معرفی کامل معماری MVVM در اندروید + روش پیاده سازی

    implementation "androidx.lifecycle:lifecycle-extensions:2.2.0"

import androidx.annotation.Nullable;
public class Model {
	@Nullable
	String email,password;
	// constructor to initialize
	// the variables
	public Model(String email, String password){
		this.email = email;
		this.password = password;
	}
	// getter and setter methods
	// for email variable
	@Nullable
	public String getEmail() {
		return email;
	}
	public void setEmail(@Nullable String email) {
		this.email = email;
	}
	// getter and setter methods
	// for password variable
	@Nullable
	public String getPassword() {
		return password;
	}
	public void setPassword(@Nullable String password) {
		this.password = password;
	}
}

import android.text.TextUtils;
import android.util.Patterns;
import androidx.lifecycle.LiveData;
import androidx.lifecycle.MutableLiveData;
import androidx.lifecycle.ViewModel;
public class MainViewModel extends ViewModel {
    // string variables for
    // toast messages
    private String successMessage = "Login successful";
    private String errorMessage = "Email or Password is not valid";
    private String email = "";
    private String password = "";
    private MutableLiveData<String> toastMessage = new MutableLiveData<>();
    public void isValid() {
        if (!TextUtils.isEmpty(email) && Patterns.EMAIL_ADDRESS.matcher(email).matches()
                && password.length() > 5) {
            toastMessage.setValue(successMessage);
        } else {
            toastMessage.setValue(errorMessage);
        }
    }
    public LiveData<String> getToastMessage() {
        return toastMessage;
    }
    public String getEmail() {
        return email;
    }
    public void setEmail(String email) {
        this.email = email;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
}

<?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:bind="http://schemas.android.com/tools">
	<!-- Provided Linear layout for the activity components -->
	<LinearLayout
		android:layout_width="match_parent"
		android:layout_height="match_parent"
		android:layout_gravity="center"
		android:layout_margin="8dp"
		android:background="#168BC34A"
		android:orientation="vertical">
		<!-- TextView for the heading of the activity -->
		<TextView
			android:id="@+id/textView"
			android:layout_width="match_parent"
			android:layout_height="wrap_content"
			android:text="@string/heading"
			android:textAlignment="center"
			android:textColor="@android:color/holo_green_dark"
			android:textSize="36sp"
			android:textStyle="bold" />
		<!-- EditText field for the Email -->
		<EditText
			android:id="@+id/inEmail"
			android:layout_width="match_parent"
			android:layout_height="wrap_content"
			android:layout_marginStart="10dp"
			android:layout_marginTop="60dp"
			android:layout_marginEnd="10dp"
			android:layout_marginBottom="20dp"
			android:hint="@string/email_hint"
			android:inputType="textEmailAddress"
			android:padding="8dp"
			android:text="@={viewModel.userEmail}" />
		<!-- EditText field for the password -->
		<EditText
			android:id="@+id/inPassword"
			android:layout_width="match_parent"
			android:layout_height="wrap_content"
			android:layout_marginStart="10dp"
			android:layout_marginEnd="10dp"
			android:hint="@string/password_hint"
			android:inputType="textPassword"
			android:padding="8dp"
			android:text="@={viewModel.userPassword}" />
		<!-- Login Button of the activity -->
		<Button
			android:id="@+id/loginBtn"
			android:layout_width="match_parent"
			android:layout_height="wrap_content"
			android:layout_marginStart="20dp"
			android:layout_marginTop="60dp"
			android:layout_marginEnd="20dp"
			android:background="#4CAF50"
			android:fontFamily="@font/roboto"
			android:text="@string/button_text"
			android:textColor="@android:color/background_light"
			android:textSize="30sp"
			android:textStyle="bold" />
		<ImageView
			android:id="@+id/imageView"
			android:layout_width="match_parent"
			android:layout_height="wrap_content"
			android:layout_marginTop="135dp"
			app:srcCompat="@drawable/banner" />
	</LinearLayout>
</layout>

