LANCommander/LANCommander.Server/UI/Components/InputRegistry.razor

<AntDesign.Input Type="InputType.Text" @bind-Value="Path" OnBlur="() => OnChanged()">
    <AddOnBefore>
        <SimpleSelect @bind-Value="Hive" Style="width: auto;" OnSelectedItemsChanged="() => OnChanged()">
            <SelectOptions>
                @foreach (var hive in AvailableHives)
                {
                    <SimpleSelectOption Value="@hive" Label="@hive"></SimpleSelectOption>
                }
            </SelectOptions>
        </SimpleSelect>
    </AddOnBefore>
</AntDesign.Input>

@code {
    [Parameter] public string Value { get; set; } = "";
    [Parameter] public EventCallback<string> ValueChanged { get; set; }

    string Hive = "HKCU:\\";
    string Path = "SOFTWARE";

    string[] AvailableHives = new string[]
    {
        "HKCR:\\",
        "HKCU:\\",
        "HKLM:\\",
        "HKU:\\",
        "HKCC:\\"
    };

    protected override async Task OnInitializedAsync()
    {
        if (Hive == null)
            Hive = "HKCU:\\";

        if (Value == null)
            Value = Hive;
        
        if (!String.IsNullOrWhiteSpace(Value))
            Hive = AvailableHives.FirstOrDefault(h => Value != null && Value.StartsWith(h));

        Path = Value.Substring(Hive.Length);
    }

    private async void OnChanged()
    {
        Value = Hive + Path;

        if (ValueChanged.HasDelegate)
            await ValueChanged.InvokeAsync(Value);

        StateHasChanged();
    }
}