why doesn't it push the result to data?

define(["dojo/_base/declare","dojo/request/xhr","dojo/dom","dojo/dom-construct","dojo/on"],
function(declare, xhr,dom,domConst,on){
return declare(null,{
    data : [],

    constructor : function( ){
            this.getdata();
        },

        //gets Data
    getdata : function(){
        xhr("sqlaccess.php?order=0").then(function(text){
                                                                                        this.prepare_str(text.toString().split(";"));});
            return this.data;
        },
        //push Data to Array
    prepare_str : function(str){
        alert(str);
        for(var index = 0; index < str.length; index++)
        {
            data.push({name:str[index], id: index});
        }
        //get
        },


    //constructor




        //Insert New Entry
    setdata : function(str)
    {
        xhr("http://localhost/sql/sqlaccess.php?order=1&val="+str).then(function(text){
                                                                                                            alert("Result = " + text);
                                                                                                        });
    },

    //update Entry
    updatedata : function(str,former){
        xhr("http://localhost/sql/sqlaccess.php?order=2&val="+str+"&former="+former).then(function(text){
                                                                                                                                alert("Result = " + text);
                                                                                                                            });
        },

        //Delete Entry
    deletedata : function(str) {
        xhr("http://localhost/sql/sqlaccess.php?order=3&val="+str).then(function(text){
                                                                                                            alert("Result = "+text);
                                                                                                        });
        },
});
});