Firebase Realtime Database (Android-Java)- "Class does not define a no-argument constructor"

Question

I am trying to read data from Firebase Realtime Database on a Java Android project. I am using Android Studio 4.2.2.

I can get the JSON string fine. The problems start when I try to deserialize the data.

At that point I get an exception: "does not define a no-argument constructor. If you are using ProGuard, make sure these constructors are not stripped."

The point is that I have already defined a no-argument constructor. I have also checked the docs here https://firebase.google.com/docs/database/android/read-and-write

My questions are:

What I am doing wrong?
How can I parse a JSON with multiple levels?
Does the name of the variables must to be the same than the names of the keys of the JSON?

Thanks in advance!

JSON looks like this:

Data Tree

In Logcat I can see the JSON arrives safe to the app:

{ key = 1, value = {phone=123456789, name=Mike} }

Here there is the code:

public class DataBaseHelper {

private DatabaseReference mDatabase;
public TestData result;

public DataBaseHelper() {
    mDatabase = FirebaseDatabase.getInstance().getReference();

    // Creamos query
    Query query = mDatabase.child("TestData");


    query.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            for (DataSnapshot userSnapshot : dataSnapshot.getChildren()) {
                try {
                    Log.w("datosdb", userSnapshot.toString());
                    result = userSnapshot.getValue(TestData.class);

                } catch (Exception e) {
                    Log.w("datosdb", "Parse failed", e);
                }
            }
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {
            // Getting Post failed, log a message
            Log.w("datosdb", "loadPost:onCancelled", databaseError.toException());
            // ...
        }
    });


}


public class TestData {
    public TestData() {
    }

    public String name;
    public int phone;

    public String getName() {
        return this.name;
    }

    public int getPhone() {
        return this.phone;
    }
}

}

Here is the exception:

2021-07-12 00:58:01.631 25262-25262/com.example.purinasa W/datosdb: DataSnapshot { key = 1, value = {phone=123456789, name=Mike} } 2021-07-12 00:58:01.637 25262-25262/com.example.purinasa W/datosdb: Parse failed com.google.firebase.database.DatabaseException: Class com.example.purinasa.application.dataBase.DataBaseHelper$TestData does not define a no-argument constructor. If you are using ProGuard, make sure these constructors are not stripped. at com.google.firebase.database.core.utilities.encoding.CustomClassMapper$BeanMapper.deserialize(CustomClassMapper.java:570) at com.google.firebase.database.core.utilities.encoding.CustomClassMapper$BeanMapper.deserialize(CustomClassMapper.java:563) at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertBean(CustomClassMapper.java:433) at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.deserializeToClass(CustomClassMapper.java:232) at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertToCustomClass(CustomClassMapper.java:80) at com.google.firebase.database.DataSnapshot.getValue(DataSnapshot.java:203) at com.example.purinasa.application.dataBase.DataBaseHelper$1.onDataChange(DataBaseHelper.java:33) at com.google.firebase.database.core.ValueEventRegistration.fireEvent(ValueEventRegistration.java:75) at com.google.firebase.database.core.view.DataEvent.fire(DataEvent.java:63) at com.google.firebase.database.core.view.EventRaiser$1.run(EventRaiser.java:55) at android.os.Handler.handleCallback(Handler.java:938) at android.os.Handler.dispatchMessage(Handler.java:99) at android.os.Looper.loop(Looper.java:223) at android.app.ActivityThread.main(ActivityThread.java:7656) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)

Update:

After doing some test with @Ticherhaz-FreePalestine we managed to deserialize the data individually using this lines:

 String name = userSnapshot.child("name").getValue(String.class);
                    Log.w("datosdb", "String is here!!!" + name);

                    long phone = userSnapshot.child("phone").getValue(Long.class);
                    Log.w("datosdb", "Long is here!!!" + phone);

BTW, I cant find the way of using this another code without trowing an exception.

score 1 · Accepted Answer · answered Jul 12 '21 at 02:03

Finally it works by Using TestData as an independent class instead of an internal class. I made a new file TestData.java and moved its code there.

