Android Studio Java：如果产品已经存在于我的购物车活动中，我如何更新我的数量？

Question

我面临的问题是，我不知道如何更新购物车活动中已经存在的产品数量。我正在尝试从firebase中检索数据，但无法执行此操作。

这是我的代码：

private void addToCart() {
    DatabaseReference databaseReference = FirebaseDatabase.getInstance().getReference("User Type").child(firebaseAuth.getUid());
    databaseReference
            .addListenerForSingleValueEvent(new ValueEventListener() {
                @Override
                public void onDataChange(@NonNull DataSnapshot snapshot) {
                    for (DataSnapshot dataSnapshot : snapshot.getChildren()) {
                            if (dataSnapshot.child(firebaseAuth.getUid()).child("Cart").child(productID).exists()){
                                //update to firebase
                                String addedQty1 = "" + snapshot.child("addedQuantity").getValue();
                                int getQty = Integer.parseInt(addedQty1);
                                int currentQty = Integer.parseInt(addedQty);

                                int newAddedQty = getQty + currentQty;

                                String addedNewQty = String.valueOf(newAddedQty);

                                HashMap<String, Object> hashMap1 = new HashMap<>();
                                hashMap1.put("addedQuantity", "" + addedNewQty);

                                DatabaseReference databaseReference = FirebaseDatabase.getInstance().getReference("User Type");
                                databaseReference.child(firebaseAuth.getUid()).child("Cart").child(productID).updateChildren(hashMap1)
                                        .addOnSuccessListener(new OnSuccessListener<Void>() {
                                            @Override
                                            public void onSuccess(Void aVoid) {
                                                //updated
                                                progressDialog.dismiss();
                                                Toast.makeText(ViewProductDetails.this, "Added successfully.", Toast.LENGTH_SHORT).show();
                                            }
                                        })
                                        .addOnFailureListener(new OnFailureListener() {
                                            @Override
                                            public void onFailure(@NonNull Exception e) {
                                                //failed to update
                                                progressDialog.dismiss();
                                                Toast.makeText(ViewProductDetails.this, "" + e.getMessage(), Toast.LENGTH_LONG).show();
                                            }
                                        });
                            } else {
                                //Add to firebase
                                final String timestamp = "" + System.currentTimeMillis();

                                HashMap<String, Object> hashMap = new HashMap<>();
                                hashMap.put("cartID", "" + timestamp);
                                hashMap.put("accountID", "" + accountID);
                                hashMap.put("productID", "" + productID);
                                hashMap.put("orderFrom", "" + shopName);
                                hashMap.put("discountNote", "" + discountNote);
                                hashMap.put("originalPrice", "" + oriPrice);
                                hashMap.put("discountPrice", "" + discountedPrice);
                                hashMap.put("price", "" + price);
                                hashMap.put("productTitle", "" + productTitle);
                                hashMap.put("productCategory", "" + category);
                                hashMap.put("productSize", "" + size);
                                hashMap.put("productQuantity", "" + availableQty);
                                hashMap.put("addedQuantity", "" + addedQty);

                                //add to firebase
                                DatabaseReference databaseReference = FirebaseDatabase.getInstance().getReference("User Type");
                                databaseReference.child(firebaseAuth.getUid()).child("Cart").child(productID).setValue(hashMap)
                                        .addOnSuccessListener(new OnSuccessListener<Void>() {
                                            @Override
                                            public void onSuccess(Void aVoid) {
                                              
                                                progressDialog.dismiss();
                                                Toast.makeText(ViewProductDetails.this, "Added successfully.", Toast.LENGTH_SHORT).show();
                                                
                                            }
                                        })
                                        .addOnFailureListener(new OnFailureListener() {
                                            @Override
                                            public void onFailure(@NonNull Exception e) {
                                                //failed to update
                                                progressDialog.dismiss();
                                                Toast.makeText(ViewProductDetails.this, "" + e.getMessage(), Toast.LENGTH_LONG).show();
                                            }
                                        });
                            }
                        }
                    }

                @Override
                public void onCancelled(@NonNull DatabaseError error) {

                }
            });

}

我已经分享了代码片段，其中“其他”语句运行正常，而“如果”语句运行失败。希望有人能帮助我。我真的很感激！

Answer 1

您的基本解决方案应该看起来像下面的伪代码：

if (product already in cart) {
  get current product count from cart
  increment product count
  store new count back in cart
}

这是一个测试和三个操作。检查所有四个都存在并且所有四个都工作。如果可以，最好分开测试，这样你就可以更容易地隔离错误。