Android Architecture Components : Room DB insert , fetch, update , delete operations

Hi All,

In my previous post , I have shared the introduction of Room DB . Now in this tutorial I have shared you one demo to insert , retrieve , update and delete operations.

Here I have taken one database , named Emp.db , and table name is employee . In this table we have following rows:

• emp_id (int & primary key)
• name (string)
• dept (string)
• designation  (string)
• exp (string)

Now I have created this database schema , externally with the help of Sqlite Browser software. And saved it in assets folder of my project.

Let's take a look on following screenshots , for better understanding:

  


I am also sharing my source demo code .You can download this and run it by yourself:

Demo Source Code

I will create 3 buttons for insert , update and show the list of employees. Now let's take a look into coding part :

First  add following dependencies in build.gradle(app) :

implementation 'androidx.room:room-runtime:2.0.0-alpha1'

annotationProcessor 'androidx.room:room-compiler:2.0.0-alpha1'

Now for resources I have added 3 layouts , one for the buttons , one for insert/update employee details and one for showing the list of stored employees, named :

1. activity_main.xml (this is showing the various buttons)
2. emp_detail_layout.xml (this is for insert/update employee details)
3. emp_list_layout.xml (this is for insert/update employee details)
4. emp_item_layout.xml (this is to design the row of list )

activity_main.xml

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

<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">

    <Button

        android:id="@+id/btn_insert"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_alignParentStart="true"

        android:layout_alignParentTop="true"

        android:layout_margin="10dp"

        android:text="Insert Emp Detail" />

    <Button

        android:id="@+id/btn_update"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_below="@+id/btn_insert"

        android:layout_alignParentLeft="true"

        android:layout_margin="10dp"

        android:text="Update Emp Detail" />

    <Button

        android:id="@+id/btn_show"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_below="@+id/btn_update"

        android:layout_alignParentLeft="true"

        android:layout_margin="10dp"

        android:text="Show Emp List" />

</RelativeLayout>

emp_detail_layout.xml 

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

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

    <EditText
        android:id="@+id/edttxt_name"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ems="10"
        android:layout_margin="20dp"
        android:inputType="textPersonName"
        android:hint="Name" />

    <EditText
        android:id="@+id/edttxt_dept"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ems="10"
        android:inputType="textPersonName"
        android:layout_margin="20dp"
        android:hint="Department" />

    <EditText
        android:id="@+id/edttxt_desig"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ems="10"
        android:layout_margin="20dp"
        android:inputType="textPersonName"
        android:hint="Designation" />

    <EditText
        android:id="@+id/edttxt_exp"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ems="10"
        android:inputType="number"
        android:layout_margin="20dp"
        android:hint="Experience(in months)" />

    <Button
        android:id="@+id/btn_save"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="10dp"
        android:layout_gravity="center_horizontal"
        android:text="Save" />
</LinearLayout>

    <ProgressBar
        android:id="@+id/progressBar"
        style="?android:attr/progressBarStyle"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"/>

</RelativeLayout>

emp_item_layout.xml

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

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"

    xmlns:app="http://schemas.android.com/apk/res-auto"

    android:orientation="vertical" android:layout_width="match_parent"

    android:layout_height="wrap_content"

    android:padding="10dp"

    android:layout_margin="5dp"

    android:background="#232222">

    <TextView

        android:id="@+id/textView"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_alignParentStart="true"

        android:layout_alignParentTop="true"

        android:layout_margin="5dp"

        android:textSize="18sp"

        android:textStyle="bold"

        android:textColor="#b7afaf"

        android:text="TextView" />

    <TextView

        android:id="@+id/textView2"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_below="@+id/textView"

        android:layout_margin="5dp"

        android:textSize="13sp"

        android:textColor="#b7afaf"

        android:text="TextView" />

    <TextView

        android:id="@+id/textView3"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_below="@+id/textView2"

        android:layout_margin="5dp"

        android:textSize="13sp"

        android:textColor="#b7afaf"

        android:text="TextView" />

    <TextView

        android:id="@+id/textView4"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_below="@+id/textView3"

        android:layout_margin="5dp"

        android:textSize="13sp"

        android:textColor="#b7afaf"

        android:text="TextView" />

    <ImageView

        android:id="@+id/imageView2"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_alignParentRight="true"

        android:layout_centerVertical="true"

        android:layout_marginEnd="5dp"

        android:padding="5dp"

        app:srcCompat="@android:drawable/ic_menu_delete" />

    <ImageView

        android:id="@+id/imageView3"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_toLeftOf="@+id/imageView2"

        android:layout_centerVertical="true"

        android:layout_marginEnd="12dp"

        android:padding="5dp"

        app:srcCompat="@android:drawable/ic_menu_edit" />

</RelativeLayout>

emp_list_layout.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <ProgressBar
        android:id="@+id/progressBar"
        style="?android:attr/progressBarStyle"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"/>


    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recycler"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_alignParentStart="true"
        android:layout_below="@+id/btn_insert"
        android:layout_marginTop="20dp" />


</RelativeLayout>

Now for java files I have created following main classes that are  : 

1. RoomDbDemoApplication.java (This is application class)
2. MainActivity.java (This is activity for showing buttons)
3. EmployeeDetailActivity.java (This is to insert/update the employee detail)
4. EmployeeListActivity.java (This is to list the employee details)

Apart of this , I have created some more classes to define the components of Room DB, that are:

1. EmployeeDbDao.java (This is the dao interface)
2. EmployeeRoomDb.java (This is room db builder class)
3. EmpEntity.java (This is the entity class used for mapping)

Also , I have created some more helper classes as well for ex: to save and get data from shared preference , to show alert dialog or to add click listener in recycler view etc. 

First let's take a look on the coding part of the components of  Room DB :

-> EmpEntity.java :

import androidx.annotation.NonNull;

import androidx.room.ColumnInfo;

import androidx.room.Entity;

import androidx.room.PrimaryKey;

@Entity(tableName = "employee")

public class EmpEntity {

    @PrimaryKey

    @NonNull

    @ColumnInfo(name = "emp_id")

    int emp_id;

    @ColumnInfo(name = "name")

    String name;

    @ColumnInfo(name = "dept")

    String dept;

    @ColumnInfo(name = "designation")

    String design;

    @ColumnInfo(name = "exp")

    String exp;

    public EmpEntity(@NonNull int emp_id, String name, String dept, String design, String exp) {

        this.emp_id = emp_id;

        this.name = name;

        this.dept = dept;

        this.design = design;

        this.exp = exp;

    }

    @NonNull

    public int getEmp_id() {

        return emp_id;

    }

    public void setEmp_id(@NonNull int emp_id) {

        this.emp_id = emp_id;

    }

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

    public String getDept() {

        return dept;

    }

    public void setDept(String dept) {

        this.dept = dept;

    }

    public String getDesign() {

        return design;

    }

    public void setDesign(String design) {

        this.design = design;

    }

    public String getExp() {

        return exp;

    }

    public void setExp(String exp) {

        this.exp = exp;

    }

}

The above is the entity class , it is used to create mapping between Data Object and Database.

Annotation  @ColumnInfo is used to define the column name , it must be same as the db table . 

Annotation @Entity is used to define the table name .

Annotation  @PrimaryKey is define here to show the primary key column.

-> EmployeeDbDao.java

import com.roomdbdemo.entity.EmpEntity;

import java.util.List;

import androidx.room.Dao;

import androidx.room.Delete;

import androidx.room.Insert;

import androidx.room.Query;

import androidx.room.Update;

@Dao

public interface EmployeeDbDao {

    @Insert

    void insertEmpInfo(EmpEntity myBooksEntity);

    @Update

    void updateEmpInfo(EmpEntity myBooksEntity);

    @Delete

    void deleteEmpInfo(EmpEntity myBooksEntity);

   // with query

    @Query("SELECT * FROM employee")

    List<EmpEntity> showAll();

    // with query

    @Query("SELECT * FROM employee WHERE emp_id = :emp_id")

    EmpEntity fetchEmpDetail(int emp_id);

}

This is the dao interface, it is used to write all the queries which is required . I have defined here insert , update , delete and some more queries. For basic operations that are insert , update , delete , it provides the annotations (as you can see in above code) , and if it is required to fetch data using specific query , then we have @Query (as you can see in above code) . 

