Visualizing ADXL345 Accelerometer Output In Windows Forms From Raspberry PI 2

26. September 2016 21:21

C# Raspberry Pi Windows  0 Comments

I have been playing a lot with Raspberry PI and Python these days and have also started a side project to create robot car controller with a Xbox 360 wireless controller. I am planning to controller a robot car using a custom interface from my Windows machine. Initially I tried with PyQt but I dropped the idea for now as Python is not my primary expertise and it will take some time for me to learn the basics and get into some serious coding. Controlling something remotely or visualizing the information from your device on the UI is always better. For a proof of concept I built a Windows Forms application which will request the output from Raspberry PI over TCP and then visualize it on the UI using a wonderful chart library that I found today. There is a slight change in the Python code as I have to transmit readings from Raspberry PI over TCP so my Windows Forms application can read the output and utilize it to visualize it.

Raspberry PI Python Application

Reading the ADXL345 output is fairly simple and you can do this without any problem by using Adafruit's ADXL345 Python library. This library will get you started in a jiffy and you will have your readings. I am not going into the details about the different features of the library I am using and ADXL345. The only thing you will have to do is to wire ADXL345 to your Raspberry PI and fire the example code you got from Adafruit's repository from Github. If you have set it up correctly this, you will see X, Y, Z values on your terminal. If the terminal displays 0s for all the three axis then there is something wrong with the wiring (assuming you are using the example code). This is how your writing should be like.

Now I have made slight changes in the code so that I can send the data over TCP. I have created a simple TCP server which exposes Raspberry PI through IP address and a port number. This is the complete code for reading values from ADXL345.
import Adafruit_ADXL345
import socket

HOST = "192.168.1.8"
PORT = 50007

accel = Adafruit_ADXL345.ADXL345()

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind((HOST, PORT))
s.listen(1)
conn, addr = s.accept()

while 1:
    data = conn.recv(1024)

    if data.strip() == "adxl":
        x, y, z = accel.read()
        data = 'X:' + str(x) + '|Y:' + str(y) + '|Z:' + str(z)
        conn.send(data)
In the code, you can see that I am not just transmitting the readings just like that. I only transmit when there is a request from another application is there to get the readings. This is a good approach as I don't the PI to transmit the readings even if nobody is requesting it. I am sending a single string as a response which I am going to read at my Windows Forms application and use it.
You need to change the IP address and port number according to your Pi's configuration.
Once this is done you can then execute the script from the terminal by firing the below command
sudo python adxl.py

This is it from Raspberry PI side. Let's take a look from the Windows side now.

Windows Forms Application

This will be a simple Windows Forms application which will connect to the Raspberry PI using the Pi's IP address and the port on which the server is running. The Windows Form application is also a TCP client which sends a request to Raspberry PI for the updated readings from ADXL345. As I mentioned above in the Python code that the readings are not just being transmitted but a client has to send a request to to get the readings.

Let's get started with the visualizing part. While was searching for a perfect charting library, I came across this wonderful library called Live Charts. This library is open-source, easy to use, has lots of awesome charts and a very robust documentation and moreover it supports Windows Forms as well as on WPF applications. I highly recommend you to look at the examples to get the idea about this library.

As usual, I will be using Nuget command to install the library.

PM> Install-Package LiveCharts.WinForms
You also have to add the custom controls in the toolbox. You can follow the steps here to add the Live Charts control in the toolbox. In the design mode, choose the Cartesian Chart control from the toolbox and add it to the form. After adding the control to the form, I have dock it to the top of the form so I can utilize the lower section of the form to display the readings in numbers. Here is how my form looks like in design mode.
After the designing for the form is complete, I can initialize the chart to display the readings from Raspberry PI. The chart require few things to be setup before it can start displaying the data correctly. The accelerometer I am using is a 3-axis accelerometer and therefore it is going to send me readings for 3 axis i.e X, Y and Z. This means I will be needing 3 line series to visualize the information from accelerometer. To have 3 line series display the data I have to use CharValues class which will let me display the readings in the line series. As I have to update my chart when I request the new readings from Raspberry PI, I have to use ObservableValue type. The ObservableValue will make sure that whenever there is a change in the value, it gets reflected in the chart and therefore keeping the chart always up to date.
public ChartValues<ObservableValue> Values_X { get; set; }
public ChartValues<ObservableValue> Values_Y { get; set; }
public ChartValues<ObservableValue> Values_Z { get; set; }
Because I am going to make request to the server running on my Raspberry PI and request for the ADXL345 readings, I have to create a TCP client in order to do so.
Socket server;
IPEndPoint ipEndPoint;
byte[] data;
When the application is loaded, I want to make connection to Raspberry PI by using it's IP address and port number on which the server is running on. To do this I will add the below code to the constructor of my application.
data = new byte[1024];

