Simple MVVM architecture on Android with AndroidX on Java

Question

I'm getting really annoyed trying to figure out how the frick creates a simple MVVM pattern Android activity.

What I want is simply bind a view model public method (which prints a "Eureka!" log), to a Button (with onClick action).

To achieve this, what I did since now is:

data_activity.xml

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    tools:context="it.XXXXX.XXXXX.ui.data.DataActivity"
    >

    <data>
        <variable
            name="viewModel"
            type="it.XXXXX.XXXXX.ui.data.DataViewModel" />
    </data>

    <androidx.constraintlayout.widget.ConstraintLayout
        android:orientation="vertical"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:orientation="vertical">

            <TextView
                android:id="@+id/some_useless_id_1"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:gravity="center_horizontal"
                android:textAppearance="@style/TextAppearance.AppCompat.Body1"
                tools:text="Press this beautiful button ;)" />

            <Button
                android:id="@+id/some_useless_id_2"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:onClick="@{() -> viewModel.test()}"
                android:text="@string/button" />
        </LinearLayout>
    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

DataViewModel.java

package it.XXXXX.XXXXX.ui.data;

import android.util.Log;

import androidx.lifecycle.ViewModel;

public class DataViewModel extends ViewModel {
    public void test() {
        Log.d("test", "EUREKA!");
    }
}

DataActivity.java

package it.XXXXX.XXXXX.ui.data;

import androidx.appcompat.app.AppCompatActivity;
import androidx.lifecycle.ViewModelProvider;

import android.os.Bundle;

import it.XXXXX.XXXXX.R;

public class DataActivity extends AppCompatActivity {

    private DataViewModel mViewModel;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.data_activity);
        this.mViewModel = new ViewModelProvider(this).get(DataViewModel.class);
    }
}

...finally (since I'm working on an existent application) I call the View with:

...
        ((Button)this.findViewById(R.id.btnDataSync2)).setOnClickListener(new OnClickListener(){
            public void onClick(View arg0) {
                Intent i = new Intent(MainActivity.this, DataActivity.class);
                MainActivity.this.startActivity(i);
            }
        });
...

The expected behavior is to read a log by pressing on the DataView (which is loaded), but nothing happens (except the button press animation).

Does anyone have any idea what the problem might be?
Thank you in advance!

MedaiP90 · Accepted Answer · 2020-02-04 13:14:42Z

Step to enable data binding in an Android app:

add android.databinding.enableV2=true in your "gradle.properties" file;
add dataBinding { enabled = true } in the app "build.gradle" file, in the android section:

android {
    compileSdkVersion 28

    ...

    dataBinding {
        enabled = true
    }
}

run a gradle sync and build in Android Studio.

Update

I forgot to tell you have to modify your onCreate method like this:

package it.XXXXX.XXXXX.ui.data;

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

import android.os.Bundle;

import it.XXXXX.XXXXX.R;
import it.XXXXX.XXXXX.databinding.DataActivityBinding;

public class DataActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        DataViewModel mViewModel = new DataViewModel();

        DataActivityBinding binding = DataBindingUtil.setContentView(this, R.layout.data_activity);
        binding.setViewModel(mViewModel);
    }
}

Massimo De Luisa · Accepted Answer · 2020-02-04 14:09:09Z

0

I figure that I was not binding correctly the ViewModel from the Activity:

DataActivity.java

public class DataActivity extends AppCompatActivity {

    private DataViewModel mViewModel;
    private DataActivityBinding mBinding;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        this.mViewModel = new DataViewModel();
        this.mBinding = DataBindingUtil.setContentView(this, R.layout.data_activity);
        this.mBinding.setViewModel(this.mViewModel);
    }
}

hope this will help someone.

Ps. thanks @medaip90 for the useful advice!

answered Feb 4, 2020 at 14:09

Massimo De Luisa

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