Dynamic picker

Hi I'm developing a Android app and i'm using Titanium SDK 3.2.3. In my application i've to create one picker which receive data from a remote webservice (one title per row). I developed the following code, but I know that's not correct. Can anyone help me? I suppose that onload function isn't correct. ps: I just use the following url to test.

var picker = Ti.UI.createPicker({
    textAlign:"center",
    width:'100%',
    height:'14%',
    backgroundColor:"blue",
    color:"white"
});
view_buttons.add(picker);
 
var url="http://apod.nasa.gov/apod.rss"; 
var xhr = Titanium.Network.createHTTPClient();
xhr.onload = function() {
    var doc = this.responseXML.documentElement;
    var items = doc.getElementsByTagName("item");
    for (var i=0;i<items.length;i++) {  
             picker.add(Ti.UI.createPickerRow({title: items.title}));
    }
};
 
xhr.onerror = function(e) {
    alert('Error '+e.error);
};
 
picker.selectionIndicator = true;
xhr.open('GET',url);
xhr.send();