ipEndPoint = new IPEndPoint(
                IPAddress.Parse("192.168.1.8"), 50007);

server = new Socket(AddressFamily.InterNetwork,
               SocketType.Stream, ProtocolType.Tcp);

try
{
    server.Connect(ipEndPoint);
}
catch (SocketException)
{
    MessageBox.Show("Unable to connect to server.", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
    return;
}

The above code is self-explanatory as I am just connecting to Raspberry PI.

In the form load event, I have to initialize chart values and add 3 line series to my CartesianChart for X, Y and Z axis respectively. In my case the name of the Cartesian Chart is ADXLViz.

Values_X = new ChartValues<ObservableValue>();
Values_Y = new ChartValues<ObservableValue>();
Values_Z = new ChartValues<ObservableValue>();

ADXLViz.Series.Add(new LineSeries
{
    Values = Values_X,
    Title = "X",
    StrokeThickness = 4,
    PointGeometrySize = 0,
    DataLabels = true
});

ADXLViz.Series.Add(new LineSeries
{
    Values = Values_Y,
    Title = "Y",
    StrokeThickness = 4,
    PointGeometrySize = 0,
    DataLabels = true
});

ADXLViz.Series.Add(new LineSeries
{
    Values = Values_Z,
    Title = "Z",
    StrokeThickness = 4,
    PointGeometrySize = 0,
    DataLabels = true
});

Play around with different properties in the LineSeries class and set the output that suits your need or your eye. Notice the Values properties in the LineSeries class which holds the value which is received from Raspberry PI.

I am requesting the readings from Raspberry PI every 500ms and to do this I am using a Timer class. This is easy to use and configure. Just drag and drop the Timer control from the toolbox. In the properties change the Interval property to 500 and Enabled to True. After this I set the Tick event which will request the new readings every 500ms.

string stringData;
server.Send(Encoding.ASCII.GetBytes("adxl"));
data = new byte[1024];
int recv = server.Receive(data);
stringData = Encoding.ASCII.GetString(data, 0, recv);
string[] adxl = stringData.Replace(" ", "").Split('|');

Values_X.Add(new ObservableValue(Convert.ToDouble(adxl[0].Split(':')[1])));
Values_Y.Add(new ObservableValue(Convert.ToDouble(adxl[1].Split(':')[1])));
Values_Z.Add(new ObservableValue(Convert.ToDouble(adxl[2].Split(':')[1])));

if (Values_X.Count > 10) Values_X.RemoveAt(0);
if (Values_Y.Count > 10) Values_Y.RemoveAt(0);
if (Values_Z.Count > 10) Values_Z.RemoveAt(0);

X_Label.Text = Convert.ToString(adxl[0].Split(':')[1]);
Y_Label.Text = Convert.ToString(adxl[1].Split(':')[1]);
Z_Label.Text = Convert.ToString(adxl[2].Split(':')[1]);
The stringData variable holds the response or reading which is received from Raspberry PI. If you check the Python code above you will see that the response is being sent in a single string called data. I am splitting the string here and extracting the values and setting it to ChartValues<ObservableValue> object. This will render all the 3 line series chart and update it with the readings received from PI. But the problem here will be that in few minutes the chart will be hard to see due to lot of data congestion in chart. In order to overcome this problem, I have removed the first value from all the 3 line series when the chart displays more than 10 values. You can change the value from 10 to whatever suits you.
The overall idea of building this application is to see whether it is possible or easy to communicate from Raspberry PI apart from using frameworks like WebioPI or Flask. The complete source code for Raspberry PI and Windows Forms application is available on Github along with Fritzing sketch file and additional instructions to install the dependencies.
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.NET Projects You Should Be Follwing On Github

19. July 2015 04:51

API ASP.NET ASP.NET MVC C# Musings Web  0 Comments

Open-source has entirely change the programming and developers world. Today you can create any application, game, mobile app without spending a single penny. Thanks to open-source software and awesome community of developers and people behind them. As a .NET developer I have been developing enterprise applications for quite a long time and now I have shifted my focus towards developing products and understanding what it takes to make a successful product launch.

