android - build java method to change two textViews -
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i have 2 buttons , 2 textviews , when click "add2_a" ,then "score1" updated , increment 2 .
the same "add2_b" increment "score2"
i want use 1 method both of them ..the problem app crash !
this java code :
import android.support.v7.app.appcompatactivity; import android.os.bundle; import android.view.view; import android.widget.textview; public class app2 extends appcompatactivity implements view.onclicklistener { public int number =0; public int id; textview txt1= (textview) findviewbyid(r.id.score1); textview txt2 = (textview) findviewbyid(r.id.score2); @override public void oncreate(bundle savedinstancestate) { super.oncreate(savedinstancestate); setcontentview(r.layout.activity_app2); } @override public void onclick(view v){ id=v.getid(); } public void increment2(){ number =number +2; if(id ==r.id.add2_a) txt1.settext(number); if(id== r.id.add2_b) txt2.settext(string.valueof(number)); }} edit : xml code calling "increment2" method :
<button android:layout_width="match_parent" android:layout_height="wrap_content" android:text="@string/points2" android:layout_margin="8dp" android:id="@+id/add2_a" android:onclick="increment2"/> edit : solved , works ..this code after editing :
public class app2 extends appcompatactivity { public int number =0; public int id; public textview txt1; public textview txt2; @override public void oncreate(bundle savedinstancestate) { super.oncreate(savedinstancestate); setcontentview(r.layout.activity_app2); txt1= (textview) findviewbyid(r.id.score1); txt2 = (textview) findviewbyid(r.id.score2); } public void increment2(view v) { number = number + 2; id = v.getid(); if (id == r.id.add2_a) { txt1 = (textview) findviewbyid(r.id.score1); txt1.settext(string.valueof(number)); } if (id == r.id.add2_b) { txt2 = (textview) findviewbyid(r.id.score2); txt2.settext(string.valueof(number)); } } edit : appears in logcat , there's no other messages in message bar :
process: com.example.mayouza.myapplication2, pid: 2553 java.lang.runtimeexception: unable instantiate activity componentinfo{com.example.mayouza.myapplication2/com.example.mayouza.myapplication2.app2}: java.lang.nullpointerexception: attempt invoke virtual method 'android.view.window$callback android.view.window.getcallback()' on null object reference @ android.app.activitythread.performlaunchactivity(activitythread.java:2567) @ android.app.activitythread.handlelaunchactivity(activitythread.java:2726) @ android.app.activitythread.-wrap12(activitythread.java) @ android.app.activitythread$h.handlemessage(activitythread.java:1477) @ android.os.handler.dispatchmessage(handler.java:102) @ android.os.looper.loop(looper.java:154) @ android.app.activitythread.main(activitythread.java:6119) @ java.lang.reflect.method.invoke(native method) @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:886) @ com.android.internal.os.zygoteinit.main(zygoteinit.java:776) caused by: java.lang.nullpointerexception: attempt invoke virtual method 'android.view.window$callback android.view.window.getcallback()' on null object reference @ android.support.v7.app.appcompatdelegateimplbase.<init>(appcompatdelegateimplbase.java:120) @ android.support.v7.app.appcompatdelegateimplv9.<init>(appcompatdelegateimplv9.java:151) @ android.support.v7.app.appcompatdelegateimplv11.<init>(appcompatdelegateimplv11.java:31) @ android.support.v7.app.appcompatdelegateimplv14.<init>(appcompatdelegateimplv14.java:55) @ android.support.v7.app.appcompatdelegateimplv23.<init>(appcompatdelegateimplv23.java:33) @ android.support.v7.app.appcompatdelegateimpln.<init>(appcompatdelegateimpln.java:33) @ android.support.v7.app.appcompatdelegate.create(appcompatdelegate.java:201) @ android.support.v7.app.appcompatdelegate.create(appcompatdelegate.java:185) @ android.support.v7.app.appcompatactivity.getdelegate(appcompatactivity.java:519) @ android.support.v7.app.appcompatactivity.findviewbyid(appcompatactivity.java:190) @ com.example.mayouza.myapplication2.app2.<init>(app2.java:11) @ java.lang.class.newinstance(native method) @ android.app.instrumentation.newactivity(instrumentation.java:1078) @ android.app.activitythread.performlaunchactivity(activitythread.java:2557) @ android.app.activitythread.handlelaunchactivity(activitythread.java:2726) @ android.app.activitythread.-wrap12(activitythread.java) @ android.app.activitythread$h.handlemessage(activitythread.java:1477) @ android.os.handler.dispatchmessage(handler.java:102) @ android.os.looper.loop(looper.java:154) @ android.app.activitythread.main(activitythread.java:6119) @ java.lang.reflect.method.invoke(native method) @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:886) @ com.android.internal.os.zygoteinit.main(zygoteinit.java:776)
you not able call findviewbyid() before call setcontentview() because view hiearchy has not built yet.
you need move call findviewbyid() after call setcontentview().
setcontentview(r.layout.activity_app2); txt1= (textview) findviewbyid(r.id.score1); txt2 = (textview) findviewbyid(r.id.score2); wiki
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