Reading data from firebase database to a custom listView

Question

I am trying to read data that I inserted into firebase database, I want to display the data in custom listView. I am using this method but it seems that I am missing something. I can't insert data into my arraylist. UPDATED I inserted the values and now it gives me

attempt to invoke a virtual method on a null object reference on my get methods

private void showData(DataSnapshot dataSnapshot) {
    for (DataSnapshot ds : dataSnapshot.getChildren()) {
        PatientInformation patientInfo = new PatientInformation();
        patientInfo.setName(ds.child(userID).getValue(PatientInformation.class).getName());
        patientInfo.setAge(ds.child(userID).getValue(PatientInformation.class).getAge());
        patientInfo.setDate(ds.child(userID).getValue(PatientInformation.class).getDate());
        ArrayList<PatientInformation> arrayList = new ArrayList<>();
        arrayList.add(patientInfo);
        PatientInformationAdapter pAdapter = new PatientInformationAdapter(this, arrayList);
        listView.setAdapter(pAdapter);
    }

Answer 1

Your arrayList is of type PatientInformation so I think you could just add patientInfo which is of type PatientInformation also.

private void showData(DataSnapshot dataSnapshot) {
for (DataSnapshot ds : dataSnapshot.getChildren()) {
    PatientInformation patientInfo = new PatientInformation();
    patientInfo.setName(ds.child(userID).getValue(PatientInformation.class).getName());
    patientInfo.setAge(ds.child(userID).getValue(PatientInformation.class).getAge());
    patientInfo.setDate(ds.child(userID).getValue(PatientInformation.class).getDate());
    ArrayList<PatientInformation> arrayList = new ArrayList<>();
    arrayList.add(patientInfo);

    PatientInformationAdapter pAdapter = new PatientInformationAdapter(this, arrayList);
    listView.setAdapter(pAdapter);
}

Answer 2

You're creating a new array list and adapter for every child node of the results. You probably want to create only one array list and adapter, like this:

private void showData(DataSnapshot dataSnapshot) {
    ArrayList<PatientInformation> arrayList = new ArrayList<>();
    for (DataSnapshot ds : dataSnapshot.getChildren()) {
        PatientInformation patientInfo = ds.child(userID).getValue(PatientInformation.class)
        arrayList.add(patientInfo);
    }
    PatientInformationAdapter pAdapter = new PatientInformationAdapter(this, arrayList);
    listView.setAdapter(pAdapter);
}