java - Android 中的 fragment 重叠

Question

我试图在 fragment 之间切换而不丢失以前的内容，所以我决定实现这种方式来做到这一点:

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();
    }
}

使用此方法，我检查 fragment 是否已打开:如果是，我会显示它，如果没有，我会添加它。然后我将其声明为“alreadyOpened”。问题是，当我在 fragment 之间切换时，我看到所有三个 fragment 都重叠。我该如何解决？这是我调用 loadFragment 方法时的菜单栏:

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();
}

Answer 1

您不应该在每次导航点击时创建新的 fragment 。在某处创建一次并将它们保存在List<Fragment> fragments中大批。然后使用 fragmentManager.beginTransaction().replace(R.id.fragment_layout, fragment);这是一个小例子:

    FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
    ft.setCustomAnimations(R.anim.slide_in_left, R.anim.slide_out_left); //optional 
    ft.replace(R.id.fragment_layout, fragments.get(selectedFragment));
    ft.addToBackStack(null);
    ft.commit();

来自您的onNavigationItemSelected发送selectedFragment变量，并匹配 fragments 中的位置列表。

编辑:这个怎么样:

public HomeFragment homeFragment;
public PopularFragment popularFragment;
public PlayingFragment playingFragment;

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

@Override
public boolean onNavigationItemSelected(@NonNull MenuItem item) {
    switch (item.getItemId()) {
        case R.id.bbn_item1:
           if(homeFragment == null){ homeFragment  =new HomeFragment();}
           loadFragment(homeFragment )
            return true;
        case R.id.bbn_item2:
            if(homeFragment == null){ popularFragment  =new PopularFragment();}
            loadFragment(popularFragment)
            return true;
        case R.id.bbn_item3:
             if(homeFragment == null){ playingFragment  =new PlayingFragment();}
            loadFragment(playingFragment);
            return true;
    }
    return false;
}

};

public void loadFragment(Fragment fragment){
  FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
    ft.setCustomAnimations(R.anim.slide_in_left, R.anim.slide_out_left); //optional 
    ft.replace(R.id.fragment_layout, fragment);
    ft.addToBackStack(null);
    ft.commit();

}