Radio fields allow the user to specify one of multiple, predefined values. These fields should all be defined in your add-on's constructor.

$this->add_on->add_field(
    'property_type',
    'Property Type',
    'radio',
    array(
        'rent' => 'For Rent/Lease',
        'buy' => 'For Sale'
    )
);

The keys in the options array are the actual values that will be passed to the import function. The values are the labels that will be shown to the user in the interface:

If the values in the user’s XML/CSV file are different than the values required by your radio field, the user can use the built-in mapping interface to translate them:

Related

Add-On Structure

Text Fields

Image Fields

Nested Fields