为什么我的 else 块没有在 java android 工作室的 OnClickListener 中执行

Question

i created a feature that lets my app users favorite shops. now if a user already favorited a shop and clicks on the button again it should delete the record from the firestore database.

my code works only if there is a match to the query and the task is successful, but doesnt execute my else part of the code. why is that?

and here isthe below code works fine when there is a match for the query and the task is successful , but when there isn't it doesnt execute the else part. anyone know why?

public void onClick(View view) {
        Task ref = fStore.collection("Favorites")
           .whereEqualTo("shopID", SID).whereEqualTo("usersID", UID)
                      .get()
          .addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
                       @Override
     public void onComplete(@NonNull Task<QuerySnapshot> task) {
                    if (task.isSuccessful()) {
             for (QueryDocumentSnapshot document : task.getResult()) {
                              document.getReference().delete();
                                        }
                   } else {
      Map<String, Object> fav = new HashMap<>();
    
                         

         fav.put("shopID", SID);
         fav.put("usersID", UID);
         fav.put("ShopHeaderImg", sHI);
         fav.put("ShopProfileImg", sPI);
         fav.put("address", sA);
         fav.put("costEst", sCost);
         fav.put("country", sC);
         fav.put("latitude", sLat);
         fav.put("location", sL);
         fav.put("name", sN);
         fav.put("numTables", sNumTable);
         fav.put("ratings", sR);
         fav.put("summary", sSummary);
         fav.put("timing", sT);
    
    
                                      
      fStore.collection("Favorites").add(fav)
.addOnSuccessListener(new OnSuccessListener<DocumentReference>() {
                       @Override
     public void onSuccess(DocumentReference documentReference) {
                                                Toast.makeText(DetailsActivity.this, "Saved", Toast.LENGTH_SHORT).show();
     }).addOnFailureListener(new OnFailureListener() {
    public void onFailure(@NonNull Exception e) {
   Toast.makeText(DetailsActivity.this, "Something went wrong", Toast.LENGTH_SHORT).show();
                                            }
                                        });
                                    }
                                }
                          

  });

Answer 1

I think you are misunderstanding what task.isSuccessful() means. That method will return true if there were no errors during the execution of the query. A query that returns no documents isn't an error. That situation is perfectly normal, and considered successful. An error only happens when you try to execute a query that Firestore can't actually run.

If you want to check if a query returned no documents, you should look at the QuerySnapshot contained in the task results. It has a method isEmpty() that will tell you if there are documents.

public void onComplete(@NonNull Task<QuerySnapshot> task) {
    if (task.isSuccessful()) {
        QuerySnapshot querySnapshot = task.getResult();
        if (querySnapshot.isEmpty()) {
            // put code here to deal with no documents in the result
        }
        else {
            // put code here to deal with documents present in the result
            for (QueryDocumentSnapshot document : querySnapshot) {
            }
        }
    }
}