❔ Validating user input

The king of kings · 2023-06-26T12:06:25.937Z

I have created a project and I need to learn how to validate user inputs

P

Pobiega•6/26/23, 12:06 PM

What kind of project? What kind of user input?

T

The king of kingsOP•6/26/23, 12:07 PM

I'll show you in a minute

T

The king of kingsOP•6/26/23, 12:10 PM

public class UserAccount
    {

        public string FirstName { get; }
        public string LastName { get; }
        public int Age { get; }
        public string EmailAddress { get; }
        public string HomeAddress { get; }
        public string PhoneNumber { get; }
        public string ID { get; }
        public UserAccount(string firstname, string lastname, string emailaddress, string homeaddress, string phonenumber, string id)
        {
            

            FirstName = firstname;
            LastName = lastname;
            EmailAddress = emailaddress;
            HomeAddress = homeaddress;
            PhoneNumber = phonenumber;
            ID = id;

        }

        public static string ValidateUserInput(string validate)
        {
            if (validate != null)
            {
                Console.WriteLine(validate);
            }
            else
            {
                Console.WriteLine("Invalid input!");
            }
            return validate;
        }

public class UserAccount
    {

        public string FirstName { get; }
        public string LastName { get; }
        public int Age { get; }
        public string EmailAddress { get; }
        public string HomeAddress { get; }
        public string PhoneNumber { get; }
        public string ID { get; }
        public UserAccount(string firstname, string lastname, string emailaddress, string homeaddress, string phonenumber, string id)
        {
            

            FirstName = firstname;
            LastName = lastname;
            EmailAddress = emailaddress;
            HomeAddress = homeaddress;
            PhoneNumber = phonenumber;
            ID = id;

        }

        public static string ValidateUserInput(string validate)
        {
            if (validate != null)
            {
                Console.WriteLine(validate);
            }
            else
            {
                Console.WriteLine("Invalid input!");
            }
            return validate;
        }

public class UserAccount
    {

        public string FirstName { get; }
        public string LastName { get; }
        public int Age { get; }
        public string EmailAddress { get; }
        public string HomeAddress { get; }
        public string PhoneNumber { get; }
        public string ID { get; }
        public UserAccount(string firstname, string lastname, string emailaddress, string homeaddress, string phonenumber, string id)
        {
            

            FirstName = firstname;
            LastName = lastname;
            EmailAddress = emailaddress;
            HomeAddress = homeaddress;
            PhoneNumber = phonenumber;
            ID = id;

        }

        public static string ValidateUserInput(string validate)
        {
            if (validate != null)
            {
                Console.WriteLine(validate);
            }
            else
            {
                Console.WriteLine("Invalid input!");
            }
            return validate;
        }

public class UserAccount
    {

        public string FirstName { get; }
        public string LastName { get; }
        public int Age { get; }
        public string EmailAddress { get; }
        public string HomeAddress { get; }
        public string PhoneNumber { get; }
        public string ID { get; }
        public UserAccount(string firstname, string lastname, string emailaddress, string homeaddress, string phonenumber, string id)
        {
            

            FirstName = firstname;
            LastName = lastname;
            EmailAddress = emailaddress;
            HomeAddress = homeaddress;
            PhoneNumber = phonenumber;
            ID = id;

        }

        public static string ValidateUserInput(string validate)
        {
            if (validate != null)
            {
                Console.WriteLine(validate);
            }
            else
            {
                Console.WriteLine("Invalid input!");
            }
            return validate;
        }

P

Pobiega•6/26/23, 12:11 PM

this makes no sense

T

The king of kingsOP•6/26/23, 12:11 PM

Ok

P

Pobiega•6/26/23, 12:12 PM

the class seems to be an entity/dto/model, and it has a static

ValidateUserInput

ValidateUserInput

ValidateUserInput

ValidateUserInput method that.. prints an optional message, and if no message was provided... what is going on?

T

The king of kingsOP•6/26/23, 12:13 PM

I just wanna say to the users you either enter a name or I will throw you an invalid message if leave it empty or null.

P

Pobiega•6/26/23, 12:13 PM

what kind of input could a single string hold that would be deemed "valid" or "invalid" in terms of a UserAccount anyways?

P

Pobiega•6/26/23, 12:13 PM

validation of user input usually means checking if the provided values are "okay" or not, this does not include checking if they match an existing item in your database

P

Pobiega•6/26/23, 12:14 PM

its stuff like "did the provided account ID match our expected format"

T

The king of kingsOP•6/26/23, 12:15 PM

Well! It's just a console application that I'm creating, so it should only validate if user input is null or not that's all.

T

The king of kingsOP•6/26/23, 12:16 PM

If you do it your self, how would you modify this logic?

