Develop Reference

ASP.Net Core view as popupbox

I am currently working on a form. In the form, if there is not an item needed you can click the add button and it takes you to a new form where you can add the item. Instead of my view going to another page, I want it to pop up above the form so that the user can just quickly add the item and not have to travel pages.
Here is a snipit from my Create.cshtml
<div class="form-group">
<label asp-for="INT_CertificationsID" class="col-md-2 control-label"></label>
<div class="col-md-3">
<select asp-for="INT_CertificationsID" class ="form-control" asp-items="ViewBag.INT_CertificationsID"></select>
</div>
<a class="btn btn-default" asp-area="" asp-controller="INT_Certifications" asp-action="Create">Add Certification</></a>
</div>
When the add certification attribute is clicked I would like a box to pop up to the Create.cshtml for the certification. So that they may quickly add it to the list and continue to fill out the form.
I have looked up several examples to do this but most of them are either too old, too long, or don't work in .netcore due to nuget package errors with JqueryUI.

You need to make a controller method that returns the page you want in the popup as a PartialView.
I think you mean modal and not "popup"... you need to use a modal mechanism to create a modal window and get (or post) your partial via AJAX and use the result to display in the modal window.
I like bootbox which is a wrapper for bootstraps modal functionality.

I would load partial view in a hidden div together with the pages that needs them and dynamically display them with JavaScript when needed. Don't use forms to send http request, instead use AJAX.
Using pop-ups can work against you because browsers comes by default with pop-up blockers. Might work on your devbox but it could have a completely different behaviour somewhere else.
Using forms to send request requires the page to be reloaded which does not provide a good user experience.
Fix your solution, don't use nugget for client side script. Use bower instead. Here's a link https://learn.microsoft.com/en-us/aspnet/core/client-side/

Send Ajax Requests vs Sending Entire Form By Id

The client should be able to send everything with a button, so I can do the following:
Send everything as form fields named like invoiceId_detail_text where invoiceId would be the id of the invoice, detail the part, and text the kind of field.
Example:
<form id="invoices" name="invoice">
#foreach(var Invoce in Model.Invoices) {
<div>
<input type="number" id="#String.Format("{0}_amount", Invoice.InvoiceId)"/>
</div>
/*More Input Fields for the Invoice*/
<div>
<button type="submit"></button>
</div>
}
</form>
Or I can put every invoice separated in its own form, and send them by ajax, every form success I send the next one and so on.
Example:
#foreach(var Invoice in Model.Invoices) {
string formName = String.Format("{0}_form", Invoce.InvoceId);
<form id="#formName" class="invoiceForm" id="#formName" action="#Url.Action("EditIndividualInvoice","InvoicingEdit")">
<input type="hidden" name="InvoiceId" value="#Invoice.InvoiceId"/>
<div>
<input type="number"/>
</div>
/*More Input Fields for the Invoice*/
</form>
}
<button type="button" onclick="SendAllForms();">Send</button>
I did some research between some of my co-workers and many of them told me to just go with a post with all the invoices at the same time and then access every field by item id because I don't have knowledge of how many invoices are going to be sent, but i can get all of them by class on JQuery so it shouldn't be a problem.
I also read this article from a UX point of view and it keeps me thinking about it.
By doing it with AJAX the cliend could be able to see a loading bar and it would be great, but if he closes the page the request would be incomplete and it could be complicated.
Which option could be better and why and what are the security implications of using one over another?

I think the solution depends principally of the behavior that you wish.
By doing it with AJAX the cliend could be able to see a loading bar and it would be great, but if he closes the page the request would be incomplete and it could be complicated.
In the 2 solutions, if the user closes the page after clicking the button, this will not cancel the save. Once the request sent, it cannot be cancelled. So you shouldn't have "security" problems whatever the choosen solution.
The only thing you need to be careful, is to disable all AJAX buttons during an AJAX request, to avoid the user sending several request in the same time (that can provoke saving inconsistency data).
The classic solution is generally most simple to implement.
The AJAX solution can be most complicated to implement (more code), but provides a friendliest behavior.

