How to pass model list to controller [duplicate] - asp.net

Question

This question already has answers here:
What is a NullReferenceException, and how do I fix it?
(27 answers)
Closed 4 years ago.
I am trying to post a list of objects from View to controller.
Below is my code:
View :
#using Models
#model IList<Add>
#{
ViewData["Title"] = "AddNewFields";
}
<form asp-controller="Trans" asp-action="InsertFields" method="post" class="form-horizontal card-body" role="form">
<td><input type="text" class="form-control" value="Field Size" asp-for="#Model[i].TypeFlag"/></td>
<td><input type="text" class="form-control" value="Field Value" asp-for="#Model[i].FieldValue"/></td>
<td><input type="text" class="form-control" value="Field Format" asp-for="#Model[i].FieldFormat"/></td>
</form>
I will be adding mo these text fields again on button click.
Model:
public class Add
{
public string TypeFlag { get; set; }
public string FieldValue { get; set; }
public string FieldFormat { get; set; }
}
Controller:
public string InsertFields(IList<Add> fields)
{
//some logic
}
When I run the application, I am getting the below error:
NullReferenceException: Object reference not set to an instance of an object.
AspNetCore.Views_Trans_Add.<ExecuteAsync>b__27_0() in AddNewFields.cshtml
#for (int i = 0; i < Model.Count; i++)
Microsoft.AspNetCore.Razor.Runtime.TagHelpers.TagHelperExecutionContext.GetChildContentAsync(bool useCachedResult, HtmlEncoder encoder)
Microsoft.AspNetCore.Mvc.TagHelpers.RenderAtEndOfFormTagHelper.ProcessAsync(TagHelperContext context, TagHelperOutput output)
Microsoft.AspNetCore.Razor.Runtime.TagHelpers.TagHelperRunner.RunAsync(TagHelperExecutionContext executionContext)
Please help me...I am stuck here from 2 days..

Answer 1

2 issues:
Model is null
Action will not get values.
solution:
Your HTML should be this style
#{
var fields = (Model ?? Enumerable.Empty<Add>()).ToList(); //this variable must be same with the parameter in action.
}
<form asp-action="Test" method="post">
<table class="table">
<tbody>
<tr>
<td>
<div class="form-group">
<input type="submit" value="Submit" />
</div>
</td>
</tr>
#for (var i = 0; i < fields.Count; i++) //you must use for, not foreach
{
<tr>
<td>
<div class="form-group">
<input type="hidden" asp-for="#fields[i].Id" />
<input asp-for="#fields[i].Name" class="form-control" />
</div>
</td>
</tr>
}
</tbody>
</table>
</form>
your controller should be this:
[HttpPost]
public async Task<IActionResult> Test(IEnumerable<Add> fields)
//be aware: the parameter name "fields" must be same with your html
//the type should be "IEnumerable<Add>", more compatible with different versions of MVC
{
.....your logic
return Json(new { ... });
}
the generated html is this style:
<tr>
<td>
<div class="form-group">
<input type="hidden" id="fields_0__Id" name="fields[0].Id" value="14">
<input class="form-control" type="text" id="fields_0__Name" name="fields[0].Name" value="xxxxx">
</div>
</td>
</tr>
<tr>
<td>
<div class="form-group">
<input type="hidden" id="fields_1__Id" name="fields[1].Id" value="1">
<input class="form-control" type="text" id="fields_1__Name" name="fields[1].Name" value="xxxx">
</div>
</td>
</tr>
you will see the reason: the parameter fields is just a field of html form, they must match each other.