C#•3y ago

WinForms Course Registration/Validation Homework

I just started my C# class for college and I've been having a real tough time trying to get my WinForms Course registration project to work. With this assignment, the only code I needed to write was the code under the courseComboBox_SelectedIndexChanged method and the code under the private void completeRegistrationButton_Click(object sender, EventArgs e) method. I included the validation in the first method but I'm not sure if that needs to be its own file or not. I've inserted the code needed for the courseComboBox_SelectedIndexChanged so it can handle the selection of the courses in the comboBox by validating the selection and adding the course number to the list of registered courses in the ListBox. I've also written the code for the button's event handler method so that when the user clicks the button to submit the completed registration, the program writes the list of registered courses to the output file. Visual Studio says I have no issues but when I run my code, it throws an issue as shown in the last picture. Also when I run the program, the form does not store the classes that I select and I am not able to progress so I'm not sure if that's the courseComboBox_SelectedIndexChanged method acting up or where I'm messing up. For reference, I am referencing the courses project in my WinForms project. This is my first time really submitting anything programming related anywhere so I apologize if I miss some key details I'm trying to insert everything I can think of. I am also really fresh in the programming world so I'm still in the basics. I'd appreciate any help with this, I don't want someone to do it for me, but rather help me find the solution so I can learn what I did wrong and what I'm missing. Thank you.

Mayor McCheese•11/26/23, 11:23 PM

I'm not very familiar with winforms, but try to change your courses to a BindingList instead of a List, and add courses to that instead

MMayor McCheese I'm not very familiar with winforms, but try to change your courses to a Binding...

CalenOP•11/27/23, 1:18 AM

I changed the list to a BindingList but it did not fix my errors. I still have the exception user-unhandled error and am not able to save my selections on the form. Would you have any suggestions on what videos or sites are good resources for WinForms?

Mayor McCheese•11/27/23, 1:35 AM

Can you paste your code, not photos?

Mayor McCheese•11/27/23, 1:35 AM

$paste

MMayor McCheese $paste

MODiX•11/27/23, 1:35 AM

If your code is too long, you can post to https://paste.mod.gg/ and copy the link into chat for others to see your shared code!

Mayor McCheese•11/27/23, 1:35 AM

$code

MMayor McCheese $code

MODiX•11/27/23, 1:35 AM

To post C# code type the following:
```cs
// code here
```

Get an example by typing

$codegif

$codegif

in chat

For longer snippets, use: https://paste.mod.gg/

CalenOP•11/27/23, 1:50 AM

$codegif

CCalen $codegif

MODiX•11/27/23, 1:50 AM

https://cdn.discordapp.com/attachments/364492811489509376/892176158312001586/code.gif

CalenOP•11/27/23, 1:51 AM

namespace Courses
{
    public class Course
    {
        // Parameterized constructor sets values for all properties
        public Course(string courseNumber, string courseTitle, int credits, int weeks)
        {
            CourseNumber = courseNumber;
            CourseTitle = courseTitle;
            Credits = credits;
            LengthInWeeks = weeks;
            // Initialize IsRegistered to false
            IsRegistered = false;
        }

        // These properties are auto-implemented and read only (init allows setting via constructor).
        public string CourseNumber { get; init; }
        public string CourseTitle { get; init; }
        public int Credits { get; init; }
        public int LengthInWeeks { get; init; }
        // IsRegistered is read-write
        public bool IsRegistered { get; set; }

    }
}

namespace Courses
{
    public class Course
    {
        // Parameterized constructor sets values for all properties
        public Course(string courseNumber, string courseTitle, int credits, int weeks)
        {
            CourseNumber = courseNumber;
            CourseTitle = courseTitle;
            Credits = credits;
            LengthInWeeks = weeks;
            // Initialize IsRegistered to false
            IsRegistered = false;
        }

        // These properties are auto-implemented and read only (init allows setting via constructor).
        public string CourseNumber { get; init; }
        public string CourseTitle { get; init; }
        public int Credits { get; init; }
        public int LengthInWeeks { get; init; }
        // IsRegistered is read-write
        public bool IsRegistered { get; set; }

    }
}

CalenOP•11/27/23, 1:52 AM

https://paste.mod.gg/chjgjygibeie/0

BlazeBin - chjgjygibeie

A tool for sharing your source code with the world!

