Scott Hanselman

Playing with an Onion Omega IoT device to show live Blood Sugar on an OLED screen

December 14, '16 Comments [16] Posted in Hardware | Open Source
Sponsored By

arduino_lb3dg8I've been playing with IoT stuff on my vacation. Today I'm looking at an Onion Omega. This is a US$19 computer that you can program with Python, Node.js, or C/C++. There's a current IndieGogo happening for the Onion Omega2 for $5. That's a $5 Linux computer with Wi-Fi. Realistically you'd want to spend more and get expansion docks, chargers, batteries, etc, but you get the idea. I got the original Omega along with the bluetooth dongle, Arduino compatible base, tiny OLED screen. A ton of stuff to play with for less than $100.

Note that I am not affiliated with Onion at all and I paid for it with my own money, to use for fun.

One of the most striking things about the Onion Omega line is how polished it is. There's lots of tiny Linux Machines that basically drop you at the command line and say "OK, SSH in and here's root." The Onion Omega is far more polished.

Onion Omega has a very polished Web UI

The Omega can do that for you, but if you have Bonjour installed (for zeroconf networking) and can SSH in once to setup Wi-Fi, you're able to access this lovely web-based interface.

Look at all the info about the Omega's memory, networking, device status, and more

This clean, local web server and useful UI makes the Onion Omega extremely useful as a teaching tool. The Particle line of IoT products has a similarly polished web-interfaces, but while the Onion uses a local web server and app, the Particle Photon uses a cloud-based app that bounces down to a local administrative interface on the device. There's arguments for each, but I remain impressed with how easy it was for me to update the firmware on the Omega and get a new experience. Additionally, I made a few mistakes and "bricked" it and was able - just by following some basic instructions - to totally reflash and reset it to the defaults in just about 10 minutes. Impressive docs for an impressive product.

image

Onion Omega based Glucose Display via NightScout

So it's a cool product, but how quickly can I do something trivial, but useful? Well, I have a NightScout open source diabetes management server with an API that lets me see my blood sugar. The resulting JSON looks like this:

[  
{
"_id":"5851b235b8d1fea108df8b",
"sgv":135,
"date":1481748935000,
"dateString":"2016-12-14T20:55:35.000Z",
"trend":4,
"direction":"Flat",
"device":"share2",
"type":"sgv"
}
]

That number under "sgv" (serum glucose value) is 135 mg/dl. That's my blood sugar right now. I could get n values back from the WebAPI and plot a chart, but baby steps. Note also the "direction" for my sugars is "flat." It's not rising nor falling in any major way.

Let's add the OLED Display to the Onion Omega and show my sugars. Since it's an OpenWRT Linux machine, I can just add Python!

opkg update
opkg install python

Some may (and will) argue that for a small IoT system, Linux is totally overkill. Sure, it likely it. But it's also very productive, fun to prototype with, and functional. Were I to go to market for real, I'd likely use something more hardened.

As I said, I could SSH into the machine but since the Web UI is so nice, it includes an HTML-based terminal!

A Terminal built in!

The Onion Omega includes not just libraries for expansions like the OLED Display, but also command-line utilities. This script clears the display, initializes it, and displays some text. The value of that text will come from my yet-to-be-written python script.

#!/bin/sh    

oled-exp -c

VAR=$(python ./sugar_script.py)

oled-exp -i
oled-exp write "$VAR"

Then in my Python script I could print the value that would be returned into VAR and then printed with the oled-exp command line utility.

OR, I can bypass the shell script entirely and use the Python Module for this OLED screen directly and do this. Grab the JSON, clean it up because apparently the json library sucks (?), then display it.