Back then, I used to spend most of my time in investigating the new technologies and what technology we should be using to get this thing done. I still do that today, not because it is the requirement of the project but because I have been asking a lot of questions. The list of projects I have compiled below are the projects that have helped me in learning lots of new things and insights of the programming and I hope this does the same for you as well.  Here is the list of awesome open-source project that you should be following on Github.

Pinta


We all know about Paint.net, it is an awesome tool and a complete replacement of Photoshop (at least for me). And yet there is another project which is almost the same and open-source and it works on Linux and Mac. It uses Gtk# (Gtk sharp) to run on both Window and Linux platforms. This project is a must have if you are a .NET guy and want to get yourself into some serious programming. You will learn about the insights of using gtk# in your projects. Though Microsoft already took the steps to have .NET FX on Linux but still this project is a great learning source.

Official site: http://www.pinta-project.com/

Github: https://github.com/PintaProject/Pinta

 

ShareX


I take a lot of screen shots and record screen casts as well for my personal use. But I used to use two different tools to get the work done. This is one of the tools that will not just take screen shots or just let you record your screen casts easily, it will also allow you to upload them to the 40 different image storing cloud services. Dive into the source code and see the awesomeness under the hood. Here is the project description as seen on Github.

ShareX is an open source program that lets you take screenshots or screencasts of any selected area with a single key, save them in your clipboard, hard disk or instantly upload them to over 40 different file hosting services. In addition to taking screenshots, it can upload images, text files and all other different file types.

Official site: https://getsharex.com/

Github: https://github.com/ShareX/ShareX

 

StackExchange - Data Explorer


You got a programming question, you Google it and it redirects it to StackOverflow. StackOverflow needs no introduction among programmers. StackOverflow is one of the Q&A site dedicated to the developers to get the answers for their problems. But it is just one site. In the recent years StackExchange has grew up and not just providing support for programmers but also helping folks from other fields. Now the data StackExchange has is available for anyone out there for free under creative-commons. If you are interested in looking into the source code that powers the user to query that immense amount of data bank then head over to Github and fork this project. StackExchange is all about Microsoft stack and this tool is also written in ASP.NET MVC3.

Official App: https://data.stackexchange.com/

Github: https://github.com/StackExchange/StackExchange.DataExplorer

 

Mini Blog


This is the minimalistic blog engine written in ASP.NET web pages by the author of BlogEngine.NET, Mads Kristensen. I started my bog with BlogEngine.NET and I had an amazing experience with it. MiniBlog is totally different in terms of features that are offered by BlogEngine.NET. This project will tell you the power of web pages and how you can write your own simple site without wasting much time.

Demo: http://miniblog.azurewebsites.net/ (with user name and password as demo).

Github: https://github.com/madskristensen/MiniBlog

 

Fluent Scheduler

If you want to run cron jobs or automated jobs in your application quietly, then this is the library you should be using. The documentation is pretty sleek and get you started in no time. But other than that you should take a look at the source code and see how nicely this has been done.

Github: https://github.com/jgeurts/FluentScheduler

 

Dapper

A Micro-ORM used by StackExchange sites. This is a perfect replacement for EF. This is just a single file that you can drop in your project and get started.

Dapper is a single file you can drop in to your project that will extend your IDbConnection interface.

Github: https://github.com/StackExchange/dapper-dot-net

 

LINQ-toWIKI

A .NET library to access MediaWiki API. The library is almost 3 years old but the source code will worth the look. Excerpt from Github:

LinqToWiki is a library for accessing sites running MediaWiki (including Wikipedia) through the MediaWiki API from .Net languages like C# and VB.NET.