So finally DatabaseHelper loos like this:

public class DatabaseHelper {

private DatabaseReference mDatabase;
TestData result;

public DatabaseHelper() {
    mDatabase = FirebaseDatabase.getInstance().getReference();

    // We create a query
    Query query = mDatabase.child("TestData");

    //We recive query
    query.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            for (DataSnapshot userSnapshot : dataSnapshot.getChildren()) {
                Log.w("datosdb", "Tenemos el resultado de la query.");
                try {
                    Log.w("datosdb", userSnapshot.toString());

                    // Deserializing only name
                    String name = userSnapshot.child("name").getValue(String.class);
                    Log.w("datosdb", "String is here!!!" + name);

                    // Deserializing only phone
                    long phone = userSnapshot.child("phone").getValue(Long.class);
                    Log.w("datosdb", "Long is here!!!" + phone);

                    // Deserializing into a TestData object
                    TestData result = userSnapshot.getValue(TestData.class);
                    Log.w("datosdb", "Parse success!!!");

                } catch (Exception e) {
                    Log.w("datosdb", "Parse failed", e);
                }
            }
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {
            // Getting Post failed, log a message
            Log.w("datosdb", "loadPost:onCancelled", databaseError.toException());
            // ...
        }
    });


}

}

And TestData looks like this (on its own .java file now):

public class TestData {
private String name;
private long phone;

public TestData(){}

public TestData(String name, long phone){
    this.name = name;
    this.phone = phone;
}

public String getName() {
    return this.name;
}

public void setName(String name) {
    this.name = name;
}

public long getPhone() {
    return this.phone;
}

public void setPhone(long phone) {
    this.phone = phone;
}

}

Ticherhaz FreePalestine · Answer 2 · 2021-07-11T23:28:16.313

0

You already have an empty constructor. So need another constructor which is it has all the properties.

@Keep
public class TestData {
    private String name;
    private int phone;

    public TestData() {
    }

    public TestData(String name, int phone) {
        this.name = name;
        this.phone = phone;
    }

    public String getName() {
        return this.name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getPhone() {
        return this.phone;
    }

    public void setPhone(int phone) {
        this.phone = phone;
    }
}

edited Jul 11 '21 at 23:28

answered Jul 11 '21 at 23:14

Ticherhaz FreePalestine

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Thanks Ticherhaz! Im sorry, I tried it, but the problem didn't solve. It keeps throwing: Class com.example.purinasa.application.dataBase.DataBaseHelper$TestData does not define a no-argument constructor. If you are using ProGuard, make sure these constructors are not stripped. – Iroqas Jul 11 '21 at 23:22
Did you enable ProGuard? @Iroqas – Ticherhaz FreePalestine Jul 11 '21 at 23:24
I didnt. I am quite new in Android Studio. Is it enabled by default? I was checking it out and seems it is not... ¿How sould I check it? – Iroqas Jul 11 '21 at 23:26
@Iroqas I have updated the answer. can try again – Ticherhaz FreePalestine Jul 11 '21 at 23:28
I guess this lines at bould.gradle mean it is disabled buildTypes { release { minifyEnabled false proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro' } – Iroqas Jul 11 '21 at 23:32
It keeps crashing after updating the code. What a mistery... – Iroqas Jul 11 '21 at 23:40
@Iroqas what does logcat says ? – Ticherhaz FreePalestine Jul 11 '21 at 23:45
Here is a pastebin with the log: https://pastebin.com/m1Y4Wm1b BTW, I added a line to disable logcat at build.gradle file android/buildTypes/release/ -> useProguiard false. It keeps crashing. – Iroqas Jul 11 '21 at 23:49
@Iroqas can you try invalidate cache – Ticherhaz FreePalestine Jul 11 '21 at 23:56
I added this line to proguard-rules.pro file. Keeps crashing... -keepclassmembers class com.example.purinasa.application.dataBase.DataBaseHelper { public *; } – Iroqas Jul 11 '21 at 23:57
I am doing it now – Iroqas Jul 11 '21 at 23:59
I am so sorry, but it keeps crashing after cache invalidate and restart. – Iroqas Jul 12 '21 at 00:01
@Iroqas do you want to do TeamViewer/Anydesk ? – Ticherhaz FreePalestine Jul 12 '21 at 00:03
I am sorry but I cant do TeamViewer at this laptop for security reasons. Is discord ok? – Iroqas Jul 12 '21 at 00:07
@Iroqas yes sure. Ticherhaz#7548 – Ticherhaz FreePalestine Jul 12 '21 at 00:07

Firebase Realtime Database (Android-Java)- "Class does not define a no-argument constructor"

2 Answers2