Android get String in Fragment using custom class

Question

Learning Android and Java.

I have lot of strings and tedious to type long methods chain so decided to create a class so can use on multiple fragments and activities.

This class method should allows to get string by it's name. For instance

Instead of using this code in fragment

getResources().getString(R.string.string_name);

I want result using the class method

utils.getStringItem("string_name");

Java Class

import android.content.Context;

public class Utils {
    Context context;
    String  resource;

    public Utils(Context context) {
        this.context = context;
    }

    public String getStringItem(String resource) {
        String packageName = context.getPackageName();
        int    resId       = context.getResources().getIdentifier(resource, "string", packageName);
        return context.getString(resId);
    }
}

Fragment Class

import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.v4.app.Fragment;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import java.util.ArrayList;


/**
 * A simple {@link Fragment} subclass.
 */
public class PlacesFragment extends Fragment {

    ArrayList<Place>           mPlaces;
    RecyclerView               mRecyclerView;
    RecyclerView.LayoutManager mLayoutManager;
    RecyclerView.Adapter       mAdapter;
    Utils                      utils = new Utils(getActivity());


    public PlacesFragment() {
        // Required empty public constructor
    }


    @Override
    public View onCreateView(
            @NonNull LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState
    ) {

        View rootView = inflater.inflate(R.layout.fragment_places, container, false);

        mRecyclerView = rootView.findViewById(R.id.recyclerView);

        mPlaces = new ArrayList<>();

        mPlaces.add(new Place(
                utils.getStringItem("string_name"),
                "content text goes here.",
                R.drawable.img.cdd,
                4.0f
        ));

        mRecyclerView.setHasFixedSize(true);
        mLayoutManager = new LinearLayoutManager(getActivity());
        mAdapter = new PlacesAdapter(mPlaces);
        mRecyclerView.setLayoutManager(mLayoutManager);
        mRecyclerView.setAdapter(mAdapter);

        return rootView;

    }

}

This is giving me error and app is getting crash on startup.

Error Message

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
        at com.codepaints.myapp.Utils.getStringItem(Utils.java:14)
        at com.codepaints.myapp.PlacesFragment.onCreateView(PlacesFragment.java:48)

what is the error? can u edit post and add your stack trace? — Master Fathi, Jan 04 '19 at 09:22
I have added error message. Please have a look updated question. — Code Lover, Jan 04 '19 at 09:23
you can simply pass context while calling function utils.getStringItem(getActivity()),"string_name"); and add context parameter in your function — mitesh makwana, Jan 04 '19 at 09:32
`utils.getStringItem("string_name");` not a good idea. You lose compile-time check guarantee that a given string resource exists. Just use `context.getString(R.string.blah)` — EpicPandaForce, Jan 04 '19 at 09:57
@EpicPandaForce oh I didn't aware of it. Do you mean using custom class is not a good idea? — Code Lover, Jan 04 '19 at 10:06
I think giving it a `"stringidentifier"` as a string is a bad idea. The utils however won't know anything more if you use `context.getString` directly. — EpicPandaForce, Jan 04 '19 at 10:59

score 3 · Answer 1 · answered Jan 04 '19 at 09:25

3

Context is null. See that even thou you are passing context into constructor, it may be null. And in you case it is. You are initializing Utils in wrong place.

Try to move initialization to onCreateView method - context from there should not be null.

answered Jan 04 '19 at 09:25

Lukas Novicky

921
1
19
44

sushildlh · Accepted Answer · 2019-01-04T09:54:55.840

try this ....

public class PlacesFragment extends Fragment {

    ArrayList<Place>           mPlaces;
    RecyclerView               mRecyclerView;
    RecyclerView.LayoutManager mLayoutManager;
    RecyclerView.Adapter       mAdapter;
    Utils                      utils ; //change line


    public PlacesFragment() {
        // Required empty public constructor
    }


    @Override
    public View onCreateView(
            @NonNull LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState
    ) {

        utils = new Utils(getActivity());//add line

        View rootView = inflater.inflate(R.layout.fragment_places, container, false);

        mRecyclerView = rootView.findViewById(R.id.recyclerView);

        mPlaces = new ArrayList<>();

        mPlaces.add(new Place(
                utils.getStringItem("string_name"),
                "content text goes here.",
                R.drawable.img.cdd,
                4.0f
        ));

        mRecyclerView.setHasFixedSize(true);
        mLayoutManager = new LinearLayoutManager(getActivity());
        mAdapter = new PlacesAdapter(mPlaces);
        mRecyclerView.setLayoutManager(mLayoutManager);
        mRecyclerView.setAdapter(mAdapter);

        return rootView;

    }

}

Note:- You are getting NPE bcoz Utils utils = new Utils(getActivity()); here getActivity() is null. So context you are using in Utility is giving you NPE

Always try to get your activity instance in onAttach() method. It is good practice for further uses or you will get lots of Exception in future bcoz of using getActivity() method.

Like this ...

private Activity activity;

 @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        activity = (Activity) context;
        utils = new Utils(context);
    }

Thanks for the clarification. It is clear to understand with the code. One more question. Is there any way to use it outside onCreateView method? Something like i setting up in constructor? — Code Lover, Jan 04 '19 at 09:42
that was me. `onAttach(Activity a)` is depreciated with `onAttach(Context context)`. Previously this method giving you `Activity` instance and it is changed into `Context` now. — sushildlh, Jan 04 '19 at 09:48

score 0 · Answer 3 · answered Jan 04 '19 at 09:27

0

initialise utils here

@Override
public void onAttach(Activity activity){
    utils = new Utils(getActivity());
}

answered Jan 04 '19 at 09:27

akshay_shahane

4,423
2
17
30

`onAttach(Activity activity)` is deprecated. Currently you can only use `onAttach(Context context)` – sushildlh Jan 04 '19 at 09:37

Android get String in Fragment using custom class

Java Class

Fragment Class

Error Message

3 Answers3