell your value proposition. Highrise recently went through a jobs-to-be-done exercise with their customers, and came out with three main points, which you’ll now find on their homepage. So it makes sense to have this on the landing page, along with sign up / sign in options. (Here’s another example of this pattern from Charlin Agramonte). As in Charlin’s example, and this one, it’s a good idea to have some sort of movable media to draw the user’s attention. In this case I’m using the wonderfully cross-platform Lottie Animation Xamarin Bindings from Martijn van Dijk.

Points of interest on this page:
  • Xamarin Forms animation is used to sequentially animate the buttons and ‘more about highrise’ controls
  • the layout and logo image sizing is adaptive to the orientation of the device.
  • The Syncfusion Rotator control is used to automatically cycle through the value proposition animations
  • A ‘learn more’ link in case the user needs some more information before submitting credentials — such as pricing etc.

The Sign In / Sign Up Page

These pages are pretty basic. Keep it simple. Animations purposefully left out of this page as they would detract from the important info, which is the data entry.
Points of interest:
  • Making use of the floating label design pattern for data entry. This increases the available real estate when working with entry controls
  • The button animates in to draw attention to the text. Don’t worry — it doesn’t flash, that’s just the gif animation recycling :P
  • The logo becomes invisible when the device is in landscape mode to ensure enough real estate for the entry fields

The Landing Page

Okay, so the user made it through the signup process, but still has no idea (or at least very little) what the app can do. The idea conveyed here is to guide the user with visual queues, and get them to do the simplest action that is the main value proposition of the app. In this case it’s creating a contact.

One other thing I wanted to play around with was gamification. So once you’ve created that first contact, the app gives an immediate reward of unlocking your first achievement, along with links to other help topics and features the user may find useful.

The other thing to be aware of, is giving your users opportunities to share their app experience via social messaging. The Landing Page has a generic ‘I think Highrise is awesome’ share button in the toolbar, and each user achievement has a ‘I just achieved X with Highrise’ share link.

Some more links for related reading

Syncfusion Controls
I used the Rotator and ListView (with left and right swipe actions) controls for this project. I also added an animating radial menu control to the contact page, but it’s not working atm.
Have any thoughts on mobile app on-boarding? Feedback and share them in the comments.

Wednesday, October 11, 2017

Health Care Provider Booking Platform: Proof of Concept Cross Platform App using Xamarin and Syncfusion

So about a month ago, fueled by a conversation with a startup CEO, I decided to write a small app as a proof of concept for building an app that is cross platform, in a short period of time.

You can find the original Medium post here

Good stuff first: Demo Video Time :) 

You can find the source code on GitHub 

In there you'll find code for:

  • Using the geolocator plugin to find the current gps location. code
  • Launch the native device map with a location for directions. code
  • Store data in a sqlite repository. code
  • Schedule Picker control from syncfusion. code
  • Image Circle plugin. code
  • Some fade in animations on the login page. code
  • Syncfusion ListView control with swipe action templates. code
  • Share plugin to share content via registered apps like email and twitter. code
... and a bit more generic stuff like MVVM & Command pattern implementations ; navigation service ; dependency injection using Autofac etc.

Xamarin Forms really is a super productive, fully native and completely extensible option for cross platform mobile development :)

Daily Links 11 Oct 2017

Xamarin Test Box, the first local test server.

Creating an extension method for attaching key-value pairs to scope state using ASP.NET Core

Running xUnit Tests with VSTS

Little ASP.NET Core Book

Beautiful Xamarin – Facebook Clone in Xamarin.Forms

How to configure log4net on Azure App Service

Develop (and test) a dockerized, PostgreSQL backed, ASP.NET Core microservice in less than an hour

3 Reasons to Try Xamarin Previews in Visual Studio 2017

5 Common Pitfalls In Enterprise Mobile Development

Handling System Failures during Payment Communication

Bringing WebVR to everyone with the Windows 10 Fall Creators Update

Xamarin.Forms Updates