Getting data from fragments on button click in host activity

Question

So I'm creating this app that allows users to search for recipes by ingredients, categories, and preparation time.

Initially, I had 3 activities:

• IngredientActivity, where the user chooses ingredients they have.
• CategoryActivity, where they can choose multiple food categories from a list.
• TimeActivity, which allows users to choose maximum preparation time.

However, it was such a hassle this way as I had to pass the data the user chose with an Intent to the next activity with a next button, and it was a mess always getting and adding extras until I got to the last activity, plus I wanted to be able to move freely between the 3 "pages", and not be restricted to going through them one by one.

This didn't seem efficient to me so I decided to change those activities into fragments and use a ViewPager to display them in tabs in a host activity (MainActivity), but it seems it's a different kind of hassle now.

I have a Search button in the MainActivity, and I'm having difficulty getting the data the user chose from all 3 fragments all at once when the Search button is clicked. I read about interfaces, but I'm not sure if it's the solution. I thought maybe I could define an OnSearchClickListener interface in all 3 fragments, but can I implement one interface for 3 fragments, with each fragment returning different data?

Did I make a mistake transitioning to fragments? However, it seemed the most efficient way to do it... How can I get all the data from the fragments when the search button is clicked?

Answer 1

Note: updated upon clarifications in comments

I would do the following:

1. In each of the three fragments, implement method getSearchCriteria, with each returning value specific to that fragment.

2. Implement one OnClickListener for the search button - at the activity level.

3. Inside that listener, call getSearchCriteria on each of the fragments - and do whatever you need to do with all the collated results, something like this:

   findViewById(R.id.button_search).setOnClickListener(new OnClickListener() {
       public void onClick(View v) {
           List<String> ingredients = ingredientFragment.getSearchCriteria();
           List<String> categories = categoryFragment.getSearchCriteria();
           int maxMinutes = timeFragment.getSearchCriteria();
   
           // now you have all three things together - do what you need to with them
       }
   });
   

Answer 2

If you notify the MainActivity every time the criteria is updated, you can update their respective criterias and have them available to use when searching (see onSearchClicked)

IngredientFragment.java

public class IngredientFragment extends Fragment {
    EditText editText;
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        View view = inflater.inflate(R.layout.fragment_ingredient, container, false);
        editText = (EditText)view.findViewById(R.id.edit_text);//assuming user type in the criteria in an edit box
        return view;
    }

    public void onClick(View view){//user interaction to signal criteria updated. Replace this with onItemClickListener etc, if you are using ListView
        if (mListener != null) {
            mListener.onIngredientCriteriaUpdated(String.valueOf(editText.getText()));
        }
    }

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        if (context instanceof OnIngredientFragmentListener) {
            mListener = (OnIngredientFragmentListener) context;
        } else {
            throw new RuntimeException(context.toString()
                    + " must implement OnIngredientFragmentListener");
        }
    }

    @Override
    public void onDetach() {
        super.onDetach();
        mListener = null;
    }

    public interface OnIngredientFragmentListener {
        // TODO: Update argument type and name
        void onIngredientCriteriaUpdated(String criteria);
    }
}

CategoryFragment.java

public class CategoryFragment extends Fragment {
    EditText editText;
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        View view = inflater.inflate(R.layout.fragment_category, container, false);
        editText = (EditText)view.findViewById(R.id.edit_text);//assuming user type in the criteria in an edit box
        return view;
    }

    public void onClick(View view){//user interaction to signal criteria updated. Replace this with onItemClickListener etc, if you are using ListView
        if (mListener != null) {
            mListener.onCategoryCriteriaUpdated(String.valueOf(editText.getText()));
        }
    }

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        if (context instanceof OnCategoryFragmentListener) {
            mListener = (OnCategoryFragmentListener) context;
        } else {
            throw new RuntimeException(context.toString()
                    + " must implement OnCategoryFragmentListener");
        }
    }

    @Override
    public void onDetach() {
        super.onDetach();
        mListener = null;
    }

    public interface OnCategoryFragmentListener {
        // TODO: Update argument type and name
        void onCategoryCriteriaUpdated(String criteria);
    }
}

TimeFragment.java

public class TimeFragment extends Fragment {
    EditText editText;
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        View view = inflater.inflate(R.layout.fragment_category, container, false);
        editText = (EditText)view.findViewById(R.id.edit_text);//assuming user type in the criteria in an edit box
        return view;
    }

    public void onClick(View view){//user interaction to signal criteria updated
        if (mListener != null) {
            mListener.onTimeCriteriaUpdated(String.valueOf(editText.getText()));
        }
    }

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        if (context instanceof OnTimeFragmentListener) {
            mListener = (OnTimeFragmentListener) context;
        } else {
            throw new RuntimeException(context.toString()
                    + " must implement OnTimeFragmentListener");
        }
    }

    @Override
    public void onDetach() {
        super.onDetach();
        mListener = null;
    }

    public interface OnTimeFragmentListener {
        // TODO: Update argument type and name
        void onTimeCriteriaUpdated(String criteria);
    }
}

MainActivity.java (partial code)

public class MainActivity extends AppCompatActivity implements
    IngredientFragment.OnIngredientFragmentListener,
    CategoryFragment.OnCategoryFragmentListener,
    TimeFragment.OnTimeFragmentListener {

    private String ingredientCriteria;
    private String categoryCriteria;
    private String timeCriteria;

    :
    :
    :

    @Override
    public void onIngredientCriteriaUpdated(String criteria) {
        ingredientCriteria = criteria;
    }

    @Override
    public void onCategoryCriteriaUpdated(String criteria) {
        categoryCriteria = criteria;
    }

    @Override
    public void onTimeCriteriaUpdated(String criteria) {
        timeCriteria = criteria;
    }

    public void onSearchClicked(View view){//handler for your search button
        //do search using value of ingredientCriteria + categoryCriteria + timeCriteria
    }
}