Modify the HTML Helpers in ASP.NET MVC 2

Question

I want to modify helpers such as this one:

<%= Html.CheckBoxFor(m => m.Current, new { @class = "economicTextBox", propertyName = "Current", onchange = "UseCurrent();UpdateField(this);" })%>

to also take as a parameter another string that signifies a permission in the app, and then INSIDE the method I would determine whether or not to return the actual HTML or nothing, depending on their permission.

How would I do this?

UPDATE 2: Checkbox not rendering as readonly

When I debug and check the value of htmlHelper.CheckBoxFor(expression, mergedHtmlAttributes)._value, I get this

<input checked="checked" class="economicTextBox" id="Current" name="Current" onchange="UseCurrent();UpdateField(this);" propertyName="Current" readonly="true" type="checkbox" value="true" /><input name="Current" type="hidden" value="false" />

but the checkbox is still rendering allowing me to change it and achieve full functionality. Why?

Darin Dimitrov Darin Dimitrov · Accepted Answer · 2011-01-13T15:21:43

You could write a custom helper:

public static MvcHtmlString MyCheckBoxFor<TModel>(
    this HtmlHelper<TModel> htmlHelper,
    Expression<Func<TModel, bool>> expression, 
    string permission, 
    object htmlAttributes
)
{
    if (permission == "foo bar")
    {
        // the user has the foo bar permission => render the checkbox
        return htmlHelper.CheckBoxFor(expression, htmlAttributes);
    }
    // the user has no permission => render empty string
    return MvcHtmlString.Empty;
}

and then:

<%= Html.CheckBoxFor(
    m => m.Current, 
    "some permission string",
    new {  
        @class = "economicTextBox", 
        propertyName = "Current", 
        onchange = "UseCurrent();UpdateField(this);" 
    }) 
%>

UPDATE:

Here's how you could modify the HTML helper so that it renders a readonly checkbox instead of an empty string if the user has no permissions:

public static MvcHtmlString MyCheckBoxFor<TModel>(
    this HtmlHelper<TModel> htmlHelper,
    Expression<Func<TModel, bool>> expression,
    string permission,
    object htmlAttributes
)
{
    if (permission == "foo bar")
    {
        // the user has the foo bar permission => render the checkbox
        return htmlHelper.CheckBoxFor(expression, htmlAttributes);
    }
    // the user has no permission => render a readonly checkbox
    var mergedHtmlAttributes = new RouteValueDictionary(htmlAttributes);
    mergedHtmlAttributes["readonly"] = "readonly";
    return htmlHelper.CheckBoxFor(expression, mergedHtmlAttributes);
}

Modify the HTML Helpers in ASP.NET MVC 2

2 Answers