How can I fix this DataBinding and LiveData code?

Question

I am trying to connect DataBinding with LiveData, but run into some problems, that i dont know how to fix. I am not sure if i did something wrong with the LifecycleOwner, but its not working. Also some explanation why the correct way is right is aprecciated. The app aint even starting and i dont know what my mistake is. Thanks for the help

package com.example.teststuff;

import androidx.appcompat.app.AppCompatActivity;
import androidx.databinding.DataBindingUtil;
import androidx.databinding.Observable;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModelProviders;

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

import com.example.teststuff.databinding.ActivityMainBinding;

public class MainActivity extends AppCompatActivity {

    ActivityMainBinding binding;
    MainActivityViewModel model;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        binding = DataBindingUtil.setContentView(this,R.layout.activity_main);
        model = ViewModelProviders.of(this).get(MainActivityViewModel.class);
        binding.setViewmodel(model);
        model.setText("Hello");
        binding.setLifecycleOwner(this);

    }
}

<?xml version="1.0" encoding="utf-8"?>
<layout>

    <data>
        <variable name="viewmodel" type="com.example.teststuff.MainActivityViewModel" />
    </data>

    <RelativeLayout 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"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".MainActivity">

        <EditText
            android:text="@{viewmodel.text}"
            android:layout_width="match_parent"
            android:layout_height="wrap_content" />

    </RelativeLayout>
</layout>

package com.example.teststuff;

import android.widget.Button;

import androidx.lifecycle.MutableLiveData;
import androidx.lifecycle.ViewModel;

public class MainActivityViewModel extends ViewModel {

    private MutableLiveData<String> text;

    public MutableLiveData<String> getText() {
        return text;
    }

    public void setText(String text) {
        this.text.setValue(text);
    }
}

Answer 1

Your code is generally correct.

You need to make sure that there are lines in your build.gradle:

android {
    ...
    dataBinding {
        enabled = true
    }
}

dependencies {
    ...
    implementation 'androidx.lifecycle:lifecycle-extensions:2.0.0'
}

Corrected version of your code

package com.example.teststuff;

import androidx.appcompat.app.AppCompatActivity;
import androidx.databinding.DataBindingUtil;
import androidx.lifecycle.ViewModelProviders;

import android.os.Bundle;

import com.example.teststuff.databinding.ActivityMainBinding;

public class MainActivity extends AppCompatActivity {

    ActivityMainBinding binding;
    MainActivityViewModel model;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        binding = DataBindingUtil.setContentView(this,R.layout.activity_main);
        model = ViewModelProviders.of(this).get(MainActivityViewModel.class);
        binding.setViewmodel(model);
        model.setText("Hello");
        binding.setLifecycleOwner(this);
    }
}

<?xml version="1.0" encoding="utf-8"?>
<layout>

    <data>
        <variable name="viewmodel" type="com.example.teststuff.MainActivityViewModel" />
    </data>

    <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".MainActivity">

        <EditText
            android:text="@{viewmodel.text}"
            android:layout_width="match_parent"
            android:layout_height="wrap_content" />

    </RelativeLayout>
</layout>

package com.example.teststuff;

import androidx.lifecycle.MutableLiveData;
import androidx.lifecycle.ViewModel;

public class MainActivityViewModel extends ViewModel {

    private MutableLiveData<String> text = new MutableLiveData<>();

    public MutableLiveData<String> getText() {
        return text;
    }

    public void setText(String text) {
        this.text.setValue(text);
    }
}