#!/usr/bin/env python                                                                                                        

from OmegaExpansion import oledExp
import urllib
import json

site="https://hanselmansugars.something/api/v1/entries/sgv.json?count=1"
jfile=urllib.urlopen(site)
jsfile=jfile.read()
jsfile=jsfile.replace("\n","")
jsfile=jsfile.replace("/","")
jsfile=jsfile.replace("]","")
jsfile=jsfile.replace("[","")

a=json.loads(jsfile)
sugar=a['sgv']
direction=a['direction']
info="\n" + str(sugar)+" mg/dl and "+direction

oledExp.driverInit()
oledExp.clear()
oledExp.write(info)

Now here's a pic of my live blood sugar on the Onion Omega with the OLED! I could put this to run on a timer and I'm off to the races.

The OLED Screen says "149 mg/dl and Flat"

The next step might be to clean up the output, parse the date better, and perhaps even dynamically generate a sparkline and display the graphic on the small B&W OLED Screen.

Have you used a small Linux IoT device like the Onion Omega?


Sponsor: Do you deploy the same application multiple times for each of your end customers? The team at Octopus have taken the pain out of multi-tenant deployments. Check out their latest 3.4 release

About Scott

Scott Hanselman is a former professor, former Chief Architect in finance, now speaker, consultant, father, diabetic, and Microsoft employee. He is a failed stand-up comic, a cornrower, and a book author.

facebook twitter subscribe
About   Newsletter
Sponsored By
Hosting By
Dedicated Windows Server Hosting by ORCS Web

Exploring Wyam - a .NET Static Site Content Generator

December 11, '16 Comments [28] Posted in ASP.NET | Open Source
Sponsored By

It's a bit of a renaissance out there when it comes to Static Site Generators. There's Jekyll and GitBook, Hugo and Hexo. Middleman and Pelican, Brunch and Octopress. There's dozens, if not hundreds of static site content generators, and "long tail is long."

Wyam is a great .NET based open source static site generator

Static Generators a nice for sites that DO get updated with dynamic content, but just not updated every few minutes. That means a Static Site Generator can be great for documentation, blogs, your brochure-ware home page, product catalogs, resumes, and lots more. Why install WordPress when you don't need to hit a database or generate HTML on every page view? Why not generate your site only when it changes?

I recently heard about a .NET Core-based open source generator called Wyam and wanted to check it out.

Wyam is a simple to use, highly modular, and extremely configurable static content generator that can be used to generate web sites, produce documentation, create ebooks, and much more.

Wyam is a module system with a pipeline that you can configure and chain processes together however you like. You can generate HTML from Markdown, from Razor, even XSLT2 - anything you like, really. Wyam also integrates nicely into your continuous build systems like Cake and others, so you can also get the Nuget Tools package for Wyam.

There's a few ways to get Wyam but I downloaded the setup.exe from GitHub Releases. You can also just get a ZIP and download it to any folder. When I ran the setup.exe it flashed (I didn't see a dialog, but it's beta so I'll chalk it up to that) and it installed to C:\Users\scott\AppData\Local\Wyam with what looked like the Squirrel installer from GitHub and Paul Betts.

Wyam has a number of nice features that .NET Folks will find useful.

Let's see what I can do with http://wyam.io in just a few minutes!

Scaffolding a Blog

Wyam has a similar command line syntax as dotnet.exe and it uses "recipes" so I can say --recipe Blog and I'll get:

C:\Users\scott\Desktop\wyamtest>wyam new --recipe Blog
Wyam version 0.14.1-beta

,@@@@@ /@\ @@@@@
@@@@@@ @@@@@| $@@@@@h
$@@@@@ ,@@@@@@@ g@@@@@P
]@@@@@M g@@@@@@@ g@@@@@P
$@@@@@ @@@@@@@@@ g@@@@@P
j@@@@@ g@@@@@@@@@p ,@@@@@@@
$@@@@@g@@@@@@@@B@@@@@@@@@@@P
`$@@@@@@@@@@@` ]@@@@@@@@@`
$@@@@@@@P` ?$@@@@@P
`^`` *P*`
**NEW**
Scaffold directory C:/Users/scott/Desktop/wyamtest/input does not exist and will be created
Installing NuGet packages
NuGet packages installed in 101813 ms
Recursively loading assemblies
Assemblies loaded in 2349 ms
Cataloging classes
Classes cataloged in 277 ms

One could imagine recipes for product catalogs, little league sites, etc. You can make your own custom recipes as well.

