java - Null pointer exception: invoking virtual method -
i trying design basic chat app. app build without errors click button on emulator app crashes , log shows following error:
07-01 22:50:39.367 30016-30032/com.example.ibm_admin.chat e/buffer error﹕ error converting result java.lang.nullpointerexception: lock == null 07-01 22:50:39.367 30016-30032/com.example.ibm_admin.chat e/json parser﹕ error parsing data org.json.jsonexception: end of input @ character 0 of 07-01 22:50:39.370 30016-30016/com.example.ibm_admin.chat d/androidruntime﹕ shutting down vm 07-01 22:50:39.370 30016-30016/com.example.ibm_admin.chat e/androidruntime﹕ fatal exception: main process: com.example.ibm_admin.chat, pid: 30016 java.lang.nullpointerexception: attempt invoke virtual method 'int org.json.jsonarray.length()' on null object reference @ com.example.ibm_admin.chat.userfragment$load.onpostexecute(userfragment.java:84) @ com.example.ibm_admin.chat.userfragment$load.onpostexecute(userfragment.java:71) @ android.os.asynctask.finish(asynctask.java:632) @ android.os.asynctask.access$600(asynctask.java:177) @ android.os.asynctask$internalhandler.handlemessage(asynctask.java:645) @ android.os.handler.dispatchmessage(handler.java:102) @ android.os.looper.loop(looper.java:135) @ android.app.activitythread.main(activitythread.java:5221) @ java.lang.reflect.method.invoke(native method) @ java.lang.reflect.method.invoke(method.java:372) @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:899) @ com.android.internal.os.zygoteinit.main(zygoteinit.java:694) 07-01 22:50:40.975 30016-30023/com.example.ibm_admin.chat w/art﹕ suspending threads took: 15.530ms 07-01 22:51:02.766 30016-30023/com.example.ibm_admin.chat w/art﹕ suspending threads took: 6.893ms mainactivity.java
import android.app.activity; import android.app.fragment; import android.app.fragmenttransaction; import android.content.context; import android.content.sharedpreferences; import android.os.asynctask; import android.os.bundle; import android.util.log; import android.widget.toast; import com.google.android.gms.common.connectionresult; import com.google.android.gms.common.googleplayservicesutil; import com.google.android.gms.gcm.googlecloudmessaging; import java.io.ioexception; public class mainactivity extends activity { private final static int play_services_resolution_request = 9000; string sender_id = "your project number"; static final string tag = "l2c"; googlecloudmessaging gcm; sharedpreferences prefs; context context; string regid; @override protected void oncreate(bundle savedinstancestate) { super.oncreate(savedinstancestate); setcontentview(r.layout.activity_main); prefs = getsharedpreferences("chat", 0); context = getapplicationcontext(); if(!prefs.getstring("reg_from","").isempty()){ fragment user = new userfragment(); fragmenttransaction ft = getfragmentmanager().begintransaction(); ft.replace(r.id.content_frame, user); ft.settransition(fragmenttransaction.transit_fragment_fade); ft.addtobackstack(null); ft.commit(); }else if(!prefs.getstring("reg_id", "").isempty()){ fragment reg = new loginfragment(); fragmenttransaction ft = getfragmentmanager().begintransaction(); ft.replace(r.id.content_frame, reg); ft.settransition(fragmenttransaction.transit_fragment_fade); ft.addtobackstack(null); ft.commit(); }else if(checkplayservices()){ new register().execute(); }else{ toast.maketext(getapplicationcontext(),"this device not supported",toast.length_short).show(); } } private boolean checkplayservices() { int resultcode = googleplayservicesutil.isgoogleplayservicesavailable(this); if (resultcode != connectionresult.success) { if (googleplayservicesutil.isuserrecoverableerror(resultcode)) { googleplayservicesutil.geterrordialog(resultcode, this, play_services_resolution_request).show(); } else { log.i(tag, "this device not supported."); finish(); } return false; } return true; } private class register extends asynctask<string, string, string> { @override protected string doinbackground(string... args) { try { if (gcm == null) { gcm = googlecloudmessaging.getinstance(context); regid = gcm.register(sender_id); log.e("regid",regid); sharedpreferences.editor edit = prefs.edit(); edit.putstring("reg_id", regid); edit.commit(); } return regid; } catch (ioexception ex) { log.e("error", ex.getmessage()); return "fails"; } } @override protected void onpostexecute(string json) { fragment reg = new loginfragment(); fragmenttransaction ft = getfragmentmanager().begintransaction(); ft.replace(r.id.content_frame, reg); ft.settransition(fragmenttransaction.transit_fragment_fade); ft.addtobackstack(null); ft.commit(); } } } jsonparser.java