It can be used to do almost anything that can be done from the web interface and more, including things like editing articles, listing articles in categories, listing all kinds of links on a page and much more. Querying the various lists available can be done using LINQ queries, which then get translated into efficient API requests.

Github: https://github.com/svick/LINQ-to-Wiki

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Getting Started With ASP.NET 5 On Ubuntu

16. June 2015 22:59

.NET Framework ASP.NET ASP.NET MVC C# Microsoft  Ubuntu Visual Studio Web  6 Comments

Ever since the .NET stack went open source last year, there is a huge excitement among the developers about the .NET stuff and developing apps using .NET which are no longer limited to Windows platform. I tried to install ASP.NET VNext on Ubuntu VM in which I terribly failed in the first go. Why? because the tutorial I used was quite old and I messed up the installation of pre-requisites. But I get everything working in the second try. So here are the steps and commands that will get you started with ASP.NET VNext on Ubuntu.

I am setting up a fresh VM for development on Ubuntu 14.04.2 LTS

Installing Mono

First thing is to install Mono. For folks who are new to Linux environment, Mono is a community driven project which allows developers to build and run .NET application on Linux platforms. Here is the set of commands that I have to execute to install Mono.

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF

echo "deb http://download.mono-project.com/repo/debian wheezy main" | sudo tee /etc/apt/sources.list.d/mono-xamarin.list
sudo apt-get update

Install the latest version of Mono available.

sudo apt-get install mono-complete

To check if Mono is successfully installed or to determine the version of Mono on you machine run the below command in the terminal.

mono --version

Installing LibUV

As stated on Github:

Libuv is a multi-platform asynchronous IO library that is used by the KestrelHttpServer that we will use to host our web applications.

Running the below command will install LibUV along with the dependencies require to build it.

sudo apt-get install automake libtool

Getting the source and building and installing it.

curl -sSL https://github.com/libuv/libuv/archive/v1.9.0.tar.gz | sudo tar zxfv - -C /usr/local/src
cd /usr/local/src/libuv-1.9.0
sudo sh autogen.sh
sudo ./configure
sudo make 
sudo make install
sudo rm -rf /usr/local/src/libuv-1.9.0 && cd ~/
sudo ldconfig

Here is a note at Githb repo that explains what the above set of commands are doing.

NOTE: make install puts libuv.so.1 in /usr/local/lib, in the above commands ldconfig is used to update ld.so.cache so that dlopen (see man dlopen) can load it. If you are getting libuv some other way or not running make install then you need to ensure that dlopen is capable of loading libuv.so.1

Getting .NET Version Manager (DNVM)

DNVM is a command line tool which allows you to get new build of the DNX (.NET Execution Environment) and allows you to switch between them. To get DNVM running fire the below command in the terminal.

curl -sSL https://raw.githubusercontent.com/aspnet/Home/dev/dnvminstall.sh | DNX_BRANCH=dev sh && source ~/.dnx/dnvm/dnvm.sh

To check if the DNVM is successfully installed on your machine, type DNVM in the terminal. The output should be something like this:

At any point of time if you want to list out the installed DNX runtimes, run the below command

dnvm list

The next step after this, is to upgrade the DNVM so you can use the dnx and dnu commands. Run the following command in the terminal

dnvm upgrade

Once this is done, we are all set to run ASP.NET VNext application on Ubuntu box. Clone the aspnet/Home repository from Github. If you don't have Git installed then install it with this simple command.

sudo apt-get install git

For simplicity, I have created a new directory on Ubuntu desktop named vnext. You can name the directory as you wish. Navigate to this directory in the terminal and clone the aspnet/Home repository.

git clone https://github.com/aspnet/Home.git

After cloning of repository is done, navigate to the 1.0.0-beta4 directory.

You can see three sample applications that you can test. For this tutorial I am going to checkout HelloMvc application. Get inside the HelloMvc directory and then, run the command 

dnu restore

This will take some time to execute. I didn't face this problem but there is a chance that someone will. When you run this command, the project.json.lock file gets created and the restore of the package will start. In the end when the restore is finalizing, it may say permission is denied. To resolve this error you can change the permission of the folder by running the following command.

sudo chmod -R 755 HelloMvc

You should always change permission to 755 for directories and 644 for files.

