Blazor - Model Binding InputText and String

[casper7526]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

Public string? X

Bind the string to an InputText, post the form. X is null.
Type something into the field than delete the text, post the string. X is now an empty string.

Work around was just adding a check on my setter but the fact that an empty text box can represent both null and empty string is not clear.

Expected Behavior

String should always be null when blank except when explicitly told otherwise.

Steps To Reproduce

No response

Exceptions (if any)

No response

.NET Version

6

Anything else?

No response

[casper7526]

The way I found this was by putting a minlength annotation on my string but not required. So it passes validation unless the string is modified.

[rafikiassumani-msft]

@casper7526 Can you provide a link to a GitHub repo to reproduce this ?

Hi @casper7526. We have added the "Needs: Author Feedback" label to this issue, which indicates that we have an open question for you before we can take further action. This issue will be closed automatically in 7 days if we do not hear back from you by then - please feel free to re-open it if you come back to this issue after that time.

[casper7526]

https://github.com/casper7526/BlazorTextInputBug

Add Text to the InputText box and cause a Blur --- The value is now NOT NULL
Delete All Text from the InputText box and cause a Blur -- The value remains NOT NULL -- Empty.String

The problem is caused by the 2 following lines of code inside of
Components/Web/src/Forms/InputBase.cs

 public override Task SetParametersAsync(ParameterView parameters)
......
_nullableUnderlyingType = Nullable.GetUnderlyingType(typeof(TValue));

This sets _nullableUnderlyingType to NULL when ran on a string? (reference type)

 protected string? CurrentValueAsString
    {
        get => FormatValueAsString(CurrentValue);
        set
        {
            _parsingValidationMessages?.Clear();

            bool parsingFailed;

            if (_nullableUnderlyingType != null && string.IsNullOrEmpty(value))

The first IF-CHECK could be triggered in this scenario and cause CurrentValue to be null.

I believe simply by changing the following the bug will be fixed and working as intended.

[-] if (_nullableUnderlyingType != null && string.IsNullOrEmpty(value))
[+] if ((_nullableUnderlyingType != null || TValue is string) && string.IsNullOrEmpty(value))

[casper7526]

I'm not sure without lots of playing around, but this should ONLY happen with a string? (nullable)
If the property was to be a string, than possibly an empty string would be the expected behavior.

[javiercn]

I suspect this is expected as it only reflects the value from the underlying input element.

The initial value for the binding is null, when you type something, the value from the textbox is updated, and the binding is updated to reflect that. When you delete the text, the value (in JS) is the empty string, and the binding is updated accordingly.

For other data types doesn't behave that way because I believe the binding filters values that it can't parse and won't set the associated value. That doesn't happen with InputText because any value is always a valid value.