Android中的片段重叠

我试图在片段之间切换而又不丢失先前的内容，所以我决定实现这种方式：

private void loadFragment(Fragment fragment) {
    FragmentManager fragmentManager = getSupportFragmentManager();
    fragmentManager.beginTransaction().hide(fragment);
    if (!alreadyOpened[currentIndex]) {
        alreadyOpened[currentIndex] = true;
        fragmentManager.beginTransaction().add(R.id.fragment_container,fragment).commit();
    } else {
        fragmentManager.beginTransaction().show(fragment).commit();
    }
}

使用这种方法，我检查片段是否已经打开：如果是，则显示它，如果没有，则添加它。然后，我将其声明为“ alreadyOpened”。问题是，当我在片段之间切换时，我看到所有三个片段重叠。我该如何解决？当我调用loadFragment方法时，这是菜单栏：

private BottomNavigationView.OnNavigationItemSelectedListener mOnNavigationItemSelectedListener
        = new BottomNavigationView.OnNavigationItemSelectedListener() {

    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem item) {
        switch (item.getItemId()) {
            case R.id.bbn_item1:
                currentIndex = 0;
                loadFragment(new HomeFragment());
                return true;
            case R.id.bbn_item2:
                currentIndex = 1;
                loadFragment(new PopularFragment());
                return true;
            case R.id.bbn_item3:
                 currentIndex = 2;
                loadFragment(new PlayingFragment());
                return true;
        }
        return false;
    }
};

编辑：新代码

List<Fragment> fragments = new ArrayList<>();

private void loadFragment(Fragment fragment) {
    FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
    if (alreadyOpened[currentIndex]) {
        ft.replace(R.id.fragment_container, fragments.get(currentIndex));
    } else {
        fragments.add(currentIndex, fragment);
        alreadyOpened[currentIndex] = true;
        ft.replace(R.id.fragment_container, fragment);
    }
    ft.addToBackStack(null);
    ft.commit();
}

问题来源：Stack Overflow