ViewDataDictionary does not get activated via Activate attribute in TagHelpers

[ajaybhargavb]

In this scenario, the ViewDataDictionary is not getting activated.

public class DummyTagHelper : TagHelper
{
    public string Expression { get; set; }

    [Activate]
    public ViewDataDictionary ViewDataDictionary { get; set; }

    public override void Process(TagHelperContext context, TagHelperOutput output)
    {
        if (!string.IsNullOrEmpty(Expression))
        {
            output.Content = (string)ViewDataDictionary.Eval(Expression);
        }
    }
}

[dougbu]

Currently DefaultTagHelperActivator injects ViewContext and anything available in DI. Since ViewContext contains a reference to the ViewDataDictionary and an isolated (per-helper) ViewDataDictionary isn't very useful, what exactly is missing?

Note users can give themselves a ViewData property using

[Activate]
public ViewContext ViewContext { get; set; }

private ViewDataDictionary ViewData
{
  get
  {
    return ViewContext?.ViewData;
  }
}

[pranavkm]

It ends up being inconsistent with activation in Razor pages and View components.
Acitvating a ViewDataDictionary works in both these scenarios versus for tag helpers it produces an exception stating the service could not be located. We should attempt to have the services we activate be consistent.

[dougbu]

RazorPageActivator won't activate a ViewContext property (handles only ViewDataDictionary properties and services from DI). And DefaultControllerActivator handles a few additional properties hanging off the main ActionContext it activates -- HttpContext, HttpRequest, and HttpResponse. So what is the consistency goal?

Further support for activating ViewDataDictionary properties is a bit problematic because such properties set up easy inconsistencies e.g. between RazorPage.ViewData and RazorPage.ViewContext.ViewData. Since the ViewContext.ViewData property is settable, would be more consistent for ViewDataDictionary properties in RazorPage, ITagHelper, or ViewComponent to read / write through to ViewContext.

[pranavkm]

RazorPageActivator won't activate a ViewContext property (handles only ViewDataDictionary properties and services from DI). And DefaultControllerActivator handles a few additional properties hanging off the main ActionContext it activates -- HttpContext, HttpRequest, and HttpResponse. So what is the consistency goal?

Shouldn't we address the lot in that case?

[ajaybhargavb]

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