import java.io.bufferedreader; import java.io.ioexception; import java.io.inputstream; import java.io.inputstreamreader; import java.io.unsupportedencodingexception; import java.util.list; import org.apache.http.httpentity; import org.apache.http.httpresponse; import org.apache.http.namevaluepair; import org.apache.http.client.clientprotocolexception; import org.apache.http.client.entity.urlencodedformentity; import org.apache.http.client.methods.httppost; import org.apache.http.impl.client.defaulthttpclient; import org.json.jsonarray; import org.json.jsonexception; import org.json.jsonobject; import android.util.log; public class jsonparser { static inputstream = null; static jsonobject jobj = null; static jsonarray jary = null; static string json = ""; // constructor public jsonparser() { } public jsonobject getjsonfromurl(string url,list<namevaluepair> params) { // making http request try { // defaulthttpclient defaulthttpclient httpclient = new defaulthttpclient(); httppost httppost = new httppost(url); if(params != null){ httppost.setentity(new urlencodedformentity(params)); } httpresponse httpresponse = httpclient.execute(httppost); httpentity httpentity = httpresponse.getentity(); = httpentity.getcontent(); } catch (unsupportedencodingexception e) { e.printstacktrace(); } catch (clientprotocolexception e) { e.printstacktrace(); } catch (ioexception e) { e.printstacktrace(); } try { bufferedreader reader = new bufferedreader(new inputstreamreader( is, "iso-8859-1"), 8); stringbuilder sb = new stringbuilder(); string line = null; while ((line = reader.readline()) != null) { sb.append(line + "n"); } is.close(); json = sb.tostring(); } catch (exception e) { log.e("buffer error", "error converting result " + e.tostring()); } // try parse string json object try { jobj = new jsonobject(json); } catch (jsonexception e) { log.e("json parser", "error parsing data " + e.tostring()); } // return json string return jobj; } public jsonarray getjsonarray(string url,list<namevaluepair> params) { // making http request try { // defaulthttpclient defaulthttpclient httpclient = new defaulthttpclient(); httppost httppost = new httppost(url); httppost.setentity(new urlencodedformentity(params)); httpresponse httpresponse = httpclient.execute(httppost); httpentity httpentity = httpresponse.getentity(); = httpentity.getcontent(); } catch (unsupportedencodingexception e) { e.printstacktrace(); } catch (clientprotocolexception e) { e.printstacktrace(); } catch (ioexception e) { e.printstacktrace(); } try { bufferedreader reader = new bufferedreader(new inputstreamreader( is, "iso-8859-1"), 8); stringbuilder sb = new stringbuilder(); string line = null; while ((line = reader.readline()) != null) { sb.append(line + "n"); } is.close(); json = sb.tostring(); log.e("jss",json); } catch (exception e) { log.e("buffer error", "error converting result " + e.tostring()); } // try parse string json object try { jary = new jsonarray(json); } catch (jsonexception e) { log.e("json parser", "error parsing data " + e.tostring()); } // return json string return jary; } } loginfragment.java