CalenOP•11/27/23, 1:52 AM

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace u04a1_Registration_WinForm
{
    static class Program
    {
        /// <summary>
        /// The main entry point for the application.
        /// </summary>
        [STAThread]
        static void Main()
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            Application.Run(new Form1());
        }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace u04a1_Registration_WinForm
{
    static class Program
    {
        /// <summary>
        /// The main entry point for the application.
        /// </summary>
        [STAThread]
        static void Main()
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            Application.Run(new Form1());
        }
    }
}

Mayor McCheese•11/27/23, 2:08 AM

Apologies looking on phone for the moment

Mayor McCheese•11/27/23, 2:08 AM

What is the data source courseComboBox?

Mayor McCheese•11/27/23, 2:08 AM

Is it courses?

CalenOP•11/27/23, 2:17 AM

so that is supposed to be the object on the form that the user will use to make their selections from my understanding.

CalenOP•11/27/23, 2:17 AM

That drop down box

Mayor McCheese•11/27/23, 2:22 AM

So the error is complaining that you can't change that items collection right?

CalenOP•11/27/23, 2:44 AM

From what I'm understanding, yes that's correct. the form won't store the course when the user selects it and continue the loop

Mayor McCheese•11/27/23, 2:49 AM

So let's look at a couple methods here

Mayor McCheese•11/27/23, 2:49 AM

private void courseComboBox_SelectedIndexChanged(object sender, EventArgs e)
{
    //courseComboBox.SelectedIndex = -1;
    
    Course selectedCourse = courseComboBox.SelectedItem as Course;

    if (selectedCourse == null)
    {
        statusMessageText.Text = "Please select a course: ";
        return;
    }

    if (selectedCourse.IsRegistered)
    {
        statusMessageText.Text = "You are already registered for this course: ";
        return;
    }

    //Register for the Course
    selectedCourse.IsRegistered = true;

    //update the ComboBox displaying the registered courses
    courseComboBox.Items.Add(selectedCourse.CourseTitle);

    //update total credits
    totalCredits += selectedCourse.Credits;

    //Display a success message
    statusMessageText.Text = $"Registered for {selectedCourse.CourseTitle}";
}

private void courseComboBox_SelectedIndexChanged(object sender, EventArgs e)
{
    //courseComboBox.SelectedIndex = -1;
    
    Course selectedCourse = courseComboBox.SelectedItem as Course;

    if (selectedCourse == null)
    {
        statusMessageText.Text = "Please select a course: ";
        return;
    }

    if (selectedCourse.IsRegistered)
    {
        statusMessageText.Text = "You are already registered for this course: ";
        return;
    }

    //Register for the Course
    selectedCourse.IsRegistered = true;

    //update the ComboBox displaying the registered courses
    courseComboBox.Items.Add(selectedCourse.CourseTitle);

    //update total credits
    totalCredits += selectedCourse.Credits;

    //Display a success message
    statusMessageText.Text = $"Registered for {selectedCourse.CourseTitle}";
}

Mayor McCheese•11/27/23, 2:50 AM

This method fires because the the "Selected Index Changed", I'm making a somewhat safe assumption that this is when courseComboBox has a selected index change event raised.

Mayor McCheese•11/27/23, 2:51 AM

I say somewhat safe because despite what the name of method is, it's actually not correlated to control couseComboBox

Mayor McCheese•11/27/23, 2:52 AM

so on line 81:

courseComboBox.Items.Add(selectedCourse.CourseTitle);

courseComboBox.Items.Add(selectedCourse.CourseTitle);

Mayor McCheese•11/27/23, 2:52 AM

what do you expect this line to do?

