Checkbox

@using System.ComponentModel.DataAnnotations

<Form Model="Model" FormName="checkbox-terms" OnValidSubmit="Save" MaxWidth="28.Rem" Grow>
    <Checkbox @bind-Value="Model!.AcceptLicense">
        Publish under the <Anchor Href="https://opensource.org/license/mit" External>MIT license</Anchor>
    </Checkbox>
    <Row><Button Submit>Publish package</Button></Row>
    @if (_published)
    {
        <Alert Status="Status.Success">Published under the MIT license.</Alert>
    }
</Form>

@code {
    [SupplyParameterFromForm(FormName = "checkbox-terms")]
    private Package? Model { get; set; }

    private bool _published;

    protected override void OnInitialized() => Model ??= new();

    private void Save() => _published = true;

    public sealed class Package
    {
        // [Required] has the browser stop the post until it's checked. A bool is never null, so
        // [Required] alone passes on the server: [Range] is the server's check.
        [Required(ErrorMessage = "Agree to the license to publish")]
        [Range(typeof(bool), "true", "true", ErrorMessage = "Agree to the license to publish")]
        [Display(Name = "License")]
        public bool AcceptLicense { get; set; }
    }
}

@using System.ComponentModel.DataAnnotations
@using Microsoft.AspNetCore.Http

<Form Model="Model" FormName="checkbox-group-everything" OnValidSubmit="Save" MaxWidth="24.Rem" Grow>
    <CheckboxGroup @bind-Value="Model!.Topics" Items="Enum.GetValues<Topic>()" SelectAll SelectAllText="Everything" />
    <Row Gap="3" Align="Align.Center" Wrap>
        <Button Submit>Save</Button>
        @if (_saved is not null)
        {
            <TextBlock Size="TextSize.Sm" Color="Color.Muted">Last saved: @_saved</TextBlock>
        }
    </Row>
</Form>

@code {
    [SupplyParameterFromForm(FormName = "checkbox-group-everything")]
    private Notifications? Model { get; set; }

    private string? _saved;

    [CascadingParameter] private HttpContext? HttpContext { get; set; }

    // With nothing checked the group posts nothing: give the defaults only when this form didn't post.
    protected override void OnInitialized()
    {
        var posted = HttpContext?.Request.HasFormContentType == true
            && HttpContext.Request.Form["_handler"] == "checkbox-group-everything";
        Model ??= posted ? new() : new() { Topics = [Topic.Comments] };
    }

    // What was saved, not the field: on an interactive page it changes as boxes are checked.
    private void Save() => _saved = Model!.Topics is { Count: > 0 } topics
        ? string.Join(", ", Enum.GetValues<Topic>().Where(topics.Contains)) + "."
        : "nothing.";

    public sealed class Notifications
    {
        [Display(Name = "Notify me about")]
        public List<Topic>? Topics { get; set; } = [];
    }

    public enum Topic { Comments, Mentions, Releases }
}

<Form Model="Model" FormName="checkbox-sizes" Grow>
    <Row Gap="5" Wrap>
        <Checkbox @bind-Value="Model!.Small" Label="Small" Size="ControlSize.Sm" />
        <Checkbox @bind-Value="Model!.Medium" Label="Medium" />
        <Checkbox @bind-Value="Model!.Large" Label="Large" Size="ControlSize.Lg" />
    </Row>
    <Row Gap="5" Wrap>
        <Checkbox @bind-Value="Model!.Locked" Label="Disabled" Disabled />
        <Checkbox @bind-Value="Model!.LockedOn" Label="Disabled, checked" Disabled />
    </Row>
</Form>

@code {
    [SupplyParameterFromForm(FormName = "checkbox-sizes")]
    private Options? Model { get; set; }

    protected override void OnInitialized() => Model ??= new();

    public sealed class Options
    {
        public bool Small { get; set; } = true;
        public bool Medium { get; set; } = true;
        public bool Large { get; set; } = true;
        public bool Locked { get; set; }
        public bool LockedOn { get; set; } = true;
    }
}