Calling database helper from fragment

Question

I need your help to find a way to call database queries from a fragment.

I read some topics about it and the use of getActivity() seems to be the best solution, which doesn't help me.

Here is my source code

//package


//imports

public class CategoriesFragment extends Fragment
{
    DatabaseHelper db;

    ArrayList<String> mCategoryList;
    DynamicListView lvCategories;
    StableArrayAdapter stableArrayAdapter;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        View rootView = inflater.inflate(R.layout.fragment_categories, container, false);

        lvCategories = (DynamicListView) rootView.findViewById(R.id.lvCategories);

        db = new DatabaseHelper(getActivity());

        mCategoryList = new ArrayList<>();

        stableArrayAdapter = new StableArrayAdapter(getActivity(), R.layout.text_view, mCategoryList);

        return rootView;
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        try {
            super.onCreate(savedInstanceState);

            lvCategories.setCheeseList(mCategoryList);
            lvCategories.setAdapter(stableArrayAdapter);
            lvCategories.setChoiceMode(ListView.CHOICE_MODE_SINGLE);

            lvCategories.setOnItemClickListener(new AdapterView.OnItemClickListener() {
                @Override
                public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                    //not defined
                }
            });

            //If listview is empty
            if (lvCategories.getCount() == 0) {
                lvCategories.setVisibility(View.GONE);
            } else {
                lvCategories.setVisibility(View.VISIBLE);
            }
        }catch (Exception e) {
            Toast.makeText(getActivity(), String.valueOf(e), Toast.LENGTH_LONG).show();
        }
    }

    public void AddCategoryItem(String word, String reportId) {


        //get category item by name
        Category cat = db.getCategory(word);


        //Adding both ids to table CategoryReport
        db.createCategoryReport(new CategoryReport(cat.getId(), Integer.parseInt(reportId)));

    }

    public String FormatCategory(String word) {

        String formated = word;

        int occurence = 1;

        if (mCategoryList.contains(formated)) {

            //Salon, Salon #2, Salon #3, etc.
            while (mCategoryList.contains(formated)) {
                occurence++;

                //formated and word are separated to prevent 'Chambre #1 #2' output syntax
                formated = word + " #" + String.valueOf(occurence);
            }
        }

        return formated;
    }

    public void RefreshList(String report_id) {

        //database
        List<Category> categories = db.getCategoriesByReport(report_id);

        //populate liste
        mCategoryList.clear();

        for (Category c : categories) {
            mCategoryList.add(FormatCategory(c.getName()));
        }

        //refresh
        stableArrayAdapter = new StableArrayAdapter(getActivity(), R.layout.text_view, mCategoryList);
        lvCategories.setCheeseList(mCategoryList);
        lvCategories.setAdapter(stableArrayAdapter);
        lvCategories.setChoiceMode(ListView.CHOICE_MODE_SINGLE);

        if (lvCategories.getCount() == 0) {
            lvCategories.setVisibility(View.GONE);
        } else {
            lvCategories.setVisibility(View.VISIBLE);
        }
    }

}

And the error message :

java.lang.NullPointerException: Attempt to invoke virtual method 'java.util.List [my package name].DatabaseHelper.getCategoriesByReport(java.lang.String)' on a null object reference.

This error is thrown at the first line of the RefreshList method.

I know it is not about a query error, because I have tested the same directly in the activity and everything were fine.

Thanks for your help :D

"Attempt to invoke virtual method 'java.util.List [my package name].DatabaseHelper.getCategoriesByReport(java.lang.String)'" here object db is null. Post the DatabaseHelper class. — Sudheesh Mohan, Jun 08 '16 at 15:22
Possible duplicate of [What is a NullPointerException, and how do I fix it?](http://stackoverflow.com/questions/218384/what-is-a-nullpointerexception-and-how-do-i-fix-it) — Selvin, Jun 08 '16 at 15:23
RefreshList is called from the activity onResume() callback method. The databasehelper class is fine, because queries work when called from the acitivty. The lifecycle may cause the problem like @MrJM said. I will try their solutions. — Alexandre Martin, Jun 08 '16 at 15:24
I know that object db is null, but DatabaseHelper class isn't the cause. db is all fine in the activity. I tried a lot of queries from there. I think the way I manage both activity and fragment lifecycle is the problem. — Alexandre Martin, Jun 08 '16 at 15:28

score 3 · Accepted Answer · answered Jun 08 '16 at 15:20

3

It looks like your DatabaseHelper instance will be null. I guess you are calling the refresh method from your Activity?

The Fragment-Activity lifecycle might be causing the RefreshList(String report_id) being called before an instance of your DatabaseHelper is created.

you can add something like this

private void initDatabaseHelper(){
    if(db == null){
        db = new DatabaseHelper(getActivity());
    }
}

call this method in your onCreate() and at the start of your RefreshList()

answered Jun 08 '16 at 15:20

MrJM

1,214
1
12
26

It throws : *NullPointerException Attempt to invoke method [...].openOrCreateDatabase on a null object reference* – Alexandre Martin Jun 08 '16 at 15:40
Make sure you call this method in addCategoryItem as well. If this is not working, can you post the code of your DatabaseHelper class? – MrJM Jun 08 '16 at 15:41
I can't share it because of sensitive informations. It is not a personal project. But I repeat again that everything is fine in this class, because queries called from the activity work. – Alexandre Martin Jun 08 '16 at 15:49
Ok now it's fine, but I get *Null Exception on getSystemService*. I never called this method in my class :( – Alexandre Martin Jun 08 '16 at 16:18
Please post the logcat @AlexandreMartin – Sudheesh Mohan Jun 08 '16 at 16:23

score 1 · Answer 2 · answered Jun 08 '16 at 15:18

Because db object might be null when you are invoking RefreshList method. Try this

public void RefreshList(String report_id) {

        db = new DatabaseHelper(getActivity());//reinitialize your DB object
        //database
        List<Category> categories = db.getCategoriesByReport(report_id);

ciccioska · Answer 3 · 2016-06-12T21:24:17.717

-1

I can suggest you to initialize your DatabaseHelper with getApplicationContext() instead getActivity(). For do that reference to static Context stored in Application

edited Jun 12 '16 at 21:24

answered Jun 08 '16 at 16:30

ciccioska

1,291
16
22

It works with getActivity() but I tried your solution because I am curious. Unfortunately, I can't call getApplicationContext from my fragment... – Alexandre Martin Jun 08 '16 at 17:09
Reference it in Application with a static `Context` – ciccioska Jun 08 '16 at 20:34

Calling database helper from fragment

3 Answers3