I'll make a config.wyam file with this inside:

Settings.Host = "test.hanselman.com";
GlobalMetadata["Title"] = "Scott Hanselman";
GlobalMetadata["Description"] = "The personal wyam-made blog of Scott Hanselman";
GlobalMetadata["Intro"] = "Hi, welcome to my blog!";

Then I'll run wyam with:

C:\Users\scott\Desktop\wyamtest>wyam -r Blog
Wyam version 0.14.1-beta
**BUILD**
Loading configuration from file:///C:/Users/scott/Desktop/wyamtest/config.wyam
Installing NuGet packages
NuGet packages installed in 30059 ms
Recursively loading assemblies
Assemblies loaded in 368 ms
Cataloging classes
Classes cataloged in 406 ms
Evaluating configuration script
Evaluated configuration script in 2594 ms
Root path:
file:///C:/Users/scott/Desktop/wyamtest
Input path(s):
file:///C:/Users/scott/.nuget/packages/Wyam.Blog.CleanBlog.0.14.1-beta/content
theme
input
Output path:
output
Cleaning output path output
Cleaned output directory
Executing 7 pipelines
Executing pipeline "Pages" (1/7) with 8 child module(s)
Executed pipeline "Pages" (1/7) in 221 ms resulting in 13 output document(s)
Executing pipeline "RawPosts" (2/7) with 7 child module(s)
Executed pipeline "RawPosts" (2/7) in 18 ms resulting in 1 output document(s)
Executing pipeline "Tags" (3/7) with 10 child module(s)
Executed pipeline "Tags" (3/7) in 1578 ms resulting in 1 output document(s)
Executing pipeline "Posts" (4/7) with 6 child module(s)
Executed pipeline "Posts" (4/7) in 620 ms resulting in 1 output document(s)
Executing pipeline "Feed" (5/7) with 3 child module(s)
Executed pipeline "Feed" (5/7) in 134 ms resulting in 2 output document(s)
Executing pipeline "RenderPages" (6/7) with 3 child module(s)
Executed pipeline "RenderPages" (6/7) in 333 ms resulting in 4 output document(s)
Executing pipeline "Resources" (7/7) with 1 child module(s)
Executed pipeline "Resources" (7/7) in 19 ms resulting in 14 output document(s)
Executed 7/7 pipelines in 2936 ms

I can also run it with -t for different themes, like "wyam -r Blog -t Phantom":

Wyam supports themes

As with most Static Site Generators I can start with a markdown file like "first-post.md" and included name value pairs of metadata at the top:

Title: First Post
Published: 2016-01-01
Tags: Introduction
---
This is my first post!

If I'm working on my site a lot, I could run Wyam with the -w (WATCH) switch and then edit my posts in Visual Studio Code and Wyam will WATCH the input folder and automatically run over and over, regenerating the site each time I change the inputs! A nice little touch, indeed.

There's a lot of cool examples at https://github.com/Wyamio/Wyam/tree/develop/examples that show you how to generate RSS, do pagination, use Razor but still generate statically, as well as mixing Razor for layouts and Markdown for posts.

The AdventureTime sample is fairly sophisticated (be sure to read the comments in the config.wyam for gotcha) example that includes a custom Pipeline, use of Yaml for front matter, and mixes markdown and Razor.

