Question

在我的简单应用程序中，我在NavigationView上有一个textView，我有这个异常：java.lang.NullPointerException：尝试在空对象引用上调用虚方法'void android.widget.TextView.setVisibility（int）'。我不明白，因为它告诉我在null对象上调用方法。代码：

 public class MainActivity extends AppCompatActivity
        implements NavigationView.OnNavigationItemSelectedListener, ReadRssListener {

    RecyclerView recyclerView;
    private PrefUtil prefUtil;
    private ImageView profileImgView;
    private TextView info;
    AccessTokenTracker accessTokenTracker;

    LoginButton loginButton;
    SwipeRefreshLayout refreshLayout;
    private CallbackManager callbackManager;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
        navigationView.setNavigationItemSelectedListener(this);
        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();
        FacebookSdk.sdkInitialize(getApplicationContext());
        AppEventsLogger.activateApp(this);
        callbackManager = CallbackManager.Factory.create();
        prefUtil = new PrefUtil(this);
        profileImgView = (ImageView) findViewById(R.id.thumb_img);

        info = (TextView) findViewById(R.id.name);
        if(PrefUtils.getCurrentUser(MainActivity.this)==null)
        {
            info.setVisibility(View.INVISIBLE);
            profileImgView.setBackgroundResource(R.drawable.wallpaper_for_facebook_profile_photo);

        }
        else
        {
            Log.e("sono loggato", "si");
            info.setVisibility(View.VISIBLE);
            profileImgView.setVisibility(View.VISIBLE);
            User user= PrefUtils.getCurrentUser(MainActivity.this);
            Log.e("urlImage", user.profileName);
            Glide.with(MainActivity.this)
                    .load(user.imageUrl)
                    .into(profileImgView);
            if (Profile.getCurrentProfile() != null) {
                info.setText(Profile.getCurrentProfile().getName());}
        }

mainactivity.xml

    <?xml version="1.0" encoding="utf-8"?>
<android.support.v4.widget.DrawerLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/drawer_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:openDrawer="start">

    <include
        layout="@layout/app_bar_main"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

    <android.support.design.widget.NavigationView
        android:id="@+id/nav_view"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_gravity="start"
        android:fitsSystemWindows="true"
        app:headerLayout="@layout/nav_header_main"
        app:menu="@menu/activity_main_drawer" />

</android.support.v4.widget.DrawerLayout>

nav_header_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    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:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:theme="@style/ThemeOverlay.AppCompat.Dark">

    <ImageView
        android:id="@+id/thumb_img"
        android:layout_width="70dp"
        android:layout_height="70dp"
        android:src="@drawable/wallpaper_for_facebook_profile_photo"/>
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:id="@+id/name"
        android:textAppearance="@style/TextAppearance.AppCompat.Body1" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Sports News"
        android:textAppearance="@style/TextAppearance.AppCompat.Body1" />


    <TextView
        android:id="@+id/date_text"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
         />

</LinearLayout>

Answer 1

我认为您可能需要从TextView找到NavigationView。

所以尝试改变

info = (TextView) findViewById(R.id.name);

到

info = (TextView) navigationView.findViewById(R.id.name);

Answer 2

根本原因是您在name引用的xml中没有标识为R.layout.activity_main的TexView，因此此查找失败：

    info = (TextView) findViewById(R.id.name);

文本视图上的android null指针异常

2 个答案: