Question

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：但是在尝试这两个方法时，我总会得到

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>

options.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来处理所有内容，则无法理解，那么创建的UI视图和片段应该在哪里更新？为什么它们为空？

默认导航抽屉活动的问题

0 个答案: