非常简短而甜蜜的回答:

getActivity().onBackPressed();

我案例的整个场景说明:

我在MainActivity中有FragmentA， 我从FragmentA打开FragmentB (FragmentB是FragmentA的子或嵌套片段)

 Fragment duedateFrag = new FragmentB();
 FragmentTransaction ft  = getFragmentManager().beginTransaction();
 ft.replace(R.id.container_body, duedateFrag);
 ft.addToBackStack(null);
 ft.commit();

现在如果你想从FragmentB访问FragmentA你可以简单地输入getActivity().onBackPressed();在FragmentB。

private boolean isMainFragment = true;

@Override
public void onBackPressed() {

    if (isMainFragment){
        finish();
    }else {
        getSupportFragmentManager().popBackStack();
        isMainFragment = true;
    }
}

当打开花药片段时，只需添加

isMainFragment = false;

这是我的工作

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";

使用导航组件，你可以这样做:

Java

public class MyFragment extends Fragment {

@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    // This callback will only be called when MyFragment is at least Started.
    OnBackPressedCallback callback = new OnBackPressedCallback(true /* enabled by default */) {
        @Override
        public void handleOnBackPressed() {
            // Handle the back button event
        }
    });
    requireActivity().getOnBackPressedDispatcher().addCallback(this, callback);

    // The callback can be enabled or disabled here or in handleOnBackPressed()
}
...
}

科特林

class MyFragment : Fragment() {

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)

    // This callback will only be called when MyFragment is at least Started.
    val callback = requireActivity().onBackPressedDispatcher.addCallback(this) {
        // Handle the back button event
    }

    // The callback can be enabled or disabled here or in the lambda
}
...
}

onBackPressed()导致Fragment从Activity中分离。

根据斯特林·迪亚兹的回答，我认为他是对的。但有些情况是错误的。(例如:旋转屏幕)

所以，我认为我们可以检测是否isremoval()来实现目标。

你可以在onDetach()或onDestroyView()上写。它是工作。

@Override
public void onDetach() {
    super.onDetach();
    if(isRemoving()){
        // onBackPressed()
    }
}

@Override
public void onDestroyView() {
    super.onDestroyView();
    if(isRemoving()){
        // onBackPressed()
    }
}

在mainActivity实现回调接口中

protected mainActivity.OnBackPressedListener onBackPressedListener;

public interface OnBackPressedListener {
    void doBack();
}

public void setOnBackPressedListener(mainActivity.OnBackPressedListener onBackPressedListener) {
    this.onBackPressedListener = onBackPressedListener;
}

@Override
public void onBackPressed() {
    if (onBackPressedListener != null) {
        onBackPressedListener.doBack();
    } else { 
        super.onBackPressed();
    }
}

在片段实现接口OnBackPressedListener，我们写在mainActivity

implements mainActivity.OnBackPressedListener

mainActivity是我的基本活动，在你的片段onCreateView方法中编写以下代码

((mainActivity) getActivity()).setOnBackPressedListener(this);

并实现OnBackPressedListener接口方法doBack

@Override
public void doBack() {
    //call base fragment 
}

现在使用doBack()方法调用你想要调用的fragment