How can I make my custom FieldType show up in an element index?
To make it possible to select fields from a custom FieldType in the Customizable Element Indexes interface, your FieldType class needs to implement the IPreviewableFieldType interface, like this:

class ExamplePluginHandleFieldType extends BaseFieldType implements IPreviewableFieldType
{
    ...


If you want to modify how the values from your custom FieldType displays in element indexes, you need to add a getTableAttributeHtml method to your FieldType class:

public function getTableAttributeHtml($value)
{
    return $value ? $value-&gt;id : null;
}