Android ViewModel tutorial

ViewModel:

As define in Android developer,

The ViewModel class is designed to store and manage UI-related data in a lifecycle conscious way. TheViewModel class allows data to survive configuration changes such as screen rotations.

Let us assume, we are showing EMPLOYEE data on screen,

To implement ViewModel,

Step 1:

Create a DataModel class,

public class User {

  public String empId;

  public String empName;

 

  public User(String empId, String empName) {

      this.empId = empId;

      this.empName = empName;

  

  }

  public String getEmpId() {

      return empId;

  }

  public void setEmpId(String empId) {

      this.empId = empId;

  }

  public String getEmpName() {

      return empName;

  }

  public void setEmpName(String empName) {

      this.empName = empName;

  }

}

Step 2:

Create a Repository, which will communicate between ViewModel and Data,

public class MainActivityRepo {

  private static MainActivityRepo instance;

  private ArrayList<User> dataset=new ArrayList<>();

  public static MainActivityRepo getInstance(){

      if(instance==null){

          instance=new MainActivityRepo();

      }

      return instance;

  }

  public MutableLiveData<List<User>> getUser(){

      setUserData();

      MutableLiveData<List<User>> data=new MutableLiveData<>();

      data.setValue(dataset);

      return data;

  }

  private void setUserData(){

      dataset.add(

              new User("emp001","John Doe","http://lorempixel.com/400/200/sports/1/"));

      dataset.add(

              new User("emp002","Ray Ban","http://lorempixel.com/400/200/sports/2/"));

      dataset.add(

              new User("emp003","Don Brown","http://lorempixel.com/400/200/sports/3/"));

  }

Step 3:

Create ViewModel,

public class MainActivityViewModel extends ViewModel {

  private MutableLiveData<List<User>> users;

  private MainActivityRepo mRepo;

  public void init(){

      if(users!=null){

          return;

      }

      mRepo=MainActivityRepo.getInstance();

      users=mRepo.getUser();

  }

  public LiveData<List<User>> getUser(){

      if(users==null){

          users=new MutableLiveData<List<User>>();

      }

      return users;

  }

}

Step 4:

Create a layout xml,

<RelativeLayout

      android:layout_width="match_parent"

      android:layout_height="match_parent"

      tools:context=".oneWayBinding.oneWayBinding.MainActivity">

  <TextView

           android:id="@+id/tv_empId"

          android:layout_width="match_parent"

          android:layout_height="wrap_content"

           />

</RelativeLayout>

Step 5:

Create a MainActivity class,

public class MainActivityJv extends AppCompatActivity {

   @Override

  protected void onCreate(@Nullable Bundle savedInstanceState) {

      super.onCreate(savedInstanceState);

      setContentView(R.layout.activity_main);

      MainActivityViewModel model = ViewModelProviders.of(this)

                                      .get(MainActivityViewModel.class);

      model.init();

      model.getUser().observe(this, new Observer<List<User>>() {

          @Override

          public void onChanged(@Nullable List<User> users) {

              changeUI(users);

          }});

  }

  private void changeUI(List<User> user){

/** can get all user data from loop**/

//        for(int i=0;i<user.size();i++){

//         // Log.d("data:value",user.get(i).empId);

//

//        }

     TextView tv_empId=findViewById(R.id.tv_empId);

    tv_empId.setText(user.get(0).empId);

  }

}

Now rotate your screen , which will not effect on your activity and data.

Enjoy benefit the use of ViewModel,