aspnetcore/src/Microsoft.AspNetCore.Mvc.ViewFeatures/FormContext.cs

// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

using System;
using System.Collections.Generic;
using Microsoft.AspNetCore.Html;

namespace Microsoft.AspNetCore.Mvc.ViewFeatures
{
    /// <summary>
    /// Information about the current &lt;form&gt;.
    /// </summary>
    /// <remarks>
    /// Literal &lt;form&gt; elements in a view will share the default <see cref="FormContext"/> instance unless tag
    /// helpers are enabled.
    /// </remarks>
    public class FormContext
    {
        private Dictionary<string, bool> _renderedFields;
        private Dictionary<string, object> _formData;
        private IList<IHtmlContent> _endOfFormContent;

        /// <summary>
        /// Gets a property bag for any information you wish to associate with a &lt;form/&gt; in an
        /// <see cref="Rendering.IHtmlHelper"/> implementation or extension method.
        /// </summary>
        public IDictionary<string, object> FormData
        {
            get
            {
                if (_formData == null)
                {
                    _formData = new Dictionary<string, object>(StringComparer.Ordinal);
                }

                return _formData;
            }
        }

        /// <summary>
        /// Gets or sets an indication the current &lt;form&gt; element contains an antiforgery token. Do not use
        /// unless <see cref="CanRenderAtEndOfForm"/> is <c>true</c>.
        /// </summary>
        /// <value>
        /// <c>true</c> if the current &lt;form&gt; element contains an antiforgery token; <c>false</c> otherwise.
        /// </value>
        public bool HasAntiforgeryToken { get; set; }

        /// <summary>
        /// Gets an indication the <see cref="FormData"/> property bag has been used and likely contains entries.
        /// </summary>
        /// <value>
        /// <c>true</c> if the backing field for <see cref="FormData"/> is non-<c>null</c>; <c>false</c> otherwise.
        /// </value>
        public bool HasFormData => _formData != null;

        /// <summary>
        /// Gets an indication the <see cref="EndOfFormContent"/> collection has been used and likely contains entries.
        /// </summary>
        /// <value>
        /// <c>true</c> if the backing field for <see cref="EndOfFormContent"/> is non-<c>null</c>; <c>false</c>
        /// otherwise.
        /// </value>
        public bool HasEndOfFormContent => _endOfFormContent != null;

        /// <summary>
        /// Gets an <see cref="IHtmlContent"/> collection that should be rendered just prior to the next &lt;/form&gt;
        /// end tag. Do not use unless <see cref="CanRenderAtEndOfForm"/> is <c>true</c>.
        /// </summary>
        public IList<IHtmlContent> EndOfFormContent
        {
            get
            {
                if (_endOfFormContent == null)
                {
                    _endOfFormContent = new List<IHtmlContent>();
                }

                return _endOfFormContent;
            }
        }

        /// <summary>
        /// Gets or sets an indication whether extra content can be rendered at the end of the content of this
        /// &lt;form&gt; element. That is, <see cref="EndOfFormContent"/> will be rendered just prior to the
        /// &lt;/form&gt; end tag.
        /// </summary>
        /// <value>
        /// <c>true</c> if the framework will render <see cref="EndOfFormContent"/>; <c>false</c> otherwise. In
        /// particular, <c>true</c> if the current &lt;form&gt; is associated with a tag helper or will be generated by
        /// an HTML helper; <c>false</c> when using the default <see cref="FormContext"/> instance.
        /// </value>
        public bool CanRenderAtEndOfForm { get; set; }

        /// <summary>
        /// Gets a dictionary mapping full HTML field names to indications that the named field has been rendered in
        /// this &lt;form&gt;.
        /// </summary>
        private Dictionary<string, bool> RenderedFields
        {
            get
            {
                if (_renderedFields == null)
                {
                    _renderedFields = new Dictionary<string, bool>(StringComparer.Ordinal);
                }

                return _renderedFields;
            }
        }

        /// <summary>
        /// Returns an indication based on <see cref="RenderedFields"/> that the given <paramref name="fieldName"/> has
        /// been rendered in this &lt;form&gt;.
        /// </summary>
        /// <param name="fieldName">The full HTML name of a field that may have been rendered.</param>
        /// <returns>
        /// <c>true</c> if the given <paramref name="fieldName"/> has been rendered; <c>false</c> otherwise.
        /// </returns>
        public bool RenderedField(string fieldName)
        {
            if (fieldName == null)
            {
                throw new ArgumentNullException(nameof(fieldName));
            }

            bool result;
            RenderedFields.TryGetValue(fieldName, out result);

            return result;
        }

        /// <summary>
        /// Updates <see cref="RenderedFields"/> to indicate <paramref name="fieldName"/> has been rendered in this
        /// &lt;form&gt;.
        /// </summary>
        /// <param name="fieldName">The full HTML name of a field that may have been rendered.</param>
        /// <param name="value">If <c>true</c>, the given <paramref name="fieldName"/> has been rendered.</param>
        public void RenderedField(string fieldName, bool value)
        {
            if (fieldName == null)
            {
                throw new ArgumentNullException(nameof(fieldName));
            }

            RenderedFields[fieldName] = value;
        }
    }
}