android - How to interpret Debugging information? -

this 2 questions. first relates program, , second more general question regarding debugging.

in code, have 2 button listeners. when first clicked, onclicklistener creates locationlistener, locationmanager requests updates locationlistener. (see below...)

locationmanager locationmanager = (locationmanager)  getsystemservice(context.location_service); locationmanager.requestlocationupdates(locationmanager.gps_provider, 0, 0, locationlistener); 

on click of second button, try unregister listener follows...

locationmanager.removeupdates(locationlistener);

however, end force close , following info in debugger...

error/androidruntime(310): fatal exception: main error/androidruntime(310): java.lang.nullpointerexception error/androidruntime(310):     @ com.ryan.gcal.gruncal$2.onclick(gruncal.java:94) error/androidruntime(310):     @ android.view.view.performclick(view.java:2408) error/androidruntime(310):     @ android.view.view$performclick.run(view.java:8816) error/androidruntime(310):     @ android.os.handler.handlecallback(handler.java:587) error/androidruntime(310):     @ android.os.handler.dispatchmessage(handler.java:92) error/androidruntime(310):     @ android.os.looper.loop(looper.java:123) error/androidruntime(310):     @ android.app.activitythread.main(activitythread.java:4627) error/androidruntime(310):     @ java.lang.reflect.method.invokenative(native method) error/androidruntime(310):     @ java.lang.reflect.method.invoke(method.java:521) error/androidruntime(310):     @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:868) error/androidruntime(310):     @ com.android.internal.os.zygoteinit.main(zygoteinit.java:626) error/androidruntime(310):     @ dalvik.system.nativestart.main(native method) 

line 94 of code, error originates, tried remove location listener. assume not removing location listener properly, not sure wrong. locationmanager declared @ start of code...

locationmanager locationmanager; 

my first question is, doing wrong in removing listener? , secondly, can provide tips/advice on learning interpret debug errors meaningfully? thanks.

you need either:

a) define locationmanager instance class variable, or retrieve again in onclick.

locationmanager locationmanager;  public void onclick1() {     locationmanager = (locationmanager)  getsystemservice(context.location_service);             locationmanager.requestlocationupdates(locationmanager.gps_provider, 0, 0, locationlistener);  }  public void onclick2() {     locationmanager.removeupdates(locationlistener); } 

you need make sure in onclick1() instead of

locationmanager locationmanager = (locationmanager)  getsystemservice(context.location_service); 

you put

locationmanager = (locationmanager)  getsystemservice(context.location_service); 

specifying locationmanager locationmanager makes scope of declaration enclosed method assign in, rather in scope of class. means in 2nd click locationmanager infact null.