CODEWITHSUNDEEP
c#asp.netrazorasp.net-coreasp.net-core-mvc
Travis Boatman
Travis Boatman

Reputation: 2282

How can I hold a collection of strings to post back?

From my controller I send a ViewModel with a collection of strings to be used in a <select> tag like so...

Controller:

        var model = new InviteViewModel
        {
            SelectItems = new SelectViewModel
            {
                Companies = _companyRepository.GetCompanyNames()
            }
        };

Razor View:

<select class="form-control company_select" asp-for="Company" asp-items="@(new SelectList(Model.SelectItems.Companies))"></select>

This works perfectly and will display all the items in the drop down box. However when I go to submit the form the Companies object will be null and when the View is sent back I get a null reference exception. Normally I would create a hidden <input> tag to hold the value, but how can I do this with a collection?

Upvotes: 1

Views: 71

Answers (1)

Travis J
Travis J

Reputation: 82267

There are so many ways to do this.

It seems like you may have a fundamental misunderstanding of the disconnect between Razor and html. Razor executes server side, and its result is simply a string that gets written to the response stream. Once written, razor's scope is gone and cannot hold data.

One option would be to store the collection in the application cache or session cache with a guid as the dictionary key, and then use a hidden input for the cache key. When the view is being recreated you would then have access to the server and could gather the collection.

This makes the assumption that the collection hasn't changed during the time the view was active, which given some user habits could have been a long time. There should also be some sort of metrics used when caching to invalidate old data, if this is the route you take.

Another option is to simply regenerate the collection from wherever (database?) it came from.

Lastly, you mention that the view is being returned with the empty collection, are you returning a view from a post method? That is bad practice. Look up the "post-redirect-get pattern" for why and how to avoid it.

Upvotes: 1

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