Ensure that HttpConfiguration.EnsureInitialized()

Question

I\'ve installed Visual Studio 2013 and when I run my app I get the error below.

I\'ve got no idea as to where I\'m to initialized this object.

What to do?

Answer 1

If you do it at the end of Application_Start it will be too late, as WebApiConfig.Register has been called.

The best way to resolve this is to use new initialization method by replacing in Global.asax :

WebApiConfig.Register(GlobalConfiguration.Configuration);

by

GlobalConfiguration.Configure(WebApiConfig.Register);

Answer 2

This is old, but is the first result on google when searching for this error. After quite a bit of digging I was able to figure out what was going on.

tldr:
All GlobalConfiguration.Configure does is invoke your action and call EnsureInitialized(). config.MapAttributeRoutes() must be called before EnsureInitialized() since EnsureInitialized only runs once.

Meaning: if you're coming from an existing Mvc project, all you have to do is:

1. Add GlobalConfiguration.Configuration.EnsureInitialized(); to the bottom of your Application_Start method.

OR

2. Move your entire configuration into a single call to GlobalConfiguration.Configure:

GlobalConfiguration.Configure(config => 
{
    WebApiConfig.Register(config);
    config.MapAttributeRoutes();
    ...
});

---

Digging Deeper

HttpConfiguration.Configuration has an "Initializer" property defined like this:

public Action<HttpConfiguration> Initializer;

HttpConfiguration.EnsureInitialized() runs this action and sets _initialized to true

public void EnsureInitialized()
{ 
    if (_initialized)
    {
        return;
    }
    _initialized = true;
    Initializer(this);            
}

HttpConfiguration.MapAttributeRoutes calls internal method AttributeRoutingMapper.MapAttributeRoutes which sets HttpConfiguration.Initializer

public static void MapAttributeRoutes(...)
{
    RouteCollectionRoute aggregateRoute = new RouteCollectionRoute();
    configuration.Routes.Add(AttributeRouteName, aggregateRoute);

    ...

    Action<HttpConfiguration> previousInitializer = configuration.Initializer;
    configuration.Initializer = config =>
    {
        previousInitializer(config);
        ...
    };
}

GlobalConfiguration.Configure runs EnsureInitialized immediately after invoking your action:

public static void Configure(Action<HttpConfiguration> configurationCallback)
{
    if (configurationCallback == null)
    {
        throw new ArgumentNullException("configurationCallback");
    }

    configurationCallback.Invoke(Configuration);
    Configuration.EnsureInitialized();
}

Don't forget, if you run in to a wall, the source for asp.net is available at http://aspnetwebstack.codeplex.com/SourceControl/latest

Answer 3

I've had a related issue. Sometimes calling GlobalConfiguration.Configure multiple times triggers this error. As a workaround, I've put all configuration initialization logic in one place.

Answer 4

For me, the problem was that I was trying to use named parameters for query string fields in my routes:

[Route("my-route?field={field}")]
public void MyRoute([FromUri] string field)
{
}

Query string fields are automatically mapped to parameters and aren't actually part of the route definition. This works:

[Route("my-route")]
public void MyRoute([FromUri] string field)
{
}

Answer 5

IF THIS ERROR SEEMS TO HAVE COME "OUT OF NOWHERE", i.e. your app was working perfectly fine for a while, ask yourself: Did I add an action to a controller or change any routes prior to seeing this error?

If the answer is yes (and it probably is), you likely made a mistake in the process. Incorrect formatting, copy/pasting an action and forgetting to make sure the endpoint names are unique, etc. will all end you up here. The suggestion that this error makes on how to resolve it can send you barking up the wrong tree.

Answer 6

One typically gets this exception when route templates in "Attribute Routing" are not proper.

For example, i got this when i wrote the following code:

[Route("{dirName:string}/contents")] //incorrect
public HttpResponseMessage GetDirContents(string dirName) { ... }

In route constraints syntax {parameter:constraint}, constraint by default is of type string. No need to mention it explicitly.

[Route("{dirName}/contents")] //correct
public HttpResponseMessage GetDirContents(string dirName) { ... }