How to pass model plus additional parameter from view to controller - asp.net

Question

Using ASP.NET MVC, in my view, I list some files and show them as a button. By clicking each button the corresponding file should be downloaded.
To show the list of files, I pass a model to view and when a user clicks on each of those buttons, I have to send the filename plus the original model back to the controller.
I found answers for a similar question but in my case, I don't have only one button. I have one button for each filename that I render on view.
This is the code for my view:
#using (Html.BeginForm("DownloadFile", "SharedFolder", FormMethod.Post))
{
<div class="col-sm-6">
<div class="panel panel-info">
<div class="panel-heading">Files</div>
<div class="panel-body" style="max-height:300px; height:300px; overflow-y:scroll">
#foreach (var file in Model.Files)
{
<button type="button" class="btn btn-link btn-sm" onclick="location.href='#Url.Action("DownloadFile", "SharedFolder", new { fileToDownload = file, data = Model })'">
<div class="glyphicon glyphicon-file" style="color:dodgerblue">
<span style="color:black;">#file</span>
</div>
</button>
<br />
}
</div>
</div>
</div>
}
And my controller action:
[HttpPost]
public ActionResult DownloadFile(string fileToDownload, FolderExplorerViewModel data)
{
// download the file and return Index view
return RedirectToAction("Index");
}
When I click on a file to download it, I get below error:
The resource cannot be found.
Requested URL: /SharedFolder/DownloadFile
Update:
This is my ViewModel
public class FolderExplorerViewModel
{
public int ID { get; set; }
public List<Folder> Folders { get; set; }
public List<string> Files { get; set; }
public string SelectedPath { get; set; }
}

Answer 1

You shouldn't store data = Model like this causes the performance and security problem.
You just store one fileToDownload value from View. After that, in Controller, You should get file by fileToDownload param.
[HttpPost]
public ActionResult DownloadFile(string fileToDownload)
{
// download the file by `fileToDownload` param here
return RedirectToAction("Index");
}

Answer 2

The reason why you are getting that error is because, its trying to do form post and there are no form html elements representing fileToDownload and data.
Actually, instead of using form POST you can use anchor tags invoking controller GET action (since its just download, no need to use POST here). As #Phong mentioned, using fileToDownload you probably can retrieve other information which is needed for redirection to Index.
#foreach (var file in Model.Files)
{
#file
}
and then your controller action will be:
public ActionResult DownloadFile(string fileToDownload)
{
// do the stuff
// download would return FileResult on success, not sure what you meant by RedirectToAction("Index")
// download the file and return Index view
return RedirectToAction("Index");
}
If you still wanted to send Model, then you can do that via javascript button click event with ajax.