MVC3 Conditionally disable Html.TextBoxFor()

问题:

I have a C# .Net web app. In that app I need to conditionally disable Html.TextBoxFor controls (also Html.DropDownListFor controls) based on who is logged into the system. I tried using

 @Html.TextBoxFor(model => model.ProposalName, new { @ViewBag.IsDisabled })

Where @ViewBag.IsDisabled is set to either String.Empty or "disabled" in the Controller. However, this renders as IsDisabled='disabled' or IsDisabled="" so the control is not disabled. When I tried

@Html.TextBoxFor(model => model.ProposalName, new { @ViewBag.Disabled })

The control was always disabled even if ViewBag.Disabled contained no text. How can I conditionally disable the Html.TextBoxFor() controls?

回答1:

Try

@Html.TextBoxFor(model => model.ProposalName, ViewBag.Disabled ? (object)new { disabled="disabled" } : new {})

回答2:

The solution posted by @epignosisx works, but it may be a problem if you want to add some other attribute because you will have to add it it both objects (the one with disabled and the one now its empty).

Even worse if you have some other bool property because you will have four different objects, each one for each combination.

The best solution here (with a little more code) is to build an extension method for HtmlHelper to receive your boolean property as a parameter.

public static MvcHtmlString TextBoxDisabledFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression, bool disabled, object htmlAttributes = null)
{
    return TextBoxDisabledFor(htmlHelper, expression, disabled, HtmlHelper.AnonymousObjectToHtmlAttributes(htmlAttributes));
}

public static MvcHtmlString TextBoxDisabledFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression, bool disabled, IDictionary<string, object> htmlAttributes)
{
    if (htmlAttributes == null)
        htmlAttributes = new Dictionary<string, object>();
    if (disabled)
        htmlAttributes["disabled"] = "disabled";
    return htmlHelper.TextBoxFor(expression, htmlAttributes);
}

Here there is another example

回答3:

I had this same problem and decided to write my own HtmlHelper extension method.

public static MvcHtmlString Disable(this MvcHtmlString helper, bool disabled)
    {
        if (helper == null)
            throw new ArgumentNullException();

        if (disabled)
        {
            string html = helper.ToString();
            int startIndex = html.IndexOf('>');

            html = html.Insert(startIndex, " disabled=\"disabled\"");
            return MvcHtmlString.Create(html);
        }

        return helper;
    }

This will accept a boolean to indicate if the control should be disabled or not. It just appends disabled="disabled" just inside the first > it comes across in a string.

You can use it like below.

@Html.TextBoxFor(model => model.ProposalName).Disable(true)

回答4:

Here is the method I use, which doesn't require extensions, and doesn't limit you to only one HTML attribute. It assumes there is a boolean property named "Disabled" in your model, but you could put whatever you wanted in there, as long as it evaluates to boolean for the ternary operator:

@Html.TextBoxFor(model => model.Whatever,
  new Dictionary<string, object>() {
    { "size", "5" },
    { "class", "someclasshere" },
    { model.Disabled ? "disabled" : "data-notdisabled", "disabled" }
  })

The limitation with the standard shortcut notation is that the name of the attribute cannot be dynamic. By creating a dictionary of the correct type, you can then make the attribute name dynamic, and you then pass that dictionary to the textbox as the dictionary of attributes. When the field is not to be disabled, it passes an attribute named "data-notdisabled" instead of one named "disabled", which the browser will then ignore.

回答5:

Extending @James's answer, I wrote this HtmlHelper extension that updates/removes the disabled attribute if it's already present, or adds it if not:

public static MvcHtmlString Disable(this MvcHtmlString helper, bool disabled) {
    string html = helper.ToString();
    var regex = new Regex("(disabled(?:=\".*\")?)");
    if (regex.IsMatch(html)) {
        html = regex.Replace(html, disabled ? "disabled=\"disabled\"" : "", 1);
    } else {
        regex = new Regex(@"(\/?>)");
        html = regex.Replace(html, disabled ? "disabled=\"disabled\"$1" : "$1", 1);
    }
    return MvcHtmlString.Create(html);
}

It also plays nicely with self-closing tags (like <input />).

Usage is the same:

@Html.TextBoxFor(model => model.PropertyName).Disable(true)

Tested on both @Html.DropDownListFor() and @Html.TextBoxFor().