How to Retrieve a List object from the firebase in android

Question

I am having trouble retrieving a List from the Firebase. I have no trouble storing it, but as soon as I try to cast dataSnapshot.getValue() to ArrayList my app crashes, giving an exception:

HashMap cannot be casted to ArrayList

But when I tried to cast it to a HashMap, it also crashes, giving exception:

ArrayList can't be casted to hashmap

Need help please! Here is the code that is creating the problem:

Fire.addValueEventListener(new ValueEventListener() {     @Override     public void onDataChange(DataSnapshot dataSnapshot) {         List<TaskDes> td = (ArrayList<TaskDes>) dataSnapshot.getValue()         notifyDataSetChanged();     }      @Override     public void onCancelled(FirebaseError firebaseError) {      } }); 

I want to retrieve all the data in the Firebase as one List. The class TaskDes contains three fields:

class TaskDes { // definition     boolean done     String taskDescription     String taskTitle } 

Answer 1

You need to create a GenericTypeIndicator object to pass as DataSnapshot.getValue() parameter.

Code:

GenericTypeIndicator<List<String>> t = new GenericTypeIndicator<List<String>>() {};  List<String> yourStringArray = dataSnapshot.getValue(t); 

Answer 2

Your Model

public class TaskDes {     private boolean done;     private String taskDescription;     private String taskTitle;      public TaskDes() {     }      public boolean isDone() {         return done;     }      public void setDone(boolean done) {         this.done = done;     }      public String getTaskDescription() {         return taskDescription;     }      public void setTaskDescription(String taskDescription) {         this.taskDescription = taskDescription;     }      public String getTaskTitle() {         return taskTitle;     }      public void setTaskTitle(String taskTitle) {         this.taskTitle = taskTitle;     }  } 

You need to create a GenericTypeIndicator object to pass as DataSnapshot.getValue() parameter.

In Activity

 private static final String TAG=MainActivity.class.getSimpleName();  private FirebaseDatabase database;  private DatabaseReference myRef=null;   @Override  protected void onCreate(Bundle savedInstanceState){     super.onCreate(savedInstanceState);     setContentView(R.layout.activity_main);      database=FirebaseDatabase.getInstance();     myRef=database.getReference("ADD_YOUR_REFERECE");       myRef.addValueEventListener(new ValueEventListener(){        @Override        public void onDataChange(DataSnapshot dataSnapshot){           /* This method is called once with the initial value and again whenever data at this location is updated.*/           long value=dataSnapshot.getChildrenCount();           Log.d(TAG,"no of children: "+value);            GenericTypeIndicator<List<TaskDes>> genericTypeIndicator =new GenericTypeIndicator<List<TaskDes>>(){};            List<TaskDes> taskDesList=dataSnapshot.getValue(genericTypeIndicator);            for(int i=0;i<taskDesList.size();i++){              Toast.makeText(MainActivity.this,"TaskTitle = "+taskDesList.get(i).getTaskTitle(),Toast.LENGTH_LONG).show();           }        }         @Override        public void onCancelled(DatabaseError error){           // Failed to read value           Log.w(TAG,"Failed to read value.",error.toException());        }     });  }