After the execution is completed, you can start the server by running the command.

dnx . kestrel

This command will work for both web and mvc application. If you plan to test out the console application then you can run the following command.

dnx . run

The server runs at port 5004. Fire up the browser and type in http://localhost:5004/

Hope this is helpful for the first time users of Linux.

Currently rated 5.0 by 1 person

How Generic The Code Can Be - Resolving Type T at Compile Time

7. June 2015 08:07

.NET Framework C#  2 Comments

It is fun working with Generics, but sometimes it just won't work as I intended it to work. While working on a personal project, I was trying to write the code as generic as possible so I can re-use the functions or extension methods in my other projects as well. But it is not always the case, things will not always work as you want it to be. Here is the case of what I was trying to do.

I am working extensively on JSON in this project, so I thought of creating an extension method for the classes I want to serialize to JSON and save it to the file system. Creating the extension method was not a problem, but it turned out to my surprise that I just can’t use the extension method on type T. If I would have paid attention to the detail here before writing the function, I would have noticed the problem. Before I tell you what I did here, here is the extension method which will serialize class to JSON string.

public static string ToJSON<T>(this T Entity) where T : class
{
    return JsonConvert.SerializeObject(Entity);
}

As I want only classes to be serialize, I have a constraint in place that assure me that this extension method should be used when the T is of type Class. I agree with the fact the creating an extension method just for a simple work is an over kill but I am just lazy about writing this line again and again. The application I am working on can support multiple databases and for that I am using Dependency Injection (DI). I wrote this function keeping in mind that I just have to pass the model name i.e. class object and this function will then save the JSON string from the serialized class to the file system.

public bool Save<T>(T Entity, string Path) where T : class
{
    bool IsSaved = false;
    try
    {
        if (!Path.IsNullOrEmpty())
        {
            File.AppendAllText(Path, Entity.ToJSON());
            IsSaved = true;
        }
        return IsSaved;
    }
    catch (Exception x)
    {
        throw x;
    }
}

The above code will not compile. This is because, there is no way for the compiler to know the type of Entity object we are passing. The constraints has nothing to do with it. It is just the compiler who has to know what kind of type it is dealing with. In this case we have a type T which is not resolved at compile time and hence the ToJSON() extension method I am using above, is an assumption from my part that Entity is a class, is not going to work. The important point here is that T is going to resolve at runtime and before that if we try to use the extension method (meant only for class) on type T, the intellisense will never show the ToJSON() extension method in the list.

Now to overcome this problem, we have to make some changes to the above code in order to have the information which the compiler can use and allow us to make use of the ToJSON()extension method. As there is a constraint in place for this function which will only allow us to pass class object as a first parameter, but the case is still the same. The Save function will never know what is the actual type of the Entity. Therefore we can use the Entity object and get the name of the Class like so.

string className = Entity.GetType().Name;

This gives us the name of the class and now we can use it to get the actual type of T and convert it to that type (which will be class). Once we have a class we can then use our ToJSON() extension method. Here is the updated code.

public bool Save<T>(T Entity, string Path) where T : class
{
    bool IsSaved = false;
    try
    {
        if (!Path.IsNullOrEmpty())
        {
            if (Entity.GetType().Name == "Board")
                File.AppendAllText(Path, Convert.ChangeType(Entity, typeof(Board)).ToJSON());
            else if (Entity.GetType().Name == "Story")
                File.AppendAllText(Path, Convert.ChangeType(Entity, typeof(Story)).ToJSON());

            IsSaved = true;
        }
        return IsSaved;
    }
    catch (Exception x)
    {
        throw x;
    }
}

This code will compile and saves the JSON string to the specified path on execution. Notice the Convert.ChangeType function. It’s simple function which you can use to convert one type to your desired type. The only drawback here will be that you have to come here and update the function whenever you have a type of class added in the project which you want to serialize to JSON. The code is still pretty sleek according to me for the type of task I am trying to accomplish.

The type T is very useful, but sometimes it may not solve all your problem.

