Android fragment lifecycle issue with actionbar

问题:

I want to realize the navigation of the fragments using the following code:

public abstract class BaseFragment extends Fragment {
    private static String TAG = "BaseFragment";
    private BaseFragmentActions baseFragmentActions;
    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        Activity activity = null;
        if (context instanceof Activity){
            activity = (Activity) context;
        }
        Log.i(TAG, "onAttach = ");
        try {
            baseFragmentActions = (BaseFragmentActions)activity;

        } catch (ClassCastException e) {
        }
        Log.i("onAttach",""+(getBackStackCount()!=0));
        baseFragmentActions.resetToolbarNavigation(getBackStackCount()!=0);
    }
    @Override
    public void onDetach() {
        super.onDetach();
        Log.i("BaseFragment", "onDestroy = " + (getBackStackCount() - 1));
        baseFragmentActions.resetToolbarNavigation((getBackStackCount() - 1) != 0);
    }

    @Override
    public void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
    }

    private int getBackStackCount() {
        int b = getActivity().getSupportFragmentManager().getBackStackEntryCount();
        Log.i("getBackStackEntryCount", "====== "+b);
        return b;
    }

    public interface BaseFragmentActions {
        public void resetToolbarNavigation(boolean backNavigationEnabled);
    }
}

All my fragments extend this Base Activity. And inside my main activity i implement BaseFragmentActions, and implemented this method:

 @Override
    public void resetToolbarNavigation(boolean backNavigationEnabled) {
        Log.i("BaseActivity", "reset " + backNavigationEnabled);
            getSupportActionBar().setDisplayHomeAsUpEnabled(backNavigationEnabled);
            if (backNavigationEnabled) {
                mToolbar.setNavigationOnClickListener(new View.OnClickListener() {
                    @Override
                    public void onClick(View view) {
                        Log.i("resetToolbarNavigation", "setNavigationOnClickListener");
                        onBackPressed();
                    }
                });
            } else {
                initNavigation();
                syncState();
            }
    }

Everything works fine but when I change the screen orientation we obtain error that getSupportActionBar = null. This is because of what I call going to attach. How can I fix this error? I tried to make checking whether getSupportActionBar is not zero. I'm not getting an error, but "up" Arrow replaced hamburger...

Advise what you can do in this case. Also share links to navigate the implementation of such fragments. Sorry if something wrong written, or I made a grammatical error)).

回答1:

Hi sorry for the delay in the answer, the problem you're having is because when onAttach is called the getSupportActionBar() is not set yet, instead you need to make sure the Activity is already created when interacting with Activity components, so just put your call inside the onActivityCreated method of your Fragment like this:

@Override
public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);
    baseFragmentActions.resetToolbarNavigation(getBackStackCount()!=0);
}