android - Get NullPointerException from method call, but arguments are not null -

my apologies in advance length of post, inclusion of 2 logcat outputs necessary explain problem.

i getting nullpointerexception when call 1 of interface methods of listener custom viewgroup. exception occurs @ line 264 in code below.

260    valuetab valuetab = mtabhost.getcurrentlyselectedvaluetab(); 261    if (this != null && valuetab != null) { 262        log.i("tabbedslider", this.tostring()); 263        log.i("valuetab", valuetab.tostring()); 264        montabbedsliderchangelistener.onslidervaluechanged(this, valuetab); 265    } 

i have put method call inside if statement ensure neither of arguments null. have included couple of log statements clarify state of arguments when call made.

• this ... instance of custom viewgroup called tabbedslider
• valuetab ... instance of custom child view of tabbedslider of type called valuetab displays title , float value.

the sequence below explains when method call occurs:

• an instance of tabbedslider instantiated.
• its various properties set up.
• it added mainactivity.
• an instance of valuetab instantiated.
• its various properties set including assigning value.
• it added instance of tabbedslider.
• the offending method call made.

i have set break point on problem method call , run debug. when inspect this , valuetab, setup expect.

since method call made after adding valuetab tabbedslider, have not yet been measured, laid out , drawn screen (hence 0 values bounds when log tostring()), these objects not null.

this logcat output:

10-07 10:28:17.952: d/dalvikvm(13357): gc_for_alloc freed 341k, 6% free 7644k/8048k, paused 36ms, total 37ms 10-07 10:28:17.972: i/tabbedslider(13357): com.soundconception.tabbedslider.tabbedslider{42075068 v.e..... ......i. 0,0-0,0 #7f040002 app:id/testslidera} 10-07 10:28:17.972: i/valuetab(13357): com.soundconception.tabbedslider.valuetab{420d8908 vfed..c. ..s...i. 0,0-0,0} 10-07 10:28:17.972: d/androidruntime(13357): shutting down vm 10-07 10:28:17.972: w/dalvikvm(13357): threadid=1: thread exiting uncaught exception (group=0x41911700) 10-07 10:28:17.972: e/androidruntime(13357): fatal exception: main 10-07 10:28:17.972: e/androidruntime(13357): java.lang.runtimeexception: unable start activity componentinfo{com.soundconception.tabbedslider/com.soundconception.tabbedslider.mainactivity}: java.lang.nullpointerexception 10-07 10:28:17.972: e/androidruntime(13357):    @ android.app.activitythread.performlaunchactivity(activitythread.java:2211) 10-07 10:28:17.972: e/androidruntime(13357):    @ android.app.activitythread.handlelaunchactivity(activitythread.java:2261) 10-07 10:28:17.972: e/androidruntime(13357):    @ android.app.activitythread.access$600(activitythread.java:141) 10-07 10:28:17.972: e/androidruntime(13357):    @ android.app.activitythread$h.handlemessage(activitythread.java:1256) 10-07 10:28:17.972: e/androidruntime(13357):    @ android.os.handler.dispatchmessage(handler.java:99) 10-07 10:28:17.972: e/androidruntime(13357):    @ android.os.looper.loop(looper.java:137) 10-07 10:28:17.972: e/androidruntime(13357):    @ android.app.activitythread.main(activitythread.java:5103) 10-07 10:28:17.972: e/androidruntime(13357):    @ java.lang.reflect.method.invokenative(native method) 10-07 10:28:17.972: e/androidruntime(13357):    @ java.lang.reflect.method.invoke(method.java:525) 10-07 10:28:17.972: e/androidruntime(13357):    @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:737) 10-07 10:28:17.972: e/androidruntime(13357):    @ com.android.internal.os.zygoteinit.main(zygoteinit.java:553) 10-07 10:28:17.972: e/androidruntime(13357):    @ dalvik.system.nativestart.main(native method) 10-07 10:28:17.972: e/androidruntime(13357): caused by: java.lang.nullpointerexception 10-07 10:28:17.972: e/androidruntime(13357):    @ com.soundconception.tabbedslider.tabbedslider.configuresliderforvaluetab(tabbedslider.java:264) 10-07 10:28:17.972: e/androidruntime(13357):    @ com.soundconception.tabbedslider.tabbedslider.access$1(tabbedslider.java:256) 10-07 10:28:17.972: e/androidruntime(13357):    @ com.soundconception.tabbedslider.tabbedslider$2.onvaluetabselectionchange(tabbedslider.java:164) 10-07 10:28:17.972: e/androidruntime(13357):    @ com.soundconception.tabbedslider.tabhost.selectvaluetab(tabhost.java:88) 10-07 10:28:17.972: e/androidruntime(13357):    @ com.soundconception.tabbedslider.tabhost.valuetabsetup(tabhost.java:72) 10-07 10:28:17.972: e/androidruntime(13357):    @ com.soundconception.tabbedslider.tabhost.addvaluetab(tabhost.java:51) 10-07 10:28:17.972: e/androidruntime(13357):    @ com.soundconception.tabbedslider.tabbedslider.addvaluetab(tabbedslider.java:249) 10-07 10:28:17.972: e/androidruntime(13357):    @ com.soundconception.tabbedslider.mainactivity.oncreate(mainactivity.java:18) 10-07 10:28:17.972: e/androidruntime(13357):    @ android.app.activity.performcreate(activity.java:5133) 10-07 10:28:17.972: e/androidruntime(13357):    @ android.app.instrumentation.callactivityoncreate(instrumentation.java:1087) 10-07 10:28:17.972: e/androidruntime(13357):    @ android.app.activitythread.performlaunchactivity(activitythread.java:2175) 10-07 10:28:17.972: e/androidruntime(13357):    ... 11 more 

i can work around issue putting method call in try/catch block shown below:

    valuetab valuetab = mtabhost.getcurrentlyselectedvaluetab();     if (this != null && valuetab != null) {         log.i("tabbedslider", this.tostring());         log.i("valuetab", valuetab.tostring());         try {             montabbedsliderchangelistener.onslidervaluechanged(this, valuetab);         } catch (nullpointerexception e) {             log.i("tabbedslider", "caught nullpointerexception");         }                } 

when run this, nullpointerexception caught first time method called each of 3 tabbedslider instances, subsequent calls after first call work fine without raising exception, can seen in following new logcat output.

10-07 11:36:53.822: d/dalvikvm(14479): gc_for_alloc freed 347k, 6% free 7643k/8052k, paused 36ms, total 38ms 10-07 11:36:53.852: i/tabbedslider(14479): com.soundconception.tabbedslider.tabbedslider{42076c68 v.e..... ......i. 0,0-0,0 #7f040002 app:id/testslidera} 10-07 11:36:53.852: i/valuetab(14479): com.soundconception.tabbedslider.valuetab{420da508 vfed..c. ..s...i. 0,0-0,0} 10-07 11:36:53.852: i/tabbedslider(14479): caught nullpointerexception 10-07 11:36:53.862: i/tabbedslider(14479): com.soundconception.tabbedslider.tabbedslider{420b7768 v.e..... ......i. 0,0-0,0 #7f040003 app:id/testsliderb} 10-07 11:36:53.862: i/valuetab(14479): com.soundconception.tabbedslider.valuetab{4206e0c0 vfed..c. ..s...i. 0,0-0,0} 10-07 11:36:53.862: i/tabbedslider(14479): caught nullpointerexception 10-07 11:36:53.882: i/tabbedslider(14479): com.soundconception.tabbedslider.tabbedslider{420c8378 v.e..... ......i. 0,0-0,0 #7f040004 app:id/testsliderc} 10-07 11:36:53.882: i/valuetab(14479): com.soundconception.tabbedslider.valuetab{42077768 vfed..c. ..s...i. 0,0-0,0} 10-07 11:36:53.882: i/tabbedslider(14479): caught nullpointerexception 10-07 11:36:53.902: d/hardwarerenderer(14479): profiling hardware renderer 10-07 11:36:53.952: d/libegl(14479): loaded /system/lib/egl/libegl_tegra.so 10-07 11:36:53.972: d/libegl(14479): loaded /system/lib/egl/libglesv1_cm_tegra.so 10-07 11:36:53.982: d/libegl(14479): loaded /system/lib/egl/libglesv2_tegra.so 10-07 11:36:54.022: d/openglrenderer(14479): enabling debug mode 0 10-07 11:37:15.252: i/tabbedslider(14479): com.soundconception.tabbedslider.tabbedslider{420b7768 v.e..... ......id 21,127-779,233 #7f040003 app:id/testsliderb} 10-07 11:37:15.262: i/valuetab(14479): com.soundconception.tabbedslider.valuetab{420581e8 vfed..c. ..sp..id 93,0-186,54} 10-07 11:37:29.292: i/tabbedslider(14479): com.soundconception.tabbedslider.tabbedslider{420c8378 v.e..... ......id 21,233-779,339 #7f040004 app:id/testsliderc} 10-07 11:37:29.292: i/valuetab(14479): com.soundconception.tabbedslider.valuetab{42074f48 vfed..c. ..sp..id 186,0-279,54} 10-07 11:37:32.572: i/tabbedslider(14479): com.soundconception.tabbedslider.tabbedslider{42076c68 v.e..... ......id 21,21-779,127 #7f040002 app:id/testslidera} 10-07 11:37:32.572: i/valuetab(14479): com.soundconception.tabbedslider.valuetab{4209bcc8 vfed..c. ..sp..id 188,0-282,54} 

it appear boils down views not being drawn yet @ time of first call, not understand why. view objects @ instant not null, why nullpointerexception raised? there hole in understanding.

while can work around problem try/catch block, not understanding why exception occurs in first place going drive me crazy. explanations appreciated, , code monkey keep sanity.