Friday, December 30, 2022

Creating a master/detail web application with ASP.NET Razor Pages

In this tutorial, you will create a master/detail web application using ASP.NET Razor Pages. The data used will be read from your operating system. Specifically, we will query the local operating system with the number of processes that are running and then display details about each process. We shall use Visual Studio Code for our editor.

Source Code: https://github.com/medhatelmasry/OsProcess
Companion video: https://youtu.be/u_CT0aUz4lc

Getting started

Inside a working directory, run the following command in a terminal window to create a Razor Pages web application in a folder names OsProcess:

dotnet new razor -o OsProcess

Change into the newly created directory with:

cd OsProcess

To run the application in watch mode type:

dotnet watch

The following web app will appear in your default browser:



Our objective is to display all the processes that are running in your operating system.

Displaying processes on the home page

Stop the web server by hitting CTRL C in the terminal window. Then, open the project in VS Code by typing the following in the same folder:

code .

Open Pages/Index.cshtml.cs in the editor.  Add the following using statement at the top of the IndexModel class:

using System.Diagnostics;

Find the OnGet() method and add the following code into it:

Process[] processes = Process.GetProcesses();
ViewData["P"] = processes;

The above code uses the Process class’s static method GetProcesses() to read all the processes that are running in your operating system. The next step is to display this information in the view. Open Pages/Index.cshtml in the editor. Replace the contents of Pages/Index.cshtml with the following:

@page
@using System.Diagnostics
@model IndexModel
@{
    ViewData["Title"] = "OS Processes";
    Process[]? processes = ViewData["P"] as Process[];
}

<div class="text-center">
    <h1 class="display-4">@ViewData["Title"]!</h1>
        @foreach (var item in processes!)
        {
            @if (item.ProcessName.Trim().Length > 0)
            {
                <p><a asp-page="./Details" asp-route-id="@item.Id">@item.ProcessName</a></p>
            }
        }
</div>

The above code assigns a ViewData object, passed from the code behind, to an array of Process objects. It then displays the array items in a series of links.

Run the app in watch mode by typing the following command:

dotnet watch

This is what I see on my mac computer. You will experience different data on your computer depending on your operating system and the background applications that are currently running on your computer.



When you click on any of the links, you will notice that it does nothing. Let’s analyze the anchor tag:

<a asp-page="./Details" asp-route-id="@item.Id">@item.ProcessName</a>

This suggests that there is a ./Details page that is missing. Let us add this page by typing the following scaffolding command in the terminal window:

dotnet new page --namespace OsProcess.Pages --name Details --output Pages

The above creates files Pages/Details.cshtml and Pages/Details.cshtml.cs.


Open Pages/Details.cshtml.cs in the editor. Just like we did before, add the following using statement at the top of the DetailsModel class:

using System.Diagnostics;

Also, in Pages/Details.cshtml.cs, replace the OnGet() method with the following:

public void OnGet(int id) {
    ViewData["P"] = Process.GetProcessById(id);
}

The above code retrieves details about a specific process from its ID and feeds the result into the ViewData dictionary with key P.

Open Pages/Details.cshtml in the editor. Replace the contents of this file with the following:

@page
@using System.Diagnostics
@model OsProcess.Pages.DetailsModel
@{
    Process? process = ViewData["P"] as Process;
    ViewData["Title"] = $"Process with ID={process!.Id}";
}

<h1>@ViewData["Title"]</h1>

<div>
    <hr />
    <table class="table table-striped">
        <tr>
            <td>Process Name</td><td>@process.ProcessName</td>
        </tr>
        <tr>
            <td>Number of threads</td><td>@process.Threads.Count</td>
        </tr>
    </table>
</div>
<div>
    <a asp-page="./Index">Back to List</a>
</div>

The above code displays the details of a specific process. These do not, by any means, represent all the properties of a process. In the interest of simplicity, we are only looking at four properties. Run the web app in your browser and you will see the following behavior:


Using property approach

If you do not wish to use ViewData or ViewBag objects, there is another better way of achieving the same outcome. Let’s starts with the master page involving Pages/Index.cshtml and Pages/Index.cshtml.cs. Open Pages/Index.cshtml.cs in the editor and make the following highlighted changes to it:

using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.RazorPages;
using System.Diagnostics;

namespace OsProcess.Pages;

public class IndexModel : PageModel
{
    private readonly ILogger<IndexModel> _logger;

    public IList<Process> Processes { get;set; } = default!;

    public IndexModel(ILogger<IndexModel> logger)
    {
        _logger = logger;
    }

    public void OnGet()
    {
        Processes = Process.GetProcesses().ToList();
    }
}

In the above code, we set the value of the class’s Processes property with the list of processes. This property can get directly accessed from the view file.

