LiveData(MutableLiveData) and Databinding rise error (Failed to call observer method)

Question

I have an app that uses ViewModel and MutableLiveData to bind live data to my UI. After hours westing my time! and review all sample on the internet I couldn't find the reason for the problem.

My activity:

public class DetailActivity extends DaggerAppCompatActivity {
    ActivityStudentBinding mViewDataBinding;    
    MyModel myModel;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mViewDataBinding = DataBindingUtil.setContentView(this, R.layout.activity_student);
        mViewDataBinding.setLifecycleOwner(this);
        myModel = ViewModelProviders.of(this).get(MyModel.class);
        mViewDataBinding.setViewmodel(myModel);
    }

And my model class:

public class MyModel extends ViewModel
{
    public MutableLiveData<StudentData.Student> student = new MutableLiveData<>();

    public MyModel() {
        this.student=student;
        StudentData.Student student = new StudentData().getFirstStudent();
        this.student.setValue(student);
    }    
}

And layout(I'vd cleaned extra codes here):

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools">
    <data >
        <variable
             name="viewmodel"
            type="googlearchitecturecomponents.ferdos.com.dagger211.detail.MyModel"/>
    </data>
        <TextView               
            android:text="@{viewmodel.student.id}" />    
        <TextView
            android:text="@{viewmodel.student.family}" />    
        <TextView
            android:text="@{viewmodel.student.id}"/>    
</layout>

On runtime and on creating activity I get this error:

java.lang.RuntimeException: Unable to start activity ComponentInfo{googlearchitecturecomponents.ferdos.com.dagger211/googlearchitecturecomponents.ferdos.com.dagger211.detail.DetailActivity}: java.lang.RuntimeException: Failed to call observer method--------- Stack trace ---------

android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)

android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)

android.app.ActivityThread.access$800(ActivityThread.java:144)

android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)

android.os.Handler.dispatchMessage(Handler.java:102)

android.os.Looper.loop(Looper.java:135)

android.app.ActivityThread.main(ActivityThread.java:5221)

java.lang.reflect.Method.invoke(Native Method)

java.lang.reflect.Method.invoke(Method.java:372)

com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)

com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)

Please help me with this confusing error!!

Answer 1

You must use string value for set android:text

      <TextView
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="@{String.valueOf(viewmodel.student.id)}" />