java - How can I set doInbackground finish its task before continuing the mainActivity? -

these mainactivity:

    database_connector wp_terms = new database_connector("select *  `dse120071750`.`wp_terms` ",progressdialog,this);     wp_terms.execute();     wp_terms.onpreexecute();     try {          (int i=0; i<wp_terms.getjsonarray().length(); i++){             jsonobject obj = wp_terms.getjsonarray().getjsonobject(i);             this.wp_terms.put(obj.getstring("term_id"), obj.getstring("name"));         }     } catch (jsonexception e) {         e.printstacktrace();     } 

databaseconnector:

package hk.hoome.www.mobilehoome;  public class database_connector extends asynctask<void,void, void> {  //string mode; httpresponse response; string sql; jsonarray jsonarray; searchpage searchpage;  public database_connector(string sql, searchpage searchpage){     //this.mode = mode;     this.sql = sql;     this.searchpage = searchpage;     jsonarray = new jsonarray(); }  @override protected void doinbackground(void... params) {     connect();     publishprogress();     return null; }    @override protected void onprogressupdate(void... values) {  }  public void connect() {     list<namevaluepair> namevaluepair = new arraylist<namevaluepair>(1);     namevaluepair.add(new basicnamevaluepair("sql", sql));     //namevaluepair.add(new basicnamevaluepair("mode", mode));     try {         httpclient httpclient = new defaulthttpclient();         httppost httppost = new httppost("http://www.hoome.hk/hoomemobileapps/connectdb.php");         httppost.setentity(new urlencodedformentity(namevaluepair, "utf-8"));         response = httpclient.execute(httppost);         httpentity httpentity  = response.getentity();         string entityresponse  = entityutils.tostring(httpentity);         log.e("entity response ", entityresponse.substring(2));         jsonarray = new jsonarray(entityresponse.substring(2));      } catch (unsupportedencodingexception e) {         e.printstacktrace();     } catch (ioexception e) {         e.printstacktrace();     } catch (jsonexception e) {         e.printstacktrace();     } }    public jsonarray getjsonarray(){     return jsonarray; } 

}

when ran code, for (int i=0; i<wp_terms.getjsonarray().length(); i++){ results in nullpointerexception.

i believe because doinbackground hasn't finished process mainactivity keeps running. how can set doinbackground has done before continue running mainactivity?

solution?

   try {         while (wp_posts.getjsonarray().equals(null))             thread.sleep(1000);                      } catch(interruptedexception ex) {         thread.currentthread().interrupt();     } 

is solution?

use callback in database connector class , pass completion callback. simplicity i'm using runnable interface. in general, try have own interface , pass params between background thread , main thread on custom interface.

package hk.hoome.www.mobilehoome;  public class database_connector extends asynctask<void,void, void> {  //string mode; httpresponse response; string sql; jsonarray jsonarray; searchpage searchpage; private runnable activitycallback;  public void setcallback(runnable callback) {     this.activitycallback = callback; }  public database_connector(string sql, searchpage searchpage){     //this.mode = mode;     this.sql = sql;     this.searchpage = searchpage;     jsonarray = new jsonarray(); }  @override protected void doinbackground(void... params) {     connect();     publishprogress();     return null; }  protected void onpostexecute(void result) {      if(activitycallback != null) {         activitycallback.run();     } }   @override protected void onprogressupdate(void... values) {  }  public void connect() {     list<namevaluepair> namevaluepair = new arraylist<namevaluepair>(1);     namevaluepair.add(new basicnamevaluepair("sql", sql));     //namevaluepair.add(new basicnamevaluepair("mode", mode));     try {         httpclient httpclient = new defaulthttpclient();         httppost httppost = new httppost("http://www.hoome.hk/hoomemobileapps/connectdb.php");         httppost.setentity(new urlencodedformentity(namevaluepair, "utf-8"));         response = httpclient.execute(httppost);         httpentity httpentity  = response.getentity();         string entityresponse  = entityutils.tostring(httpentity);         log.e("entity response ", entityresponse.substring(2));         jsonarray = new jsonarray(entityresponse.substring(2));      } catch (unsupportedencodingexception e) {         e.printstacktrace();     } catch (ioexception e) {         e.printstacktrace();     } catch (jsonexception e) {         e.printstacktrace();     } }    public jsonarray getjsonarray(){     return jsonarray; } } 

in mainactivity

database_connector wp_terms = new database_connector("select *  `dse120071750`.`wp_terms` ",progressdialog,this); wp_terms.setcallback(new runnable() {          public void run() {          try {                  (int i=0; i<wp_terms.getjsonarray().length(); i++){                     jsonobject obj = wp_terms.getjsonarray().getjsonobject(i);                     this.wp_terms.put(obj.getstring("term_id"),      obj.getstring("name"));                 }             } catch (jsonexception e) {                 e.printstacktrace();             }         }     });     wp_terms.execute();