java - Android app crashing when i hit a button -

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• what nullpointerexception, , how fix it? 12 answers

hey guys when hit particular button supposed take me layout. everytime hit it, entire app crashes. here oncreate method page im trying to:

protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         setcontentview(r.layout.activity_bench_data_entry);         //opens database         opendb();         //initializes , declares sensors, , accelerometer         minitialized = false;         msensormanager = (sensormanager) getsystemservice(context.sensor_service);         maccelerometer = msensormanager.getdefaultsensor(sensor.type_accelerometer);         msensormanager.registerlistener(this, maccelerometer, sensormanager.sensor_delay_normal);       //  tv.settext("aasfdaf");    } 

here onclick button pressing:

 public void onclick_bench(view v){         //intent create new activity         intent intent = new intent(mainmenuactivity.this, benchdataentry.class);         //goes data entry screen         startactivity(intent);     } 

and here error log getting when press button:

08-08 17:30:30.785  31113-31113/com.example.jacob.repcapture e/androidruntime﹕ fatal exception: main     process: com.example.jacob.repcapture, pid: 31113     java.lang.runtimeexception: unable instantiate activity componentinfo{com.example.jacob.repcapture/com.example.jacob.repcapture.benchdataentry}: java.lang.nullpointerexception: attempt invoke virtual method 'android.view.view android.view.window.findviewbyid(int)' on null object reference             @ android.app.activitythread.performlaunchactivity(activitythread.java:2327)             @ android.app.activitythread.handlelaunchactivity(activitythread.java:2476)             @ android.app.activitythread.-wrap11(activitythread.java)             @ android.app.activitythread$h.handlemessage(activitythread.java:1344)             @ android.os.handler.dispatchmessage(handler.java:102)             @ android.os.looper.loop(looper.java:148)             @ android.app.activitythread.main(activitythread.java:5422)             @ java.lang.reflect.method.invoke(native method)             @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:726)             @ com.android.internal.os.zygoteinit.main(zygoteinit.java:616)      caused by: java.lang.nullpointerexception: attempt invoke virtual method 'android.view.view android.view.window.findviewbyid(int)' on null object reference             @ android.app.activity.findviewbyid(activity.java:2096)             @ com.example.jacob.repcapture.benchdataentry.<init>(benchdataentry.java:49)             @ java.lang.class.newinstance(native method)             @ android.app.instrumentation.newactivity(instrumentation.java:1067)             @ android.app.activitythread.performlaunchactivity(activitythread.java:2317)             at android.app.activitythread.handlelaunchactivity(activitythread.java:2476)             at android.app.activitythread.-wrap11(activitythread.java)             at android.app.activitythread$h.handlemessage(activitythread.java:1344)             at android.os.handler.dispatchmessage(handler.java:102)             at android.os.looper.loop(looper.java:148)             at android.app.activitythread.main(activitythread.java:5422)             at java.lang.reflect.method.invoke(native method)             at com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:726)             at com.android.internal.os.zygoteinit.main(zygoteinit.java:616) 

i think error not in these code blocks logcat android.view.view android.view.window.findviewbyid(int)' on null object reference

first - clean project under build-menu, , restart emulator. after exception went away in situation. second - check findviewbyid items need initialize them in the oncreate too.