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。

在kotlin中，这要简单得多。

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    requireActivity().onBackPressedDispatcher.addCallback(viewLifecycleOwner, object : OnBackPressedCallback(true) {
        override fun handleOnBackPressed() {
            //
        }
    })
}

我是这样做的，对我很管用

简单的界面

FragmentOnBackClickInterface.java

public interface FragmentOnBackClickInterface {
    void onClick();
}

示例实现

MyFragment.java

public class MyFragment extends Fragment implements FragmentOnBackClickInterface {

// other stuff

public void onClick() {
       // what you want to call onBackPressed?
}

然后在activity中重写onBackPressed

    @Override
public void onBackPressed() {
    int count = getSupportFragmentManager().getBackStackEntryCount();
    List<Fragment> frags = getSupportFragmentManager().getFragments();
    Fragment lastFrag = getLastNotNull(frags);
    //nothing else in back stack || nothing in back stack is instance of our interface
    if (count == 0 || !(lastFrag instanceof FragmentOnBackClickInterface)) {
        super.onBackPressed();
    } else {
        ((FragmentOnBackClickInterface) lastFrag).onClick();
    }
}

private Fragment getLastNotNull(List<Fragment> list){
    for (int i= list.size()-1;i>=0;i--){
        Fragment frag = list.get(i);
        if (frag != null){
            return frag;
        }
    }
    return null;
}

 requireActivity().onBackPressedDispatcher.addCallback(viewLifecycleOwner) {
        //your code 
    }

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

你可以像这样使用父活动的onBackPressedDispatcher:

val backpress = requireActivity().onBackPressedDispatcher.addCallback(viewLifecycleOwner, true) {
            // here dispatcher works for any action when back pressed
}

你也可以从fragment中启用/禁用backpress按钮，如下所示:

backpress.isEnabled = true/false