Firebase 评论查看错误 - 反序列化时需要一个列表，但有一个类 java.util.HashMap

Question

当我尝试在列表中显示 cmets 时出现此错误 - com.google.firebase.database.DatabaseException：反序列化时需要一个列表，但得到一个类 java.util.HashMap 在 com.google.firebase.database.core.utilities.encoding.CustomClassMapper.deserializeToParameterizedType(CustomClassMapper.java:251) 在 com.google.firebase.database.core.utilities.encoding.CustomClassMapper.deserializeToType(CustomClassMapper.java:177) 在 com.google.firebase.database.core.utilities.encoding.CustomClassMapper.access$100(CustomClassMapper.java:48) 在 com.google.firebase.database.core.utilities.encoding.CustomClassMapper$BeanMapper.deserialize(CustomClassMapper.java:593) 在 com.google.firebase.database.core.utilities.encoding.CustomClassMapper$BeanMapper.deserialize(CustomClassMapper.java:563) 在 com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertBean(CustomClassMapper.java:433) 在 com.google.firebase.database.core.utilities.encoding.CustomClassMapper.deserializeToClass(CustomClassMapper.java:232) 在 com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertToCustomClass(CustomClassMapper.java:80)

我的评论显示活动 -

myRef.child("Photo")
            .child(mphoto.getPhoto_id())
            .child("comments")
            .addChildEventListener(new ChildEventListener() {
                @Override
                public void onChildAdded(@NonNull DataSnapshot snapshot, @Nullable String previousChildName) {

                    Log.d(TAG, "onChildAdded: child added.");

                    Query query = myRef
                            .child("Photo")
                            .orderByChild("photo_id")
                            .equalTo(mphoto.getPhoto_id());
                    query.addListenerForSingleValueEvent(new ValueEventListener() {
                        @Override
                        public void onDataChange(@NonNull DataSnapshot dsnapshot) {
                            for ( DataSnapshot singleSnapshot :  dsnapshot.getChildren()){
                                Photo photo = new Photo();
                                Map<String, Object> objectMap = (HashMap<String, Object>) singleSnapshot.getValue();

                                photo.setCaption(objectMap.get("caption").toString());
                                photo.setTags(objectMap.get("tags").toString());
                                photo.setPhoto_id(objectMap.get("photo_id").toString());
                                photo.setUser_id(objectMap.get("user_id").toString());
                                photo.setDate_Created(objectMap.get("date_Created").toString());
                                photo.setImage_Path(objectMap.get("image_Path").toString());

                                mComments.clear();
                                Comments firstComment = new Comments();
                                firstComment.setUser_id(mphoto.getUser_id());
                                firstComment.setComment(mphoto.getCaption());
                                firstComment.setDate_created(mphoto.getDate_Created());
                                mComments.add(firstComment);

                                List<Comments> commentsList = new ArrayList<Comments>();
                                for (DataSnapshot dSnapshot : singleSnapshot
                                        .child("comments").getChildren()){
                                    Comments comments = new Comments();
                                    comments.setUser_id(dSnapshot.getValue(Comments.class).getUser_id());
                                    comments.setComment(dSnapshot.getValue(Comments.class).getComment());
                                    comments.setDate_created(dSnapshot.getValue(Comments.class).getDate_created());
                                    mComments.add(comments);
                                }
                                photo.setComments(mComments);
                                mphoto=photo;
                                setupWidgets();
                            }
                        }

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

                        }
                    });


                }

                @Override
                public void onChildChanged(@NonNull DataSnapshot snapshot, @Nullable String previousChildName) {

                }

                @Override
                public void onChildRemoved(@NonNull DataSnapshot snapshot) {

                }

                @Override
                public void onChildMoved(@NonNull DataSnapshot snapshot, @Nullable String previousChildName) {

                }

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

                }
            });

Answer 1

错误提示

反序列化时需要一个列表，但得到了一个类 java.util.HashMap

这可能会出错

Map<String, Object> objectMap = (HashMap<String, Object>) singleSnapshot.getValue();

您可以更改它并使其变得简单，如下所示

String caption = singleSnapshot.child("caption").getValue(String.class);

photo.setCaption(objectMap.get("caption").toString());//So you wont able to do this

photo.setCaption(caption);//And you can use like this                         

而不是使用这个

Map<String, Object> objectMap = (HashMap<String, Object>) singleSnapshot.getValue();

                            photo.setCaption(objectMap.get("caption").toString());
                            photo.setTags(objectMap.get("tags").toString());
                            photo.setPhoto_id(objectMap.get("photo_id").toString());
                            photo.setUser_id(objectMap.get("user_id").toString());
                            photo.setDate_Created(objectMap.get("date_Created").toString());
                            photo.setImage_Path(objectMap.get("image_Path").toString());

用这个替换它

 String caption=singleSnapshot.child("caption").getValue(String.class);
 String tags= singleSnapshot.child("tags").getValue(String.class);
 String photo_id=singleSnapshot.child("photo_id").getValue(String.class);
 String user_id= singleSnapshot.child("user_id").getValue(String.class);
 String date_Created = singleSnapshot.child("date_Created").getValue(String.class);
 String image_Path= singleSnapshot.child("image_Path").getValue(String.class);


 photo.setCaption(caption);                      
 photo.setTags(tags);                     
 photo.setPhoto_id(photo_id);                      
 photo.setUser_id(user_id);                      
 photo.setDate_Created(date_Created);       
 photo.setImage_Path(image_Path);

你可以看到没有objectMap