-> EmployeeRoomDb.java

import com.roomdbdemo.entity.EmpEntity;
import androidx.room.Database;
import androidx.room.RoomDatabase;
import androidx.room.migration.Migration;
import androidx.sqlite.db.SupportSQLiteDatabase;

@Database(entities = {EmpEntity.class},version = 2, exportSchema = false)
public abstract class EmployeeRoomDb extends RoomDatabase {
public static EmployeeRoomDb INSTANCE;

public abstract EmployeeDbDao employeeDbDao();

public static final Migration MIGRATION_1_2 = new Migration(1, 2) {
@Override
public void migrate(SupportSQLiteDatabase database) {
}
};
}

The above is abstract class defined, with the abstract method employeeDbDao() . This class is known as a database builder class.

Now let's  move to the activity classes code:

In MainActivity.class , I just defined the click listener for  all buttons , so just showing that part of the class:

btn_insert.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Intent intent = new Intent(getApplicationContext(), EmployeeDetailActivity.class);
intent.putExtra("comes_from","insert");
intent.putExtra("emp_id","");
startActivity(intent);
}
});

btn_update.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Utils utils = new Utils();
utils.showEditDialog(MainActivity.this);
}
});

btn_show.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Intent intent = new Intent(getApplicationContext(), EmployeeListActivity.class);
startActivity(intent);
}
});

I have used same class for inserting the employee detail and updating the employee detail i.e. EmployeeDetailActivity.class

In Utils class , I have defined one alert dialog with edittext which is used to get the employee id value from the user , to update the detail of that user.

Alert dialog in Utils.class:

public void showEditDialog(final Activity activity) {

AlertDialog.Builder alert = new AlertDialog.Builder(activity, R.style.AppTheme);
final EditText edittext = new EditText(activity);
edittext.setInputType(InputType.TYPE_CLASS_NUMBER | InputType.TYPE_NUMBER_FLAG_SIGNED);
edittext.setSingleLine(true);
alert.setMessage("Enter Employee Id , you want to update!");
alert.setTitle("Update");
alert.setView(edittext);

alert.setPositiveButton("Enter", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int whichButton) {
if (!TextUtils.isEmpty(edittext.getText())) {

int emp_id = Integer.parseInt(edittext.getText().toString());
Intent intent = new Intent(activity, EmployeeDetailActivity.class);
intent.putExtra("comes_from", "update");
intent.putExtra("emp_id", emp_id);
activity.startActivity(intent);

}

}
});

alert.setNegativeButton("Exit", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int whichButton) {
dialog.dismiss();
}
});

alert.show();
}

This alert will show , when we click update button . It will ask user for employee-id , whose detail user wants to update.

Now please take a close look on EmployeeDetailActivity.class, as this class is used for insert and update both .

EmployeeDetailActivity.class:

public class EmployeeDetailActivity extends AppCompatActivity {

private EditText edttxtName, edttxtDepart, edttxtDesig, edttxtExp;
private Button btnSave;
private String comes_from ;
private int emp_id;
private ProgressBar progressBar;
private Preference preference;
private int empIdStored = 0, empIdForNew; //we will save it in shared preference , will increase by 1 everytime


@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.emp_detail_layout);
inItViews();
Intent in = getIntent();
comes_from = in.getStringExtra("comes_from");
emp_id = in.getIntExtra("emp_id",0);

if (comes_from.equalsIgnoreCase("update")){
new getEmployeeInfo(emp_id).execute();
}
btnSave.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
if (comes_from.equalsIgnoreCase("insert")){
insertEmployeeDetail();
}
else if (comes_from.equalsIgnoreCase("update")){
updateEmployeeDetail(emp_id);
}
}
});
}

private void inItViews() {
preference = Preference.getInstance(this);
edttxtName = (EditText)findViewById(R.id.edttxt_name);
edttxtDepart = (EditText)findViewById(R.id.edttxt_dept);
edttxtDesig = (EditText)findViewById(R.id.edttxt_desig);
edttxtExp = (EditText)findViewById(R.id.edttxt_exp);
btnSave = (Button)findViewById(R.id.btn_save);
progressBar = (ProgressBar)findViewById(R.id.progressBar);
progressBar.setVisibility(View.GONE);
}

