如何在 OnDestroy 中删除此 firebase 侦听器以减少内存泄漏？

Question

This is my product showing function. When I access this activity from another, the other activity gets destroyed maybe because of memory leaks. How do I fix this issue? How do I close the listeners? I want to destroy this is OnDestroy method because it might be causing a memory leak and also I've read that it's a good practice to do so.

private void getProductDetails(String productID) {
        DatabaseReference productsRef = FirebaseDatabase.getInstance().getReference().child("Products");
        productsRef.child(productID).addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NotNull DataSnapshot dataSnapshot) {
                if (dataSnapshot.exists()){
                    Products products = dataSnapshot.getValue(Products.class);
                    productName.setText(products.getPname());
                    productPrice.setText(products.getPrice());
                    if (products.getInStock().equals("Yes")){
                        inStock.setText("In Stock");
                        inStock.setTextColor(ContextCompat.getColor(ProductDetailsActivity.this,R.color.primary));
                    }else {
                        inStock.setText("Not In Stock");
                        inStock.setTextColor(ContextCompat.getColor(ProductDetailsActivity.this,R.color.red));
                        addToCartBtn.setEnabled(false);
                    }
                    ifFreeDelivery = "No";
                    DatabaseReference mref;
                    final String[] phone = new String[1];
                    mref = FirebaseDatabase.getInstance().getReference("Values").child("deliveryCharge");
                    mref.addListenerForSingleValueEvent(new ValueEventListener() {
                        @Override
                        public void onDataChange(DataSnapshot dataSnapshot) {
                            phone[0] = dataSnapshot.getValue(String.class);
                            deliveryCharge = Integer.parseInt(phone[0]);
                            //do what you want with the likes
                        }

                        @Override
                        public void onCancelled(DatabaseError databaseError) {

                        }
                    });


                    Products productsImg = dataSnapshot.getValue(Products.class);
                    ArrayList<String> test = productsImg.getImage();
                    DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
                    DatabaseReference myRef = rootRef.child("Products").child(products.getPid()).child("image");
                    myRef.addChildEventListener(new ChildEventListener() {
                        @Override
                        public void onChildAdded(DataSnapshot dataSnapshot, String s) {
                            //this will be called for every child in your list
                            test.add(s);
                        }

                        @Override
                        public void onChildChanged(DataSnapshot dataSnapshot, String s) {
                            //this will be called for every child changed in your list
                        }

                        @Override
                        public void onChildRemoved(DataSnapshot dataSnapshot) {

                        }

                        @Override
                        public void onChildMoved(DataSnapshot dataSnapshot, String s) {

                        }

                        @Override
                        public void onCancelled(DatabaseError databaseError) {

                        }

                    });
                    ArrayList<SlideModel> images = new ArrayList<>();
                    for(int i = 0; i < test.size() ; i++) {
                        images.add(new SlideModel(test.get(i),null));

                    }
                    productImage.setImageList(images);
                    productImgDownloadBtn.setOnClickListener(v -> {
                        for(int i = 0; i < products.getPicCount() ; i++) {
                            String url = test.get(i).replace(" ","");
                            DownloadImage(url);



                        }
                    });


                    productDescription.setText(products.getDescription());
                    productDetailsCopyBtn.setOnClickListener(new View.OnClickListener() {
                        @Override
                        public void onClick(View view) {
                            ClipboardManager clipboard = (ClipboardManager) getSystemService(Context.CLIPBOARD_SERVICE);
                            ClipData clip = ClipData.newPlainText("Product description",products.getDescription());
                            clipboard.setPrimaryClip(clip);
                            Toast.makeText(ProductDetailsActivity.this, "Product description copied..", Toast.LENGTH_SHORT).show();
                        }
                    });
                    //Picasso.get().load(products.getImage().get(0)).into(productImage);
                }
            }


            @Override
            public void onCancelled(@NonNull @NotNull DatabaseError databaseError) {

            }

        });
        

    }

Answer 1

As I see in your code, you are using in the first part addValueEventListener() , which means that you are listening for real-time updates. That kind of listener should be removed according to the life cycle of your activity . Please also note, that the onDestroy is not always called .

However, when using addListenerForSingleValueEvent() , there is no need to remove any listener, because it only reads the data once.