Rendering a spark view to a string

I'm trying to render a partial view as a string so it can be returned as HTML to a jquery ajax call. After a lot of searching I found this code.

public string RenderAsString(string viewName, string modelName, object model)
{
    // Set up your spark engine goodness.
    var settings = new SparkSettings().SetPageBaseType(typeof(SparkView));
    var templates = new FileSystemViewFolder(Server.MapPath("~/Views"));
    var engine = new SparkViewEngine(settings) { ViewFolder = templates };


    // "Describe" the view (the template, it is a template after all), and its details.
    var descriptor = new SparkViewDescriptor().AddTemplate(@"Shared\" + viewName + ".spark");

    // Create a spark view engine instance
 开发者_JAVA技巧   var view = (SparkView)engine.CreateInstance(descriptor);

    // Add the model to the view data for the view to use.
    view.ViewData[modelName] = model;

    // Render the view to a text writer.
    var writer = new StringWriter(); view.RenderView(writer);

    // Convert to string
    return writer.ToString();
}

But when the following line executes:

var view = (SparkView)engine.CreateInstance(descriptor);

I get the following error:

Dynamic view compilation failed. An object reference is required for the non-static field, method, or property 'DomainModel.Entities.Region.Id.get.

This is my partial view:

<ViewData Model="Region" />

<div id="${ Region.Id }" class="active-translation-region-widget" >
    <label>${Region.RegionName}</label>
        ${ Html.CheckBox("Active") }
</div> 

It doesn't seem to recognise the model.

P.S. When I call the view from a parent view like so

<for each="var region in Model">
    <ActiveTranslationRegion Region="region" if="region.Active==true"></ActiveTranslationRegion>
</for>

It renders perfectly. What am I doing wrong?

---

Just from looking at it, I think the following line is the problem:

<ViewData Model="Region" />

Instead it should read:

<viewata model="Region" />

Note the lower case "model". This is because model is a special case since behind the scenes it performs a cast to a strongly typed viewmodel. The top one will define a variable called Model in the generated view class and assign the value Region to it. Using the lowercase option below will actually create a Model variable, but also cast it to strongly typed instance of Region that comes from the ViewData dictionary.

Note When using Model in the code though, like you did in the for each loop, it needs to be upper case which is correct in your case. Once again, this is the only special case because it's pulling a strongly typed model from the ViewData dictionary.

One other thing - <viewata model="Region" /> must be declared in the parent view, and it can only be defined once per page, so you cannot redefine it in a partial view. If it's a partial view, you should rather use it by passing in a part of the model like you have done in your second example above.

The reason for your exception above is because it's trying to get the Id property as a static item off the Region Type, rather than querying the Id property on your instance of Region as part of your viewmodel.

As a side note, the code to get where you want is a little mangled. You can find neater ways of doing what you want by checking out some of the Direct Usage Samples, but I understand this was probably just a spike to see it working... :)

Update in response to your follow up question/answer

I'm fairly sure that the problem is with passing the Region into the following call:

<ActiveTranslationRegion Region="region" if="region.Active==true">

... is again down to naming. Yes, you can only have one model per view as I said before, so what you need to do is remove the following from the top of your partial:

<viewdata model="Region" />

That's what's causing an issue. I would then rename the item going into your partial like so:

<ActiveTranslationRegion ActiveRegion="region" if="region.Active==true">

and then your partial would look like this:

<form action="/Translation/DeactivateRegion" class="ui-widget-content active-translation-region-widget">
    <input type="hidden" name="Id" value="${ActiveRegion.Id}" />        
    <label class="region-name">${ ActiveRegion.RegionName }</label>
    <input class="deactivate-region-button" type="image" src=${Url.Content("~/Content/Images/Deactivate.png")} alt="Deactivate" />
</form>

Note I'm using ActiveRegion because in the Spark parser, ActiveRegion gets declared as a variable and assigned the value of region in the current scope as you loop through the for loop. No need to stick religiously to the model - because you've gone and passed in a piece of the model now that you've declared as ActiveRegion. Oh, and you could stick with the name Region if you really want, I just changed it to make a point, and because you've got a Type called Region in your code and I'm not a big fan of the quirky issues using the same name for a variable as a type can bring about. Plus it makes it a little clearer.

