C# – Detect if action is a POST or GET method

asp.net-mvcc

In MVC 3, is it possible to determine if an action is a result of a POST or GET method? I know you can decorate the actions with [HttpPost] and [HttpGet] to fire a specific action if one of those happens. What I'd like to do is leave those attributes off and programmatically determine which one caused the action.

The reason is, because of the way my search page is architected, I'm storing the search model in TempData. The initial search causes a POST to the search results page, but the paging links are all just links to "/results/2" (for page 2). They examine TempData to see if the model is in there an use it if so.

This causes problems when someone uses the back button to go to the search form and resubmit it. It's still picking up the model in TempData instead of using the new search criteria. So if it's a POST (i.e. someone just submitted the search form), I want to clear out TempData first.

Best Answer

The HttpMethod property on the HttpRequest object will get it for you. You can just use:

if (HttpContext.Current.Request.HttpMethod == "POST")
{
    // The action is a POST.
}

Or you can get the Request object straight off of the current controller. It's just a property.

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C# – Create Generic method constraining T to an Enum

Since Enum Type implements IConvertible interface, a better implementation should be something like this:

public T GetEnumFromString<T>(string value) where T : struct, IConvertible
{
   if (!typeof(T).IsEnum) 
   {
      throw new ArgumentException("T must be an enumerated type");
   }

   //...
}

This will still permit passing of value types implementing IConvertible. The chances are rare though.

C# – Why is it important to override GetHashCode when Equals method is overridden

Yes, it is important if your item will be used as a key in a dictionary, or HashSet<T>, etc - since this is used (in the absence of a custom IEqualityComparer<T>) to group items into buckets. If the hash-code for two items does not match, they may never be considered equal (Equals will simply never be called).

The GetHashCode() method should reflect the Equals logic; the rules are:

if two things are equal (Equals(...) == true) then they must return the same value for GetHashCode()
if the GetHashCode() is equal, it is not necessary for them to be the same; this is a collision, and Equals will be called to see if it is a real equality or not.

In this case, it looks like "return FooId;" is a suitable GetHashCode() implementation. If you are testing multiple properties, it is common to combine them using code like below, to reduce diagonal collisions (i.e. so that new Foo(3,5) has a different hash-code to new Foo(5,3)):

unchecked // only needed if you're compiling with arithmetic checks enabled
{ // (the default compiler behaviour is *disabled*, so most folks won't need this)
    int hash = 13;
    hash = (hash * 7) + field1.GetHashCode();
    hash = (hash * 7) + field2.GetHashCode();
    ...
    return hash;
}

Oh - for convenience, you might also consider providing == and != operators when overriding Equals and GetHashCode.

A demonstration of what happens when you get this wrong is here.

Best Answer

Related Solutions

C# – Create Generic method constraining T to an Enum

C# – Why is it important to override GetHashCode when Equals method is overridden

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