ASP.Net Postback Broke After Changing Form Attribute

I have an ASP.Net form which looks like the following when rendered (many lines of markup removed for brevity):
<form onsubmit="document.body.style.cursor='wait';showLoader();" action="mypage.aspx">
<!-- form elements and controls -->
<input type="submit" />
</form>
In mypage.aspx.cs's Page_Load I am doing:
if(Page.IsPostBack)
{
Foo();
} else {
Bar();
}
Quux();
Without modifying the HTML page using the Chrome Dev Tools, if I submit the form it executes Bar(). But If I removed or replaced the onsubmit attribute in the form with my own, ASP.Net thinks that the page is doing a post back and executes Foo().
I find this behavior weird because the inline JS code in onsubmit does not change anything related to the form submission. Its function is only to add a loading GIF while the form is reloading. Could there be something I am missing here?

Instead of adding a submit button, try adding a regular button, and call your gif functionality from it:
<input type="button" onclick="document.body.style.cursor='wait';showLoader();" value="Click Me" />
This will not post anything, which is what you want. <input type='submit'> will always cause a postback, unless you cancel it with JavaScript.
JSFiddle: http://jsfiddle.net/0gd8t7ew/

Open a new window with Same session using jquery/C# Razor

I am trying to open a new window with same session as the current one. I wrote some code below but its no luck yet.
For example lets say i have a form with a label (Name), textbox (where the text goes in)
and a button when pressed takes me to a new window.
If i press the button it should open a new window with the same form elements and text in the textbox if it was put in before.
Also please note the new window must be opened as a new tab in the browser with the same state and same elements as in the previous browsers.
Anyone got an idea on this (using razor view engine or jquery/javascript) ? Thanks in advance.
<label for="Name">Name</label>
<input type="textbox" value="nothing" id="text" />
<input type="button" value="press me" id="submitButton" />
$(document).ready(function()
{
$('#submitButton').click(function()
{
var currentUrl=document.URL;
window.open(currentUrl,"newWindow",300);
event.preventDefault();
});
});

You may be able to accomplish this by using modals instead of popup windows. Jquery UI has built in modal support: http://jqueryui.com/dialog/
The advantage to this approach is that no data needs to be passed into a separate page. Your modal code would look something like this, with jQuery Dialog. This would go on the same page as your initial inputs:
<div id="dialog" title="Basic dialog">
<input type="text" id="popupText" name="popupText" />
</div>
and your click event would modified update the modal input and show the modal:
$(document).ready(function(event)
{
$('#submitButton').click(function()
{
$("#popupText").val($("#text").val());
$("#dialog").dialog();
event.preventDefault();
});
});
This could definitely be cleaned up but I believe it'll do what you need pretty simply. The dialog can contain any html elements, so you can add a separate form if necessary.

Handing forms in ViewUserControls

I am rendering out a ViewUserControl (.ascx file) in a view:
<% Html.RenderPartial("Comments", Model.Comments); %>
This ViewUserControl shows associated comments on an entry. I would like this control to render out a form as well, so users of my application can contribute.
How would you add a form to a ViewUserControl and handle it's postback?

Just add the form in there the same as you would on any page. In MVC, the form does not postback as such - it simply submits itself and its content (input controls) via HTTP Post to a URL.
Simply create an action in your controller (and hence a URL) which the form will post and do whatever activity is required there...

There is no postaback, like in standard asp.net, there can be only form tag that posts data to some url (controller/action).
Inside your partial user control, write:
<form action="controller/actionname" method="post">
<input type="text" name="inputText" />
<input type="submit" value="Post data to server" />
</form>
In MVC, only input type="submit" triggers form submit. In standard ASP.NET webforms, you can have many Linkbuttons, Buttons, ... but under cover, they all triggers this simple click on input type="submit" through javascript event. One form can post data to only one URL (controller/action), but that can be changed with javascript (as we can see in html source of 'old' asp.net webforms).
then, in controller you can handle post data:
[AcceptVerb(HttpVerb.Post)] // optionally
public ActionResult ActionName(string inputText) ...

Like others have answered already, you simply render a form and handle it's submit with an ActionResult.
For example, if your form (which could be rendered anywhere in your site) was submitting to http://www.yoururl.com/home/save, you would create an ActionResult method named save on the home controller to handle the submit (likely post/get method).