import androidx.appcompat.app.AppCompatActivity;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModelProvider;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity {
    private MainViewModel mainViewModel;
    private EditText emailEt;
    private EditText passwordEt;
    private Button loginBtn;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mainViewModel = new ViewModelProvider(this).get(MainViewModel.class);
        mainViewModel.getToastMessage().observe(this, new Observer<String>() {
            @Override
            public void onChanged(String s) {
                Toast.makeText(MainActivity.this, s, Toast.LENGTH_SHORT);
            }
        });
        emailEt = findViewById(R.id.inEmail);
        passwordEt = findViewById(R.id.inPassword);
        loginBtn = findViewById(R.id.loginBtn);
        if (mainViewModel.getEmail() != null) {
            emailEt.setText(mainViewModel.getEmail());
        }
        if (mainViewModel.getPassword() != null) {
            passwordEt.setText(mainViewModel.getPassword());
        }
        loginBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                mainViewModel.setEmail(String.valueOf(emailEt.getText()));
                mainViewModel.setPassword(String.valueOf(passwordEt.getText()));
                mainViewModel.isValid();
            }
        });
    }
}

android {
   dataBinding {
       enabled = true
      }
}

def life_versions = "1.1.1"
// Lifecycle components
implementation "android.arch.lifecycle:extensions:$life_versions"
annotationProcessor "android.arch.lifecycle:compiler:$life_versions"

<resources>
	<string name="app_name">GfG | MVVM Architecture</string>
	<string name="heading">MVVM Architecture Pattern</string>
	<string name="email_hint">Enter your Email ID</string>
	<string name="password_hint">Enter your password</string>
	<string name="button_text">Login</string>
</resources>

import androidx.annotation.Nullable;
public class Model {
	@Nullable
	String email,password;
	// constructor to initialize
	// the variables
	public Model(String email, String password){
		this.email = email;
		this.password = password;
	}
	// getter and setter methods
	// for email variable
	@Nullable
	public String getEmail() {
		return email;
	}
	public void setEmail(@Nullable String email) {
		this.email = email;
	}
	// getter and setter methods
	// for password variable
	@Nullable
	public String getPassword() {
		return password;
	}
	public void setPassword(@Nullable String password) {
		this.password = password;
	}
}

<?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:bind="http://schemas.android.com/tools">
	<!-- binding object of ViewModel to the XML layout -->
	<data>
		<variable
			name="viewModel"
			type="com.example.mvvmarchitecture.AppViewModel" />
	</data>
	<!-- Provided Linear layout for the activity components -->
	<LinearLayout
		android:layout_width="match_parent"
		android:layout_height="match_parent"
		android:layout_gravity="center"
		android:layout_margin="8dp"
		android:background="#168BC34A"
		android:orientation="vertical">
		<!-- TextView for the heading of the activity -->
		<TextView
			android:id="@+id/textView"
			android:layout_width="match_parent"
			android:layout_height="wrap_content"
			android:text="@string/heading"
			android:textAlignment="center"
			android:textColor="@android:color/holo_green_dark"
			android:textSize="36sp"
			android:textStyle="bold" />
		<!-- EditText field for the Email -->
		<EditText
			android:id="@+id/inEmail"
			android:layout_width="match_parent"
			android:layout_height="wrap_content"
			android:layout_marginStart="10dp"
			android:layout_marginTop="60dp"
			android:layout_marginEnd="10dp"
			android:layout_marginBottom="20dp"
			android:hint="@string/email_hint"
			android:inputType="textEmailAddress"
			android:padding="8dp"
			android:text="@={viewModel.userEmail}" />
		<!-- EditText field for the password -->
		<EditText
			android:id="@+id/inPassword"
			android:layout_width="match_parent"
			android:layout_height="wrap_content"
			android:layout_marginStart="10dp"
			android:layout_marginEnd="10dp"
			android:hint="@string/password_hint"
			android:inputType="textPassword"
			android:padding="8dp"
			android:text="@={viewModel.userPassword}" />
		<!-- Login Button of the activity -->
		<Button
			android:layout_width="match_parent"
			android:layout_height="wrap_content"
			android:layout_marginStart="20dp"
			android:layout_marginTop="60dp"
			android:layout_marginEnd="20dp"
			android:background="#4CAF50"
			android:fontFamily="@font/roboto"
			android:onClick="@{()-> viewModel.onButtonClicked()}"
			android:text="@string/button_text"
			android:textColor="@android:color/background_light"
			android:textSize="30sp"
			android:textStyle="bold"
			bind:toastMessage="@{viewModel.toastMessage}" />
		<ImageView
			android:id="@+id/imageView"
			android:layout_width="match_parent"
			android:layout_height="wrap_content"
			android:layout_marginTop="135dp"
			app:srcCompat="@drawable/banner" />
	</LinearLayout>
</layout>

