为什么我的SearchView menuItem是一个空对象？

Question

所以我只想在我的菜单中显示搜索图标（或SearchView），如果当前选择了搜索导航项，但是如果我尝试在onNavigationItemSelected中执行setVisible，我会收到错误说：

 java.lang.NullPointerException: Attempt to invoke interface method 'android.view.MenuItem android.view.MenuItem.setVisible(boolean)' on a null object reference

onNavigationItemSelected：

public boolean onNavigationItemSelected(@NonNull MenuItem item) {
    // Handle navigation view item clicks here.
    int id = item.getItemId();

    if (id == R.id.nav_search) {

        Context context = getApplicationContext();
        Toast.makeText(context, "Debug: Search Navigation Item Selected", Toast.LENGTH_LONG).show();
        setContentView(R.layout.activity_content);
        Log.d("FCM", "Instance ID: " + FirebaseInstanceId.getInstance().getToken());

        Toolbar toolbar = findViewById(R.id.toolbarS);
        setSupportActionBar(toolbar);
        DrawerLayout drawer = findViewById(R.id.drawer_layout);
        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.addDrawerListener(toggle);
        toggle.syncState();

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

        navigationView.getMenu().getItem(1).setChecked(true);

        MenuItem search = findViewById(R.id.menuSearch);
        search.setVisible(false);




    } else if (id == R.id.nav_watchlist) {
        Context context = getApplicationContext();
        Toast.makeText(context, "Debug: Watchlist Navigation Item Selected", Toast.LENGTH_LONG).show();
        setContentView(R.layout.activity_main);
        Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        DrawerLayout drawer = findViewById(R.id.drawer_layout);
        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.addDrawerListener(toggle);
        toggle.syncState();

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

        navigationView.getMenu().getItem(0).setChecked(true);




    } else if (id == R.id.nav_share) {


    } else if (id == R.id.nav_login) {
        this.startActivity(new Intent(this, AuthUiActivity.class));

        FirebaseUser currentFirebaseUser = FirebaseAuth.getInstance().getCurrentUser();
        try {
            if (currentFirebaseUser != null) {
                Log.d("AUTH", currentFirebaseUser.getUid());
                Log.d("AUTH", currentFirebaseUser.getDisplayName());
                Log.d("AUTH", currentFirebaseUser.getEmail());
                Log.d("AUTH", currentFirebaseUser.getPhoneNumber());
                Log.d("AUTH", currentFirebaseUser.getProviderId());
            }
        } catch (NullPointerException e) {
            Log.d("AUTH", "At least one Firebase parameter is undefined: " + e.toString());
        }
    }

    DrawerLayout drawer = findViewById(R.id.drawer_layout);
    drawer.closeDrawer(GravityCompat.START);
    return true;
}

menu_search.xml：

    <?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:myapp="http://schemas.android.com/apk/res-auto"
xmlns:app="http://schemas.android.com/tools">
<item
    android:id="@+id/menuSearch"
    android:icon="@android:drawable/ic_menu_search"
    android:title="@string/search"

    myapp:actionViewClass="android.widget.SearchView"
    myapp:showAsAction="collapseActionView|ifRoom"> 
</item>
<item
    android:id="@+id/action_settings"
    android:orderInCategory="100"
    android:title="@string/language"
    app:showAsAction="never" />
</menu>

但是，setVisible方法适用于onCreateOptionsMenu。

public boolean onCreateOptionsMenu(final Menu menu) {
    MenuInflater inflater = getMenuInflater();
    inflater.inflate(R.menu.menu_search, menu);
    MenuItem menuItem = menu.findItem(R.id.menuSearch);
    menuuu = menu;


    final SearchView searchView = (SearchView)menuItem.getActionView();

    searchView.setOnQueryTextListener(new SearchView.OnQueryTextListener() {
        @Override
        public boolean onQueryTextSubmit(String s) {
            Toast.makeText(getApplicationContext(), s, Toast.LENGTH_LONG).show();

            ListView lvR = findViewById(R.id.listViewResultsS);
            lvR.setAdapter(null);

            try {
                postNewSeriesByName(getApplicationContext(), s);
            } catch (JSONException e) {
                Toast.makeText(getApplicationContext(), "Error with tvdb API.", Toast.LENGTH_LONG).show();
            }


            return false;
        }

        @Override
        public boolean onQueryTextChange(String s) {
            //handle query changes here, helpful for auto complete stuff

            //make textboxes go away when you start typing
            try {
                TextView textview3 = findViewById(R.id.textView3);
                textview3.setVisibility(View.GONE);
            } catch (NullPointerException e) {
                Log.e("SEARCH", "wrong view you fuck (3)");
            }
            try {
                TextView textview2 = findViewById(R.id.textView2);
                textview2.setVisibility(View.GONE);
            } catch (NullPointerException e) {
                Log.e("SEARCH", "wrong view you fuck (2)");
            }
            return false;
        }
    });

    menuItem.setVisible(false);

    return super.onCreateOptionsMenu(menu);
}

我感谢您提供的任何帮助。

Answer 1

在一个Activity中多次调用setContentView不是一个好主意。这里有一个解决问题的答案

Android: is using setContentView multiple times bad while changing layouts?

在我看来，每次要显示其他屏幕时，您都可以使用片段而不是调用setContentView