CalenOP•11/27/23, 2:56 AM

I expected that line of code to add the course by its course title to the already registered box

Mayor McCheese•11/27/23, 2:57 AM

What is the already registered box?

CalenOP•11/27/23, 2:57 AM

IsRegistered* I apologize

Mayor McCheese•11/27/23, 2:58 AM

kk let's backwalk this a bit

Mayor McCheese•11/27/23, 2:58 AM

Firstly we have

private BindingList<Course> courses = new BindingList<Course>();

private BindingList<Course> courses = new BindingList<Course>();

Mayor McCheese•11/27/23, 2:59 AM

BindingList has some black magic in the background that should help the control stay current against it's databound collection

Mayor McCheese•11/27/23, 2:59 AM

so in Form1_Load

Mayor McCheese•11/27/23, 3:00 AM

We're reading data here

 using (StreamReader sr = new StreamReader(@"Data\course.data.txt"))
{
    string line;
    while ((line = sr.ReadLine()) != null)
    {
        // Parse data and add Course objects to courses List as they are created
        string[] data = line.Split(',');
        // Need to convert credits and weeks to integers
        courses.Add(new Course(data[0], data[1], Convert.ToInt16(data[2]), 
            Convert.ToInt16(data[3])));
    }
}

 using (StreamReader sr = new StreamReader(@"Data\course.data.txt"))
{
    string line;
    while ((line = sr.ReadLine()) != null)
    {
        // Parse data and add Course objects to courses List as they are created
        string[] data = line.Split(',');
        // Need to convert credits and weeks to integers
        courses.Add(new Course(data[0], data[1], Convert.ToInt16(data[2]), 
            Convert.ToInt16(data[3])));
    }
}

Which fills that same collection, courses, via courses.Add

CalenOP•11/27/23, 3:00 AM

I will ask, the only code I wrote was the code under the two methods i mentioned above. the rest of it was already written by the professor. So would it be safe to change the List to a BindingList if he had wrote it originally as a List?

Mayor McCheese•11/27/23, 3:01 AM

you can safely change it back

Mayor McCheese•11/27/23, 3:01 AM

I thought we were solving a different problem

Mayor McCheese•11/27/23, 3:01 AM

when I mentioned that

Mayor McCheese•11/27/23, 3:01 AM

see the aforementioned, I'm helping on my phone

Mayor McCheese•11/27/23, 3:01 AM

now I'm not helping on my phone

CalenOP•11/27/23, 3:02 AM

No worries, I should've clarified that's on me

Mayor McCheese•11/27/23, 3:02 AM

so, back to Form_Load

CCalen No worries, I should've clarified that's on me

Mayor McCheese•11/27/23, 3:02 AM

nah you're fine, I just want to make sure we're on the same page, and that the rest of the code makes some sense

Mayor McCheese•11/27/23, 3:02 AM

so here,

courseComboBox.DataSource = courses;

courseComboBox.DataSource = courses;

Mayor McCheese•11/27/23, 3:03 AM

we're telling courseComboBox that it's DataSource is that list

Mayor McCheese•11/27/23, 3:04 AM

which is a List<Course>; for the moment, the easiest way to think of List<Course> is that's a collection of courses and it can ONLY contain courses.

Mayor McCheese•11/27/23, 3:04 AM

so if you try to add widgets they're the wrong shape and they won't fit

Mayor McCheese•11/27/23, 3:05 AM

so back to our datasource in form_load

Mayor McCheese•11/27/23, 3:07 AM

you can see....

courseComboBox.DataSource = courses;
courseComboBox.DisplayMember = "CourseNumber";
courseComboBox.ValueMember = "CourseNumber";

courseComboBox.DataSource = courses;
courseComboBox.DisplayMember = "CourseNumber";
courseComboBox.ValueMember = "CourseNumber";

Here we're telling courseComboBox that the thing to show in the Box is the "member" CourseNumber

Mayor McCheese•11/27/23, 3:07 AM

and same for the value

Mayor McCheese•11/27/23, 3:07 AM

the underlying data, is still a Course, but, to show it you'll use the CourseNumber