private void updateEmployeeDetail(int emp_id) {
// fetch & insert the emp detail
if(!(TextUtils.isEmpty(edttxtName.getText()))&&
!(TextUtils.isEmpty(edttxtDepart.getText()))&&
!(TextUtils.isEmpty(edttxtDesig.getText()))&&
!(TextUtils.isEmpty(edttxtExp.getText()))){
// insert in db
EmpEntity empEntity = new EmpEntity(emp_id,edttxtName.getText().toString()
,edttxtDepart.getText().toString()
,edttxtDesig.getText().toString()
,edttxtExp.getText().toString());
new insertupdateEmpDetail(empEntity).execute();
}
else{
Toast.makeText(getApplicationContext(),"Please fill all the fields!",Toast.LENGTH_LONG).show();
}
}

private void insertEmployeeDetail() {

empIdStored = preference.getEmployeeId();
empIdForNew = empIdStored+1;

if(!(TextUtils.isEmpty(edttxtName.getText()))&&
!(TextUtils.isEmpty(edttxtDepart.getText()))&&
!(TextUtils.isEmpty(edttxtDesig.getText()))&&
!(TextUtils.isEmpty(edttxtExp.getText()))){
// insert in db
EmpEntity empEntity = new EmpEntity(empIdForNew,edttxtName.getText().toString()
,edttxtDepart.getText().toString()
,edttxtDesig.getText().toString()
,edttxtExp.getText().toString());
new insertupdateEmpDetail(empEntity).execute();
}
else{
Toast.makeText(getApplicationContext(),"Please fill all the fields!",Toast.LENGTH_LONG).show();
}
}

private class insertupdateEmpDetail extends AsyncTask<String, String, String> {

EmpEntity empEntity ;

public insertupdateEmpDetail(EmpEntity empEntity) {
this.empEntity = empEntity;

}

@Override
protected void onPreExecute() {
super.onPreExecute();
progressBar.setVisibility(View.VISIBLE);
}

@Override
protected String doInBackground(String... strings) {
if (comes_from.equalsIgnoreCase("insert")){
RoomDbDemoApplication.getInstance().getDb().employeeDbDao().insertEmpInfo(empEntity);
}
else{
RoomDbDemoApplication.getInstance().getDb().employeeDbDao().updateEmpInfo(empEntity);
}
return null;
}

@Override
protected void onPostExecute(String s) {
super.onPostExecute(s);
progressBar.setVisibility(View.GONE);
edttxtName.getText().clear();
edttxtDepart.getText().clear();
edttxtDesig.getText().clear();
edttxtExp.getText().clear();
if (comes_from.equalsIgnoreCase("insert")){
preference.setEmployeeId(empEntity.getEmp_id());
Toast.makeText(getApplicationContext(),"Employee record saved successfully!",Toast.LENGTH_LONG).show();
}
else{
Toast.makeText(getApplicationContext(),"Employee record updated successfully!",Toast.LENGTH_LONG).show();
}
finish();
}
}

private class getEmployeeInfo extends AsyncTask<String, String, String>{
int empId ;
EmpEntity empEntity;
public getEmployeeInfo(int emp_id) {
this.empId = emp_id;
}

@Override
protected void onPreExecute() {
super.onPreExecute();
progressBar.setVisibility(View.VISIBLE);
}

@Override
protected String doInBackground(String... strings) {
empEntity = RoomDbDemoApplication.getInstance().getDb().employeeDbDao().fetchEmpDetail(empId);
return null;
}

@Override
protected void onPostExecute(String s) {
super.onPostExecute(s);
progressBar.setVisibility(View.GONE);
if (empEntity!=null){
edttxtName.setText(empEntity.getName());
edttxtDepart.setText(empEntity.getDept());
edttxtDesig.setText(empEntity.getDesign());
edttxtExp.setText(empEntity.getExp());
}

else{
Toast.makeText(getApplicationContext(),"No Employee found with this employee-id!",Toast.LENGTH_LONG).show();
finish();
}

}
}
}

Here I have used   empIdForNew variable is used . This is to create the new employee id on every new insertion. Initially it is 1 after when new employee details has been inserted , it will saved in shared preference and in next time it is fetched and incremented by 1 , then used at the time second employee detail insertion.

