C#•2y ago

✅ Index expressions are only supported with constants - Avalonia ReactiveUI

IObservable<bool> okUsername = (IObservable<bool>)this.WhenAnyValue(
  x => x.Username,
  x => IValidate.IsValidUsername(x.Username));

public class InputValidation
{
    public bool IsValidUsername(string username)
    {
        if (string.IsNullOrEmpty(username))
        {
            return false;
        }

        string pattern = @"^[a-zA-Z0-9!@#$%^&*_-]{7,12}$";
        return Regex.IsMatch(username, pattern);
    }

IObservable<bool> okUsername = (IObservable<bool>)this.WhenAnyValue(
  x => x.Username,
  x => IValidate.IsValidUsername(x.Username));

public class InputValidation
{
    public bool IsValidUsername(string username)
    {
        if (string.IsNullOrEmpty(username))
        {
            return false;
        }

        string pattern = @"^[a-zA-Z0-9!@#$%^&*_-]{7,12}$";
        return Regex.IsMatch(username, pattern);
    }

I keep getting a run-time error (only shows up when I attempt to launch the application) that says

Index expressions are only supported with constants

Index expressions are only supported with constants

on the

IObservable<bool>

IObservable<bool>

and I'm not quite understanding why and google doesn't offer much help.

Buddy•3/4/24, 2:10 AM

do not reuse

for one

MekOP•3/4/24, 2:11 AM

what do you mean?

MekOP•3/4/24, 2:12 AM

https://www.reactiveui.net/docs/handbook/commands/

That's how the library shows to use it

Buddy•3/4/24, 2:12 AM

I assume this is for CanExecute?

MekOP•3/4/24, 2:12 AM

correct

Buddy•3/4/24, 2:12 AM

https://www.reactiveui.net/docs/handbook/when-any#reactivecommandcanexecute-observable

Buddy•3/4/24, 2:14 AM

I have rarely ever used ReactiveUI, but I assume you cannot use an instance of an object, the method in question must be static

BBuddy I have rarely ever used ReactiveUI, but I assume you cannot use an instance of a...

MekOP•3/4/24, 2:16 AM

so then it would be something like this? Which I mirrored from https://www.reactiveui.net/docs/handbook/when-any#reactivecommandcanexecute-observable

Buddy•3/4/24, 2:17 AM

Pretty much, yeah.

MekOP•3/4/24, 2:17 AM

ok bet. tyvm. you just helped me save lines of code on other projects that do multiple IObservables and then concat then all together

Buddy•3/4/24, 2:18 AM

Also good to add DistinctUntilChanged

Buddy•3/4/24, 2:18 AM

So it does not spam you

This operator stands guard, ensuring that you're not bombarded with repetitive information. Imagine if your best friend kept repeating the same story to you every time you met. It'd get old, right? The DistinctUntilChanged operator does just that; it prevents subsequent identical emissions from an observable.