There's also a ton of modules you can use to extend the build however you like. For example, you could have source images be large and then auto-generate thumbnails like this:

Pipelines.Add("Images",
ReadFiles("*").Where(x => x.Contains("images\\") && new[] { ".jpg", ".jpeg", ".gif", ".png"}.Contains(Path.GetExtension(x))),
Image()
.SetJpegQuality(100).Resize(400,209).SetSuffix("-thumb"),
WriteFiles("*")
);

There's a TON of options. You could even use Excel as the source data for your site, generate CSVs from the Excel OOXML and then generate your site from those CSVs. Sounds crazy, but if you run a small business or non-profit you could quickly make a nice workflow for someone to take control of their own site!

GOTCHA: When generating a site locally your initial reaction may be to open the /output folder and open the index.html in your local browser. You MAY be disappointed with you use a static site generator. Often they generate absolute paths for CSS and Javascript so you'll see a lousy version of your website locally. Either change your templates to generate relative paths OR use a staging site and look at your sites live online. Even better, use the Wyam "preview web server" and run Wyam with a "-p" argument and then visit http://localhost:5080 to see your actual site as it will show up online.

Wyam looks like a really interesting start to a great open source project. It's got a lot of code, good docs, and it's easy to get started. It also has a bunch of advanced features that would enable me to easily embed static site generation in a dynamic app. From the comments, it seems that Dave Glick is doing most of the work himself. I'm sure he'd appreciate you reaching out and helping with some issues.

As always, don't just send a PR without talking and working with the maintainers of your favorite open source projects. Also, ask if they have issues that are friendly to http://www.firsttimersonly.com.


Sponsor: Big thanks to Redgate! Help your team write better, shareable SQL faster. Discover how your whole team can write better, shareable SQL faster with a free trial of SQL Prompt. Write, refactor and share SQL effortlessly, try it now!

About Scott

Scott Hanselman is a former professor, former Chief Architect in finance, now speaker, consultant, father, diabetic, and Microsoft employee. He is a failed stand-up comic, a cornrower, and a book author.

facebook twitter subscribe
About   Newsletter
Sponsored By
Hosting By
Dedicated Windows Server Hosting by ORCS Web

Docker on a Synology NAS - Also running ASP.NET and .NET Core!

November 29, '16 Comments [32] Posted in Open Source
Sponsored By

Docker on Synology is amazingI love my Synology NAS (Network Attached Storage) device. It has sat quietly in my server closet for almost 5 years now. It was a fantastic investment. I've filled it with 8TB of inexpensive Seagate Drives and it does its own flavor of RAID to give me roughly 5TB (which, for my house is effectively infinite) of storage. In my house it's just \\SERVER or http://server. It's a little GNU Linux machine that is easier to manage and maintain (and generally deal with) that just chills in the closet. It's a personal cloud.

It also runs:

  • Plex - It's a media server with over 15 years of home movies and photos. It's even more magical when used with an Xbox One. It transcodes videos that then download to my Windows tablets or iPad...then I watch them offline on the plane.
  • VPN Server - I can remotely connect to my house. Even stream Netflix when I'm overseas.
  • Surveillance Station - It acts as a DVR and manages streams from a dozen cameras both inside and outside the house, scanning for motion and storing nearly a week of video.
  • Murmur/Mumble Server - Your own private VOIP chat service. Used for podcasts, gaming, private calls that aren't over Skype, etc.
  • Cloud Sync/Backup - I have files in Google Drive, Dropbox, and OneDrive...but I have them entirely backed up on my Synology with their Cloud Sync.

51FvMne3PyL._SL1280_Every year my Synology gets better with software upgrades. The biggest and most significant upgrade to Synology has been the addition of Docker and the Docker ecosystem. There is first class support for Docker on Synology. There are some Synology devices that are cheaper and use ARM processors. Make sure you get one with an Intel processor for best compatibility. Get the best one you can and you'll find new uses for it all the time! I have the 1511 (now 1515) and it's amazing.