The disadvantage of calling the Html.RenderPartial method is not immediately obvious. One thing you lose is the 3-pass rendering that Spark provides. If you use the tag syntax (which is preferable) you'll be able to stack partials within partials to multiple levels down passing variables that feed each partial what they need down the stack. It gets really powerful - start thinking data grid type structures where rows and cells are individual partials that are fed the variables they need from the model, all kept nice and clean in separate manageable view files. Don't stop there though, start thinking about targeting header and footer content base on variables or three column layouts that create a dashboard that renders all sorts on individually stacked partials many levels deep.

You lose all of that flexibility when you use the bog standard ASP.NET MVC Helper method Html.RenderPartial() - careful of doing that, there's more than likely a solution like the one above.

Let me know if that works...
All the best
Rob G

---

I refactored the code and views quite a bit. In the end all I'm really trying to acheive is have a parent view (not shown) iterate over an IEnumerable and for each iteration render a partial view (ActiveTranslationRegion) which renders some Html to represent a region model.

I also want to be a able to call an action method via an ajax call to render an indivual ActiveTranslationRegion partial view by passing it an individual region model. I've refactored the code accordingly.

Partial view (_ActiveTranslationRegion.spark)

<viewdata model="Region" />

<form action="/Translation/DeactivateRegion" class="ui-widget-content active-translation-region-widget">
    <input type="hidden" name="Id" value="${Model.Id}" />        
    <label class="region-name">${ Model.RegionName }</label>
    <input class="deactivate-region-button" type="image" src=${Url.Content("~/Content/Images/Deactivate.png")} alt="Deactivate" />
</form>

Notice by using I can refer to Model within the view as RobertTheGrey suggested (see above) .

I removed all the code to return the view as a string and simply created an action method method that returned a partialViewResult:

[UnitOfWork]
public PartialViewResult ActivateRegion(int id)
{
    var region = _repos.Get(id);
    if (region != null)
    {    
        region.Active = true;
        _repos.SaveOrUpdate(region);
    }

    return PartialView("_ActiveTranslationRegion", region);
}

One thing I had to do was amend my parent view to look like so:

<div id="inactive-translation-regions-panel">
    <h3 class="ui-widget-header">Inactive Regions</h3>
    <for each="var region in Model">
        <span if="region.Active==false">
                # Html.RenderPartial("_InActiveTranslationRegion", region);
        </span>
    </for>
</div>

Where previously I had the following:

<div id="inactive-translation-regions-panel">
   <for each="var region in Model">
          <ActiveTranslationRegion Region="region" if="region.Active==true"></ActiveTranslationRegion>
   </for>
</div>

Notice I have to call the Html.RenderPartial rather than use the element. If I try and use the element (which I would prefer to do) I get the following error:

Only one viewdata model can be declared. IEnumerable<Region> != Region

Is there a way round that problem?

Update:

I tried your recommendation but with no luck. To recap the problem, I want to use the partial in 2 different situations. In the first instance I have a parent view that uses a model of IEnumerable<Region>, the partial simply uses Region as its model. So in the parent I iterate over the IEnumerable and pass Region to the partial. In the second instance I want to call PartialView("_ActiveTranslationRegion", region) from an action method. If I remove the <viewdata model="Region" /> from the partial I get an error complaining about the model. The best way round the problem I have found is to add a binding to the bindings.xml file:

<element name="partial"># Html.RenderPartial("@name", @model);</element>

(Note: It seems very important to keep this entry in the bindings file all on te same line)

This way I can still call the partial from the action method as described above and pass it a Region as the model, but I can also replace my call to Html.RenderPartial in the parent view with a more 'html' like tag:

<partial name="_ActiveTranslationRegion" model="region" />

So my parent view now looks more like this:

<div id="inactive-translation-regions-panel">
    <h3 class="ui-widget-header">Inactive Regions</h3>
    <for each="var region in Model">
        <span if="region.Active==false">
               <partial name="_ActiveTranslationRegion" model="region" />
        </span>
    </for>
</div>

Of course under the hood its still making a call to

# Html.RenderPartial("_ActiveTranslationRegion", region);

But its the best solution we could come up with.

Regards, Simon