In the previous articles, we have seen three operations of CRUD operations such as create, read and update operations in our Android app. In this article, we will take a look at adding delete operation for deleting our items stored in the SQLite database.
What we are going to build in this article?
We will be building a simple application in which we will be deleting the course from our SQLite database in our Android app. A sample video is given below to get an idea about what we are going to do in this article.
Step by Step Implementation
Step 1: Updating our DBHandler class
As we have to delete data from our SQLite database. For that, we have to create a method to delete our data from the SQLite database. Navigate to the app > java > your app’s package name > DBHandler and add the below code to it.
// below is the method for deleting our course. public void deleteCourse(String courseName) {
// on below line we are creating
// a variable to write our database.
SQLiteDatabase db = this .getWritableDatabase();
// on below line we are calling a method to delete our
// course and we are comparing it with our course name.
db.delete(TABLE_NAME, "name=?" , new String[]{courseName});
db.close();
} |
Below is the updated code for the DBHandler.java file after adding the above code snippet.
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import java.util.ArrayList;
public class DBHandler extends SQLiteOpenHelper {
// creating a constant variables for our database.
// below variable is for our database name.
private static final String DB_NAME = "coursedb" ;
// below int is our database version
private static final int DB_VERSION = 1 ;
// below variable is for our table name.
private static final String TABLE_NAME = "mycourses" ;
// below variable is for our id column.
private static final String ID_COL = "id" ;
// below variable is for our course name column
private static final String NAME_COL = "name" ;
// below variable id for our course duration column.
private static final String DURATION_COL = "duration" ;
// below variable for our course description column.
private static final String DESCRIPTION_COL = "description" ;
// below variable is for our course tracks column.
private static final String TRACKS_COL = "tracks" ;
// creating a constructor for our database handler.
public DBHandler(Context context) {
super (context, DB_NAME, null , DB_VERSION);
}
// below method is for creating a database by running a sqlite query
@Override
public void onCreate(SQLiteDatabase db) {
// on below line we are creating
// an sqlite query and we are
// setting our column names
// along with their data types.
String query = "CREATE TABLE " + TABLE_NAME + " ("
+ ID_COL + " INTEGER PRIMARY KEY AUTOINCREMENT, "
+ NAME_COL + " TEXT,"
+ DURATION_COL + " TEXT,"
+ DESCRIPTION_COL + " TEXT,"
+ TRACKS_COL + " TEXT)" ;
// at last we are calling a exec sql
// method to execute above sql query
db.execSQL(query);
}
// this method is use to add new course to our sqlite database.
public void addNewCourse(String courseName, String courseDuration, String courseDescription, String courseTracks) {
// on below line we are creating a variable for
// our sqlite database and calling writable method
// as we are writing data in our database.
SQLiteDatabase db = this .getWritableDatabase();
// on below line we are creating a
// variable for content values.
ContentValues values = new ContentValues();
// on below line we are passing all values
// along with its key and value pair.
values.put(NAME_COL, courseName);
values.put(DURATION_COL, courseDuration);
values.put(DESCRIPTION_COL, courseDescription);
values.put(TRACKS_COL, courseTracks);
// after adding all values we are passing
// content values to our table.
db.insert(TABLE_NAME, null , values);
// at last we are closing our
// database after adding database.
db.close();
}
// we have created a new method for reading all the courses.
public ArrayList<CourseModal> readCourses() {
// on below line we are creating a
// database for reading our database.
SQLiteDatabase db = this .getReadableDatabase();
// on below line we are creating a cursor with query to read data from database.
Cursor cursorCourses = db.rawQuery( "SELECT * FROM " + TABLE_NAME, null );
// on below line we are creating a new array list.
ArrayList<CourseModal> courseModalArrayList = new ArrayList<>();
// moving our cursor to first position.
if (cursorCourses.moveToFirst()) {
do {
// on below line we are adding the data from cursor to our array list.
courseModalArrayList.add( new CourseModal(cursorCourses.getString( 1 ),
cursorCourses.getString( 4 ),
cursorCourses.getString( 2 ),
cursorCourses.getString( 3 )));
} while (cursorCourses.moveToNext());
// moving our cursor to next.
}
// at last closing our cursor
// and returning our array list.
cursorCourses.close();
return courseModalArrayList;
}
// below is the method for updating our courses
public void updateCourse(String originalCourseName, String courseName, String courseDescription,
String courseTracks, String courseDuration) {
// calling a method to get writable database.
SQLiteDatabase db = this .getWritableDatabase();
ContentValues values = new ContentValues();
// on below line we are passing all values
// along with its key and value pair.
values.put(NAME_COL, courseName);
values.put(DURATION_COL, courseDuration);
values.put(DESCRIPTION_COL, courseDescription);
values.put(TRACKS_COL, courseTracks);
// on below line we are calling a update method to update our database and passing our values.
// and we are comparing it with name of our course which is stored in original name variable.
db.update(TABLE_NAME, values, "name=?" , new String[]{originalCourseName});
db.close();
}
// below is the method for deleting our course.
public void deleteCourse(String courseName) {
// on below line we are creating
// a variable to write our database.
SQLiteDatabase db = this .getWritableDatabase();
// on below line we are calling a method to delete our
// course and we are comparing it with our course name.
db.delete(TABLE_NAME, "name=?" , new String[]{courseName});
db.close();
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// this method is called to check if the table exists already.
db.execSQL( "DROP TABLE IF EXISTS " + TABLE_NAME);
onCreate(db);
}
} |
Step 2: Adding a button to delete our course
Navigate to the app > res > layout > activity_update_course.xml file and add a Button inside this layout for deleting a course. Below is the code for that file.
<!--button for deleting our course--> < Button
android:id = "@+id/idBtnDelete"
android:layout_width = "match_parent"
android:layout_height = "wrap_content"
android:layout_margin = "10dp"
android:text = "Delete Course"
android:textAllCaps = "false" />
|
Below is the updated code for the activity_update_course.xml file after adding the above code snippet.
<? xml version = "1.0" encoding = "utf-8" ?>
< LinearLayout
android:layout_width = "match_parent"
android:layout_height = "match_parent"
android:orientation = "vertical"
tools:context = ".UpdateCourseActivity" >
<!--Edit text to enter course name-->
< EditText
android:id = "@+id/idEdtCourseName"
android:layout_width = "match_parent"
android:layout_height = "wrap_content"
android:layout_margin = "10dp"
android:hint = "Enter course Name" />
<!--edit text to enter course duration-->
< EditText
android:id = "@+id/idEdtCourseDuration"
android:layout_width = "match_parent"
android:layout_height = "wrap_content"
android:layout_margin = "10dp"
android:hint = "Enter Course Duration" />
<!--edit text to display course tracks-->
< EditText
android:id = "@+id/idEdtCourseTracks"
android:layout_width = "match_parent"
android:layout_height = "wrap_content"
android:layout_margin = "10dp"
android:hint = "Enter Course Tracks" />
<!--edit text for course description-->
< EditText
android:id = "@+id/idEdtCourseDescription"
android:layout_width = "match_parent"
android:layout_height = "wrap_content"
android:layout_margin = "10dp"
android:hint = "Enter Course Description" />
<!--button for updating our course-->
< Button
android:id = "@+id/idBtnUpdateCourse"
android:layout_width = "match_parent"
android:layout_height = "wrap_content"
android:layout_margin = "10dp"
android:text = "Update Course"
android:textAllCaps = "false" />
<!--button for deleting our course-->
< Button
android:id = "@+id/idBtnDelete"
android:layout_width = "match_parent"
android:layout_height = "wrap_content"
android:layout_margin = "10dp"
android:text = "Delete Course"
android:textAllCaps = "false" />
</ LinearLayout >
|
Step 3: Initializing our button to delete our course
Navigate to the app > java > your app’s package name > UpdateCourseActivity.java file and add the below code to it.
// adding on click listener for delete button to delete our course. deleteCourseBtn.setOnClickListener( new View.OnClickListener() {
@Override
public void onClick(View v) {
// calling a method to delete our course.
dbHandler.deleteCourse(courseName);
Toast.makeText(UpdateCourseActivity. this , "Deleted the course" , Toast.LENGTH_SHORT).show();
Intent i = new Intent(UpdateCourseActivity. this , MainActivity. class );
startActivity(i);
}
}); |
Below is the updated code for the UpdateCourseActivity.java file after adding the above code snippet.
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
import androidx.appcompat.app.AppCompatActivity;
public class UpdateCourseActivity extends AppCompatActivity {
// variables for our edit text, button, strings and dbhandler class.
private EditText courseNameEdt, courseTracksEdt, courseDurationEdt, courseDescriptionEdt;
private Button updateCourseBtn, deleteCourseBtn;
private DBHandler dbHandler;
String courseName, courseDesc, courseDuration, courseTracks;
@Override
protected void onCreate(Bundle savedInstanceState) {
super .onCreate(savedInstanceState);
setContentView(R.layout.activity_update_course);
// initializing all our variables.
courseNameEdt = findViewById(R.id.idEdtCourseName);
courseTracksEdt = findViewById(R.id.idEdtCourseTracks);
courseDurationEdt = findViewById(R.id.idEdtCourseDuration);
courseDescriptionEdt = findViewById(R.id.idEdtCourseDescription);
updateCourseBtn = findViewById(R.id.idBtnUpdateCourse);
deleteCourseBtn = findViewById(R.id.idBtnDelete);
// on below line we are initializing our dbhandler class.
dbHandler = new DBHandler(UpdateCourseActivity. this );
// on below lines we are getting data which
// we passed in our adapter class.
courseName = getIntent().getStringExtra( "name" );
courseDesc = getIntent().getStringExtra( "description" );
courseDuration = getIntent().getStringExtra( "duration" );
courseTracks = getIntent().getStringExtra( "tracks" );
// setting data to edit text
// of our update activity.
courseNameEdt.setText(courseName);
courseDescriptionEdt.setText(courseDesc);
courseTracksEdt.setText(courseTracks);
courseDurationEdt.setText(courseDuration);
// adding on click listener to our update course button.
updateCourseBtn.setOnClickListener( new View.OnClickListener() {
@Override
public void onClick(View v) {
// inside this method we are calling an update course
// method and passing all our edit text values.
dbHandler.updateCourse(courseName, courseNameEdt.getText().toString(), courseDescriptionEdt.getText().toString(), courseTracksEdt.getText().toString(), courseDurationEdt.getText().toString());
// displaying a toast message that our course has been updated.
Toast.makeText(UpdateCourseActivity. this , "Course Updated.." , Toast.LENGTH_SHORT).show();
// launching our main activity.
Intent i = new Intent(UpdateCourseActivity. this , MainActivity. class );
startActivity(i);
}
});
// adding on click listener for delete button to delete our course.
deleteCourseBtn.setOnClickListener( new View.OnClickListener() {
@Override
public void onClick(View v) {
// calling a method to delete our course.
dbHandler.deleteCourse(courseName);
Toast.makeText(UpdateCourseActivity. this , "Deleted the course" , Toast.LENGTH_SHORT).show();
Intent i = new Intent(UpdateCourseActivity. this , MainActivity. class );
startActivity(i);
}
});
}
} |
Now run your app and see the output of the app. Make sure to add data to our database before deleting it.
Output:
Below is the complete project file structure after performing the delete operation: