C# – ASP.NET MVC: What is the correct way to redirect to pages/actions in MVC

asp.net-mvccredirect

I am fairly new to MVC but not sure exactly which Redirect… replaces the standard redirect used in WebForms is the standard Response.Redirect()

For instance, I need to redirect to other pages in a couple of scenarios:

WHen the user logs out (Forms signout in Action) I want to redirect to a login page.
In a Controller or base Controller event e.g. Initialize, I want to redirect to another page (AbsoluteRootUrl + Controller + Action)

It seems that multiple redirects get called in some cases which causes errors, something to do with the fact a page is already being redirected? How can cancel the current request and just redirect?

Update:

The answer to this question (System.Web.Mvc.Controller Initialize) indicates that Initialize should not be used and OnActionExecuting should be used?

Any comments on why Initialize should not be used or why OnAuthorization is not a better option?

More Info:

This blog post (http://blog.wekeroad.com/blog/aspnet-mvc-securing-your-controller-actions/) indicates that OnActionExecuting is useful for authentication (as indicated in the link above) I guess adding this to that event in the base Controller class is fine as every page runs an Action in MVC so shouldn't make much difference and having the ability to redirect should be easier. This does make sense, but it also seems to make sense to me that things could be done in an event before this event and makes we question what those events are for? Will be giving OnActionExecuting a go..

Best Answer

1) When the user logs out (Forms signout in Action) I want to redirect to a login page.

public ActionResult Logout() {
    //log out the user
    return RedirectToAction("Login");
}

2) In a Controller or base Controller event eg Initialze, I want to redirect to another page (AbsoluteRootUrl + Controller + Action)

Why would you want to redirect from a controller init?

the routing engine automatically handles requests that come in, if you mean you want to redirect from the index action on a controller simply do:

public ActionResult Index() {
    return RedirectToAction("whateverAction", "whateverController");
}

This is the style that Microsoft tends to use in their examples.

It appears that the guidance in this area may have changed, as StyleCop now enforces the use of the C# specific aliases.

C# – What does the [Flags] Enum Attribute mean in C#

The [Flags] attribute should be used whenever the enumerable represents a collection of possible values, rather than a single value. Such collections are often used with bitwise operators, for example:

var allowedColors = MyColor.Red | MyColor.Green | MyColor.Blue;

Note that the [Flags] attribute doesn't enable this by itself - all it does is allow a nice representation by the .ToString() method:

enum Suits { Spades = 1, Clubs = 2, Diamonds = 4, Hearts = 8 }
[Flags] enum SuitsFlags { Spades = 1, Clubs = 2, Diamonds = 4, Hearts = 8 }

...

var str1 = (Suits.Spades | Suits.Diamonds).ToString();
           // "5"
var str2 = (SuitsFlags.Spades | SuitsFlags.Diamonds).ToString();
           // "Spades, Diamonds"

It is also important to note that [Flags] does not automatically make the enum values powers of two. If you omit the numeric values, the enum will not work as one might expect in bitwise operations, because by default the values start with 0 and increment.

Incorrect declaration:

[Flags]
public enum MyColors
{
    Yellow,  // 0
    Green,   // 1
    Red,     // 2
    Blue     // 3
}

The values, if declared this way, will be Yellow = 0, Green = 1, Red = 2, Blue = 3. This will render it useless as flags.

Here's an example of a correct declaration:

[Flags]
public enum MyColors
{
    Yellow = 1,
    Green = 2,
    Red = 4,
    Blue = 8
}

To retrieve the distinct values in your property, one can do this:

if (myProperties.AllowedColors.HasFlag(MyColor.Yellow))
{
    // Yellow is allowed...
}

or prior to .NET 4:

if((myProperties.AllowedColors & MyColor.Yellow) == MyColor.Yellow)
{
    // Yellow is allowed...
}

if((myProperties.AllowedColors & MyColor.Green) == MyColor.Green)
{
    // Green is allowed...
}

Under the covers

This works because you used powers of two in your enumeration. Under the covers, your enumeration values look like this in binary ones and zeros:

 Yellow: 00000001
 Green:  00000010
 Red:    00000100
 Blue:   00001000

Similarly, after you've set your property AllowedColors to Red, Green and Blue using the binary bitwise OR | operator, AllowedColors looks like this:

myProperties.AllowedColors: 00001110

So when you retrieve the value you are actually performing bitwise AND & on the values:

myProperties.AllowedColors: 00001110
             MyColor.Green: 00000010
             -----------------------
                            00000010 // Hey, this is the same as MyColor.Green!

The None = 0 value

And regarding the use of 0 in your enumeration, quoting from MSDN:

[Flags]
public enum MyColors
{
    None = 0,
    ....
}

Use None as the name of the flag enumerated constant whose value is zero. You cannot use the None enumerated constant in a bitwise AND operation to test for a flag because the result is always zero. However, you can perform a logical, not a bitwise, comparison between the numeric value and the None enumerated constant to determine whether any bits in the numeric value are set.

You can find more info about the flags attribute and its usage at msdn and designing flags at msdn

Best Answer

Related Solutions

C# – the difference between String and string in C#

This is the style that Microsoft tends to use in their examples.

C# – What does the [Flags] Enum Attribute mean in C#

Related Topic