May 13 2009

ASP.NET MVC HtmlHelper for Uploadify, Take One

Category: ASP.NET | MVC | JavaScriptMatt @ 06:56

As I’ve mentioned before, I really, really hate the way most people seem to be creating reusable UI “controls” with ASP.NET MVC.  I do not like emitting JavaScript, HTML, etc. from within C# code.  It’s cumbersome to create, difficult to really test, and just a real PITA in general.

Based on feedback I received from Rob after my attempts at creating a helper for jqGrid, I decided to take a completely different approach when it was time to wrap another jQuery plug-in: Uploadify.  My goal was to minimize the amount of tag-soup embedded in my C# code while still maintaining the ease-of-use of the jqGrid helper, which required only a single HtmlHelper call to go from nothing to full grid.

Well, one painful afternoon later, I think I’ve arrived at something that makes some sense.  First, I couldn’t completely eliminate the tag soup, but I did minimize it (I think) while still keeping the thing extremely simple to use and (hopefully) maintain.  Let’s start with how you would use it:

<asp:Content ContentPlaceHolderID="HeadContent" runat="server">
    <%=Html.Uploadify("fileInput", 
        new UploadifyOptions
           {
               UploadUrl = Html.BuildUrlFromExpression<SandboxController>(c => c.HandleUpload(null)),
            FileExtensions = "*.xls;*.xlsx",
            FileDescription = "Excel Files",
            AuthenticationToken = Request.Cookies[FormsAuthentication.FormsCookieName] == null ?
                string.Empty :
                Request.Cookies[FormsAuthentication.FormsCookieName].Value,
            ErrorFunction = "onError",
            CompleteFunction = "onComplete"
           }) %>
           
    <script type="text/javascript">
        function onError() {
            alert('Something went wrong.');
        }
        function onComplete() {
            alert('File saved!');
        }
    </script>                                                   
</asp:Content>

The first parameter is the name of the input control to convert to an uploadify control, the second contains all the optional settings you can customize.  I prefer to use an options class like this rather than provide 50,000 overloads.  By using a dedicated options class, I can add new settings without breaking existing code or having to create new overloads.  The options should be fairly self explanatory, but here they are:

/// <summary>
/// Defines all options for <see cref="HtmlHelperExtensions.Uploadify"/>.
/// </summary>
public class UploadifyOptions
{
    #region Public Properties

    /// <summary>
    /// The URL to the action that will process uploaded files.
    /// </summary>
    public string UploadUrl { get; set; }

    /// <summary>
    /// The file extensions to accept.
    /// </summary>
    public string FileExtensions { get; set; }

    /// <summary>
    /// Description corresponding to <see cref="FileExtensions"/>.
    /// </summary>
    public string FileDescription { get; set; }

    /// <summary>
    /// The ASP.NET forms authentication token.
    /// </summary>
    /// <example>
    /// You can get this in a view using:
    /// <code>
    /// Request.Cookies[FormsAuthentication.FormsCookieName].Value
    /// </code>
    /// You should check for the existence of the cookie before accessing
    /// its value.
    /// </example>
    public string AuthenticationToken { get; set; }

    /// <summary>
    /// The name of a JavaScript function to call if an error occurs
    /// during the upload.
    /// </summary>
    public string ErrorFunction { get; set; }

    /// <summary>
    /// The name of a JavaScript function to call when an upload
    /// completes successfully. 
    /// </summary>
    public string CompleteFunction { get; set; }

    #endregion
}

Next, we have the actual HtmlHelper extension method:

/// <summary>
/// Renders JavaScript to turn the specified file input control into an 
/// Uploadify upload control.
/// </summary>
/// <param name="helper"></param>
/// <param name="name"></param>
/// <param name="options"></param>
/// <returns></returns>
public static string Uploadify(this HtmlHelper helper, string name, UploadifyOptions options)
{
    string scriptPath = helper.ResolveUrl("~/Content/jqueryPlugins/uploadify/");

    StringBuilder sb = new StringBuilder();
    //Include the JS file.
    sb.Append(helper.ScriptInclude("~/Content/jqueryPlugins/uploadify/jquery.uploadify.js"));
    sb.Append(helper.ScriptInclude("~/Content/jqueryPlugins/uploadify/jquery.uploadify.init.js"));

    //Dump the script to initialze Uploadify
    sb.AppendLine("<script type=\"text/javascript\">");
    sb.AppendLine("$(document).ready(function() {");
    sb.AppendFormat("initUploadify($('#{0}'),'{1}','{2}','{3}','{4}','{5}',{6},{7});", name, options.UploadUrl,
                    scriptPath, options.FileExtensions, options.FileDescription, options.AuthenticationToken,
                    options.ErrorFunction ?? "null", options.CompleteFunction ?? "null");
    sb.AppendLine();
    sb.AppendLine("});");
    sb.AppendLine("</script");

    return sb.ToString();
}

The helper uses a StringBuilder (yeah, I hate them, and I’m open to suggestions) to include two JavaScript files.  The first is the standard uploadify script, but the second is something custom, which I’ll get to in just a second.    Finally, the helper outputs a call to initUploadify inside of the page load event, passing in all the options that were specified.

And that brings us to that second JavaScript include:

//This is used in conjunction with the HtmlHelper.Uploadify extension method.
function initUploadify(control, uploadUrl, baseUrl, fileExtensions, fileDescription, authenticationToken, errorFunction, completeFunction) {
    var options = {};

    options.script = uploadUrl;
    options.uploader = baseUrl + 'uploader.swf';
    options.cancelImg = baseUrl + 'cancel.png';
    //TODO: Make this an option?
    options.auto = true;
    options.scriptData = { AuthenticationToken: authenticationToken };
    options.fileExt = fileExtensions;
    options.fileDesc = fileDescription;

    if (errorFunction != null) {
        options.onError = errorFunction;
    }

    if (completeFunction != null) {
        options.onComplete = completeFunction;
    }

    control.fileUpload(options);
}

In here, I’ve created a simple JavaScript function that actually calls the uploadify JavaScript plug-in.  By using this method instead of using C# to emit the configuration code directly, I’m cutting out a fair amount of tag soup, and I’m wrapping things up in a way that will be easier to change in the future.  Hopefully.  The down side to this approach is that you have to create a new JavaScript method and include for every plug-in you want to use, but combining the scripts and correctly setting cache headers should reduce the request overhead.

I’m not claiming that this is the best way to do this.  In fact, I really hope it isn’t, because I still don’t like it.  But I think that I like it better than the approach I took for jqGrid.  If you have any suggestions or feedback, please share.  Feel free to tell me that I’m doing things completely wrong.

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