Now below is code to show the list of Employee detail which are saved in database.

EmployeeListActivity.java

import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.widget.ProgressBar;
import android.widget.Toast;
import com.roomdbdemo.adapter.EmpListAdapter;
import com.roomdbdemo.entity.EmpEntity;
import com.roomdbdemo.helper.ClickListener;
import com.roomdbdemo.helper.RecyclerTouchListener;
import java.util.ArrayList;
import java.util.List;
import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.DefaultItemAnimator;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

public class EmployeeListActivity extends AppCompatActivity {

ArrayList<EmpEntity> empList = new ArrayList<>();
ProgressBar progressBar;
RecyclerView recyclerView;
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.emp_list_layout);
progressBar = (ProgressBar)findViewById(R.id.progressBar);
progressBar.setVisibility(View.GONE);
recyclerView = (RecyclerView)findViewById(R.id.recycler);
recyclerView.setVisibility(View.GONE);
loadEmpList();

}

private void loadEmpList() {
//fetch emp list from DB
new LoadEmpListAsyncTask().execute();
}

private void showEmpList(List<EmpEntity> empEntities) {

EmpListAdapter mAdapter = new EmpListAdapter(EmployeeListActivity.this,empEntities);
recyclerView.setLayoutManager(new LinearLayoutManager(EmployeeListActivity.this));
recyclerView.setItemAnimator(new DefaultItemAnimator());
recyclerView.setAdapter(mAdapter);
}

private class LoadEmpListAsyncTask extends AsyncTask<String,String,List<EmpEntity>> {
@Override
protected void onPreExecute() {
super.onPreExecute();
progressBar.setVisibility(View.VISIBLE);
}

@Override
protected List<EmpEntity> doInBackground(String... strings) {
List<EmpEntity> empEntities = RoomDbDemoApplication.getInstance().getDb().employeeDbDao().showAll();
return empEntities;
}

@Override
protected void onPostExecute( List<EmpEntity> empEntities) {
super.onPostExecute(empEntities);
progressBar.setVisibility(View.GONE);
if (empEntities.size()>0){
recyclerView.setVisibility(View.VISIBLE);
showEmpList(empEntities);
}else{
Toast.makeText(getApplicationContext(), "No employee has been stored!!",Toast.LENGTH_LONG).show();
}

}
}
}And in Adapter class :

EmpListAdapter.class:

import android.app.Activity;
import android.content.DialogInterface;
import android.content.Intent;
import android.os.AsyncTask;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;
import com.roomdbdemo.EmployeeDetailActivity;
import com.roomdbdemo.R;
import com.roomdbdemo.RoomDbDemoApplication;
import com.roomdbdemo.entity.EmpEntity;
import java.util.List;
import androidx.appcompat.app.AlertDialog;
import androidx.recyclerview.widget.RecyclerView;

public class EmpListAdapter extends RecyclerView.Adapter<EmpListAdapter.MyViewHolder>{

Activity activity;
List<EmpEntity> empList ;
public EmpListAdapter(Activity mActivity, List<EmpEntity> empList) {
this.activity = mActivity;
this.empList = empList;
}

@Override
public EmpListAdapter.MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View itemView = LayoutInflater.from(parent.getContext())
.inflate(R.layout.emp_item_layout, parent, false);
return new EmpListAdapter.MyViewHolder(itemView);

}

@Override
public void onBindViewHolder(EmpListAdapter.MyViewHolder holder, int position) {
final EmpEntity empEntity = empList.get(position);
holder.textName.setText("Name: "+empEntity.getName() );
holder.textDesignation.setText(empEntity.getDesign()+" ("+empEntity.getDept()+") ");
holder.textExp.setText("Experience(in months): "+empEntity.getExp());
holder.textEmpId.setText( "EmployeeId: "+empEntity.getEmp_id());
holder.imageView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
//delete the employee record
showDeleteDialog(activity,empEntity);
}
});
holder.imageEdit.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
//edit the employee record
Intent intent = new Intent(activity, EmployeeDetailActivity.class);
intent.putExtra("comes_from", "update");
intent.putExtra("emp_id", empEntity.getEmp_id());
activity.startActivity(intent);
activity.finish();
}
});
}

