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;
        }
    });
}

片段: 创建一个BaseFragment，放置一个方法:

 public boolean onBackPressed();

活动:

@Override
public void onBackPressed() {
    List<Fragment> fragments = getSupportFragmentManager().getFragments();
    if (fragments != null) {
        for (Fragment fragment : fragments) {
            if (!fragment.isVisible()) continue;

            if (fragment instanceof BaseFragment && ((BaseFragment) fragment).onBackPressed()) {
                return;
            }
        }
    }

    super.onBackPressed();
}

你的活动将在附加的和可见的片段上运行，并对它们中的每一个调用onBackPressed()，如果其中一个返回'true'(意味着它已经被处理，所以没有进一步的操作)，则中止。

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;
}

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

    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
                replaceFragmentToBackStack(getActivity(), WelcomeFragment.newInstance(bundle), tags);

                return true;
            }

            return false;
        }
    });
}

在kotlin的情况下使用这个onAttach回调

        override fun onAttach(context: Context) {
          super.onAttach(context)
           val callback: OnBackPressedCallback = object : 
                 OnBackPressedCallback(true) {
                 override fun handleOnBackPressed() {
                 // your onbackpressed code 


            }
          }
      requireActivity().onBackPressedDispatcher.addCallback(this, callback)
      }

解决方法很简单:

如果您有一个所有片段都扩展的基片段类，那么将此代码添加到它的类中，否则创建这样一个基片段类

/* 
* called when on back pressed to the current fragment that is returned
*/
public void onBackPressed()
{
    // add code in super class when override
}

在你的Activity类中，重写onBackPressed如下:

private BaseFragment _currentFragment;

@Override
public void onBackPressed()
{
      super.onBackPressed();
     _currentFragment.onBackPressed();
}

在Fragment类中，添加你想要的代码:

@Override
public void onBackPressed()
{
    setUpTitle();
}