Similarly, update Pages/Index.cshtml.cs so it looks like this:

@page
@using System.Diagnostics
@model IndexModel
@{
    ViewData["Title"] = "OS Processes";
}

<div class="text-center">
    <h1 class="display-4">@ViewData["Title"]!</h1>
        @foreach (var item in Model.Processes)
        {
            @if (item.ProcessName.Trim().Length > 0)
            {
                <p><a asp-page="./Details" asp-route-id="@item.Id">@item.ProcessName</a></p>
            }
        }
</div>

Note that processes can be accessed with Model.Processes in the view. The latest solution is much more elegant and avoids the use of ViewData to pass data from the code behind file to the view. If you run the application again, you will notice that it behaves just like before.

One last thing we can do is to use the Property approach also in the Details page. Here is the code for Details.cshtml.cs & Details.cshtml:

Details.cshtml.cs

using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.RazorPages;
using System.Diagnostics;

namespace OsPorocess.Pages
{
    public class DetailsModel : PageModel
    {
        public Process SingleProcess { get; set; } = default!;
        public void OnGet(int id)
        {
            //ViewData["P"] = Process.GetProcessById(id);
            SingleProcess = Process.GetProcessById(id);
        }
    }
}

Details.cshtml

@page
@using System.Diagnostics
@model OsPorocess.Pages.DetailsModel
@{
    //Process? process = ViewData["P"] as Process;
    ViewData["Title"] = $"Process with ID={Model.SingleProcess.Id}";
}

<h1>@ViewData["Title"]</h1>

<div>
    <table class="table table-striped">
        <tr>
            <td>Process Name</td>
            <td>@Model.SingleProcess.ProcessName</td>
        </tr>
        <tr>
            <td>Number of threads</td>
            <td>@Model.SingleProcess.Threads.Count</td>
        </tr>
    </table>
    <div>
        <a asp-page="./index">Back to list</a>
    </div>
</div>

The same approach for master/detail data can be used in a variety of scenarios.

Thursday, December 29, 2022

ASP.NET Razor Pages made simple

Overview

This tutorial will show how easy it is to build web applications using .NET 7.0, C# and ASP.NET Razor Pages. You will develop a web app that calculates the future value on an investment based on a monthly contribution that you can make at a given interest rate for a number of years.

Source Code: https://github.com/medhatelmasry/SuperWeb

Companion Video: https://youtu.be/Zzu-WlkhnH8

Getting Started

To display different types of .NET applications that you can build, execute the following command in a terminal window on mac, Linux, or windows:

dotnet new --list

We want to create an ASP.NET Razor Pages application. Go to a working directory and run the following command from a terminal window to create an app in a folder named SuperWeb.

dotnet new razor -f net7.0 -o SuperWeb

OR

dotnet new webapp -f net7.0 -o SuperWeb

Change directory to the newly created folder with:

cd SuperWeb

To run the application in developer mode, run the following command:

dotnet watch

The web app will open in your default browser.

Open the web project in Visual Studio Code with the following command:

code .

Folders

Open Pages/Index.cshtml.cs in the editor and inspect its content.

using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.RazorPages;

namespace SuperWeb.Pages;

public class IndexModel : PageModel
{
    private readonly ILogger<IndexModel> _logger;

    public IndexModel(ILogger<IndexModel> logger)
    {
        _logger = logger;
    }

    public void OnGet()
    {

    }
}

Add the following line of code inside the OnGet() method:

ViewData["Name"] = "Queen Elizabeth";

The above code adds a string to a ViewData dictionary with key "Name". ViewData dictionaries can be passed from the Index.cdhtml.cs file to the Index.cshtml view file.

Open Pages/Index.cshtml in the editor.

@page
@model IndexModel
@{
    ViewData["Title"] = "Home page";
}

<div class="text-center">
    <h1 class="display-4">Welcome</h1>
    <p>Learn about <a href="https://docs.microsoft.com/aspnet/core">building Web apps with ASP.NET Core</a>.</p>

</div>

Add the following right before </div>:

<h2>@ViewData["Name"]</h2>

Our main page looks like this:

Create a new folder named Models. Inside the Models folder, add a file named FutureValue.cs with this code:

namespace SuperWeb.Models;

public class FutureValue
{
    public decimal MonthlyInvestment { get; set; }
    public decimal YearlyInterestRate { get; set; }
    public int Years { get; set; }
    public decimal CalculateFutureValue()
    {
        int months = Years * 12;
        decimal monthlyInterestRate =
        YearlyInterestRate / 12 / 100;
        decimal futureValue = 0;
        for (int i = 0; i < months; i++)
        {
            futureValue = (futureValue + MonthlyInvestment)
            * (1 + monthlyInterestRate);
        }
        return futureValue;
    }
}