ASP.NET Core on Docker on Synology

A month ago Glenn Condron and I did a Microsoft Virtual Academy on Containers and Cross-Platform .NET (coming soon!) and we made this little app and put it in Docker. It's "glennc/fancypants." That means I can easily run it anywhere with just:

docker run glennc/fancypants

Sometimes a DockerFile for ASP.NET Core can be as basic as this:

FROM microsoft/aspnetcore:1.0.1
ENTRYPOINT ["dotnet", "WebApplication4.dll"]
ARG source=.
WORKDIR /app
EXPOSE 80
COPY $source .

You could certainly use Docker Compose and have your Synology running Redis, MySql, ASP.NET Core, whatever.

Even better, since Synology has such a great UI, here is Glenn's app in the Synology web-based admin tool:

Docker on Synology - Node and ASP.NET Core Apps 

I can ssh into the Synology (you'll need to SSH in as root, or you'll want to set up Docker to allow another user to avoid this) and run docker commands directly, or I can use their excellent UI. It's really one of the nicest Docker UIs I've seen. I was able to get ASP.NET Core and the Node.js Ghost blog running in minutes with modest RAM requirements.

image

Once Containers exist in Docker on Synology you can "turn them on and off" like any service.

ASP.NET Core on Docker on Synology

This also means that your Synology can now run any Docker-based service like a private version of GitLab (good instructions here)! You could then (if you like) do cool domain mappings like gitlab.hanselman.com:someport and have your Synology do the work. The Synology could then run Jenkins or Travis as well which makes my home server fit nicely into my development workflow without use any compute resources on my main machine (or using any cloud resource at all!)

The next step for me will be to connect to Docker running on Synology remotely from my Windows machine, then setup "F5 Docker Debugging" in Visual Studio.

image

Anyone else using a Synology?

* My Amazon links pay for tacos. Please use them.


Sponsor: Big thanks to Octopus Deploy! Do you deploy the same application multiple times for each of your end customers? The team at Octopus have taken the pain out of multi-tenant deployments. Check out their latest 3.4 release!

About Scott

Scott Hanselman is a former professor, former Chief Architect in finance, now speaker, consultant, father, diabetic, and Microsoft employee. He is a failed stand-up comic, a cornrower, and a book author.

facebook twitter subscribe
About   Newsletter
Sponsored By
Hosting By
Dedicated Windows Server Hosting by ORCS Web

WinAppDriver - Test any app with Appium's Selenium-like tests on Windows

November 16, '16 Comments [12] Posted in Open Source | Win10
Sponsored By
WinAppDriver - Appium testing Windows Apps

I've found blog posts on my site where I'm using the Selenium Web Testing Framework as far back as 2007! Today there's Selenium Drivers for every web browser including Microsoft Edge. You can write Selenium tests in nearly any language these days including Ruby, Python, Java, and C#.

I'm a big Selenium fan. I like using it with systems like BrowserStack to automate across many different browser on many operating systems.

"Appium" is a great Selenium-like testing framework that implements the "WebDriver" protocol - formerly JsonWireProtocol.

WebDriver is a remote control interface that enables introspection and control of user agents. It provides a platform- and language-neutral wire protocol as a way for out-of-process programs to remotely instruct the behavior of web browsers.

From the Appium website, "Appium is 'cross-platform': it allows you to write tests against multiple platforms (iOS, Android, Windows), using the same API. This enables code reuse between iOS, Android, and Windows testsuites"

Appium is a webserver that exposes a REST API. The WinAppDriver enables Appium by using new APIs that were added in Windows 10 Anniversary Edition that allow you to test any Windows app. That means ANY Windows App. Win32, VB6, WPF, UWP, anything. Not only can you put any app in the Windows Store, you can do full and complete UI testing of those apps with a tool that is already familiar to Web Developers like myself.

Your preferred language, your preferred test runner, the Appium Server, and your app

You can write tests in C# and run them from Visual Studio's Test Runner. You can press any button and basically totally control your apps.

