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我正在尝试编辑文本以显示用户的电子邮件并向菜单项添加注销功能。我使用了默认的导航抽屉：在此处输入图像描述 但是在尝试这两个时我总是得到

原因：java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法 'void android.widget.TextView.setText(java.lang.CharSequence)'

MainActivity.class

public class Options extends AppCompatActivity {

    private AppBarConfiguration mAppBarConfiguration;
    private Toast backToast;
    private long backPressedTime;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_options);
        String email2 = LoggedIn.getEmail(this);
        Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        FloatingActionButton fab = findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });

        DrawerLayout drawer = findViewById(R.id.drawer_layout);
        NavigationView navigationView = findViewById(R.id.nav_view);
        // Passing each menu ID as a set of Ids because each
        // menu should be considered as top level destinations.
        mAppBarConfiguration = new AppBarConfiguration.Builder(
                R.id.nav_home, R.id.nav_gallery,
                R.id.nav_tools)
                .setDrawerLayout(drawer)
                .build();
        NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment);
        NavigationUI.setupActionBarWithNavController(this, navController, mAppBarConfiguration);
        NavigationUI.setupWithNavController(navigationView, navController);

/////////////////////////HERE WHERE I EDIT THE TEXTVIEW

        TextView txt_email = (TextView) findViewById(R.id.novoemailshow);
        txt_email.setText(email2);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.options, menu);
        return true;
    }

    @Override
    public boolean onSupportNavigateUp() {
        NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment);
        return NavigationUI.navigateUp(navController, mAppBarConfiguration)
                || super.onSupportNavigateUp();
    }

/////////////////////////////THE LOGOUT FUNCTION
    public void logout(View v) {
        LoggedIn.savePassword(null, this);
        LoggedIn.saveEmail(null, this);
        Intent intent = new Intent(this, MainActivity.class);
        startActivity(intent);
        finishAffinity();
    }
}

nav_header_options.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="@dimen/nav_header_height"
    android:background="@drawable/side_nav_bar"
    android:gravity="bottom"
    android:orientation="vertical"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:theme="@style/ThemeOverlay.AppCompat.Dark">


    <ImageView
        android:id="@+id/imageView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:contentDescription="@string/nav_header_desc"
        android:paddingTop="@dimen/nav_header_vertical_spacing"
        app:srcCompat="@mipmap/ic_launcher_round" />

    <TextView
        android:id="@+id/novoemailshow"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="" />


</LinearLayout>

选项.xml

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">
    <item
        android:id="@+id/action_settings"
        android:onClick="logout"
        android:orderInCategory="100"
        android:title="Logout"
        app:showAsAction="never" />
</menu>

如果创建 MainActivity.class 来处理所有它，那么我不明白它创建的 UI 视图和片段，我应该在哪里更新？为什么它们是空的？

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0 回答 0