 No Rating

Recurring Tasks Inside ASP.NET Applications Using HangFire

15. June 2014 22:46

ASP.NET ASP.NET MVC C# SQL Server Web  1 Comment

This is open-source at its best. Running background task to work in context with ASP.NET was and is still a big deal for few developers. I user QueueUserWorkItem to schedule emails when a new comment is added on my blog. This makes sure that the UI is responsive and the user can close or navigate to other post. I have been working on enterprise applications for many years now and most of the long running tasks are running in the background i.e. windows services.

HangFire is not limited to ASP.NET applications, you can even use it in your console applications.

HangFire is an open-source project which allows us to run recurring tasks within the ASP.NET application. No need of scheduling tasks and windows services. Everything will be within the ASP.NET application. When a new comment is added on my blog, an email is sent to my inbox as a notification to moderate it. In a normal scenario it will take a bit more than a normal time to add a comment because an email is also being sent to my inbox. To overcome this problem, I queued the mail process in the background like so:

bool commentSave = _db.AddComment(comment);
if (commentSave)
{
    System.Threading.ThreadPool.QueueUserWorkItem(s=> BlogEmail.SendEmail(comment));
    return Json(new { message = "Thanks for your comment. The comment is now awaiting moderation" });
}
else
    return Json(new { message = "There is an error while saving comment. Please try again later" });

As soon as a comment is added, user will be prompted that comment is added in the DB but the process of sending the email is scheduled in the background. But this approach has a drawback. What if the email sending is failed? As the admin of my blog, will I be able to see the status of the process? HangFire resolves all these questions and it comes with an awesome HangFire monitor which displays the status of all the background tasks in real-time. I will discuss about the HangFire monitor later in this post, but first let's get started with HangFire.

Installing HangFire

HangFire is available on NuGet. Firing the below command will automatically add the references in your project and takes care of all the configuration.

Install-Package HangFire
Attempting to resolve dependency 'HangFire.SqlServer (= 0.9.1)'.
Attempting to resolve dependency 'HangFire.Core (= 0.9.1)'.
Attempting to resolve dependency 'Common.Logging (= 2.1.2)'.
Attempting to resolve dependency 'Newtonsoft.Json (= 5.0.0)'.
Attempting to resolve dependency 'ncrontab (= 1.0.0)'.
Attempting to resolve dependency 'Dapper (= 1.13)'.
Attempting to resolve dependency 'HangFire.Web (= 0.9.1)'.
Attempting to resolve dependency 'CronExpressionDescriptor (= 1.10.1)'.
Attempting to resolve dependency 'WebActivatorEx (= 2.0.1)'.
Attempting to resolve dependency 'Microsoft.Web.Infrastructure (= 1.0.0.0)'.
Installing 'Common.Logging 2.1.2'.
Successfully installed 'Common.Logging 2.1.2'.
Installing 'ncrontab 1.0.0'.
Successfully installed 'ncrontab 1.0.0'.
Installing 'HangFire.Core 0.9.1'.
Successfully installed 'HangFire.Core 0.9.1'.
Installing 'Dapper 1.13'.
Successfully installed 'Dapper 1.13'.
Installing 'HangFire.SqlServer 0.9.1'.
Successfully installed 'HangFire.SqlServer 0.9.1'.
Installing 'CronExpressionDescriptor 1.10.1'.
Successfully installed 'CronExpressionDescriptor 1.10.1'.
Installing 'WebActivatorEx 2.0.1'.
Successfully installed 'WebActivatorEx 2.0.1'.
Installing 'HangFire.Web 0.9.1'.
Successfully installed 'HangFire.Web 0.9.1'.
Installing 'HangFire 0.9.1'.
Successfully installed 'HangFire 0.9.1'.
Adding 'Common.Logging 2.1.2' to HangfireDemo.
Successfully added 'Common.Logging 2.1.2' to HangfireDemo.
Adding 'ncrontab 1.0.0' to HangfireDemo.
Successfully added 'ncrontab 1.0.0' to HangfireDemo.
Adding 'HangFire.Core 0.9.1' to HangfireDemo.
Successfully added 'HangFire.Core 0.9.1' to HangfireDemo.
Adding 'Dapper 1.13' to HangfireDemo.
Successfully added 'Dapper 1.13' to HangfireDemo.
Adding 'HangFire.SqlServer 0.9.1' to HangfireDemo.
Successfully added 'HangFire.SqlServer 0.9.1' to HangfireDemo.
Adding 'CronExpressionDescriptor 1.10.1' to HangfireDemo.
Successfully added 'CronExpressionDescriptor 1.10.1' to HangfireDemo.
Adding 'WebActivatorEx 2.0.1' to HangfireDemo.
Successfully added 'WebActivatorEx 2.0.1' to HangfireDemo.
Adding 'HangFire.Web 0.9.1' to HangfireDemo.
Successfully added 'HangFire.Web 0.9.1' to HangfireDemo.
Adding 'HangFire 0.9.1' to HangfireDemo.
Successfully added 'HangFire 0.9.1' to HangfireDemo.