// Launch the calculator app
DesiredCapabilities appCapabilities = new DesiredCapabilities();
appCapabilities.SetCapability("app", "Microsoft.WindowsCalculator_8wekyb3d8bbwe!App");
CalculatorSession = new RemoteWebDriver(new Uri(WindowsApplicationDriverUrl), appCapabilities);
Assert.IsNotNull(CalculatorSession);
CalculatorSession.Manage().Timeouts().ImplicitlyWait(TimeSpan.FromSeconds(2));
// Make sure we're in standard mode
CalculatorSession.FindElementByXPath("//Button[starts-with(@Name, \"Menu\")]").Click();
OriginalCalculatorMode = CalculatorSession.FindElementByXPath("//List[@AutomationId=\"FlyoutNav\"]//ListItem[@IsSelected=\"True\"]").Text;
CalculatorSession.FindElementByXPath("//ListItem[@Name=\"Standard Calculator\"]").Click();

It's surprisingly easy once you get started.

public void Addition()
{
CalculatorSession.FindElementByName("One").Click();
CalculatorSession.FindElementByName("Plus").Click();
CalculatorSession.FindElementByName("Seven").Click();
CalculatorSession.FindElementByName("Equals").Click();
Assert.AreEqual("Display is 8 ", CalculatorResult.Text);
}

You can automate any part of Windows, even the Start Menu or Cortana.

var searchBox = CortanaSession.FindElementByAccessibilityId("SearchTextBox");
Assert.IsNotNull(searchBox);
searchBox.SendKeys("What is eight times eleven");

var bingPane = CortanaSession.FindElementByName("Bing");
Assert.IsNotNull(bingPane);

var bingResult = bingPane.FindElementByName("88");
Assert.IsNotNull(bingResult);

If you use "AccessibiltyIds" and refer to native controls in a non-locale specific way you can even reuse test code across platforms. For example, you could write sign in code for Windows, iOS, your web app, and even a VB6 Win32 app. ;)

Testing a VB6 app with WinAppDriver

Appium and WebAppDriver a nice alternative to "CodedUI Tests." CodedUI tests are great but just for Windows apps. If you're a web developer or you are writing cross platform or mobile apps you should check it out.


Sponsor: Help your team write better, shareable SQL faster! Discover how your whole team can write better, shareable SQL faster with a free trial of SQL Prompt. Write, refactor and share SQL effortlessly, try it now.

About Scott

Scott Hanselman is a former professor, former Chief Architect in finance, now speaker, consultant, father, diabetic, and Microsoft employee. He is a failed stand-up comic, a cornrower, and a book author.

facebook twitter subscribe
About   Newsletter
Sponsored By
Hosting By
Dedicated Windows Server Hosting by ORCS Web

Stateless 3.0 - A State Machine library for .NET Core

November 11, '16 Comments [38] Posted in DotNetCore | Open Source
Sponsored By

.NET StandardState Machines and business processes that describe a series of states seem like they'll be easy to code but you'll eventually regret trying to do it yourself. Sure, you'll start with a boolean, then two, then you'll need to manage three states and there will be an invalid state to avoid then you'll just consider quitting all together. ;)

"Stateless" is a simple library for creating state machines in C# code. It's recently been updated to support .NET Core 1.0. They achieved this not by targeting .NET Core but by writing to the .NET Standard. Just like API levels in Android abstract away the many underlying versions of Android, .NET Standard is a set of APIs that all .NET platforms have to implement. Even better, the folks who wrote Stateless 3.0 targeted .NET Standard 1.0, which is the broadest and most compatible standard - it basically works everywhere and is portable across the .NET Framework on Windows, .NET Core on Windows, Mac, and LInux, as well as Windows Store apps and all phones.

Sure, there's Windows Workflow, but it may be overkill for some projects. In Nicholas Blumhardt's words:

...over time, the logic that decided which actions were allowed in each state, and what the state resulting from an action should be, grew into a tangle of if and switch. Inspired by Simple State Machine, I eventually refactored this out into a little state machine class that was configured declaratively: in this state, allow this trigger, transition to this other state, and so-on.

