How to Perform Delete Operation in SQLite Database in Android

In this tutorial how to perform delete operation in SQLite Database from  an Android Application is shown.

Code:

activity_main.xml

<RelativeLayout xmlns:android=”http://schemas.android.com/apk/res/android”
xmlns:tools=”http://schemas.android.com/tools”
android:layout_width=”match_parent”
android:layout_height=”match_parent”
android:paddingBottom=”@dimen/activity_vertical_margin”
android:paddingLeft=”@dimen/activity_horizontal_margin”
android:paddingRight=”@dimen/activity_horizontal_margin”
android:paddingTop=”@dimen/activity_vertical_margin”
tools:context=”.MainActivity” >

<TextView
android:id=”@+id/textView1″
android:layout_width=”wrap_content”
android:layout_height=”wrap_content”
android:layout_alignParentTop=”true”
android:layout_centerHorizontal=”true”
android:layout_marginTop=”50dp”
android:text=”Student Details” />

<EditText
android:id=”@+id/editRollno”
android:layout_width=”wrap_content”
android:layout_height=”wrap_content”
android:layout_below=”@+id/textView1″
android:layout_centerHorizontal=”true”
android:layout_marginTop=”29dp”
android:ems=”10″
android:hint=”Enter Roll No” >

<requestFocus />
</EditText>

<EditText
android:id=”@+id/editMarks”
android:layout_width=”wrap_content”
android:layout_height=”wrap_content”
android:layout_below=”@+id/editName”
android:layout_centerHorizontal=”true”
android:layout_marginTop=”34dp”
android:ems=”10″
android:hint=”Enter Marks” />

<EditText
android:id=”@+id/editName”
android:layout_width=”wrap_content”
android:layout_height=”wrap_content”
android:layout_alignLeft=”@+id/editRollno”
android:layout_below=”@+id/editRollno”
android:layout_marginTop=”28dp”
android:ems=”10″
android:hint=”Enter Name” />

<Button
android:id=”@+id/btnDelete”
android:layout_width=”wrap_content”
android:layout_height=”wrap_content”
android:layout_alignBaseline=”@+id/btnModify”
android:layout_alignBottom=”@+id/btnModify”
android:layout_alignParentRight=”true”
android:onClick=”dbFunction”
android:text=”Delete” />

<Button
android:id=”@+id/btnReset”
android:layout_width=”wrap_content”
android:layout_height=”wrap_content”
android:layout_alignBottom=”@+id/btnViewAll”
android:layout_alignRight=”@+id/btnDelete”
android:onClick=”onReset”
android:text=”Reset” />

</RelativeLayout>

MainActivity.java

package com.example.demo;

import android.os.Bundle;
import android.app.Activity;
import android.app.AlertDialog.Builder;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

public class MainActivity extends Activity{

SQLiteDatabase db;
EditText editRollno,editName,editMarks;
Button btnAdd,btnModify,btnDelete,btnView,btnViewAll;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

db=openOrCreateDatabase(“StudDB”,Context.MODE_PRIVATE,null);
db.execSQL(“CREATE TABLE IF NOT EXISTS student(rollno VARCHAR,name VARCHAR,marks VARCHAR);”);

editRollno=(EditText)findViewById(R.id.editRollno);
editName=(EditText)findViewById(R.id.editName);
editMarks=(EditText)findViewById(R.id.editMarks);
btnAdd=(Button)findViewById(R.id.btnAdd);
}

public void dbFunction(View view)
{
if(view==btnDelete)
{
if(editRollno.getText().toString().trim().length()==0)
{
showMessage(“Error”,”Please enter Roll No”);
return;
}
else
{
Cursor c=db.rawQuery(“SELECT * FROM student WHERE rollno='”+editRollno.getText()+”‘”, null);
if(c.moveToFirst())
{
db.execSQL(“DELETE FROM student WHERE rollno='”+editRollno.getText()+”‘”);
showMessage(“Success”,”Record Deleted”);
}
else
{
showMessage(“Error”,”Invalid Roll No”);
}
}
clearText();
}
}

public void showMessage(String title,String message)
{
Builder builder=new Builder(this);
builder.setCancelable(true);
builder.setTitle(title);
builder.setMessage(message);
builder.show();
}

public void clearText()
{
editRollno.setText(“”);
editName.setText(“”);
editMarks.setText(“”);
editRollno.requestFocus();
}

public void onReset(View v)
{
editRollno.setText(“”);
editName.setText(“”);
editMarks.setText(“”);
editRollno.requestFocus();
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
//Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
}

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