大佬教程收集整理的这篇文章主要介绍了尝试在空对象引用上调用虚方法’void android.support.v7.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)’,大佬教程大佬觉得挺不错的,现在分享给大家,也给大家做个参考。
FATAL EXCEPTION: main Process: com.technerdshub.vusocial,PID: 20633 java.lang.RuntimeException: Unable to start activity ComponenTinfo{Com.technerdshub.vusocial/com.technerdshub.vusocial.Activities.studentDashboardActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.app.ActionBar.setDisplayHomeAsUpEnabled(Boolean)' on a null object reference at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2693) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2758) at android.app.ActivityThread.access$900(ActivityThread.java:177) at android.app.ActivityThread$H.handlemessage(ActivityThread.java:1448) at android.os.Handler.dispatchmessage(Handler.java:102) at android.os.Looper.loop(Looper.java:145) at android.app.ActivityThread.main(ActivityThread.java:5942) at java.lang.reflect.Method.invoke(Native Method) at java.lang.reflect.Method.invoke(Method.java:372) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1389) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1184) Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.app.ActionBar.setDisplayHomeAsUpEnabled(Boolean)' on a null object reference at com.technerdshub.vusocial.Activities.studentDashboardActivity.onCreate(studentDashboardActivity.java:50)
我的java文件是:
package com.technerdshub.vusocial.Activities; import android.app.Activity; import android.content.Intent; import android.net.Uri; import android.os.bundle; import android.support.design.widget.TabLayout; import android.support.v4.app.FragmentManager; import android.support.v4.app.FragmentPagerAdapter; import android.support.v4.view.ViewPager; import android.support.v7.app.ActionBarActivity; import android.support.v7.widget.Toolbar; import android.support.v7.app.AppCompatActivity; import com.google.android.gms.appindexing.Action; import com.google.android.gms.appindexing.AppIndex; import com.google.android.gms.common.api.GoogleApiClient; import com.technerdshub.vusocial.Fragments.TaskFragment; import com.technerdshub.vusocial.Fragments.dummy.DummyContent; import com.technerdshub.vusocial.R; import java.util.ArrayList; import java.util.List; public class studentDashboardActivity extends AppCompatActivity { //private Toolbar toolbar; private TabLayout tabLayout; private ViewPager viewPager; /** * ATTENTION: This was auto-generated to implement the App Indexing API. * See https://g.co/AppIndexing/Androidstudio for more information. */ private GoogleApiClient client; @Override protected void onCreate(Bundle savedInstanceStatE) { displayLoginActivity(); super.onCreate(savedInstanceStatE); setContentView(R.layout.activity_student_dashboard); // Parse.initialize(new Parse.Configuration.builder(this) // .applicationId("J5CIV2z6xeSCXDqdOfhE0kPSikvRFPyDyOJxqJNx") // .clientKey("bEWm4nWtWiBrMczGfOvA7s4Ulr2bAU3W3TtVSLDf") // .build() // ); getSupportActionBar().setDisplayHomeAsUpEnabled(true); getSupportActionBar().setElevation(2); viewPager = (ViewPager) findViewById(R.id.viewpager); setupViewPager(viewPager); tabLayout = (TabLayout) findViewById(R.id.tabs); tabLayout.setupWithViewPager(viewPager); // ParSEObject testObject = new ParSEObject("Task"); // testObject.put("marks",99); // testObject.saveInBACkground(); // ATTENTION: This was auto-generated to implement the App Indexing API. // See https://g.co/AppIndexing/Androidstudio for more information. client = new GoogleApiClient.builder(this).addApi(AppIndex.API).build(); } private void setupViewPager(ViewPager viewPager) { ViewPagerAdapter adapter = new ViewPagerAdapter(getSupportFragmentManager()); adapter.addFragment(new TaskFragment(),"Quiz"); adapter.addFragment(new TaskFragment(),"Assignment"); adapter.addFragment(new TaskFragment(),"GDP"); viewPager.setAdapter(adapter); } private void displayLoginActivity() { Intent i = new Intent(this,Login.class); startActivity(i); } @Override public void onStart() { super.onStart(); // ATTENTION: This was auto-generated to implement the App Indexing API. // See https://g.co/AppIndexing/Androidstudio for more information. client.connect(); Action viewAction = Action.newAction( Action.TYPE_VIEW,// TODO: choose an action type. "studentDashboard Page",// TODO: Define a title for the content shown. // TODO: If you have web page content that matches this app activity's content,// make sure this auto-generated web page URL is correct. // Otherwise,set the URL to null. Uri.parse("http://host/path"),// TODO: Make sure this auto-generated app URL is correct. Uri.parse("android-app://com.technerdshub.vusocial.Activities/http/host/path") ); AppIndex.AppIndexApi.start(client,viewAction); } @Override public void onStop() { super.onStop(); // ATTENTION: This was auto-generated to implement the App Indexing API. // See https://g.co/AppIndexing/Androidstudio for more information. Action viewAction = Action.newAction( Action.TYPE_VIEW,// TODO: Make sure this auto-generated app URL is correct. Uri.parse("android-app://com.technerdshub.vusocial.Activities/http/host/path") ); AppIndex.AppIndexApi.end(client,viewAction); client.disconnect(); } class ViewPagerAdapter extends FragmentPagerAdapter { private final List<TaskFragment> mFragmentList = new ArrayList<>(); private final List<String> mFragmenttitleList = new ArrayList<>(); public ViewPagerAdapter(FragmentManager manager) { super(manager); } @Override public TaskFragment getItem(int position) { return mFragmentList.get(position); } @Override public int getCount() { return mFragmentList.size(); } public void addFragment(TaskFragment fragment,String titlE) { mFragmentList.add(fragment); mFragmenttitleList.add(titlE); } @Override public CharSequence getPagetitle(int position) { return mFragmenttitleList.get(position); } } }
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