import android.app.fragment; import android.app.fragmenttransaction; import android.app.progressdialog; import android.content.sharedpreferences; import android.os.asynctask; import android.os.bundle; import android.view.layoutinflater; import android.view.view; import android.view.viewgroup; import android.widget.button; import android.widget.edittext; import android.widget.toast; import org.apache.http.namevaluepair; import org.apache.http.message.basicnamevaluepair; import org.json.jsonexception; import org.json.jsonobject; import java.util.arraylist; import java.util.list; public class loginfragment extends fragment { sharedpreferences prefs; edittext name, mobno; button login; list<namevaluepair> params; progressdialog progress; @override public view oncreateview(layoutinflater inflater,viewgroup container, bundle savedinstancestate) { view view = inflater.inflate(r.layout.login_fragment, container, false); prefs = getactivity().getsharedpreferences("chat", 0); name = (edittext)view.findviewbyid(r.id.name); mobno = (edittext)view.findviewbyid(r.id.mobno); login = (button)view.findviewbyid(r.id.log_btn); progress = new progressdialog(getactivity()); progress.setmessage("registering ..."); progress.setprogressstyle(progressdialog.style_spinner); progress.setindeterminate(true); login.setonclicklistener(new view.onclicklistener() { @override public void onclick(view v) { progress.show(); sharedpreferences.editor edit = prefs.edit(); edit.putstring("reg_from", mobno.gettext().tostring()); edit.putstring("from_name", name.gettext().tostring()); edit.commit(); new login().execute(); } }); return view; } private class login extends asynctask<string, string, jsonobject> { @override protected jsonobject doinbackground(string... args) { jsonparser json = new jsonparser(); params = new arraylist<namevaluepair>(); params.add(new basicnamevaluepair("name", name.gettext().tostring())); params.add(new basicnamevaluepair("mobno", mobno.gettext().tostring())); params.add((new basicnamevaluepair("reg_id",prefs.getstring("reg_id","")))); jsonobject jobj = json.getjsonfromurl("http://10.0.2.2:8080/login",params); return jobj; } @override protected void onpostexecute(jsonobject json) { progress.dismiss(); try { string res = json.getstring("response"); if(res.equals("sucessfully registered")) { fragment reg = new userfragment(); fragmenttransaction ft = getfragmentmanager().begintransaction(); ft.replace(r.id.content_frame, reg); ft.settransition(fragmenttransaction.transit_fragment_fade); ft.addtobackstack(null); ft.commit(); }else{ toast.maketext(getactivity(),res,toast.length_short).show(); } } catch (jsonexception e) { e.printstacktrace(); } } } } userfragment.java
import android.app.fragment; import android.app.fragmenttransaction; import android.content.intent; import android.content.sharedpreferences; import android.os.asynctask; import android.os.bundle; import android.view.layoutinflater; import android.view.view; import android.view.viewgroup; import android.widget.adapterview; import android.widget.button; import android.widget.listadapter; import android.widget.listview; import android.widget.simpleadapter; import android.widget.toast; import org.apache.http.namevaluepair; import org.apache.http.message.basicnamevaluepair; import org.json.jsonarray; import org.json.jsonexception; import org.json.jsonobject; import java.util.arraylist; import java.util.hashmap; import java.util.list; public class userfragment extends fragment { listview list; arraylist<hashmap<string, string>> users = new arraylist<hashmap<string, string>>(); button refresh,logout; list<namevaluepair> params; sharedpreferences prefs; @override public view oncreateview(layoutinflater inflater,viewgroup container, bundle savedinstancestate) { view view =inflater.inflate(r.layout.user_fragment, container, false); prefs = getactivity().getsharedpreferences("chat", 0); list = (listview)view.findviewbyid(r.id.listview); refresh = (button)view.findviewbyid(r.id.refresh); logout = (button)view.findviewbyid(r.id.logout); logout.setonclicklistener(new view.onclicklistener() { @override public void onclick(view v) { new logout().execute(); } }); refresh.setonclicklistener(new view.onclicklistener() { @override public void onclick(view v) { getfragmentmanager().begintransaction().remove(getfragmentmanager().findfragmentbyid(r.id.content_frame)).commit(); fragment