P

Pobiega•6/26/23, 12:16 PM

There is already a method for that.

string.IsNullOrWhitespace

string.IsNullOrWhitespace

string.IsNullOrWhitespace

string.IsNullOrWhitespace

T

The king of kingsOP•6/26/23, 12:17 PM

Ok! You're right. I've used it before.

T

The king of kingsOP•6/26/23, 1:11 PM

Let me show you my implementation

T

The king of kingsOP•6/26/23, 1:29 PM

It's working now. But the only issue is that I'm repeating the readLine method twice.@pobiega

P

Pobiega•6/26/23, 1:30 PM

I'm out and about at the moment, I'll post a different solution when I get home. ETA 15

T

The king of kingsOP•6/26/23, 1:32 PM

Ok! Sounds awesome mate, thanks a lot.

P

Pobiega•6/26/23, 1:54 PM

Okay, so, lets first talk a bit about validation vs input and how they co-relate

P

Pobiega•6/26/23, 1:55 PM

any method that does validation should either return a

bool

bool

bool

bool indicating if the validation passed or failed, or throw an exception on validation failure

P

Pobiega•6/26/23, 1:55 PM

I personally greatly prefer the

bool

bool

bool

bool approach

P

Pobiega•6/26/23, 1:55 PM

second, we shouldnt allow invalid input, so we need to repeat the asking for a value until a valid value is passed

P

Pobiega•6/26/23, 1:56 PM

we also dont want to repeat ourselves, so we want to separate the input taking from the validation, so it can be reused

T

The king of kingsOP•6/26/23, 1:56 PM

OK

T

The king of kingsOP•6/26/23, 1:57 PM

Great to see you back again

P

Pobiega•6/26/23, 1:57 PM

Have you seen generic arguments before?

P

Pobiega•6/26/23, 1:57 PM

its stuff like

List<string>

List<string>

List<string>

List<string>

T

The king of kingsOP•6/26/23, 1:57 PM

I'm still reading your content

P

Pobiega•6/26/23, 2:04 PM

so our validator will look something like...

public class UserAccount
{
    public static bool ValidateName(string? name)
    {
        if (string.IsNullOrWhiteSpace(name))
        {
            Console.WriteLine("Invalid name: must be atleast one non-whitespace character");
            return false;
        }
        return true;
    }
}

public class UserAccount
{
    public static bool ValidateName(string? name)
    {
        if (string.IsNullOrWhiteSpace(name))
        {
            Console.WriteLine("Invalid name: must be atleast one non-whitespace character");
            return false;
        }
        return true;
    }
}

public class UserAccount
{
    public static bool ValidateName(string? name)
    {
        if (string.IsNullOrWhiteSpace(name))
        {
            Console.WriteLine("Invalid name: must be atleast one non-whitespace character");
            return false;
        }
        return true;
    }
}

public class UserAccount
{
    public static bool ValidateName(string? name)
    {
        if (string.IsNullOrWhiteSpace(name))
        {
            Console.WriteLine("Invalid name: must be atleast one non-whitespace character");
            return false;
        }
        return true;
    }
}

P

Pobiega•6/26/23, 2:05 PM

and we dont call it directly, instead we pass it to the input method

P

Pobiega•6/26/23, 2:05 PM

internal class Program
{
    private static void Main(string[] args)
    {
        var validName = GetStringInput("Enter an account name: ", UserAccount.ValidateName);
    }

    public static string GetStringInput(string prompt, Func<string, bool> validator)
    {
        while (true)
        {
            Console.Write(prompt);
            var input = Console.ReadLine();
            if (validator(input))
            {
                return input;
            }

            Console.WriteLine("Bad input, try again.");
        }
    }
}

internal class Program
{
    private static void Main(string[] args)
    {
        var validName = GetStringInput("Enter an account name: ", UserAccount.ValidateName);
    }

    public static string GetStringInput(string prompt, Func<string, bool> validator)
    {
        while (true)
        {
            Console.Write(prompt);
            var input = Console.ReadLine();
            if (validator(input))
            {
                return input;
            }

            Console.WriteLine("Bad input, try again.");
        }
    }
}

internal class Program
{
    private static void Main(string[] args)
    {
        var validName = GetStringInput("Enter an account name: ", UserAccount.ValidateName);
    }

    public static string GetStringInput(string prompt, Func<string, bool> validator)
    {
        while (true)
        {
            Console.Write(prompt);
            var input = Console.ReadLine();
            if (validator(input))
            {
                return input;
            }

            Console.WriteLine("Bad input, try again.");
        }
    }
}

internal class Program
{
    private static void Main(string[] args)
    {
        var validName = GetStringInput("Enter an account name: ", UserAccount.ValidateName);
    }

    public static string GetStringInput(string prompt, Func<string, bool> validator)
    {
        while (true)
        {
            Console.Write(prompt);
            var input = Console.ReadLine();
            if (validator(input))
            {
                return input;
            }

            Console.WriteLine("Bad input, try again.");
        }
    }
}

P

Pobiega•6/26/23, 2:05 PM

this guarantees a valid name

T

The king of kingsOP•6/26/23, 2:14 PM

Sorry, I just had to wash some clothes. Now, I'm back again.

