Question

我得到了异常

＆＃34;引起：java.lang.NullPointerException：尝试调用虚拟方法＆＃39; void android.os.Bundle.putParcelable（java.lang.String， android.os.Parcelable）＆＃39;在null对象引用＆＃34;上的onSaveInstanceState

public class MainActivity extends AppCompatActivity
    implements NavigationView.OnNavigationItemSelectedListener {

static Bundle state;
private final String KEY_RECYCLER_STATE = "recycler_state";
static Bundle mBundleRecyclerViewState;
List<Room> roomList = new ArrayList<>();
Room room;
static List<Booking> bookingList = new ArrayList<>();
static RecyclerView recyclerView;
static RecAdapterBooking recAdapterBooking;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    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();

    final NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
    navigationView.setNavigationItemSelectedListener(this);

    Helper.initList(roomList);

    Menu menu = navigationView.getMenu();

    for (Room r : roomList) {
        menu.add(r.getName());
    }

    LinearLayoutManager layoutManager = new LinearLayoutManager(this);
    layoutManager.setOrientation(LinearLayoutManager.VERTICAL);
    recyclerView = (RecyclerView) findViewById(R.id.booking_rec);
    recyclerView.setLayoutManager(layoutManager);

    final Calendar c = Calendar.getInstance();
    final SimpleDateFormat df = new SimpleDateFormat("MMM-dd-yyyy");
    final TextView textView = (TextView) findViewById(R.id.time_view);
    setTime(c, df, textView);

    ImageButton leftButton = (ImageButton) findViewById(R.id.left);
    ImageButton rightButton = (ImageButton) findViewById(R.id.right);
    leftButton.setOnClickListener(new Button.OnClickListener() {
        @Override
        public void onClick(View v) {
            c.add(Calendar.DATE, -1);
            textView.setText(df.format(c.getTime()));
        }
    });
    rightButton.setOnClickListener(new Button.OnClickListener() {
        @Override
        public void onClick(View v) {
            c.add(Calendar.DATE, +1);
            textView.setText(df.format(c.getTime()));
        }
    });

    if (PreferenceManager.getDefaultSharedPreferences(MainActivity.this).getBoolean("pref", true)) {
        Intent intent = new Intent(MainActivity.this, SingleRoomActivity.class);
        intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_TASK_ON_HOME);
        startActivity(intent);
        this.finish();
    }

}

public void setTime(Calendar c, SimpleDateFormat df, TextView textView) {
    final String formattedDate = df.format(c.getTime());
    textView.setText(formattedDate);
}

@Override
public void onBackPressed() {
    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    if (drawer.isDrawerOpen(GravityCompat.START)) {
        drawer.closeDrawer(GravityCompat.START);
    } else {
        super.onBackPressed();
    }
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

//settings-ზე დაჭერის activity
@Override
public boolean onOptionsItemSelected(MenuItem item) {
    int id = item.getItemId();

    if (id == R.id.action_settings) {
        ArrayList<String> roomNameList = new ArrayList<>();
        for (Room r : roomList) {
            roomNameList.add(r.getName());
        }
        Intent intent = new Intent(MainActivity.this, SettingsActivity.class);
        intent.putExtra("roomlist", roomNameList);
        startActivity(intent);
    }
    if (id == R.id.action_log_out) {
        Intent intent = new Intent(MainActivity.this, LoginActivity.class);
        startActivity(intent);
    }
    return super.onOptionsItemSelected(item);
}


//მენიუდან არჩეული ოთახის განრიგის გამოტანა
@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
    for (Room r : roomList) {
        if (item.getTitle().equals(r.getName())) {
            bookingList = r.getBookingList();
            recAdapterBooking = new RecAdapterBooking(bookingList, MainActivity.this);
            recyclerView.setAdapter(recAdapterBooking);
            setTitle(r.getName());
            room = r;
            break;
        }
    }
    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    drawer.closeDrawer(GravityCompat.START);
    return true;
}

@Override
public void onSaveInstanceState(Bundle state) {
    super.onSaveInstanceState(state);
    state.putParcelable(KEY_RECYCLER_STATE, recyclerView.getLayoutManager().onSaveInstanceState());

}

protected void onRestoreInstanceState(Bundle state) {
    super.onRestoreInstanceState(state);

    // Retrieve list state and list/item positions
    if (state != null)
        recyclerView.getLayoutManager().onRestoreInstanceState(state.getParcelable(KEY_RECYCLER_STATE));
}


@Override
public void onStop(){
    super.onStop();
    onSaveInstanceState(state);
}
@Override
public void onRestart(){
    super.onRestart();
    onRestoreInstanceState(state);
  }
}

Answer 1

检查bundle是否为null，如果是，则初始化它。

@Override
public void onSaveInstanceState(Bundle state) {
if(state==null){
  state=new Bundle();
 }
    super.onSaveInstanceState(state);
    state.putParcelable(KEY_RECYCLER_STATE, recyclerView.getLayoutManager().onSaveInstanceState());

}

保存recyclerview状态期间的例外情况

1 个答案: