Android ViewModel

Android View ModelAndroid ViewModel

ViewModel Architecture components

 It survives configuration changes like Rotation.

 Used to save large amount of data like bitmap ,listdata.

 It store and manage UI related data.

 Destroyed if owner activity is completely destroyed in oncreate().

 Communication layer between UI and DB.

 is a class that is responsible for preparing and managing the data for an Activity or a Fragment . It also handles the communication of the Activity / Fragment with the rest of the application .

 why we go for ViewModel because when user rotate screen all data is loss.

 ViewModel is an Android architecture component. It is used as a data manager in the application.

 To use ViewModel, we need to firstly add proper dependencies into our app/build.gradle app/build.gradle .

 implementation "android.arch.lifecycle:extensions:1.1.1" 

Illustrates usage of Lifecycle and ViewModel Architecture components

How to use ViewModel?

To use ViewModel, we need to firstly add proper dependencies into our app/build.gradle app/build.gradle

implementation "android.arch.lifecycle:extensions:1.0.0"

annotationProcessor "android.arch.lifecycle:compiler:1.0.0"

package viewmodel.com;

import android.arch.lifecycle.ViewModelProviders;

import android.os.Bundle;

import android.support.v7.app.AppCompatActivity;

import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

  TextView textView;

  @Override

  protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);

    setContentView(R.layout.activity_main);

    textView = (TextView) findViewById(R.id.txt_count);

    // checking without ViewModel concept

//    ViewModel_DataGenerator modelDataGenerator = new ViewModel_DataGenerator();

//    String number = modelDataGenerator.getRan_Number();

//    textView.setText(number);

    // checking with ViewModel concept

    ViewModel_DataGenerator modelDataGenerator = ViewModelProviders.of(this).get(ViewModel_DataGenerator.class);

    String number = modelDataGenerator.getRan_Number();

    textView.setText(number);

  }

}

package viewmodel.com;

import android.arch.lifecycle.ViewModel;

import java.util.Random;

public class ViewModel_DataGenerator extends ViewModel {

  private String ran_no;

  public String getRan_Number() {

    if (ran_no == null) {

      create_ran_no();

    }

    return ran_no;

  }

  private void create_ran_no() {

    Random random = new Random();

    ran_no = "Random No:--> " + String.valueOf((random.nextInt(1000 - 1) + 1));

  }

  @Override

  protected void onCleared() {

    super.onCleared();

  }

}