Menghapus Kontak di Database

Kita akan tetap menggunakan kode yang sama dengan latihan sebelumnya dengan modifikasi pada file java: MainActivity.java

1. Siapkan class pembantu (sama dengan latihan sebelumnya)

File java: DBAdapter.java (berfungsi sebagai class pembantu):

package com.example.savingtodb;  

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor; 

import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;  

public class DBAdapter {
static final String KEY_ROWID = "_id";
static final String KEY_NAME = "name";
static final String KEY_EMAIL = "email"; 

static final String TAG = "DBAdapter";
static final String DATABASE_NAME = "MyDB";
static final String DATABASE_TABLE =" contacts";
static final int DATABASE_VERSION = 1;  

static final String DATABASE_CREATE = "create table contacts (_id integer primary key autoincrement, "
+ "name text not null, email text not null);";  

final Context context;
DatabaseHelper DBHelper;
SQLiteDatabase db;  

public DBAdapter(Context ctx){
this.context = ctx;
DBHelper = new DatabaseHelper(context);
}
private static class DatabaseHelper extends SQLiteOpenHelper
{
DatabaseHelper(Context context)
{
super(context, DATABASE_NAME,null,DATABASE_VERSION);
}  

@Override
public void onCreate(SQLiteDatabase db)
{
try {
db.execSQL(DATABASE_CREATE);
}
catch (SQLException sqle){
sqle.printStackTrace();
}
}  

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion)
{
Log.w(TAG,"Upgrading database from version " + oldVersion + " to " + newVersion +
", which will destroy all old data");
db.execSQL("DROP TABLE IF EXIST contacts");
onCreate(db);
}
}  

//--open database--
public DBAdapter open() throws SQLException
{
db = DBHelper.getWritableDatabase();
return this;
}  

//--close database--
public void close()
{
DBHelper.close();
}  

//--insert a contact into database--
public long insertContact(String name, String email)
{
ContentValues initialValues = new ContentValues();
initialValues.put(KEY_NAME, name);
initialValues.put(KEY_EMAIL, email);
return db.insert(DATABASE_TABLE,null, initialValues);
}  

//--delete particular contact--
public boolean deleteContact(long rowId) {
return db.delete(DATABASE_TABLE, KEY_ROWID + "=" + rowId, null) > 0;
}  

//--retrieves all contacts--
public Cursor getAllContacts()
{
return db.query(DATABASE_TABLE, new String[] {KEY_ROWID, KEY_NAME, KEY_EMAIL}, null, null, null, null,null);
}  

//--retrieves particular contact--
public Cursor getContact(long rowId) throws SQLException
{
Cursor mCursor = db.query(true, DATABASE_TABLE, new String[] {KEY_ROWID,KEY_NAME,KEY_EMAIL}, KEY_ROWID
+ "=" + rowId, null,null,null,null,null);
if (mCursor != null) {
mCursor.moveToFirst();
}
return mCursor;
}  

//--updates a contact--
public boolean updateContact(long rowId, String name, String email)
{
ContentValues args = new ContentValues();
args.put(KEY_NAME, name);
args.put(KEY_EMAIL, email);
return db.update(DATABASE_TABLE,args, KEY_ROWID + "=" + rowId, null) > 0;
}
}

2. Modifikasi file java dari latihan sebelumnya: MainActivity.java seperti berikut:

package com.example.savingtodb;

import android.database.Cursor;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

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

DBAdapter db = new DBAdapter(this);

/*--add a contact--
db.open();
...
*/

/*--get all contacts--
db.open();
...
*/

/*--retrieve single contact--
db.open();
... 

*/   

/*--update contact--

db.open();

... 

*/    

//--delete contact--

db.open();

if (db.deleteContact(1))

Toast.makeText(this, "Delete berhasil.", Toast.LENGTH_LONG).show();

else

Toast.makeText(this, "Delete gagal.", Toast.LENGTH_LONG).show();

db.close(); 

} 

public void DisplayContact(Cursor c)
{
Toast.makeText(this, "id: "+ c.getString(0)+"\n"+
"Name: "+c.getString(1)+"\n"+
"Email: "+c.getString(2), Toast.LENGTH_LONG).show();
}
}

Jalankan di emulator

Penjelasan:

Method 'deleteContact()' dari class DBAdapter akan mengupdate satu kontak dengan menggunakan ID-nya. Hasil yang dikembalikan adalah boolean yang menunjukkan apakah update berhasil atau tidak