안드로이드 sqlite 삭제하기 (Delete)

 

1. DatabaseHelper 클래스를 만듭니다. 

2. DatabaseHelper 클래스 코딩하기 

package com.example.sqlite_sample;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

import androidx.annotation.Nullable;

public class DatabaseHelper extends SQLiteOpenHelper {
    public static final String DATABASE_NAME = "Student.db";  // 1. 데이터베이스 네임
    public static final String TABLE_NAME = "students";        //2. 테이블 네임
    // 3. 테이블 항목 네임
    public static final String COL_1 = "ID";
    public static final String COL_2 = "Name";
    public static final String COL_3 = "Surname";
    public static final String COL_4 = "Marks";



    public DatabaseHelper(@Nullable Context context) {
        super(context, DATABASE_NAME, null, 1);

    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL("create table "+ TABLE_NAME + " (ID INTEGER PRIMARY KEY AUTOINCREMENT, NAME TEXT, SURNAME TEXT, MARKS TEXT)");

    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS "+TABLE_NAME);
        onCreate(db);

    }

    // 데이터 추가하기
    public boolean insertData(String name, String surname, String marks){
        SQLiteDatabase db = this.getWritableDatabase();
        ContentValues contentValues = new ContentValues();
        contentValues.put(COL_2,name);
        contentValues.put(COL_3,surname);
        contentValues.put(COL_4,marks);
        long result = db.insert(TABLE_NAME, null,contentValues);
        if(result == -1)
            return false;
        else
            return true;
    }

    // 데이터 보여주기(읽어오기)
    public Cursor getAllData() {
        SQLiteDatabase db = this.getWritableDatabase();
        Cursor res = db.rawQuery("select * from "+TABLE_NAME, null);
        return res;
    }

    //데이터 수정하기(업데이트)
    public boolean updateDatat(String id, String name, String surname, String marks){
        SQLiteDatabase db = this.getWritableDatabase();
        ContentValues contentValues = new ContentValues();
        contentValues.put(COL_1,id);
        contentValues.put(COL_2,name);
        contentValues.put(COL_3,surname);
        contentValues.put(COL_4,marks);
        db.update(TABLE_NAME,contentValues,"ID = ?",new String[] { id });
        return true;
    }

    // 데이터 삭제하기
    public Integer deleteData(String id){
        SQLiteDatabase db = this.getWritableDatabase();
        return db.delete(TABLE_NAME,"ID = ?",new String[] {id});
    }
}

 

2. 레이아웃 XML

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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">

    <EditText
        android:id="@+id/editText_name"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="16dp"
        android:layout_marginTop="7dp"
        android:ems="10"
        android:inputType="textPersonName"
        android:text="Name"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:ignore="MissingConstraints" />

    <EditText
        android:id="@+id/editText_surname"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="14dp"
        android:layout_marginTop="19dp"
        android:ems="10"
        android:inputType="textPersonName"
        android:text="Surname"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/editText_name"
        tools:ignore="MissingConstraints" />

    <EditText
        android:id="@+id/editText_marks"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="19dp"
        android:layout_marginTop="29dp"
        android:ems="10"
        android:inputType="textPersonName"
        android:text="Marks"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/editText_surname"
        tools:ignore="MissingConstraints" />

    <Button
        android:id="@+id/button_add"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="52dp"
        android:layout_marginTop="36dp"
        android:text="ADD"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/editText_id" />

    <Button
        android:id="@+id/button_update"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="52dp"
        android:layout_marginTop="24dp"
        android:text="Update"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/button_add" />

    <Button
        android:id="@+id/button_viewall"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="52dp"
        android:layout_marginTop="36dp"
        android:text="View"
        app:layout_constraintStart_toEndOf="@+id/button_add"
        app:layout_constraintTop_toBottomOf="@+id/editText_id" />

    <EditText
        android:id="@+id/editText_id"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="16dp"
        android:layout_marginTop="16dp"
        android:ems="10"
        android:inputType="textPersonName"
        android:text="ID"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/editText_marks" />

    <Button
        android:id="@+id/button_delete"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="44dp"
        android:layout_marginTop="22dp"
        android:text="Delete"
        app:layout_constraintStart_toEndOf="@+id/button_update"
        app:layout_constraintTop_toBottomOf="@+id/button_viewall" />

</androidx.constraintlayout.widget.ConstraintLayout>

 

3. MainActivity.java 코딩하기

package com.example.sqlite_sample;

import androidx.appcompat.app.AlertDialog;
import androidx.appcompat.app.AppCompatActivity;

import android.database.Cursor;
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 {

    DatabaseHelper myDb;
    EditText editName, editSurname, editMarks, editID;
    Button btnAddData, btnviewall, btnUpdate, btnDelete;

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

        myDb = new DatabaseHelper(this);

        editName = findViewById(R.id.editText_name);
        editSurname = findViewById(R.id.editText_surname);
        editMarks = findViewById(R.id.editText_marks);
        editID = findViewById(R.id.editText_id);

        btnAddData = findViewById(R.id.button_add);
        btnviewall = findViewById(R.id.button_viewall);
        btnUpdate= findViewById(R.id.button_update);
        btnDelete = findViewById(R.id.button_delete);

        AddData(); // 데이터 추가하기
        viewAll(); // 데이터 보여주기
        UpdateData(); // 데이터 업데이트(수정)
        DeleteData(); // 데이터 삭제하기

    }

    // 데이터베이스에 추가하기
    public void AddData() {
        btnAddData.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                boolean isInserted = myDb.insertData(editName.getText().toString(),
                        editSurname.getText().toString(),
                        editMarks.getText().toString() );

                if(isInserted == true)
                    Toast.makeText(MainActivity.this,"Data Inserted",Toast.LENGTH_LONG).show();
                else
                    Toast.makeText(MainActivity.this,"Data not Inserted",Toast.LENGTH_LONG).show();
            }
        });
    }

    //데이터베이스 보여주기
    public void viewAll()
    {
        btnviewall.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Cursor res = myDb.getAllData();
                if(res.getCount() == 0) {
                    //show message
                    showMessage("에러","데이터를 찾을수 없다.");
                    return;

                }
                StringBuffer buffer = new StringBuffer();
                while(res.moveToNext()){
                    buffer.append("id : "+ res.getString(0) + "\n");
                    buffer.append("name : "+ res.getString(1) + "\n");
                    buffer.append("surname : "+ res.getString(2) + "\n");
                    buffer.append("marks : "+ res.getString(3) + "\n\n");

                }
                // Show all data
                showMessage("데이터",buffer.toString());
            }
        });
    }

    public void UpdateData(){
        btnUpdate.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                boolean isUpdated = myDb.updateDatat(editID.getText().toString(),editName.getText().toString(),editSurname.getText().toString(),editMarks.getText().toString());
                if(isUpdated == true)
                    Toast.makeText(MainActivity.this,"Data Updated",Toast.LENGTH_LONG).show();
                else
                    Toast.makeText(MainActivity.this,"Data not Updated",Toast.LENGTH_LONG).show();
            }
        });
    }

    public void DeleteData(){
        btnDelete.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Integer deleteRows = myDb.deleteData(editID.getText().toString());
                if(deleteRows > 0 )
                    Toast.makeText(MainActivity.this,"Data Deleted",Toast.LENGTH_LONG).show();
                else
                    Toast.makeText(MainActivity.this,"Data not Deleted",Toast.LENGTH_LONG).show();
            }
        });
    }


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

 

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