reg = new userfragment(); fragmenttransaction ft = getfragmentmanager().begintransaction(); ft.replace(r.id.content_frame, reg); ft.settransition(fragmenttransaction.transit_fragment_fade); ft.addtobackstack(null); ft.commit(); } }); new load().execute(); return view; } private class load extends asynctask<string, string, jsonarray> { @override protected jsonarray doinbackground(string... args) { jsonparser json = new jsonparser(); params = new arraylist<namevaluepair>(); params.add(new basicnamevaluepair("mobno", prefs.getstring("reg_from",""))); jsonarray jary = json.getjsonarray("http://10.0.2.2:8080/getuser",params); return jary; } @override protected void onpostexecute(jsonarray json) { for(int = 0; < json.length(); i++){ jsonobject c = null; try { c = json.getjsonobject(i); string name = c.getstring("name"); string mobno = c.getstring("mobno"); hashmap<string, string> map = new hashmap<string, string>(); map.put("name", name); map.put("mobno", mobno); users.add(map); } catch (jsonexception e) { e.printstacktrace(); } } listadapter adapter = new simpleadapter(getactivity(), users, r.layout.user_list_single, new string[] { "name","mobno" }, new int[] { r.id.name, r.id.mobno}); list.setadapter(adapter); list.setonitemclicklistener(new adapterview.onitemclicklistener() { @override public void onitemclick(adapterview<?> parent, view view, int position, long id) { bundle args = new bundle(); args.putstring("mobno", users.get(position).get("mobno")); intent chat = new intent(getactivity(), chatactivity.class); chat.putextra("info", args); startactivity(chat); } }); } } private class logout extends asynctask<string, string, jsonobject> { @override protected jsonobject doinbackground(string... args) { jsonparser json = new jsonparser(); params = new arraylist<namevaluepair>(); params.add(new basicnamevaluepair("mobno", prefs.getstring("reg_from",""))); jsonobject jobj = json.getjsonfromurl("http://10.0.2.2:8080/logout",params); return jobj; } @override protected void onpostexecute(jsonobject json) { string res = null; try { res = json.getstring("response"); toast.maketext(getactivity(),res,toast.length_short).show(); if(res.equals("removed sucessfully")) { fragment reg = new loginfragment(); fragmenttransaction ft = getfragmentmanager().begintransaction(); ft.replace(r.id.content_frame, reg); ft.settransition(fragmenttransaction.transit_fragment_fade); ft.addtobackstack(null); ft.commit(); sharedpreferences.editor edit = prefs.edit(); edit.putstring("reg_from", ""); edit.commit(); } } catch (jsonexception e) { e.printstacktrace(); } } } } chatactivity.java
import android.app.activity; import android.content.broadcastreceiver; import android.content.context; import android.content.intent; import android.content.intentfilter; import android.content.sharedpreferences; import android.graphics.color; import android.os.asynctask; import android.os.bundle; import android.support.v4.content.localbroadcastmanager; import android.text.html; import android.view.view; import android.widget.button; import android.widget.edittext; import android.widget.tablelayout; import android.widget.tablerow; import android.widget.textview; import android.widget.toast; import org.apache.http.namevaluepair; import org.apache.http.message.basicnamevaluepair; import org.json.jsonexception; import org.json.jsonobject; import java.util.arraylist; import java.util.list; public class chatactivity extends activity { sharedpreferences prefs; list<namevaluepair> params; edittext chat_msg; button send_btn; bundle bundle; tablelayout tab; @override protected void oncreate(bundle savedinstancestate) { super.oncreate(savedinstancestate); setcontentview(r.layout.activity_chat); tab = (tablelayout)findviewbyid(r.id.tab); prefs = getsharedpreferences("chat", 0); bundle = getintent().getbundleextra("info"); sharedpreferences.editor edit = prefs.edit(); edit.putstring("current_active", bundle.getstring("mobno")); edit.commit(); localbroadcastmanager.getinstance(this).registerreceiver(onnotice, new