import android.text.TextUtils;
import android.util.Patterns;
import androidx.databinding.BaseObservable;
import androidx.databinding.Bindable;
public class AppViewModel extends BaseObservable {
	// creating object of Model class
	private Model model;
	// string variables for
	// toast messages
	private String successMessage = "Login successful";
	private String errorMessage = "Email or Password is not valid";
	@Bindable
	// string variable for
	// toast message
	private String toastMessage = null;
	// getter and setter methods
	// for toast message
	public String getToastMessage() {
		return toastMessage;
	}
	private void setToastMessage(String toastMessage) {
		this.toastMessage = toastMessage;
		notifyPropertyChanged(BR.toastMessage);
	}
	// getter and setter methods
	// for email variable
	@Bindable
	public String getUserEmail() {
		return model.getEmail();
	}
	public void setUserEmail(String email) {
		model.setEmail(email);
		notifyPropertyChanged(BR.userEmail);
	}
	// getter and setter methods
	// for password variable
	@Bindable
	public String getUserPassword() {
		return model.getPassword();
	}
	public void setUserPassword(String password) {
		model.setPassword(password);
		notifyPropertyChanged(BR.userPassword);
	}
	// constructor of ViewModel class
	public AppViewModel() {
		// instantiating object of
		// model class
		model = new Model("","");
	}
	// actions to be performed
	// when user clicks
	// the LOGIN button
	public void onButtonClicked() {
		if (isValid())
			setToastMessage(successMessage);
		else
			setToastMessage(errorMessage);
	}
	// method to keep a check
	// that variable fields must
	// not be kept empty by user
	public boolean isValid() {
		return !TextUtils.isEmpty(getUserEmail()) && Patterns.EMAIL_ADDRESS.matcher(getUserEmail()).matches()
				&& getUserPassword().length() > 5;
	}
}

import android.os.Bundle;
import android.view.View;
import android.widget.Toast;
import androidx.appcompat.app.AppCompatActivity;
import androidx.databinding.BindingAdapter;
import androidx.databinding.DataBindingUtil;
import com.example.mvvmarchitecture.databinding.ActivityMainBinding;
public class MainActivity extends AppCompatActivity {
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		// ViewModel updates the Model
		// after observing changes in the View
		// model will also update the view
		// via the ViewModel
		ActivityMainBinding activityMainBinding = DataBindingUtil.setContentView(this, R.layout.activity_main);
		activityMainBinding.setViewModel(new AppViewModel());
		activityMainBinding.executePendingBindings();
	}
	// any change in toastMessage attribute
	// defined on the Button with bind prefix
	// invokes this method
	@BindingAdapter({"toastMessage"})
	public static void runMe( View view, String message) {
		if (message != null)
			Toast.makeText(view.getContext(), message, Toast.LENGTH_SHORT).show();
	}
}

import android.arch.lifecycle.MutableLiveData;
import android.arch.lifecycle.ViewModel;
import android.view.View;
public class LoginViewModel extends ViewModel {
    public MutableLiveData<String> EmailAddress = new MutableLiveData<>();
    public MutableLiveData<String> Password = new MutableLiveData<>();
    private MutableLiveData<LoginUser> userMutableLiveData;
    public MutableLiveData<LoginUser> getUser() {
        if (userMutableLiveData == null) {
            userMutableLiveData = new MutableLiveData<>();
        }
        return userMutableLiveData;
    }
    public void onClick(View view) {
        LoginUser loginUser = new LoginUser(EmailAddress.getValue(), Password.getValue());
        userMutableLiveData.setValue(loginUser);
    }
}

