How to get random documents from Firestore and display them in different TextViews?

Question

In my app the user should be able to choose from 3 different categories (out of 8) which are randomly generated. For this I used the approach described here.

I don't know how to use this approach to use the retrieved documents to insert them into the TextViews in my Category Activity. I created a category class to store the retrieved documents from Firestore but I also don't know if that is even the right approach. I would very much appreciate every tip!

Here is my Category Activity where the 3 documents get retrieved and in the end should be displayed in the TextViews:

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

        View view = inflater.inflate(R.layout.activity_category_selection, container, false);

        tvCategory1 = view.findViewById(R.id.text_view_category_1);
        tvCategory2 = view.findViewById(R.id.text_view_category_2);
        tvCategory3 = view.findViewById(R.id.text_view_category_3);
        textViewCategoryRound = view.findViewById(R.id.text_view_category_round);

        imageCategory1 = view.findViewById(R.id.image_category_1);
        imageCategory2 = view.findViewById(R.id.image_category_2);
        imageCategory3 = view.findViewById(R.id.image_category_3);

        categoryCollectionRef.get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
            @Override
            public void onComplete(@NonNull Task<QuerySnapshot> task) {
                if (task.isSuccessful()) {

                    List<Category> categoryList = new ArrayList<>();
                    for (DocumentSnapshot document : task.getResult()) {
                        Category category = document.toObject(Category.class);
                        categoryList.add(category);
                    }

                    int categoryListSize = categoryList.size();
                    List<Category> randomCategoryList = new ArrayList<>();
                    for (int i = 0; i < categoryListSize; i++) {
                        Category randomCategory = categoryList.get(new Random().nextInt(categoryListSize));
                        if (!randomCategoryList.contains(randomCategory)) {
                            randomCategoryList.add(randomCategory);
                            if (randomCategoryList.size() == 3) {

                                break;

                            }
                        } else {
                            Log.d(TAG, "Error getting documents: ", task.getException());
                        }
                    }

                }
            }
        });

        return view;
    }
}

Here is the category class where I hope I store the documents correctly:

public class Category {

    public String category_name;


    public String picture_id;

    public Category (){

    }


    public String getPicture_id() {
        return picture_id;
    }

    public void setPicture_id(String picture_id) {
        this.picture_id = picture_id;
    }

    public String getCategory_name() {
        return category_name;
    }

    public void setCategory_name(String category_name) {
        this.category_name = category_name;
    }

    public Category(String category_name){
        this.category_name = category_name;
    }
}

Here is the way I structured my Category collection (there are 8 documents/categories):

I don't understand which part of the problem you're stuck on. — Doug Stevenson, Jan 06 '20 at 16:07
The problem was that I did not know if I used the both code in the right way to retrieve the documents. And I also did not know how to display the documents in the TextViews in the CategoryActivity but Numan Turkeri had the right way — Kaiser, Jan 06 '20 at 16:38

score 1 · Accepted Answer · answered Jan 06 '20 at 14:36

Hi i can suggest easy way.

 List<Category> categoryList =null;

   categoryCollectionRef.get().addOnCompleteListener(new 
   OnCompleteListener<QuerySnapshot>() {
        @Override
        public void onComplete(@NonNull Task<QuerySnapshot> task) {
            if (task.isSuccessful()) {

               categoryList = new ArrayList<>();
                for (DocumentSnapshot document : task.getResult()) {
                    Category category = document.toObject(Category.class);
                    categoryList.add(category);
                }



                }

            }
        }
    });
testButtonClickListener....{
Collections.shuffle(categoryList);
    showShuffledList();
}
public void showShuffledList(){
textView1.setText(categoryList.get(0).getCategoryName())
 textView2.setText(categoryList.get(1).getCategoryName())
 textView3.setText(categoryList.get(2).getCategoryName())
}

Of course you should add null check all steps and configure more way.

score 0 · Answer 2 · answered Jan 06 '20 at 14:02

You can do 3 things:

1) when saving the docs name them with an incremental number at the end, then generate 3 random numbers in range and fetch the docs ending in those numbers.

2) add a field in all docs that holds a unique number and follow similar approach to the above but using a query on those fields.

3) create a special doc that has the names of all other docs in an array. Then fetch 3 doc names from the array based on the generated random numbers.

There might be other ways too, but those are the approaches that first come to my mind.

How to get random documents from Firestore and display them in different TextViews?

2 Answers2