Question

我有一个带有导航抽屉的活动，当我运行代码时，出现以下错误...

“试图在空对象引用上调用虚拟方法'void android.support.v7.app.ActionBar.setDisplayHomeAsUpEnabled（boolean）'”

但是此错误以前没有出现，所以我不知道这是我尝试运行的代码还是版本的问题

有人有什么建议吗？

这是我的MainActivity：

import android.Manifest;
import android.annotation.SuppressLint;
import android.annotation.TargetApi;
import android.content.Intent;
import android.graphics.Bitmap;
import android.graphics.Color;
import android.net.Uri;
import android.os.Build;
import android.os.Bundle;
import android.provider.MediaStore;
import android.support.annotation.NonNull;
import android.support.annotation.RequiresApi;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.NavigationView;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.TextView;
import android.widget.Toast;
import com.bumptech.glide.Glide;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.ValueEventListener;
import java.io.ByteArrayOutputStream;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import br.com.tecmafandroid.projeto.tecmaf.Adapter.FeedAdapter;
import br.com.tecmafandroid.projeto.tecmaf.R;
import br.com.tecmafandroid.projeto.tecmaf.config.ConfiguracaoFirebase;
import br.com.tecmafandroid.projeto.tecmaf.helper.Base64Custom;
import br.com.tecmafandroid.projeto.tecmaf.helper.Permissao;
import br.com.tecmafandroid.projeto.tecmaf.helper.Preferencias;
import br.com.tecmafandroid.projeto.tecmaf.helper.UsuarioFirebase;
import br.com.tecmafandroid.projeto.tecmaf.model.Contato;
import br.com.tecmafandroid.projeto.tecmaf.model.Feed;
import br.com.tecmafandroid.projeto.tecmaf.model.Usuario;
import de.hdodenhof.circleimageview.CircleImageView;

public class MainActivity extends AppCompatActivity implements NavigationView.OnNavigationItemSelectedListener {

    private FirebaseAuth usuarioAutenticacao;
    private Toolbar toolbar;
    private String identificadorContato;
    private DatabaseReference firebase;
    private String idUsuarioLogado;
    private DrawerLayout drawerLayout;
    private ActionBarDrawerToggle actionBarDrawerToggle;
    private FloatingActionButton floatingActionButton;
    private RecyclerView recyclerFeed;
    private FeedAdapter feedAdapter;
    private List<Feed> listaFeed = new ArrayList<>();
    private ValueEventListener valueEventListenerFeed;
    private DatabaseReference feedRef;
    private FirebaseUser firebaseUser;
    private LinearLayout linearMessages;
    private LinearLayout linearItensSalvos;
    private CircleImageView circleFacebook, circleInstagram, circleLinkedin, circleTwitter;
    private static final int SELECAO_CAMERA = 100;
    private static final int SELECAO_GALERIA = 200;
    private String[] permissoesNecessarias = new String[]{

            Manifest.permission.READ_EXTERNAL_STORAGE,
            Manifest.permission.CAMERA

    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        toolbar = (Toolbar) findViewById(R.id.toolbar);
            toolbar.setTitle("Tecmaf");

        drawerLayout = (DrawerLayout) findViewById(R.id.drawerLayout);
        actionBarDrawerToggle = new ActionBarDrawerToggle(this, drawerLayout, R.string.open_drawer, R.string.close_drawer);
        drawerLayout.addDrawerListener(actionBarDrawerToggle);
        actionBarDrawerToggle.syncState();
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
        NavigationView navigationView = (NavigationView) findViewById(R.id.navView);
        navigationView.setNavigationItemSelectedListener(this);

        navigationView.removeHeaderView(navigationView.getHeaderView(0));
        navigationView.removeHeaderView(null);

        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(this, drawerLayout, toolbar, R.string.open_drawer, R.string.close_drawer);
        drawerLayout.addDrawerListener(toggle);

        toggle.syncState();

        final View headerLayout = navigationView.inflateHeaderView(R.layout.nav_header);
        final ImageView navHeaderImageView = (ImageView) headerLayout.findViewById(R.id.nav_header_imageView);
        final TextView navHeaderUsuario = (TextView) headerLayout.findViewById(R.id.nav_header_usuario);
        final TextView navHeaderEmail = (TextView) headerLayout.findViewById(R.id.nav_header_email);

        Uri url = firebaseUser.getPhotoUrl();
        if (url != null) {
            Glide.with(MainActivity.this)
                    .load(url)
                    .into(navHeaderImageView);
        } else {
            navHeaderImageView.setImageResource(R.drawable.avatar);
        }
        navHeaderUsuario.setText("Olá, " + firebaseUser.getDisplayName() + "!");
        navHeaderEmail.setText(firebaseUser.getEmail());

    }

    @Override
    public boolean onOptionsItemSelected(MenuItem menuItem) {
        if (menuItem.getItemId() == R.id.item_pesquisar) {

            Intent intent = new Intent(MainActivity.this, PesquisarActivity.class);
            startActivity(intent);

        }
        return super.onOptionsItemSelected(menuItem);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {

        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.manu_main, menu);
        return true;

    }

}

Answer 1

基于adding a Toolbar as an ActionBar的官方文档，您还应该在配置工具栏后立即调用setSupportActionBar(toolbar)。（链接中的第5步）

只要在调用getSupportActionBar之前执行此操作，它将返回此工具栏，而不是null。这应该可以解决您的问题。

Answer 2

调用setDisplayHomeAsUpEnabled可以产生一个NPE。像这样用空检查将其包装：

 if (getSupportActionBar() != null) {

getSupportActionBar（）。setDisplayHomeAsUpEnabled（true）; }

Android中的错误[尝试在空对象引用上调用虚拟方法'void android.app.ActionBar']

2 个答案: