Error in Fetching Data from Firebase to Recyclerview. Fatal Exception: ... Does Not Define a No-Argument Constructor

Error in fetching data from Firebase to RecyclerView. FATAL EXCEPTION: ... does not define a no-argument constructor

You are getting the following error:

FATAL EXCEPTION: ... does not define a no-argument constructor

Because your RvClass class does not define a no-argument constructor.

JavaBeans require a no-argument constructor to be present.

In Java, when a class has no constructors at all, there is a default no-argument constructor automatically added by the compiler. The moment you define any constructor in the class, the default no-argument constructor goes away.

In your code, your RvClass class defines such a constructor that contains three arguments:

public RvClass(String title, String message, String time) {}

As long as this constructor is present and you don't define a no-argument constructor, that class will not have one.

To resolve this, you either remove that constructor from the class, or manually add a no-argument constructor as shown below:

public RvClass() {}

When the Firebase Realtime database SDK deserializes objects that are coming from the database, it requires that any objects in use, to have this constructor, so it can use it to instantiate the object. Fields in the objects are set by using public setter methods or direct access to public members.

If your RvClass class dosen't have a public no-arg constructor, the SDK doesn't really know how to create an instance of it. So it is mandatory to have it.

Also please note that setters and getter are not required. Setters are always optional because if there is no setter for a JSON property, the Firebase client will set the value directly onto the field. A constructor-with-arguments is also not required. Both are idiomatic and there are good cases to have classes without them. If you make the fields public, the getters are optional too.

Unable to retrieve data from firebase realtime database on to recyclerview

As per your error logs, it states that:

The User class doesnt has a default constructor with no parameters stated in the User.class file.

Add a default constructor to the User class in the User.class file like:

 public User()
    {

      }

For some reason cant deserialize object from Firebase response

The deserializer that comes with the Realtime Database (and also Cloud Firestore) Android SDKs requires that the class you pass to it look like a JavaBean type object. This means that it must have a default no-arg constuructor, as you can tell from the error message, and also setter methods that map to each database field.

Kotlin data classes don't provide a default no-arg constructor in order to ensure that all of its fields have an initial value. You can tell Kotlin that it's OK for all of the fields not to have an initial value by giving null or some other value as a default value:

data class GameUnit (
    var background: String = null,
    var description: String = null,
    var tag: String = null,
    var title: String = null,
    var type: String = null
)

For the above data class, Kotlin will generate a default no-arg constructor for the Firebase SDK to use. It will also generate setter methods for each var. Note that each property is var and provides a default null value.

If this is not what you want your data class to look like, you won't be able to use automatic deserialization. You will have to read each value out of the snapshot, make sure they are each not null, and pass them all to the constructor that Kotlin provides.

How to solve this problems? Could not deserialize object.

The no-argument constructor should not be added in the WalletFragment. It must be added in the User class. Why? Because you need to deserialize the objects that are coming from the Firestore when using the following line of code:

user = documentSnapshot.toObject(User.class);

For more information, please check my answer from the following post:

• Error in fetching data from Firebase to RecyclerView. FATAL EXCEPTION: ... does not define a no-argument constructor

Android Firebase Database exception: not define a no-argument constructor

Info and Utwory shouldn't be inner classes nested inside Album. Make them independent classes instead.

Could not deserialize object. Class does not define a no-argument constructor.If you are using ProGuard, make sure these constructors are not stripped

First thing: It was not necessary to create the field (map type) called valorb. It was resolved with value.openPercent

As I have two documents (alarme and garagem) I created two POJO classes (FireFran and FireFranB)

https://github.com/neuberfran/JThingsFinal/blob/main/app/src/main/java/neuberfran/com/jfran/model/FireFranB.kt

The secret was to treat the value.on and value.openPercent fields as maps (as facts are):

---

Related Topics