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ASP.NET Core Tag Helper Arrays

I have an ASP.NET Core 2.0 web application that generates a multi-select list box using bootstrap-multiselect (basically a prettied up list box control)
The code generated is shown:
<select class="multiselect-ui form-control" id="Issues" multiple="multiple" name="Issues">
<option selected="selected" value="1">Dilapidated Structures</option>
<option selected="selected" value="3">Junk on Premises</option>
<option selected="selected" value="4">Junk Vehicles</option>
<option selected="selected" value="5">Minor Maintenance</option>
<option selected="selected" value="6">Miscellaneous</option>
<option selected="selected" value="7">Overgrowth</option>
<option selected="selected" value="8">Right of Way</option>
<option selected="selected" value="9">Sidewalks</option>
<option selected="selected" value="10">Trash</option>
<option selected="selected" value="2">Weeds/High Grass</option>
</select>
When this is submitted in a form, I see the Issues being added to the URL like so:
/Cases?Issues=1&Issues=3&Issues=4&Issues=5 ...
This is great and I am able to retrieve the values in my controller using a List<string> object. My question is, how would I add a hyperlink to the page that uses the values already sent via GET? Basically I would like to use Tag Helpers, but there is no way to add an array of values that I've found. There are dictionary key/pairs, but of course you are not able to add multiple values with the same key. I would like to be able to reference a List<string> in the tag helper itself (the following does not work, but should give an idea of what I'm after if I am sending the List<string> back using ViewBag):
<a asp-route-Issues=#ViewBag.IssuesList>Next</a>

I found out through this link that this feature isn't implemented. I used #Url.Action to build my link as shown (where ViewBag.IssuesList contains the List<string> -- I also left out some paramters for brevity:
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Get value of Select Dropdownlist from code behind

I have a DropdownList which I have created using the Select Box as you can see below, now I am not sure how to get the value from code behind Is there anything I can use such as findcontrol in order to get the value. FYI: I am doing this in MVC using the aspx view engine not razor
Dropdownlist code:
<Select id="subjects">
<option value="Maths">Maths</option>
<option value="English">English</option>
<option value="Science">Science</option>
<option value="History">History</option>
<option value="Geography">Geography</option>
</Select>

You should move data between View and Controller using Models. The model is sent to the view when the page is loaded, the model is post back again when you submit the form.

ASP MVC3 - Marking Option as Selected

I have a form that has 2 select boxes (Country and State) that have their available options contained in partial HTML files, due to their size.
In the event of a validation error, I want to mark the option the user originally selected as "selected".
Since the options are contained in a partial HTML file, I am not sure that this is even possible:
Any suggestions would be great. Thanks
// Inside the View
<select name="State" id="State">
#Html.Partial("States", Model);
</select>
#Html.ValidationMessageFor(model => model.State)
The partial simply contains the HTML:
<option value="AL">Alabama</option>
<option value="AK">Alaska</option>
<option value="AZ">Arizona</option>
<option value="AR">Arkansas</option>
<option value="AA">Armed Forces Americas</option>
<option value="AE">Armed Forces Europe, Middle East</option>
[...]

Instead of using strange Partial, why you just do not use helper DropDownList. You can find many examples, like this one http://peternewhook.com/2013/02/asp-net-mvc-selectlist-selectedvalue-dropdownlistfor/

Dropdown list options

I am using this code on my Master page and wants to display option name on the reffered page
<select name=menu onchange="location.href=(menu.options[menu.selectedIndex].value)">
<option value="http:google.com">Google</option>
<option value="http:myurl.com">URL</option>
</select>

You need to use this to refer to event source object instead of menu the name of html element. You also have wrong url form and need to change it from http:google.com to http://google.com
Live Demo
<select name=menu onchange="window.location.href=(this.options[this.selectedIndex].value)">
<option value="http://www.google.com">Google</option>
<option value="http://www.stackoverflow.com">stackoverflow</option>
</select>​

Using databinding to populate a HtmlSelect with optgroup elements in asp.net

I am using asp.net and have a HtmlSelect element on my page (with runat="server"). Normally I will just set the DataSource to some loaded data and DataBind. However in this case the data has one level of hierarchy and I want to represent this in the HTML with an optgroup. Google hasn't come up with any joy - is this even possible?

I've had a similar problem to solve and this is how I did it. Before I continue I did find all sorts of re-fracturing methods for lists, which probably do work. However, I did not think this the best route to go for my solution. Here's what I did:
I also needed to know which option a user selected in the drop down list but found that you can't build drop down list with option groups in ASP.net. So to do this I just built a simple <select> with <optgroup>'s and <option>'s in each group. Then I placed a <div> with a hidden textbox, which had the runat="server" set. I set the "onchange" event, on the select, to change the text value of the hidden textbox to whatever the value the option was, which was selected by the user, using javascript. Then, when the post back occurs, the code behind had access to the value the user selected, via the hidden textbox's runat="server". Problem solved! The code looks something like this:
Code in the HTML (aspx):
<div id="selectDiv">
<select id="selectItems" onchange="document.getElementById('hiddenselectDiv').getElementsByTagName('input')[0].value = this.options[this.selectedIndex].value;">
<optgroup label="Johannesburg">
<option value="Wilropark">Wilropark</option>
<option value="Bryanpark">Bryanpark</option>
<option value="Hurlingham">Hurlingham</option>
<option value="Midrand ">Midrand </option>
<option value="Glenvista">Glenvista</option>
<option value="Sunninghill">Sunninghill</option>
<option value="Edenvale ">Edenvale </option>
<option value="Parkhurst">Parkhurst</option>
</optgroup>
<optgroup label="Cape Town">
<option value="Tokai">Tokai</option>
<option value="Durbanville">Durbanville</option>
</optgroup>
<optgroup label="Durban">
<option value="Musgrave">Musgrave</option>
</optgroup>
<optgroup label="Pretoria">
<option value="Hatfield">Hatfield</option>
</optgroup>
</select>
</div>
<div id="hiddenSelectDiv">
<!--
Note: You probably want to set the hidden value to the first item you have seleced when you build the <select> object.
-->
<input type="hidden" id="selectedItem" value="Wilropark">
</div>
In the Code behind (C#):
if (!string.IsNullOrEmpty(selectedItem.Value))
{
//validation or whatever you want....
}

I've been looking around for the same thing, and it doesn't look like ASP supports this natively. One Google search found someone recommending a library at http://www.codeplex.com/SharpPieces, but I've never used it and I don't know how good it is. Other people talk about writing your own renderer for optgroup support.