@Override
public int getItemCount() {
return empList.size();
}
class MyViewHolder extends RecyclerView.ViewHolder{

ImageView imageView, imageEdit;
TextView textName, textDesignation, textExp, textEmpId;
public MyViewHolder(View itemView) {
super(itemView);
imageView = (ImageView)itemView.findViewById(R.id.imageView2);
textName = (TextView)itemView.findViewById(R.id.textView);
textDesignation = (TextView)itemView.findViewById(R.id.textView2);
textExp = (TextView)itemView.findViewById(R.id.textView3);
textEmpId = (TextView)itemView.findViewById(R.id.textView4);
imageEdit = (ImageView)itemView.findViewById(R.id.imageView3);
}

}

private void showDeleteDialog(Activity activity, final EmpEntity empEntity) {

AlertDialog.Builder alert = new AlertDialog.Builder(activity, R.style.AppTheme);
alert.setMessage("Are you sure , to delete this employee record?");
alert.setTitle("Delete");

alert.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int whichButton) {
deleteEmployeeRecord(empEntity);
dialog.dismiss();
}
});

alert.setNegativeButton("No", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int whichButton) {
// what ever you want to do with No option.
dialog.dismiss();
}
});

alert.show();
}

private void deleteEmployeeRecord(EmpEntity empEntity) {
new deleteTask(empEntity).execute();
}

private class deleteTask extends AsyncTask<String,String,String> {
EmpEntity empEntity ;
public deleteTask(EmpEntity empEntity) {
this.empEntity = empEntity;
}

@Override
protected String doInBackground(String... strings) {
RoomDbDemoApplication.getInstance().getDb().employeeDbDao().deleteEmpInfo(empEntity);
return null;
}

@Override
protected void onPostExecute(String s) {
super.onPostExecute(s);
empList.remove(empEntity);
notifyDataSetChanged();
}
}
}

Here you can see the process for updationg and deleting the employee record from the list.

Now last but not least , the application class.

RoomDbDemoApplication.class:

import android.app.Application;
import com.roomdbdemo.db.EmployeeRoomDb;
import androidx.room.Room;

public class RoomDbDemoApplication extends Application {

public static RoomDbDemoApplication instance;
public EmployeeRoomDb myDatabase;
@Override
public void onCreate() {
super.onCreate();
instance = this;
myDatabase = Room.databaseBuilder(getApplicationContext(),
EmployeeRoomDb.class, "Emp.db")
.addMigrations(EmployeeRoomDb.MIGRATION_1_2)
.build();
}

public static RoomDbDemoApplication getInstance() {
return instance;
}

public EmployeeRoomDb getDb() {
return myDatabase;
}
}

That's it.However I have each and every necessary codes . But also I am attaching the source code demo link. So that it would be more understandable with running demo.

Demo Source Code

Android Architecture Components : Room DB Introduction

Hi All,

Today I am going to share my understanding about Room Database. First , let's start with why Room?
Actually when we have SQLite Open Helper class , then what is the need of Room . This can be easily understood by understanding the difference between them.

Sqlite vs Room :

• Sqlite deals with raw queries where as in Room DB there is no raw queries.
• In Sqlite , no compile time verification of raw sql queries , but in Room DB compiler checks the Sqlite statement
• In Sqlite , lots of boilerplate code we had to write to conversion between Sqlite statement and java data objects, but in Room DB boilerplate code is less due to mapping between DB objects and java objects.
• Sqlite apis are low level , so more time and more effort is required to build apps.In Room DB , it makes easy when used with Live Data and ViewModel

So , because of the above reasons , Room is a good option to work with.

What is Room: 

• Database Layer on top of Sqlite.
• Provides an abstraction layer over Sqlite to allow fluent database access
• Object Relation Mapping(ORM) library 

Room Database Components :

Entity :

•  Defines schema of database table
•  annotated with @Entity

 

Dao:

• contains method to access database
• annotated with @Dao

Database:

• It is database holder class 
• annotated with @Database

Our android application uses Dao , to access the Sqlite database.These data access objects are used to perform db related operations.

Entities are used to get and set the fields of Database table to android application.This way components of Room are related to each other.

