Reference inner class in Visualforce component

Question

I'm trying to build a VF component that references an attribute that is an instance of an inner class. I followed the suggestion here on the Apex boards but it does not compile for me using V28.0. (Note the boards post was about lists of inner class objects - I only need a single instance)

Interface, Apex class, VF component follow:

public interface VFComponentAttributable {
// To make inner classes available as VF component attributes
// http://boards.developerforce.com/t5/Visualforce-Development/Error-using-inner-class-in-component-attribute/td-p/147856
}

public with sharing class Foo {
   public class InnerBar implements VFComponentAttributable{
      public String  myVbl {get; set;}
  }
}    


<apex:component >
<!-- Generates compiler error 'Unknown property VFComponentAttributable.myVbl' -->
<apex:attribute name="bar"                      description="instance of inner class"
                type="VFComponentAttributable"          required="true"/>

<apex:outputText value="{!bar.myVbl}"/>  


<!-- This doesnt work either, generates compiler error  'Apex class InnerBar does not exist
<apex:attribute name="bar"                      description="instance of inner class"
                type="Foo.InnerBar" required="true"/>
<apex:outputText value="{!bar.myVbl}"/>             -->

I know I can refactor and make the inner class an outer class and it will work but I'd rather not if I can avoid it.

Answer 1

I've run across this as well and also resorted to refactoring my inner-class to the top level. The documentation isn't clear on this, but considering that the type attribute is considered limited, I think it's fair to assume that only top-level classes are supported. From the Visualforce Developer's Guide (pg. 285):

Only the following data types are allowed as values for the type attribute:

• Primitives, such as String, Integer, or Boolean.
• sObjects, such as Account, My_Custom_Object__c, or the generic sObject type.
• One-dimensional lists, specified using array-notation, such as String[], or Contact[].
• Maps, specified using type="map". You don't need to specify the map's specific data type.
• Custom Apex types (classes).

Answer 2

The problem here is that your Component is receiving an instance of VFComponentAttributable which does not have the myVbl field.

If you change your VFComponentAttributable and Foo definitions to the following it should work.

public interface VFComponentAttributable 
{
    // To make inner classes available as VF component attributes
    // http://boards.developerforce.com/t5/Visualforce-Development/Error-using-inner-class-in-component-attribute/td-p/147856
    String getMyVbl();
    void setMyVbl(String value);
}

public with sharing class Foo 
{
    public class InnerBar implements VFComponentAttributable
    {
        private String  myVbl;

        public String getMyVbl()
        {
            return myVbl;
        }

        public void setMyVbl(String value)
        {
            myVbl = value;
        }
    }
}  

Answer 3

Why not in Foo:

Public foo{

    Public class innerBar{
    //etc
    }

    Public innerBar myBar {get;set;}

}