Blazor key press event and KeyCodes

Question

I am creating a control in a Razor Control Library. I am trying to only allow a few keys presses to be allowed in a text box. They are:

1. Any number greater than 0. This is to include decimals
2. The letter "N" or "n"
3. Allow the user to copy/paste (control+c and control+v).
4. Allow arrows and tab key

I can easily do this in Javascript, by using the Keycode. In JS, I would do this:

keyPress: function (e) {
        var datatype = e.currentTarget.getAttribute("data-type");
        settings.valueChange.call();
        //add 110, 190 for decimal          
        if ($.inArray(e.keyCode, [46, 8, 9, 27, 13]) !== -1 ||
            // Allow: Ctrl+A,Ctrl+C,Ctrl+V, Command+A
            ((e.keyCode == 65 || e.keyCode == 86 || e.keyCode == 67) && (e.ctrlKey === true || e.metaKey === true)) ||
            // Allow: home, end, left, right, down, up
            (e.keyCode >= 35 && e.keyCode <= 40)) {
            // let it happen, don't do anything
            if (e.keyCode == 86) {
                //PASTE                
            }
            return;
        }
        if (e.keyCode === 78) {
            e.preventDefault();               
            //its an N, do some stuff
        } else if ((e.shiftKey || (e.keyCode < 48 || e.keyCode > 57)) && (e.keyCode < 96 || e.keyCode > 105)) {
            e.preventDefault();
        }
    }

But, how would I do this in Blazor/Razor? The KeyboardEventArgs does not seem to provide the KeyCode. I could use jsInterop to call my JS function, but, again, KeyboardEventArgs does not provide the JS KeyCode. How can I either accomplish this in Blazor or get the numeric KeyCode, so I can pass this to my JS function?

Answer 1

You can use more Blazor way to do that and check the string every time the text is changed.

@using System.Text.RegularExpressions;
<input @bind-value="@InputValue" @bind-value:event="oninput"/>
<h4>@InputValue </h4>

@code {
    private string _inputVal = "";
    public string InputValue {
        get => _inputVal;
        set { 
        if((double.TryParse(value,out double d) && d>0)//is the number like 1.23
          || value.ToLower()=="n" || value=="" )//or is N,n or empty str
            _inputVal = value;
        }
        }
}

Pasting and arrow keys work as expected.