PPobiega its stuff like `List<string>`

T

The king of kingsOP•6/26/23, 2:18 PM

Yes

PPobiega we also dont want to repeat ourselves, so we want to separate the input taking f...

T

The king of kingsOP•6/26/23, 2:19 PM

What do you mean by that?

P

Pobiega•6/26/23, 2:21 PM

look at the code I posted

T

The king of kingsOP•6/26/23, 2:21 PM

Yeah! Did review it actually. It looks really good to me.

T

The king of kingsOP•6/26/23, 2:22 PM

But you're using delegate like

Func<string, bool>

Func<string, bool>

Func<string, bool>

Func<string, bool> I'm not at this level yet.

T

The king of kingsOP•6/26/23, 2:25 PM

I noticed that you're defining a second method outside the main program, right?

 public static string GetStringInput(string prompt, Func<string, bool> validator)
    {
        while (true)
        {
            Console.Write(prompt);
            var input = Console.ReadLine();
            if (validator(input))
            {
                return input;
            }

            Console.WriteLine("Bad input, try again.");
        }
    }

 public static string GetStringInput(string prompt, Func<string, bool> validator)
    {
        while (true)
        {
            Console.Write(prompt);
            var input = Console.ReadLine();
            if (validator(input))
            {
                return input;
            }

            Console.WriteLine("Bad input, try again.");
        }
    }

 public static string GetStringInput(string prompt, Func<string, bool> validator)
    {
        while (true)
        {
            Console.Write(prompt);
            var input = Console.ReadLine();
            if (validator(input))
            {
                return input;
            }

            Console.WriteLine("Bad input, try again.");
        }
    }

 public static string GetStringInput(string prompt, Func<string, bool> validator)
    {
        while (true)
        {
            Console.Write(prompt);
            var input = Console.ReadLine();
            if (validator(input))
            {
                return input;
            }

            Console.WriteLine("Bad input, try again.");
        }
    }

P

Pobiega•6/26/23, 2:26 PM

Main

Main

Main

Main is a method, not a program

P

Pobiega•6/26/23, 2:26 PM

and its fairly unusual to declare methods inside other methods

T

The king of kingsOP•6/26/23, 2:26 PM

Sorry

P

Pobiega•6/26/23, 2:26 PM

even if its possible

P

Pobiega•6/26/23, 2:26 PM

so yeah, in this case I just declared it on

Program

Program

Program

Program itself.

T

The king of kingsOP•6/26/23, 2:26 PM

Yeah

P

Pobiega•6/26/23, 2:26 PM

in a real program, I'd have a

UserInput

UserInput

UserInput

UserInput static class with these methods in it

PPobiega so yeah, in this case I just declared it on `Program` itself.

T

The king of kingsOP•6/26/23, 2:27 PM

How come you didn't declare it in another class? Why underneath the main method a second method?

T

The king of kingsOP•6/26/23, 2:27 PM

Ok

P

Pobiega•6/26/23, 2:28 PM

here is one of my favorite methods, possible because of recent .NET features

P

Pobiega•6/26/23, 2:28 PM

public static T ParseInput<T>(string prompt, Func<T, bool> validator) where T : IParsable<T>
{
    while (true)
    {
        Console.Write(prompt);
        if (T.TryParse(Console.ReadLine(), null, out var result) && validator(result))
        {
            return result;
        }

        Console.WriteLine("Bad input, try again.");
    }
}

public static T ParseInput<T>(string prompt, Func<T, bool> validator) where T : IParsable<T>
{
    while (true)
    {
        Console.Write(prompt);
        if (T.TryParse(Console.ReadLine(), null, out var result) && validator(result))
        {
            return result;
        }

        Console.WriteLine("Bad input, try again.");
    }
}

public static T ParseInput<T>(string prompt, Func<T, bool> validator) where T : IParsable<T>
{
    while (true)
    {
        Console.Write(prompt);
        if (T.TryParse(Console.ReadLine(), null, out var result) && validator(result))
        {
            return result;
        }

        Console.WriteLine("Bad input, try again.");
    }
}

public static T ParseInput<T>(string prompt, Func<T, bool> validator) where T : IParsable<T>
{
    while (true)
    {
        Console.Write(prompt);
        if (T.TryParse(Console.ReadLine(), null, out var result) && validator(result))
        {
            return result;
        }

        Console.WriteLine("Bad input, try again.");
    }
}

❔ Validating user input

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