intentfilter("msg")); if(bundle.getstring("name") != null){ tablerow tr1 = new tablerow(getapplicationcontext()); tr1.setlayoutparams(new tablerow.layoutparams( tablerow.layoutparams.wrap_content, tablerow.layoutparams.wrap_content)); textview textview = new textview(getapplicationcontext()); textview.settextsize(20); textview.settextcolor(color.parsecolor("#0b0719")); textview.settext(html.fromhtml("<b>"+bundle.getstring("name")+" : </b>"+bundle.getstring("msg"))); tr1.addview(textview); tab.addview(tr1); } chat_msg = (edittext)findviewbyid(r.id.chat_msg); send_btn = (button)findviewbyid(r.id.sendbtn); send_btn.setonclicklistener(new view.onclicklistener() { @override public void onclick(view v) { tablerow tr2 = new tablerow(getapplicationcontext()); tr2.setlayoutparams(new tablerow.layoutparams( tablerow.layoutparams.wrap_content, tablerow.layoutparams.wrap_content)); textview textview = new textview(getapplicationcontext()); textview.settextsize(20); textview.settextcolor(color.parsecolor("#a901db")); textview.settext(html.fromhtml("<b>you : </b>" + chat_msg.gettext().tostring())); tr2.addview(textview); tab.addview(tr2); new send().execute(); } }); } private broadcastreceiver onnotice= new broadcastreceiver() { @override public void onreceive(context context, intent intent) { string str = intent.getstringextra("msg"); string str1 = intent.getstringextra("fromname"); string str2 = intent.getstringextra("fromu"); if(str2.equals(bundle.getstring("mobno"))){ tablerow tr1 = new tablerow(getapplicationcontext()); tr1.setlayoutparams(new tablerow.layoutparams( tablerow.layoutparams.wrap_content, tablerow.layoutparams.wrap_content)); textview textview = new textview(getapplicationcontext()); textview.settextsize(20); textview.settextcolor(color.parsecolor("#0b0719")); textview.settext(html.fromhtml("<b>"+str1+" : </b>"+str)); tr1.addview(textview); tab.addview(tr1); } } }; private class send extends asynctask<string, string, jsonobject> { @override protected jsonobject doinbackground(string... args) { jsonparser json = new jsonparser(); params = new arraylist<namevaluepair>(); params.add(new basicnamevaluepair("from", prefs.getstring("reg_from",""))); params.add(new basicnamevaluepair("fromn", prefs.getstring("from_name",""))); params.add(new basicnamevaluepair("to", bundle.getstring("mobno"))); params.add((new basicnamevaluepair("msg",chat_msg.gettext().tostring()))); jsonobject jobj = json.getjsonfromurl("http://10.0.2.2:8080/send",params); return jobj; } @override protected void onpostexecute(jsonobject json) { chat_msg.settext(""); string res = null; try { res = json.getstring("response"); if(res.equals("failure")){ toast.maketext(getapplicationcontext(),"the user has logged out. cant send message anymore !",toast.length_short).show(); } } catch (jsonexception e) { e.printstacktrace(); } } } } please can me?
this:
java.lang.nullpointerexception: attempt invoke virtual method 'int org.json.jsonarray.length()' on null object reference @ com.example.ibm_admin.chat.userfragment$load.onpostexecute(userfragment.java:84) means, in file userfragment.java @ line 84 in inner class load of class com.example.ibm_admin.chat.userfragment there method length called on object, null.
i suppose, line:
for(int = 0; < json.length(); i++){ in method parameter json equals null.
probably, in doinbackroung method, jobj.getjsonarray returns null.
it hard know happened, because jsonparser.getjsonarray suppresses exceptions , returns null, if any.
look @ next 2 lines of logcat:
07-01 22:50:39.367 30016-30032/com.example.ibm_admin.chat e/buffer error﹕ error converting result java.lang.nullpointerexception: lock == null 07-01 22:50:39.367 30016-30032/com.example.ibm_admin.chat e/json parser﹕ error parsing data org.json.jsonexception: end of input @ character 0 of that's means somewhere inside block in getjsonarray have null reference, comes topmost part of getjsonarray other exceptions suppressed, , is variable become null.
you have debug through code.
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