Android Fragment switching from navigation drawer causes app to quit

Question

I have the slider menu displayview method as:

private void displayView(int position) {
                // update the main content by replacing fragments
                Fragment fragment = null;
                switch (position) {
                    case 0:
                        fragment = new HomeFragment();

                    FragmentManager fm = getSupportFragmentManager();
                    String tag = fragment.getTag(); // instance method of a to get a tag

                    FragmentTransaction ft = fm.beginTransaction();

                    ft.replace(R.id.frame_container, fragment, tag);
                    ft.addToBackStack(tag);
                    ft.commit();

                    default:
                        break;
                }

                if (fragment != null) {
                    FragmentManager fragmentManager = getFragmentManager();
                    fragmentManager.beginTransaction()
                            .replace(R.id.frame_container, fragment).commit();

                    // update selected item and title, then close the drawer
                    drawerListView.setItemChecked(position, true);
                    drawerListView.setSelection(position);
                    setTitle(navMenuTitles[position]);
                    drawer.closeDrawer(drawerListView);
                } else {
                    // error in creating fragment
                    Log.e("MainActivity", "Error in creating fragment");
                }
            }

I have a fragment called home_fragment whose code behind is HomeFragment.java

When I click on this fragment first it works fine, but on clicking next from the siding menu at index 0 I get an error as:

Attempt to write to field 'int android.support.v4.app.Fragment.mNextAnim' on a null object reference

What am I doing wrong? Thanks.

This is where I'm having error:

case OP_REMOVE: {
                    Fragment f = op.fragment;
                    f.mNextAnim = exitAnim;
                    mManager.removeFragment(f, transition, transitionStyle);
                } break;

This code is present in BackStackRecord.java

Answer 1

You shouldn't be calling container.removeAllViewsInLayout().

The FragmentManager will handle all the view manipulation on the container when you call FragmentTransaction.replace(), including removing the current fragment view. You are probably getting an error because the FragmentManager expects a fragment's view to be in the container, but you've removed it.

All you need is this:

        private void displayView(int position) {
            // update the main content by replacing fragments
            Fragment fragment = null;
            switch (position) {
                case 0:
                    fragment = new HomeFragment();
                    break;
                case 1:
                    // set fragment to other nav target
                    fragment = ...
                    break;
                .
                .
                .
                default:
                    break;
            }

            if (fragment != null) {
                FragmentManager fragmentManager = getSupportFragmentManager();
                fragmentManager.beginTransaction()
                        .replace(R.id.frame_container, fragment).commit();

                // update selected item and title, then close the drawer
                drawerListView.setItemChecked(position, true);
                drawerListView.setSelection(position);
                setTitle(navMenuTitles[position]);
                drawer.closeDrawer(drawerListView);
            } else {
                // error in creating fragment
                Log.e("MainActivity", "Error in creating fragment");
            }
        }

Also I noticed you are using getFragmentManager(). Please check your class imports and make sure that you have the right call.

• If HomeFragment extends android.app.Fragment, use getFragmentManager().
• If HomeFragment extends android.support.v4.app.Fragment, use getSupportFragmentManager().