当用户向后摆放时，需要每个片段返回主屏幕应用中没有任何按钮

如何解决当用户向后摆放时，需要每个片段返回主屏幕应用中没有任何按钮

因此，我正在创建一个包含不同片段的基本应用程序，我希望当用户按下手机上的后退按钮时，该应用程序返回到首页片段。

主要活动

public class MainActivity extends AppCompatActivity implements NavigationView.OnNavigationItemSelectedListener {

    public void book(View view)
    {
        Toast.makeText(this,"You tried to book",Toast.LENGTH_SHORT).show();
    }
    public void submit(View view)

    {
        EditText editText = (EditText) findViewById(R.id.feedbackText);
        if (editText.getText().toString().isEmpty())
        {
            Toast.makeText(this,"Please type something first",Toast.LENGTH_SHORT).show();
        }
        else
        {
            editText.setText("");

            Toast.makeText(this,"Thank You for your feedback",Toast.LENGTH_SHORT).show();

            closeKeyboard();
        }
    }

    private void closeKeyboard()
    {
        View view = this.getCurrentFocus();
        if (view != null)
        {
            InputMethodManager imm = (InputMethodManager)getSystemService(Context.INPUT_METHOD_SERVICE);
            imm.hideSoftInputFromWindow(view.getWindowToken(),0);
        }
    }


    DrawerLayout drawerLayout;
    ActionBarDrawerToggle actionBarDrawerToggle;
    Toolbar toolbar,searchToolbar;
    NavigationView navigationView;
    FragmentManager fragmentManager;
    FragmentTransaction fragmentTransaction;
    Menu search_menu;
    MenuItem item_search;
    Button submitBtn;
    MaterialSearchView searchView;
    EditText email;
    EditText password;
    TextView titleText;
    int counter = 0;

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.search,menu);
        MenuItem item  = menu.findItem(R.id.action_search);
        searchView.setMenuItem(item);
        return true;
    }

    public void guest(View view)
    {
        fragmentManager = getSupportFragmentManager();
        fragmentTransaction = fragmentManager.beginTransaction();
        fragmentTransaction.replace(R.id.container,new Home());
        fragmentTransaction.commit();
    }


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

        searchToolbar = (Toolbar)findViewById(R.id.search_toolbar);
        setSupportActionBar(toolbar);

        toolbar.setTitleTextColor(Color.parseColor("#FFFFFF"));
        searchView=(MaterialSearchView)findViewById(R.id.search_view);

        drawerLayout = findViewById(R.id.drawer);
        navigationView = findViewById(R.id.navigationView);
        navigationView.setNavigationItemSelectedListener(this);
        actionBarDrawerToggle = new ActionBarDrawerToggle(this,drawerLayout,toolbar,R.string.Open,R.string.Close);
        drawerLayout.addDrawerListener(actionBarDrawerToggle);
        actionBarDrawerToggle.setDrawerIndicatorEnabled(true);
        actionBarDrawerToggle.syncState();

        fragmentManager = getSupportFragmentManager();
        fragmentTransaction = fragmentManager.beginTransaction();
        fragmentTransaction.replace(R.id.container,new Home());
        fragmentTransaction.commit();
        titleText.setText(R.string.home);


    }


    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem item) {
        drawerLayout.closeDrawer(GravityCompat.START);
        if (item.getItemId() == R.id.home)
        {
            fragmentManager = getSupportFragmentManager();
            fragmentTransaction = fragmentManager.beginTransaction();
            fragmentTransaction.replace(R.id.container,new Home());
            fragmentTransaction.commit();
            titleText.setText(R.string.home);

        }
        if (item.getItemId() == R.id.myOrders)
        {
            fragmentManager = getSupportFragmentManager();
            fragmentTransaction = fragmentManager.beginTransaction();
            fragmentTransaction.replace(R.id.container,new MyOrders());
            fragmentTransaction.commit();
            titleText.setText(R.string.myOrders);

        }
        if (item.getItemId() == R.id.refer)
        {
            fragmentManager = getSupportFragmentManager();
            fragmentTransaction = fragmentManager.beginTransaction();
            fragmentTransaction.replace(R.id.container,new Refer());
            fragmentTransaction.commit();
            titleText.setText(R.string.refer);

        }
        if (item.getItemId() == R.id.contact)
        {
            fragmentManager = getSupportFragmentManager();
            fragmentTransaction = fragmentManager.beginTransaction();
            fragmentTransaction.replace(R.id.container,new Contact());
            fragmentTransaction.commit();
            titleText.setText(R.string.contact);


        }
        if (item.getItemId() == R.id.feedback)
        {
            fragmentManager = getSupportFragmentManager();
            fragmentTransaction = fragmentManager.beginTransaction();
            fragmentTransaction.replace(R.id.container,new Feedback());
            fragmentTransaction.commit();
            titleText.setText(R.string.feedback);


        }
        if (item.getItemId() == R.id.settings)
        {
            fragmentManager = getSupportFragmentManager();
            fragmentTransaction = fragmentManager.beginTransaction();
            fragmentTransaction.replace(R.id.container,new Settings());
            fragmentTransaction.commit();
            titleText.setText(R.string.setting);


        }
        if (item.getItemId() == R.id.terms)
        {
            fragmentManager = getSupportFragmentManager();
            fragmentTransaction = fragmentManager.beginTransaction();
            fragmentTransaction.replace(R.id.container,new Terms());
            fragmentTransaction.commit();
            titleText.setText(R.string.terms);


        }

        return true;
    }
        
}

请帮助我解决这个问题。

解决方法

在您的onBackPress中使用Activity尝试

    @Override
    public void onBackPressed() {
        if (!(getSupportFragmentManager().findFragmentById(R.id.container) instanceof Home)) {
            fragmentManager = getSupportFragmentManager();
            fragmentTransaction = fragmentManager.beginTransaction();
            fragmentTransaction.replace(R.id.container,new Home());
            fragmentTransaction.commit();
            titleText.setText(R.string.home);
        } else {
            super.onBackPressed();
        }
    }