Two-way databinding(in xml), ObservableField, BaseObservable , which one I should use for the two-way databinding?

Question

I have used data-binding for a while, even now it is not available for JDK 8 and API 24 now. I still find a way to use the data binding in a easier way. But when I use the follo

Answer 1

I feel that ObservableField approach is the way to go as there's no need to write getters/setters OR invoke notifyPropertyChanged.

Also, if you have a custom object ObservableField<Student> studentField, and you use android:text="@{viewModel.studentField.name}, the text does get updated when you invoke studentField.set(newStudent).

I find RxJava very useful. ObservableField can be easily converted to rx.Observable and vice versa. This allows use of Rx operators. In case you are interested, you can check the implementation here: FieldUtils.java

Answer 2

Your Student_XML2WAY.java won't work with 2-way Binding, since it does not fulfill the requirements to do so (BaseObservable, Bindable or something like that).

I would use BaseObservable if I will directly access the model, just like in your Student_Extend. I will have an instance of Student_Extend in my Activity and I will set the variable in onCreate:

Student mStudent = new Student("John Doe", 42); //
binding.setStudent(mStudent);
//later:
mStudent.setAge(37);

If implemented correctly, this will also change the Age in your UI (as well as in your model).

If you do not want to access your model directly and want to use a ViewModel, I work with ObervableFields:

public class Student {
    private String name;
    private int age;
    //Corresponding setters and getters
}


public class StudentViewModel {
    private ObservableField<Student> mStudentField = new ObservableField<>();

    //if I have a large model class, and only want to use some fields, 
    //I create some getters (and setters, for the two way attributes)
    //Something like this:

    public int getAge() {
        return mStudentField.get().getAge();
    }
    public void setAge(int newAge) {
        return mStudentField.get().setAge(newAge);
    }
}

So, I create an instance of StudentViewModel in my Activity and set it to the binding. Pseudo-xml would look like this:

<layout>
    <data>
        <variable name="studentViewModel" 
                  type="locaction.of.StudentViewModel"> <!-- or do an import -->
    </data>
    <EditText 
        android:text="@={studentViewModel.age}"/>
</layout>

So, the ViewModel approach is "clearer" since you outsource almost everything that has to do with views. Put your BindingAdapter, click methods, converter methods there and keep your Activity clean. Also, you do not directly change your model. This approach can be an overkill for simple classes and projects. ;)

If you want to see a full, example that uses DataBinding and MVVM, check out Droids on roids approach on this.