从firebase检索数据并在微调器中显示它（下拉列表）

Question

我正在尝试手动将微调器数据添加到firebase，但是当我尝试在微调器下拉列表中显示它时，我收到错误：

  

无法将java.lang.String类型的对象转换为com.appname.appname.ListItem类型。

这是我从firebase检索微调器数据并在下拉微调器中显示它的方法：

 proffRefspin.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {

            Log.e("Spinner Data", "Spinner data is changed!");

            Iterable<DataSnapshot> temp = dataSnapshot.getChildren();
            ArrayList<String> list = new ArrayList<>();
            for (DataSnapshot lists : temp){
                Log.d("ddd","Array List: "+lists.getValue().toString());
                list.add(lists.getValue().toString());
                textView.setText(lists.getValue().toString());
            }
            showDataInSpinner(list);

        }

        @Override
        public void onCancelled(DatabaseError error) {
            // Failed to read value
            Log.e("Error", "Failed to read user", error.toException());
        }
    });

//在微调器中显示数据

 public void showDataInSpinner(ArrayList<String> data) {
    ArrayAdapter<String> adapter = new ArrayAdapter<>(
            this, android.R.layout.simple_spinner_item, data
    ); //Create the Adapter to set the data
    adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item); //Set the layout resource to create the drop down views.
    catSpinner.findViewById(R.id.defaultCats);
    catSpinner.setAdapter(adapter); //Set the data to your spinner
}

这是我的POJO（ListItem模型）

public class ListItem {
    private static final String TAG = "ListItem";
    @Exclude
    String userid;
    private String username,summary,status,details,profession;
    private String imageurl;

    public ListItem(){}



    public ListItem(String username, String summary, String status, String details, String profession, String imageurl) {
        this.username = username;
        this.summary = summary;
        this.status = status;
        this.details = details;
        this.profession = profession;
        this.imageurl = imageurl;
        //this.userid = userid;
    }
    public String getUserid() {
        return userid;
    }
    public void setUserid(String id) {
        this.userid = id;
    }


    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }


    public String getSummary() {
        return summary;
    }
    public void setSummary(String summary) {
        this.summary = summary;
    }

    public String getDetails() {
        return details;
    }
    public void setDetails(String details) {
        this.details = details;
    }


    public String getProfession() {
        return profession;
    }

    public void setProfession(String profession) {
        this.profession = profession;
    }




    public String getStatus() {
        return status;
    }
    public void setStatus(String status) {
        this.status = status;
    }

    public String getImageurl() {
        return imageurl;
    }

    public void setImageurl(String imageUrl) {
        this.imageurl = imageUrl;
    }
}

当我在firebase数据库中手动添加我的职业列表时，我收到了错误消息。但是当firebase db为空时，不会显示错误。我在这做错了什么？我希望能够从firebase显示微调器数据。

这是我试图检索数据的方式

 myRef = mFirebaseDatabase.getReference("Users").child("Professions").child("profession");
    myRef.addChildEventListener(new ChildEventListener() {
        @Override
        public void onChildAdded(DataSnapshot dataSnapshot, String s) {
            ListItem data = dataSnapshot.getValue(ListItem.class);
            listItems.add(data);
            adapter.notifyDataSetChanged();

        }

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

        }

        @Override
        public void onChildRemoved(DataSnapshot dataSnapshot) {

        }

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

        }

        @Override
        public void onCancelled(DatabaseError databaseError) {


        }
    });
}

这是类别片段方法，用于显示来自firebase的职业：

 private void getFirebaseData() {

    myRef = mFirebaseDatabase.getReference("Users").child("Professions").child("profession");
    myRef.addChildEventListener(new ChildEventListener() {
        @Override
        public void onChildAdded(DataSnapshot dataSnapshot, String s) {
            ProfessionsList data = dataSnapshot.getValue(ProfessionsList.class);
            proffItems.add(data);
            adapter.notifyDataSetChanged();

        }

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

        }

        @Override
        public void onChildRemoved(DataSnapshot dataSnapshot) {

        }

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

        }

        @Override
        public void onCancelled(DatabaseError databaseError) {


        }
    });
}

但我收到错误： Can't convert object of type java.lang.String to type com.appname.appname.ListItem。

图片firebase数据结构的屏幕截图： Firebase Data screenshot

Answer 1

从firebase获取数据

ArrayList<Category> categoryList = new ArrayList<>();

databaseReference.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            for (DataSnapshot postSnapshot : dataSnapshot.getChildren()) {
                categoryList.add(postSnapshot.getValue(Category.class));
            }
            loadDataInSpinner();
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });

在微调器适配器中加载数据

 private void loadDataInSpinner(){
        categoryArrayAdapter = new ArrayAdapter<>(getContext(), android.R.layout.simple_spinner_dropdown_item, categoryList);
        spinnerPostCategory.setAdapter(categoryArrayAdapter);
        spinnerPostCategory.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
            @Override
            public void onItemSelected(AdapterView<?> adapterView, View view, int i, long l) {
                Category category = (Category) adapterView.getSelectedItem();
                spinnerSelectedId= category.getCategoryId();
                spinnerSelectedName = category.getCategoryName();
            }

            @Override
            public void onNothingSelected(AdapterView<?> adapterView) {

            }
        });
    }

Answer 2

试试这个：

ArrayList<String> list = new ArrayList<>();  
proffRefspin.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
     for(DataSnapshot datas: dataSnapshot.getChildren()){
          String profession=datas.child("profession").getValue().toString();
          list.add(profession);
     ArrayAdapter<String> adapter = new ArrayAdapter<>(this, android.R.layout.simple_spinner_item, list); 
     adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
      spinner.setAdapter(adapter);
        }


    }

    @Override
    public void onCancelled(DatabaseError error) {
        // Failed to read value
        Log.e("Error", "Failed to read user", error.toException());
    }
});

只添加您在数据库中手动添加的专业，这样您就可以在微调器中拥有一个专业列表，用户以后可以选择。您可能需要更改位置（proffRefspin），具体取决于您添加professions的位置

将您的数据库更改为：

Users
 Professions
     randomid
         professionname: software engineer
     randomid
         professionname: data science

然后这样做：

  myRef = mFirebaseDatabase.getReference("Users").child("Professions");
myRef.addChildEventListener(new ChildEventListener() {
    @Override
    public void onChildAdded(DataSnapshot dataSnapshot, String s) {
        String prof=dataSnapshot.child("professionname").getValue().toString();
        proffItems.add(prof);
        adapter.notifyDataSetChanged();

    }

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

    }

    @Override
    public void onChildRemoved(DataSnapshot dataSnapshot) {

    }

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

    }

    @Override
    public void onCancelled(DatabaseError databaseError) {


    }
});