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!!

@Enzokie it causes rise an error in building level: Error:(21, 69) error: cannot find symbol class ActivityStudentBinding. Because value is not needed here — Siamak Ferdos, May 20 '18 at 10:13
If you think of it `viewmodel.student` returns `MutableLiveData` which means you can't do `viewmodel.student.id` so I assume `viewmodel.student.value.id` should work (not tested). — Enzokie, May 20 '18 at 10:16
@Enzokie As I noted it in my question: I've cleaned extra codes here ;) — Siamak Ferdos, May 20 '18 at 10:20
Don't remove crucial part of your code because other people here will mark this question [Off-topic for Typographical] reason. — Enzokie, May 20 '18 at 10:21

score 43 · Answer 1 · answered Aug 12 '18 at 14:03

43

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)}" />

answered Aug 12 '18 at 14:03

Ahmad Aghazadeh

16,571
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1

Wonderful. That was the answer. – S. Gissel Jun 05 '19 at 12:16
1

God this is really helpful. Thank you! – CodeAndWave Nov 14 '19 at 00:13
Crazy error, I guess it jumps whenever a viewDataBinding method() is used and it does not even need to be related to the providing of the data that will be bind in itself, as it can even be called with a bind.setLifecycleOwner(); .... This error makes it extremely adverse to work with for data conversion in the XML. – Delark Jun 27 '21 at 20:15

score -3 · Answer 2 · answered Nov 27 '19 at 18:24

Or you can simply do this also

       <TextView 
                 android:text="@{viewmodel.student.id.toString}" />   
       <TextView 
                 android:text="@{viewmodel.student.family.toString}" />    

       <TextView
                 android:text="@{viewmodel.student.id.toString}"/>

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

2 Answers2