Question

我有一个底部导航栏，其中包含4个片段，当选择一个选项卡时，将加载该片段的新实例。

private BottomNavigationView.OnNavigationItemSelectedListener mOnNavigationItemSelectedListener
    = new BottomNavigationView.OnNavigationItemSelectedListener() {
@Override
public boolean onNavigationItemSelected(@NonNull MenuItem item) {
    Fragment fragment = null;
    switch (item.getItemId()) {
        case R.id.navigation_home:
            fragment = HomeFragment.newInstance();
            break;
        case R.id.navigation_cards:
            fragment = CardsFragment.newInstance();
            break;
        case R.id.navigation_deals:
            fragment = DealsFragment.newInstance();
            break;
        case R.id.navigation_settings:
            fragment = SettingsFragment.newInstance();
            break;
    }
    if (fragment != null) {


        FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
        fragmentTransaction.replace(R.id.content, fragment);
        fragmentTransaction.commit();
    }
    return true;
}
};

现在我的HomeFragment中有一个RecyclerView，在“项目”上选择它会打开一个新的片段：

   myViewHolder.cardView.setOnClickListener(view -> {
            System.out.println("clicked");

            Fragment fragment = new TargetDetailsFragment();
            FragmentTransaction ft = ((AppCompatActivity) context).getSupportFragmentManager()
                    .beginTransaction();
            ft.replace(R.id.content, fragment).addToBackStack(null);
            ft.commit();





        });

我想在TargetDetails Fragments中添加一个后退按钮，以便在选择后将您带回到首页，而我尝试通过在Main活动中实现OnBackStackChangedListener来做到这一点

@Override
public void onBackStackChanged() {
    shouldDisplayHomeUp();
}

public void shouldDisplayHomeUp(){
    //Enable Up button only  if there are entries in the back stack
    boolean canback = getSupportFragmentManager().getBackStackEntryCount()>0;
    getSupportActionBar().setDisplayHomeAsUpEnabled(canback);
}

@Override
public boolean onSupportNavigateUp() {
    //This method is called when the up button is pressed. Just the pop back stack.
    getSupportFragmentManager().popBackStack();
    return true;
}

}

但是问题是，当我单击它时，它会再次重新加载HomeFragment，但我只是希望它返回到该Fragment的已保存实例

Answer 1

通过在“活动”中添加以下代码。片段返回栈可以被管理。

@Override
    public void onBackPressed() {

        int count = getFragmentManager().getBackStackEntryCount();

        if (count == 0) {
            super.onBackPressed();
            //additional code
        } else {
            getFragmentManager().popBackStack();
        }

    }

Answer 2

你好，@ Bolu Okunaiya，我认为您应该尝试this，它将帮助您将后台管理为所需的片段，而无需再次加载相同的片段。

对于停止加载先前的片段，您应该在FragmentTransaction中使用“ add”而不是“ replace”

Answer 3

这是我用于ViewPager的代码，其目的是查看当前页码是否为0，而不是继续super.onBackPressed();，否则转到上一个片段：

@Override
public void onBackPressed() {
    if(vpPager.getCurrentItem()!=0) {
        vpPager.setCurrentItem(vpPager.getCurrentItem()-1, true);
    } else {
        super.onBackPressed();
    }
}

Answer 4

在您的MainActivity内

@Override
        public void onBackStackChanged() {
            //shouldDisplayHomeUp();
            Fragment currentFragment = getActivity().getFragmentManager()
                              .findFragmentById(R.id.fragment_container);

          if (currentFragment instanceof TargetDetails) {
                  Log.v(TAG, "your current fragment is TargetDetails");
                  popBackStackImmediate(); //<<<< immediate parent fragment will open,which is your HomeFragement

                 }

        }

要使用popBackStackImmediate()，您需要*用FragmentB替换FragmentA，并在addToBackstack()之前使用commit()。

向片段添加返回按钮

4 个答案: