(Sample Code by Chris Hopkin taken from the DroidScript Google-Group)

spinner.js

//Some code before...
 
//Load some txt files in the spinner
list = app.ListFolder( "/sdcard/Folder", ".txt" );
spin.SetList( list );
 
// Returns the currently selected index from the spinner
function getSpinItemIndex()
{
    return list.indexOf(spin.GetText());
}
 
// select the next file in the spinner
function select_next_spinner_item()
{
    var listIndex = getSpinItemIndex();
 
    // Make sure there is a next file
    if(listIndex+1 < list.length)
    {
        var file = list[listIndex+1];
 
        // Show the next file in the spinner
        spin.SelectItem(file);
    }
}