 

For more information , you can check the official android developers video

That's it , for this post , in next post I will share a demo for Room DB 

Android Architecture Components : Lifecycle-aware Components

Hi,
In previous post I have explained how we can use view model with live data. Now in this post I will explain , in our Activity /Fragment , how it will be LifeCycle Aware . Now first the question is what is the need of LifeCycle Awareness . So let me explain in brief on this .

The main problem of all android developers is memory leak in codebase , cause of that is an invalid state is accessed which is not synced with the lifecycle of activity/fragment of the app.
 To avoid this we have to unregister callbacks/call cleanup methods or specific functions to re-initialize at certain points in the lifecycle of Activity/Fragment.i.e onDestroy(), onResume(), onCreate(), etc.And if in any part due to hurry (to achieve deadlines ;),obviously) sometimes the cleanup part is missed or not putting in the right place in code .

 For example, if an Activity receives a callback after it’s been stopped,then it’s pretty likely that your app is going to crash due to memory leak. Unregistering the callback is right before the Activity is destroyed is what is the needed.But if this part is missed , it may cause trouble.We have to make sure to cleanup on proper events of Activity/Fragment.

 So the solution of this problem is, our activity/ fragment should be lifecycle aware.Making the components lifecycle-aware facilitates us to not to putting more code and
 checks in application to handle the states of the activity/fragment.

Now the question how , lifecycle-aware components provides us these benefits. Let's take a look:

An activity has its own lifecycle hence it is called LifeCycleOwner.
Now in lifecycle-aware components we have a class LifeCycle , this class is having Event and State as enumeration.
These are used to determine the lifecycle of LifeCycleOwner. Each event has its own state.
Event onCreate()  -> State CREATED
Event onStart()   -> State STARTED
Event onResume()  -> State RESUMED
Event onPause()  -> State PAUSED
Event onStop()  -> State STOPPED
Event onDestroy()  -> State DESTROYED
This way each event is releated to a particular state.
We also have LifeCycleObserver , which observers the LifeCycleOwner(activity/fragment) and keep track its lifecycle.
Thus the LifeCycleObserver performs action.The action performed by this LifeCycleObserver , depends on the lifecycle of LifeCycleOwner.
Thus every activity/fragment has its own LifeCycle , and on the basis of events and states of this , LifeCycleObserver performs actions.
This way LifeCycleOwner , LifeCycle and LifeCycleObserver are connected.

Now let's move to the coding part :

->Add dependency in build.gradle(app) :

implementation "android.arch.lifecycle:runtime:1.1.1"
implementation "android.arch.lifecycle:extensions:1.1.1"
annotationProcessor "android.arch.lifecycle:compiler:1.1.1"


-> Now create a java class named : LifeCycleDemoObserver.java :

import android.arch.lifecycle.Lifecycle;
import android.arch.lifecycle.LifecycleObserver;
import android.arch.lifecycle.OnLifecycleEvent;
import android.util.Log;

public class LifeCycleDemoObserver implements LifecycleObserver {

private String TAG = this.getClass().getName();

@OnLifecycleEvent(Lifecycle.Event.ON_CREATE)
public void OnCreateObserver(){
Log.d(TAG,"On Create Observer");
}

@OnLifecycleEvent(Lifecycle.Event.ON_START)
public void OnStartObserver(){
Log.d(TAG,"On Start Observer");
}

@OnLifecycleEvent(Lifecycle.Event.ON_RESUME)
public void OnResumeObserver(){
Log.d(TAG,"On Resume Observer");
}

@OnLifecycleEvent(Lifecycle.Event.ON_PAUSE)
public void OnPauseObserver(){
Log.d(TAG,"On Pause Observer");
}

@OnLifecycleEvent(Lifecycle.Event.ON_STOP)
public void OnStopObserver(){
Log.d(TAG,"On Stop Observer");
}

@OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
public void OnDestroyObserver(){
Log.d(TAG,"On Destroy Observer");
}
}

Here I am adding the log for all events of activity lifecycle.
Now we will add this observer in onCreate method of Activity class.
Let's take a look on activity class :

import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;

import com.development.R;

public class LifeCycleDemoActivity extends AppCompatActivity {

private String TAG = this.getClass().getName();

