I'm trying to make a student registration system and I keep these students in firestore. I don't want it to add student with same number when adding student and for this, I created a singleton class. This singleton class has a flag value. I used this flag to provide control if there is a student with the same number in the firestore.
but it always returns null. I don't understand.
I'm just sharing the necessary codes.
My add student class
private ActivityOgrenciEkleBinding binding;
private FirebaseFirestore mFirestore = FirebaseFirestore.getInstance();
private LinkedHashMap<String,String> linkedHashMap;
private OgrenciyiKontrolEt ogrenciyiKontrolEt;
Singleton singleton;
public void init(){
linkedHashMap = new LinkedHashMap<>();
singleton = Singleton.getInstance();
btn_Ogrenci_EKLE();
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
binding = ActivityOgrenciEkleBinding.inflate(getLayoutInflater());
View view = binding.getRoot();
setContentView(view);
init();
}
public void btn_Ogrenci_EKLE(){
binding.btnEkleOgrenci.setOnClickListener(new View.OnClickListener()
{
@Override
public void onClick(View view) {
String email_ogr = binding.emailOgrenci.getText().toString();
String ad_ogr = binding.isimOgrenci.getText().toString();
String soyisim_ogr = binding.soyisimOgrenci.getText().toString();
String no_ogr = binding.numaraOgrenci.getText().toString();
String parola_ogr = binding.sifreOgrenci.getText().toString();
ogrenciyiKontrolEt = new
OgrenciyiKontrolEt(no_ogr,OgrenciEkleActivity.this);// I
//created object from
//control class to check students
if(email_ogr.equals("") || ad_ogr.equals("") || soyisim_ogr.equals("") || no_ogr.equals("") || parola_ogr.equals("")){
AlertDialog.Builder builder = new AlertDialog.Builder(OgrenciEkleActivity.this);
builder.setTitle("UYARI !");
builder.setMessage("Boş alan bırakmayınız !");
builder.setIcon(R.drawable.warningicon);
builder.setPositiveButton("Tamam", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialogInterface, int i) {
}
});
builder.show();
}
else{
ogrenciyiKontrolEt.OGR_KONTROL();
System.out.println("singleton get flag"+singleton.getflag()); //singleton returns null here and and it never
//goes into the if loop
if("100".equals(singleton.getflag())){
AlertDialog.Builder builder = new AlertDialog.Builder(OgrenciEkleActivity.this);
builder.setIcon(R.drawable.warningicon);
builder.setMessage(no_ogr+" numaralı öğrenci zaten kayıtlı lütfen farklı bir numara giriniz.");
builder.setTitle("UYARI");
builder.setPositiveButton("TAMAM", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialogInterface, int i) {
}
});
builder.show();
}
else{
linkedHashMap.put("name",ad_ogr);
linkedHashMap.put("lastname",soyisim_ogr);
linkedHashMap.put("number",no_ogr);
linkedHashMap.put("email",email_ogr);
linkedHashMap.put("password",parola_ogr);
mFirestore.collection("Students").add(linkedHashMap).addOnSuccessListener(new OnSuccessListener<DocumentReference>() {
@Override
public void onSuccess(@NonNull DocumentReference documentReference) {
Toast toast = Toast.makeText(OgrenciEkleActivity.this,"Öğrenci başaralı bir şekilde eklendi.",Toast.LENGTH_LONG);
toast.show();
}
}).addOnFailureListener(new OnFailureListener() {
@Override
public void onFailure(@NonNull Exception e) {
Toast toast = Toast.makeText(OgrenciEkleActivity.this,"Öğrenci eklerken bir hata ile karşılaşıldı.",Toast.LENGTH_LONG);
toast.show();
}
});
}
}
}
});
}
Control class that I created to control students
public class OgrenciyiKontrolEt {
protected String ogrenci_no;
protected String firestore_ogr_no;
protected FirebaseFirestore firebaseFirestoreDb = FirebaseFirestore.getInstance();
public Context context;
Singleton singleton = Singleton.getInstance();
public OgrenciyiKontrolEt(String ogr_no,Context context){
this.ogrenci_no = ogr_no;
this.context = context;
}
public void OGR_KONTROL(){
firebaseFirestoreDb.collection("Students")
.get()
.addOnSuccessListener(new OnSuccessListener<QuerySnapshot>() {
@Override
public void onSuccess(@NonNull QuerySnapshot queryDocumentSnapshots) {
List<DocumentSnapshot> snapshotList = queryDocumentSnapshots.getDocuments();
for(DocumentSnapshot snapshot: snapshotList ) {
firestore_ogr_no = snapshot.getString("number");
if(firestore_ogr_no.equals(ogrenci_no)) {
singleton.setflag("100"); //If there is a student with the same
number, I set the flag in the singleton to 100.
}
}
}
})
.addOnFailureListener(new OnFailureListener() {
@Override
public void onFailure(@NonNull Exception e) {
Toast toast = Toast.makeText(context,"Bir hata ile karşılaşıldı.",Toast.LENGTH_LONG);
toast.show();
}
});
}
}
My singleton class
public class Singleton {
**EDIT**
private String flag="1";
**EDIT**
private static Singleton singleton;
private Singleton() {
}
public String getflag() {
return flag;
}
public void setflag(String flag) {
this.flag = flag;
}
public static Singleton getInstance() {
if (singleton == null) {
singleton = new Singleton();
}
return singleton;
}
}
Your flag is not initialized when you call it, Either set something as default value or initialize in constructor like
private Singleton() {
this.flag = "";
}
or call your setFlag before first occurrence of getFalg