Android Proguard Javascript Interface Fail

I use in my project a piece of code as described here

http://lexandera.com/2009/01/extracting-html-from-a-webview/

I create the .apk file, install it on my device and it correctly works. If I try to use the obfuscation with proguard the project fails, the method showHTML(String html) of MyJavaScriptInterface is not reached.

My proguard configuration regarding that

-keep public class com.mypackage.MyClass.MyJavaScriptInterface
-keep public class * implements com.mypackage.MyClass.MyJavaScriptInterface
-keepclassmembers class * implements com.mypackage.MyClass.MyJavaScriptInterface { 
    <methods>; }

according to this this answer Android proguard Javascript Interface problem.

Any suggestion? Thanks in advance. Denis.

SOLVED.

As Eric suggested, I changed the Proguard configuration file like this:

-keep public class com.mypackage.MyClass$MyJavaScriptInterface
-keep public class * implements com.mypackage.MyClass$MyJavaScriptInterface
-keepclassmembers class com.mypackage.MyClass$MyJavaScriptInterface { 
    <methods>; }

Now my project works perfectly. Thanks.