A state machine diagram describing the states a Bug can go throughYou can use state machines for anything. You can certainly describe high-level business state machines, but you can also easily model IoT device state, user interfaces, and more.

Even better, Stateless also serialize your state machine to a standard text-based "DOT Graph" format that can then be generated into an SVG or PNG like this with http://www.webgraphviz.com. It's super nice to be able to visualize state machines at runtime.

Modeling a Simple State Machine with Stateless

Let's look at a few code examples. You start by describing some finite states as an enum, and some finite "triggers" that cause a state to change. Like a switch could have On and Off as states and Toggle as a trigger.

A more useful example is the Bug Tracker included in the Stateless source on GitHub. To start with here are the states of a Bug and the Triggers that cause state to change:

enum State { Open, Assigned, Deferred, Resolved, Closed }
enum Trigger { Assign, Defer, Resolve, Close }

You then have your initial state, define your StateMachine, and if you like, you can pass Parameters when a state is trigger. For example, if a Bug is triggered with Assign you can pass in "Scott" so the bug goes into the Assigned state - assigned to Scott.

State _state = State.Open;
StateMachine<State, Trigger> _machine;
StateMachine<State, Trigger>.TriggerWithParameters<string> _assignTrigger;

string _title;
string _assignee;

Then, in this example, the Bug constructor describes the state machine using a fluent interface that reads rather nicely.

public Bug(string title)
{
_title = title;

_machine = new StateMachine<State, Trigger>(() => _state, s => _state = s);

_assignTrigger = _machine.SetTriggerParameters<string>(Trigger.Assign);

_machine.Configure(State.Open)
.Permit(Trigger.Assign, State.Assigned);

_machine.Configure(State.Assigned)
.SubstateOf(State.Open)
.OnEntryFrom(_assignTrigger, assignee => OnAssigned(assignee))
.PermitReentry(Trigger.Assign)
.Permit(Trigger.Close, State.Closed)
.Permit(Trigger.Defer, State.Deferred)
.OnExit(() => OnDeassigned());

_machine.Configure(State.Deferred)
.OnEntry(() => _assignee = null)
.Permit(Trigger.Assign, State.Assigned);
}

For example, when the State is Open, it can be Assigned. But as this is written (you can change it) you can't close a Bug that is Open but not Assigned. Make sense?

When the Bug is Assigned, you can Close it, Defer it, or Assign it again. That's PermitReentry(). Also, notice that Assigned is a Substate of Open.

You can have events that are fired as states change. Those events can take actions as you like.

void OnAssigned(string assignee)
{
if (_assignee != null && assignee != _assignee)
SendEmailToAssignee("Don't forget to help the new employee.");

_assignee = assignee;
SendEmailToAssignee("You own it.");
}

void OnDeassigned()
{
SendEmailToAssignee("You're off the hook.");
}

void SendEmailToAssignee(string message)
{
Console.WriteLine("{0}, RE {1}: {2}", _assignee, _title, message);
}

With a nice State Machine library like Stateless you can quickly model states that you'd ordinarily do with a "big ol' switch statement."

What have you used for state machines like this in your projects?


Sponsor: Big thanks to Telerik! They recently published a comprehensive whitepaper on The State of C#, discussing the history of C#, what’s new in C# 7 and whether C# is still a viable language. Check it out!

About Scott

Scott Hanselman is a former professor, former Chief Architect in finance, now speaker, consultant, father, diabetic, and Microsoft employee. He is a failed stand-up comic, a cornrower, and a book author.

facebook twitter subscribe
About   Newsletter
Sponsored By
Hosting By
Dedicated Windows Server Hosting by ORCS Web
Page 1 of 41 in the Open Source category Next Page

Disclaimer: The opinions expressed herein are my own personal opinions and do not represent my employer's view in any way.