Android 在emulator和真实设备中启动新活动时，应用程序崩溃

当我开始一个新的活动，但应用程序崩溃以下错误

FATAL EXCEPTION: main
                                                                          Process: com.food.sheenishere.stark, PID: 9976
                                                                          java.lang.RuntimeException: Unable to start activity ComponentInfo{com.food.sheenishere.stark/com.food.sheenishere.stark.home}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
                                                                              at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2665)
                                                                              at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
                                                                              at android.app.ActivityThread.-wrap12(ActivityThread.java)
                                                                              at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
                                                                              at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                              at android.os.Looper.loop(Looper.java:154)
                                                                              at android.app.ActivityThread.main(ActivityThread.java:6119)
                                                                              at java.lang.reflect.Method.invoke(Native Method)
                                                                              at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
                                                                              at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
                                                                           Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
                                                                              at com.food.sheenishere.stark.home.onCreate(home.java:84)
                                                                              at android.app.Activity.performCreate(Activity.java:6679)
                                                                              at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
                                                                              at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2618)
                                                                              at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726) 
                                                                              at android.app.ActivityThread.-wrap12(ActivityThread.java) 
                                                                              at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477) 
                                                                              at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                              at android.os.Looper.loop(Looper.java:154) 
                                                                              at android.app.ActivityThread.main(ActivityThread.java:6119) 
                                                                              at java.lang.reflect.Method.invoke(Native Method)

home.java

下面的某个地方有错误。这是家庭活动守则的一部分。登录后，当我尝试打开此活动时，应用程序崩溃，错误如上所示。该应用程序之前工作正常，但突然在虚拟设备和真实设备上崩溃

public class home extends AppCompatActivity
        implements NavigationView.OnNavigationItemSelectedListener {

    FirebaseDatabase database;
    DatabaseReference category;
    TextView txtFullName;


    RecyclerView recycler_menu;
    RecyclerView.LayoutManager layoutManager;
    private ProgressDialog progressDialog;
    FirebaseRecyclerAdapter<Category,MenuViewHolder> adapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_home);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        toolbar.setTitle("Menu");
        setSupportActionBar(toolbar);
        progressDialog=new ProgressDialog(this);
        progressDialog.setMessage("Loading...");
        progressDialog.show();


        //init firebase
        database=FirebaseDatabase.getInstance();
        category=database.getReference("Category");




        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
               Intent cartIntent = new Intent(home.this, Cart.class);
                startActivity(cartIntent);
            }
        });

        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.setDrawerListener(toggle);
        toggle.syncState();

        NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
        navigationView.setNavigationItemSelectedListener(this);
        //set name for user
        View headerView = navigationView.getHeaderView(0);
        txtFullName = (TextView)findViewById(R.id.txtFullName);
        txtFullName.setText(Common.currentUser.getName());

公共类主页扩展了AppCompative活动
实现NavigationView.OnNavigationItemSelectedListener{
Firebase数据库；
数据库参考类别；
TextView txtFullName；
RecyclerView recycler_菜单；
RecyclerView.LayoutManager LayoutManager；
私有进程对话；
FirebaseRecyclerAdapter适配器；
@凌驾
创建时受保护的void（Bundle savedInstanceState）{
super.onCreate（savedInstanceState）；
setContentView（R.layout.activity_home）；
Toolbar Toolbar=（Toolbar）findViewById（R.id.Toolbar）；
工具栏。设置标题（“菜单”）；
设置支持操作栏（工具栏）；
progressDialog=新建progressDialog（此）；
progressDialog.setMessage（“加载…”）；
progressDialog.show（）；
//init firebase
database=FirebaseDatabase.getInstance（）；
category=database.getReference（“category”）；
FloatingActionButton fab=（FloatingActionButton）findViewById（R.id.fab）；
fab.setOnClickListener（新视图.OnClickListener（）{
@凌驾
公共void onClick（视图）{
Intent cartIntent=新Intent（home.this，Cart.class）；
星触觉（cartIntent）；
}
});
抽屉布局抽屉=（抽屉布局）findViewById（R.id.抽屉布局）；
ActionBarDrawerToggle切换=新建ActionBarDrawerToggle(
这，抽屉，工具栏，R.string.navigation\u drawer\u open，R.string.navigation\u drawer\u close）；
抽屉。设置抽屉定位器（开关）；
toggle.syncState（）；
NavigationView NavigationView=（NavigationView）findViewById（R.id.nav_视图）；
navigationView.setNavigationItemSelectedListener（此）；
//为用户设置名称
View headerView=navigationView.getHeaderView（0）；
txtFullName=（TextView）findViewById（R.id.txtFullName）；
txtFullName.setText（Common.currentUser.getName（））；

尝试以下代码

txtFullName = (TextView)findViewById(R.id.txtFullName); 

txtFullName = (TextView)headerView.findViewById(R.id.txtFullName);

不要使用下面的行

 txtFullName = (TextView)headerView.findViewById(R.id.txtFullName);
 txtFullName.setText(Common.currentUser.getName());

试试下面的代码

txtFullName = (TextView)findViewById(R.id.txtFullName); 

txtFullName = (TextView)headerView.findViewById(R.id.txtFullName);

---

发布您的活动\ u home.xml请发布您的xml文件，我猜在布局R.layout.activity\ u home中找不到R.id.txtFullName，而是在从中提取headerView的单独xml中。因此它应该是'headerView.findViewById（R.id.textFullName）；@Devsil它起作用了，谢谢