@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.life_cycle_layout);
Log.d(TAG, "Activity OnCreate");

getLifecycle().addObserver(new LifeCycleDemoObserver());
}

@Override
protected void onPause() {
super.onPause();
Log.d(TAG, "Activity onPause");
} 

@Override
protected void onResume() {
super.onResume();
Log.d(TAG, "Activity onResume");
}

@Override
protected void onStart() {
super.onStart();
Log.d(TAG, "Activity onStart");
}

@Override
protected void onStop() {
super.onStop();
Log.d(TAG, "Activity onStop");
}

@Override
protected void onDestroy() {
super.onDestroy();
Log.d(TAG, "Activity onDestroy");
}
}

Here I have also added logs for all the events in activity . Now on running the program, we can see that all the events of observer class will call after activity log events ,and when we change the configuration , observer method will call first. I have added the log screenshot for better understanding.

Here in above screenshot we can see that after rotation the onPause() and onStop() methods of observer class had been called first then after activity class event method had been called. In this way Lifecycle-Aware-Components take place. That's it .In next tutorial I will share a demo for Room DB .Till then happy coding. :) 

Android Architecture Components : Live Data + View Model

Hi ,

In previous posts , I have described the properties of View Model and Live Data . But if we use both together , that would be great for an individual application. So here I am going to share a demo where we can see that how both will work together .

Firstly I am creating one layout having one TextView inside , named  view_model_layout.xml -> 

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:id="@+id/textview7"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:textSize="25sp"
        android:textColor="#085937"
        android:textStyle="bold"
        android:text="TextView" />


</RelativeLayout>

Now Let's create one view model class , named as : RandomNumViewModel.java :

package com.development.view_model_live_data;

import android.arch.lifecycle.MutableLiveData;

import android.arch.lifecycle.ViewModel;

import java.util.Random;

public class RandomNumViewModel extends ViewModel {

    MutableLiveData mMutableLiveData;

    public RandomNumViewModel() {

        mMutableLiveData = new MutableLiveData<>();

    }

    private int[] items = new int[]{1, 2, 3, 44, 65, 87, 22, 65, 87, 22, 90, 63, 4, 8, 50};

    private Random random = new Random();

    /**

     * mRandomNumber , this variable should retain its value,

     * on configuration change

     */

    private int mRandomNumber = 0;

    /**

     * used to create a random number from array

     * @return

     */

    public int createNumber(){

        mRandomNumber = items[random.nextInt(items.length)];

        return mRandomNumber;

    }

    /**

     * used to get the random number

     * @return

     * @param txt

     */

    /**

     * Observe the random number

     */

    public MutableLiveData getRandArrayElement(){

        if(mRandomNumber == 0){

            mRandomNumber = createNumber();

        }

        mMutableLiveData.setValue(mRandomNumber);

        return  mMutableLiveData;

    }

}

And the Activity class will only be observe the changed value of mRandomNumber , let's have a look on Activity class, named ViewLiveDemoActivity.java:

package com.development.view_model_live_data;

import android.arch.lifecycle.Observer;

import android.arch.lifecycle.ViewModelProviders;

import android.os.Bundle;

import android.support.annotation.Nullable;

import android.support.v7.app.AppCompatActivity;

import android.widget.TextView;

import com.development.R;

public class ViewLiveDemoActivity extends AppCompatActivity {

    TextView txt;

    @Override

    protected void onCreate(@Nullable Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.view_model_layout);

        txt  = (TextView)findViewById(R.id.textview7);

        RandomNumViewModel randomNumViewModel = ViewModelProviders.of(this).get(RandomNumViewModel.class);

        randomNumViewModel.getRandArrayElement().observe(this, new Observer() {

            @Override

            public void onChanged(@Nullable Object o) {

                txt.setText(""+ o);

            }

        });

    }

}

Here you can see that , activity class only notify when variable value has been changed , and this is done by Live Data concept . If we rotate our device , then the value of variable will not be changed , this concept has been done by View Model . I have attached the screenshots for portrait and landscape modes for better understanding :

 Portrait Mode

Landscape Mode

Here in above images you can see that the variable value remains same after the rotation of device . And this all has been done both using Live Data +View Model . You can take this code and run it by yourself  . Happy Coding :)