如何读取 Firebase 实时数据库中的嵌套数据（哈希图）

Question

I follow with this tutorial and save mutliple image to my firebase database:

Gallery is hashmap, how I Can read this data?

My POJO class:

public class Tasks {
String titletask, decriptiontask, datetask, keytask, imagetask;
HashMap<String,String> gallery;

When I try with this code:

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

        for(DataSnapshot dataSnapshot1: dataSnapshot.getChildren())
        {
            Tasks task = dataSnapshot1.getValue(Tasks.class);
            list.add(task);
        }
        adapter = new TasksAdapter(getActivity(),list);
        mRecyclerView.setAdapter(adapter);
        adapter.notifyDataSetChanged();
    }

I have a error:

Failed to convert value of type java.util.HashMap to String

Answer 1

This field in your Tasks class:

HashMap<String,String> gallery;

Would translate to a JSON structure like this:

"gallery": {
  "key1": "value1",
  "key2": "value2",
  "key3": "value3"
}

Since that is not the structure you have, the mapping will fail.

---

To describe you JSON you'll either need to define a class for each gallery item:

public class GalleryItem {
  public String ImgLink;
}

And then:

HashMap<String,GalleryItem> gallery;

---

Alternatively you may be able to get away with Object :

HashMap<String,Object> gallery;

And (if this indeed works) treat the values in the gallery map as Map<String, String> themselves.