I am using HangFire with ASP.NET MVC application. Here are the few things that you need to configure before you dive in. When installing HangFire via NuGet, it adds HangFireConfig.cs under App_Start folder. HangFire supports Redis, SQL Server, SQL Azure or MSMQ. I am using SQL Server in this demo. The reason we require this storage because it is being used by the HangFire monitor to display the real-time data of the jobs. To configure HangFire to use SQL Server, open HangFireConfig.cs file and change the connection string as per your SQL Server installation.

JobStorage.Current = new SqlServerStorage(
    @"Server=GHOST\SERVER; Database=Jobs;user id=sa; password=pass#w0rd1;");

When the application first starts, all required database objects are created. 

You can find the scripts inside the downloaded package HangFire.SqlServer.0.9.1\Tools\install.sql. The jobs and monitor will be using this database to show me the real-time status of the jobs running in the background. To view the HangFire monitor, simply navigate to http://<sitename>/hangfire.axd. As it is a handler, you can see it in your web.config file. Let's see it in action:

The navigation pane on the right, lets you see the jobs and their status. It let's you even see the queues which are currently running. 

Scheduling the Jobs

Scheduling jobs using HangFire is easier then I thought it would be. Talking about the same example from my blog which sends email in my inbox when a new comment is added. If I want to schedule the mail send process as a background job I can do it easily using the BackgroundJob class.

bool commentSave = _db.AddComment(comment);
if (commentSave)
{
    BackgroundJob.Enqueue(() => BlogEmail.SendEmail(comment));
    return Json(new { message = "Thanks for your comment. The comment is now awaiting moderation" });
}
else
    return Json(new { message = "There is an error while saving comment. Please try again later" });

As I require it to run only once I just have queue it using the BackgroundJob.Enqueue() method. I can also delay the execution of the job using the Schedule method of the BackgroundJob class.

bool commentSave = _db.AddComment(comment);
if (commentSave)
{
    BackgroundJob.Schedule(() => BlogEmail.SendEmail(comment), TimeSpan.FromMinutes(60));
    return Json(new { message = "Thanks for your comment. The comment is now awaiting moderation" });
}
else
    return Json(new { message = "There is an error while saving comment. Please try again later" });

What if the email sending is failed? The SendMail method throws an exception that the mail sending is failed. HangFire will handle this by default and it will retry automatically 3 more times after a consecutive delay after each retry. But if I want to retry it more than 3 times then I can make use of the AutomaticRetry attribute and pass the number of retries I want, something like this:

[AutomaticRetry(Attempts = 5)]
public bool SendEmail(Comment comment)
{
    //Email code
}

Let's say if I do have another method that I want to run every minute (it's an overkill for my blog) then I will make use of RecurringJob class.

RecurringJob.AddOrUpdate(() => Storage.PunchIt(), Cron.Minutely);

Cron enum allows me to schedule a job daily, weekly, monthly, yearly, hourly and minutely. Now as my job is schedule in the background, time to take a look at HangFire monitor.

I have no idea why my Recurring Jobs screen is showing Next and Last execution time as 44 years ago. But you can see the Succeeded Jobs with a minute interval (#5 and #4). HangFire uses persistent storage and therefore you can trigger the job at your will or remove it when you feel like it. That means you configure the job in the code and manage it from the HangFire monitor.

What else you can do with HangFire

I just showed you how easy it can be scheduling jobs using HangFire. But there are more advanced topics which you should be looking into for more complex implementation. HangFire supports logging, dependency injection using Ninject, multiple queue processing and more.

References

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