HttpBaseProtocolFilter.ClearAuthenticationCache() throw 'System.InvalidCastException'

问题

I create an simple uwp app. The sdk version is Universal Windows 10.0.14332.0. The app does nothing, only call the function "HttpBaseProtocolFilter.ClearAuthenticationCache()". But when I call the "HttpBaseProtocolFilter.ClearAuthenticationCache()", an exception throwed:

An exception of type 'System.InvalidCastException' occurred in App2.exe but was not handled in user code

Additional information: Unable to cast object of type 'Windows.Web.Http.Filters.HttpBaseProtocolFilter' to type 'Windows.Web.Http.Filters.IHttpBaseProtocolFilter4'.

How can I use "HttpBaseProtocolFilter.ClearAuthenticationCache()"?

回答1:

According to the documentation, the ClearAuthenticationCache method is introduced in Windows.Foundation.UniversalApiContract, version 3 and is available in OS version 10.0.14295.0 and later.

It means that the Windows.Web.Http.Filters.IHttpBaseProtocolFilter4 is not available in older version and you recieve an InvalidCastException.

So if you are targetting an older version as minimum, you need to check if the API is available before calling the method:

using Windows.Foundation.Metadata;
 ...
 ...
if(ApiInformation.IsMethodPresent("Windows.Web.Http.Filters.HttpBaseProtocolFilter.ClearAuthenticationCache"))
{
    // Call the method here
}

来源：https://stackoverflow.com/questions/37200801/httpbaseprotocolfilter-clearauthenticationcache-throw-system-invalidcastexcep