<?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="LoginViewModel"
            type="com.example.umangburman.databindingwithlivedata.ViewModel.LoginViewModel" />
    </data>
    <android.support.v4.widget.NestedScrollView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:isScrollContainer="true">
        <android.support.constraint.ConstraintLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            tools:context=".View.MainActivity">
            <TextView
                android:id="@+id/lblTitle"
                android:layout_width="0dp"
                android:layout_height="wrap_content"
                android:layout_marginEnd="8dp"
                android:layout_marginStart="8dp"
                android:layout_marginTop="16dp"
                android:lineSpacingExtra="8sp"
                android:text="Login Example Using MVVM, DataBinding with LiveData"
                android:textAlignment="center"
                android:textSize="18sp"
                android:textStyle="bold"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toTopOf="parent" />
            <EditText
                android:id="@+id/txtEmailAddress"
                android:layout_width="0dp"
                android:layout_height="wrap_content"
                android:layout_marginEnd="32dp"
                android:layout_marginStart="32dp"
                android:layout_marginTop="32dp"
                android:ems="10"
                android:hint="E-Mail Address"
                android:inputType="textEmailAddress"
                android:text="@={LoginViewModel.EmailAddress}"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@+id/lblTitle" />
            <EditText
                android:id="@+id/txtPassword"
                android:layout_width="0dp"
                android:layout_height="wrap_content"
                android:layout_marginEnd="32dp"
                android:layout_marginStart="32dp"
                android:layout_marginTop="16dp"
                android:ems="10"
                android:hint="Password"
                android:inputType="textPassword"
                android:text="@={LoginViewModel.Password}"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@+id/txtEmailAddress" />
            <Button
                android:id="@+id/btnLogin"
                android:layout_width="0dp"
                android:layout_height="wrap_content"
                android:layout_marginEnd="32dp"
                android:layout_marginStart="32dp"
                android:layout_marginTop="32dp"
                android:text="Click to Login"
                android:onClick="@{(v) -> LoginViewModel.onClick(v)}"
                android:textSize="18sp"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@+id/txtPassword" />
            <TextView
                android:id="@+id/lblTagline"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginEnd="8dp"
                android:layout_marginStart="8dp"
                android:layout_marginTop="60dp"
                android:text="See the Results Below From LiveDataBinding"
                android:textColor="@android:color/background_dark"
                android:gravity="center"
                android:textSize="16sp"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@+id/btnLogin" />
            <TextView
                android:id="@+id/lblEmailAnswer"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginEnd="8dp"
                android:layout_marginStart="8dp"
                android:layout_marginTop="8dp"
                android:text="---"
                android:textColor="@android:color/holo_blue_light"
                android:textSize="20sp"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@+id/lblTagline" />
            <TextView
                android:id="@+id/lblPasswordAnswer"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginBottom="32dp"
                android:layout_marginEnd="8dp"
                android:layout_marginStart="8dp"
                android:layout_marginTop="8dp"
                android:text="---"
                android:textColor="@android:color/holo_blue_light"
                android:textSize="20sp"
                app:layout_constraintBottom_toBottomOf="parent"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@+id/lblEmailAnswer" />
        </android.support.constraint.ConstraintLayout>
    </android.support.v4.widget.NestedScrollView>
</layout>

import android.arch.lifecycle.Observer;
import android.arch.lifecycle.ViewModelProviders;
import android.databinding.DataBindingUtil;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;
import android.text.TextUtils;
public class MainActivity extends AppCompatActivity {
    private LoginViewModel loginViewModel;
    private ActivityMainBinding binding;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        loginViewModel = ViewModelProviders.of(this).get(LoginViewModel.class);
        binding = DataBindingUtil.setContentView(MainActivity.this, R.layout.activity_main);
        binding.setLifecycleOwner(this);
        binding.setLoginViewModel(loginViewModel);
        loginViewModel.getUser().observe(this, new Observer<LoginUser>() {
            @Override
            public void onChanged(@Nullable LoginUser loginUser) {
                if (TextUtils.isEmpty(Objects.requireNonNull(loginUser).getStrEmailAddress())) {
                    binding.txtEmailAddress.setError("Enter an E-Mail Address");
                    binding.txtEmailAddress.requestFocus();
                }
                else if (!loginUser.isEmailValid()) {
                    binding.txtEmailAddress.setError("Enter a Valid E-mail Address");
                    binding.txtEmailAddress.requestFocus();
                }
                else if (TextUtils.isEmpty(Objects.requireNonNull(loginUser).getStrPassword())) {
                    binding.txtPassword.setError("Enter a Password");
                    binding.txtPassword.requestFocus();
                }
                else if (!loginUser.isPasswordLengthGreaterThan5()) {
                    binding.txtPassword.setError("Enter at least 6 Digit password");
                    binding.txtPassword.requestFocus();
                }
                else {
                    binding.lblEmailAnswer.setText(loginUser.getStrEmailAddress());
                    binding.lblPasswordAnswer.setText(loginUser.getStrPassword());
                }
            }
        });
    }
}