Create a Razor page pair of files named FutureValue.cshtml and FutureValue.cshtml.cs in the Pages folder with:

dotnet new page --namespace SuperWeb.Pages --name FutureValue --output Pages

Add the below highlighted code to Pages/FutureValue.cshtml.cs:

using Microsoft.AspNetCore.Mvc.RazorPages;
using SuperWeb.Models;

namespace SuperWeb.Pages
{
    public class FutureValueModel : PageModel
    {
        public decimal MonthlyInvestment { get; set; }
        public decimal YearlyInterestRate { get; set; }
        public int Years { get; set; }

        public void OnGet()
        {
            ViewData["FV"] = 0;
        }

        public void OnPost(FutureValue model)
        {
            ViewData["FV"] = model.CalculateFutureValue();
        }
    }
}

Replace contents of Pages/FutureValue.cshtml with:

@page
@model SuperWeb.Pages.FutureValueModel
@{
    ViewData["Title"] = "Future Value Page";
}

<div>
    <form method="post">
        <div>
            <label asp-for="MonthlyInvestment">
                Monthly Investment:</label>
            <input asp-for="MonthlyInvestment" />
        </div>
        <div>
            <label asp-for="YearlyInterestRate">
                Yearly Interest Rate:</label>
            <input asp-for="YearlyInterestRate" />
        </div>
        <div>
            <label asp-for="Years">Number of Years:</label>
            <input asp-for="Years" />
        </div>
        <div>
            <label>Future Value:</label>
            <input value='@ViewBag.FV.ToString("C2")' readonly>
        </div>
        <button type="submit">Calculate</button>
        <a asp-action="Index">Clear</a>
    </form>
</div>

Start the app then point your browser to /FutureValue. You will see this page:

The above page calculates the future value of an investment that you make at a specific interest rate based on a monthly fixed contribution for a number of years. Try entering the following values, then click on Calculate:



The result should look like this:

Let us add a link to /FutureValue on the main menu of the application. Open Pages/Shared/_Layout.cshtml. Around line 26, replace (  <a class="nav-link text-dark" asp-area="" asp-page="/Privacy">Privacy</a> ) with:

<a class="nav-link text-dark" asp-area="" asp-page="/FutureValue">Future Value</a>

You will see the Future Value link on the main menu.


Let us modify the “Future Value” form so that it looks more professional using bootstrap. Simply replace the <form> . . . . </form> HTML block in Pages/FutureValue.cshtml with:

<form method="post">
<div class="form-group">
<label asp-for="MonthlyInvestment" class="control-label"></label>
<input asp-for="MonthlyInvestment" class="form-control" />
</div>


<div class="form-group">
<label asp-for="YearlyInterestRate" class="control-label"></label>
<input asp-for="YearlyInterestRate" class="form-control" />
</div>

<div class="form-group">
<label asp-for="Years" class="control-label"></label>
<input asp-for="Years" class="form-control" />
</div>

<div class="form-group">
<label class="control-label">Future Value:</label>
<input value='@ViewBag.FV.ToString("C2")' readonly class="form-control">
</div>

<div class="form-group">
           <br />
<input type="submit" value="Calculate" class="btn btn-primary" />
<a asp-action="Index" class="btn btn-success">Clear</a>
</div>
</form>

If you run the application again, this is what you will see on the “Future Value” page:

Something is wrong. The labels (MonthlyInvestment, YearlyInterestRate, & Years) are not user friendly. They should be “Monthly Investment”, “Yearly Interest Rate” & “Number of years”. This is easily fixed using annotations on the model. Add the following highlighted annotations to Pages/FutureValue.cshtml.cs:

using System.ComponentModel.DataAnnotations;
using Microsoft.AspNetCore.Mvc.RazorPages;
using SuperWeb.Models;

namespace SuperWeb.Pages
{
    public class FutureValueModel : PageModel
    {
        [Display(Name="Monthly Investment")]
        public decimal MonthlyInvestment { get; set; }
         
        [Display(Name="Yearly Interest Rate")]
        public decimal YearlyInterestRate { get; set; }

        [Display(Name="Number of years")]
        public int Years { get; set; }

        public void OnGet()
        {
            ViewData["FV"] = 0;
        }

        public void OnPost(FutureValue model)
        {
            ViewData["FV"] = model.CalculateFutureValue();
        }

    }
}

Note: You will need to import the System.ComponentModel.DataAnnotations namespace.

Now the page has user friendly labels that look like this:


There is much more you can do with razor pages and it is an easier alternative to ASP.NET MVC.