Action Arguments in ASP.NET Core

Action Arguments in ASP.NET Core: What's Best?

When handling form posts in ASP.NET Core, developers often ask:

Should I use IFormCollection, individual parameters, or a ViewModel?

The answer depends on the form size, your need for validation, and how much control you want over the incoming data. Here’s how I approach it after decades of building robust web apps and platforms.

✅ Option 1: `IFormCollection`

Use this when you want full access to the raw form data, especially for dynamic or variable-length forms.

[HttpPost]
public async Task<IActionResult> Contact(IFormCollection form)
{
    var email = form["Email"];
    var message = form["message"];
    var captcha = form["cfTurnstileResponse"];
}

🔹 Advantages:

You get all the keys and values, even if they don’t match any class or parameter.
Great for logging or analytics.
Perfect for optional fields or wizard-style forms.

❌ Downsides:

You’re on your own for validation.
Everything is a string — you’ll do more parsing and error checking.

✅ Option 2: Individual Parameters

For simple, predictable forms, direct parameters keep it clean:

[HttpPost]
public async Task<IActionResult> Contact(string email, string message, string cfTurnstileResponse)

🔹 Advantages:

Clean, readable method signatures.
Leverages automatic model binding.
Easy to validate with data annotations.

❌ Downsides:

Field names must match exactly — fragile if front-end changes.
Not scalable for big or dynamic forms.

✅ Option 3: ViewModel — The Sweet Spot

A ViewModel combines clarity, validation, and flexibility. It’s what I use in nearly every serious project.

public class ContactFormModel {
    public string Email { get; set; }
    public string Message { get; set; }
    public string CfTurnstileResponse { get; set; }
}

[HttpPost]
public async Task<IActionResult> Contact(ContactFormModel model)

🔹 Benefits:

Supports validation with [Required], [EmailAddress], etc.
Keeps controller logic tidy and testable.
Encourages separation of concerns.

If you're building on my DevStack platform, this pattern is already built-in with global model validation, anti-spam hooks, and localization.

💡 My Recommendation

Use Case	Best Practice
Simple known fields	Individual parameters or ViewModel
Many optional/dynamic fields	`IFormCollection`
Want validation + clarity	ViewModel

Why This Matters

Clean input handling is about more than preference — it affects security, maintainability, and speed of development.

If you’re working on forms now or migrating older code, I’ve already done this groundwork. My consulting services give you access to:

Battle-tested code patterns
40+ years of business experience
Clean architectural choices that scale

Need help implementing or modernizing your form handling? Let’s talk.

Also see: Pricing | My CV

Action Arguments in ASP.NET Core