Create Hashmap with object in a static function in fragment

Question

I'm trying to create a hashmap in a static function in a fragment. But I get an error creating the hashmap saying my function cannot be static. Can you tell me how can I do to keep my function static and keeping my hashmap inside?

My fragment :

public class AddMatriceResult extends Fragment {

    private static int i = 0, j = 0, l = 0;
    private static int o = MatriceActivity.n * MatriceActivity.m;


    private static HashMap<String, LinearLayout> layoutresmap = new HashMap<String, LinearLayout>();

    private static HashMap<String, TextView> textviewresmap = new HashMap<String, TextView>();


    private static List<LinearLayout> layoutreslist;

    private static List<TextView> textviewreslist;

    private static TextView noAddMatriceResult;

    private static LinearLayout layoutResultCalc;

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


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

    }

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

        View v = inflater.inflate(R.layout.add_matrice_result, container, false);

        layoutResultCalc = (LinearLayout) v.findViewById(R.id.LayoutMatriceRes);

        noAddMatriceResult = (TextView) v.findViewById(R.id.noAddMatriceResult);

        return v;
    }

    @Override
    public void onViewCreated(View view, Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);


    }

    public static void Result(){
        if(AddMatriceCalc.flag == 1)
        {
            noAddMatriceResult.setVisibility(View.GONE);
            layoutResultCalc.setVisibility(View.VISIBLE);

            for(i=0;i<MatriceActivity.m;i++) {
                layoutresmap.put("layout" + i, new LinearLayout(this.getContext()));
            }
            layoutreslist = new ArrayList<LinearLayout>(layoutresmap.values());

            for(i=0;i<o;i++) {
                textviewresmap.put("textview" + i, new TextView(this.getContext()));
            }
                textviewreslist = new ArrayList<TextView>(textviewresmap.values());

         }
}

Error : this cannot be referenced from a static context on this line :

textviewresmap.put("textview" + i, new TextView(this.getContext()));

Kristy Welsh · Accepted Answer · 2016-04-04T14:22:22.423

Add a static variable to your class:

private static Activity activity;

In your onCreate():

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    activity = getActivity();

}

Then you can write:

public static void Result() {
    if (AddMatriceCalc.flag == 1) {
        noAddMatriceResult.setVisibility(View.GONE);
        layoutResultCalc.setVisibility(View.VISIBLE);

        for (i = 0; i < MatriceActivity.m; i++) {
            layoutresmap.put("layout" + i, new LinearLayout((Context) activity));
        }
        layoutreslist = new ArrayList<LinearLayout>(layoutresmap.values());

        for (i = 0; i < o; i++) {
            textviewresmap.put("textview" + i, new TextView((Context) activity));
        }
        textviewreslist = new ArrayList<TextView>(textviewresmap.values());

    }
}

Thanks it works!! Can you just tell me if it's dangerous, a bad way to code or a good way? — Jey10, Apr 04 '16 at 09:46
I can't imagine the activity ever being null, so I wouldn't think this is a dangerous method. — Kristy Welsh, Apr 04 '16 at 14:21

score 0 · Answer 2 · answered Apr 01 '16 at 14:25

this in Java is a pointer to instance, to itself, so it can't be used with static fields, as this might not exists when you call static method.

For accessing static fields it's a good practice to call it from ClassName:

ClassName.myMap.put(a, b);

Your method can't access this pointer, you need to pass it to the method from elsewhere: public static void Result(Context context){ and get rid of this.getContext()

The solution I gave you is still very dangerous, as the context you will pass to the method might change of disappear and you will get unexpected failures.

Read this material when you have some time:

https://docs.oracle.com/javase/tutorial/java/javaOO/classvars.html

Java: when to use static methods

Create Hashmap with object in a static function in fragment

2 Answers2