不要实现ft.addToBackStack()方法，这样当你按下返回按钮时，你的活动就会结束。

proAddAccount = new ProfileAddAccount();
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.replace(R.id.fragment_container, proAddAccount);
//fragmentTransaction.addToBackStack(null);
fragmentTransaction.commit();

像这样执行 Fragment_1 -> Fragment_2 -> Fragment_3

    Button btn = (Button) rootView.findViewById(R.id.your_button_id);
    btn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

            Fragment_2 nextFrag= new Fragment_2();
            getActivity().getSupportFragmentManager().beginTransaction()
                    .replace(R.id.content_frame, nextFrag,getTag())
                    .addToBackStack(null)
                    .commit();

        }
    });

Fragment_3 -> Fragment_2 -> Fragment_1

Step_1:在Base Activity中创建一个可公开访问的字符串

step2:每当一个新的Fragment被激活时，在Base Activity中改变String的值

Step_3:然后添加onBackPressed()方法，并将字符串值传递给另一个方法，其中fagments可以被替换

在基础活动中

public static String currentFragment=null;

@Override
public void onBackPressed() 
{
        displayPreviousFragment(currentFragment);
}

public void displayPreviousFragment(String currentFragment)
{
    //creating fragment object
    Fragment fragment = null;

    //initializing the fragment object which is selected
    switch (currentFragment)
    {
        case "Fragment_2"    :   fragment = new Fargment_1();     break;
        case "Fragment_3"    :   fragment = new Fragment_2();     break;
    }

    //replacing the fragment
    if (fragment != null) {
        FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
        ft.replace(R.id.frame_to_replace_fragment, fragment);
        ft.commit();
    }
}

在Fragment_2 在OnCreateView方法内

BaseActivity.currentFragment="Fragment_2";

在Fragment_3 在OnCreateView方法内

BaseActivity.currentFragment="Fragment_3";

试试这个，如果你真的想在Fragment中启用onBackPressed()。 在浪费了一个小时的时间后，我根据我以前的经验，做出了这个完全符合需求的解决方案。

你只需要关注私有int STATUS_FRAGMENT=0的值;这就满足了片段中addToBackStack()的需求。

import android.view.MenuItem;
import android.view.View;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.Fragment;

import com.example.growfast.NavigationItemsFolder.CoreFragments.Cart;
import com.example.growfast.NavigationItemsFolder.CoreFragments.HelpDesk;
import com.example.growfast.NavigationItemsFolder.CoreFragments.Home;
import com.example.growfast.NavigationItemsFolder.CoreFragments.ProfileDetails;
import com.example.growfast.R;
import com.google.android.material.bottomnavigation.BottomNavigationView;

public class BusinessManagement extends AppCompatActivity {

    public BottomNavigationView bottomNavigationView;
    private int STATUS_FRAGMENT=0;

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

    }

    private void setBottomNavigationMenu() {
        bottomNavigationView = findViewById(R.id.navigation);
        bottomNavigationView.setVisibility(View.VISIBLE);

        bottomNavigationView.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {

            Fragment fragment = null;

            @Override
            public boolean onNavigationItemSelected(@NonNull MenuItem item) {

                switch (item.getItemId()) {

                    case R.id.action_home:
                        fragment = new Home();
                        break;

                    case R.id.action_profile:
                        fragment = new ProfileDetails();
                        break;
                    case R.id.action_cart:
                        fragment = new Cart();
                        break;
                    case R.id.action_favourites_menu:
                        fragment = new HelpDesk();
                        break;

                }
                return loadFromFragment(fragment);

            }
        });
        bottomNavigationView.setSelectedItemId(R.id.action_home);
    }

    private boolean loadFromFragment(Fragment fragment) {
        if (fragment != null) {
            getSupportFragmentManager().beginTransaction().replace(R.id.my_container, fragment)
                    .commit();
            STATUS_FRAGMENT=1;
            return true;
        }
        return false;
    }

    @Override
    public void onBackPressed() {
        if (STATUS_FRAGMENT==1) {
            bottomNavigationView.setSelectedItemId(R.id.action_home);
            STATUS_FRAGMENT=0;
            bottomNavigationView.setVisibility(View.VISIBLE);
        }
        else{
            super.onBackPressed();
        }
    }


}```

这个对我很有用:https://stackoverflow.com/a/27145007/3934111

@Override
public void onResume() {
    super.onResume();

    if(getView() == null){
        return;
    }

    getView().setFocusableInTouchMode(true);
    getView().requestFocus();
    getView().setOnKeyListener(new View.OnKeyListener() {
        @Override
        public boolean onKey(View v, int keyCode, KeyEvent event) {

            if (event.getAction() == KeyEvent.ACTION_UP && keyCode == KeyEvent.KEYCODE_BACK){
                // handle back button's click listener
                return true;
            }
            return false;
        }
    });
}

如果你使用androidx.appcompat:appcompat:1.1.0或以上，那么你可以添加一个OnBackPressedCallback到你的片段，如下所示

requireActivity()
    .onBackPressedDispatcher
    .addCallback(this, object : OnBackPressedCallback(true) {
        override fun handleOnBackPressed() {
            Log.d(TAG, "Fragment back pressed invoked")
            // Do custom work here    

            // if you want onBackPressed() to be called as normal afterwards
            if (isEnabled) {
                isEnabled = false
                requireActivity().onBackPressed()
            }
        }
    }
)

参见https://developer.android.com/guide/navigation/navigation-custom-back

只需添加addToBackStack当你在你的片段之间过渡，如下所示:

fragmentManager.beginTransaction().replace(R.id.content_frame,fragment).addToBackStack("tag").commit();

如果你写addToBackStack(null)，它会自己处理它，但如果你给了一个标签，你应该手动处理它。