如何从背面按下的活动返回片段

@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
    if (keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0) {
        // 处理背面按下事件
        return true;
    }
    return super.onKeyDown(keyCode, event);
}

FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();

// 创建要返回的片段实例
YourFragment fragment = new YourFragment();

// 替换当前片段为要返回的片段
fragmentTransaction.replace(R.id.fragment_container, fragment);
fragmentTransaction.addToBackStack(null);

// 提交事务
fragmentTransaction.commit();

<FrameLayout
    android:id="@+id/fragment_container"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />