Mengobati Aplikasi
Yang Amnesia! 🧠

package com.example.sharedpref;

import android.content.Intent;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.CheckBox;
import android.widget.EditText;
import android.widget.Toast;
import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {

    // 1. Deklarasi Nama File (Global) & Kunci Loker
    private static final String PREF_NAME = "DataApp";
    private static final String KEY_NAMA = "kunci_username";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        
        // ==========================================
        // PROSES CEK AUTO-LOGIN SAAT SPLASH SCREEN
        // ==========================================
        SharedPreferences pref = getSharedPreferences(PREF_NAME, MODE_PRIVATE);
        
        // Fungsi contains mengecek apakah kunci "kunci_username" sudah pernah dibuat sebelumnya?
        if (pref.contains(KEY_NAMA)) {
            // Jika iya, user pernah mencentang "Ingat Saya". Langsung lompat ke Home!
            startActivity(new Intent(MainActivity.this, HomeActivity.class));
            finish(); // WAJIB! Tutup layar login ini biar ngga bisa di-Back
            return;   // Stop eksekusi kode ke bawah
        }

        // Jika belum login, barulah kita tampilkan form XML-nya
        setContentView(R.layout.activity_main);

        EditText etUsername = findViewById(R.id.etUsername);
        CheckBox cbRemember = findViewById(R.id.cbRemember);
        Button btnLogin = findViewById(R.id.btnLogin);

        // ==========================================
        // PROSES TULIS DATA SAAT TOMBOL KLIK
        // ==========================================
        btnLogin.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String namaKetikan = etUsername.getText().toString();
                
                if(namaKetikan.isEmpty()) {
                    Toast.makeText(MainActivity.this, "Isi nama dulu!", Toast.LENGTH_SHORT).show();
                    return;
                }

                // Panggil agen "Editor" khusus untuk nulis/ngedit isi brankas
                SharedPreferences.Editor editor = pref.edit();

                if (cbRemember.isChecked()) {
                    // Jika dicentang, simpan ketikan secara permanen ke HP
                    editor.putString(KEY_NAMA, namaKetikan);
                    editor.apply(); 
                    Toast.makeText(MainActivity.this, "Auto-Login Aktif!", Toast.LENGTH_SHORT).show();
                } else {
                    // Jika tidak dicentang, pastikan brankas bersih (Login Sesi Sementara)
                    editor.remove(KEY_NAMA);
                    editor.apply();
                }
                
                // Pindah ke layar Dashboard / Home
                startActivity(new Intent(MainActivity.this, HomeActivity.class));
                finish(); // Tutup layar login
            }
        });
    }
}

<!-- activity_home.xml -->
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:padding="32dp"
    android:gravity="center">

    <TextView
        android:id="@+id/tvWelcome"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Halo, User!"
        android:textSize="28sp"
        android:textStyle="bold"
        android:layout_marginBottom="48dp" />

    <Button
        android:id="@+id/btnSettings"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="PENGATURAN TEMA"
        android:layout_marginBottom="16dp" />

    <Button
        android:id="@+id/btnLogout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:backgroundTint="#ef4444" <!-- Warna Merah -->
        android:text="LOGOUT (HAPUS SESI)" />

</LinearLayout>

package com.example.sharedpref;

import android.content.Intent;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;
import androidx.appcompat.app.AppCompatActivity;

public class HomeActivity extends AppCompatActivity {

    private static final String PREF_NAME = "DataApp";
    private static final String KEY_NAMA = "kunci_username";

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

        TextView tvWelcome = findViewById(R.id.tvWelcome);
        Button btnSettings = findViewById(R.id.btnSettings);
        Button btnLogout = findViewById(R.id.btnLogout);

        // 1. BACA DATA LOKER GLOBAL
        SharedPreferences pref = getSharedPreferences(PREF_NAME, MODE_PRIVATE);
        
        // Ambil namanya. Jika kosong (Login sementara), ganti dengan "Guest"
        String namaTersimpan = pref.getString(KEY_NAMA, "Guest");
        tvWelcome.setText("Halo, " + namaTersimpan + "!");

        // 2. PINDAH KE LAYAR PENGATURAN (INTENT)
        btnSettings.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                startActivity(new Intent(HomeActivity.this, ArtikelActivity.class));
            }
        });

        // 3. AKSI LOGOUT (HAPUS SESI)
        btnLogout.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // Bersihkan seluruh isi brankas loker secara permanen
                SharedPreferences.Editor editor = pref.edit();
                editor.clear(); 
                editor.apply();
                
                Toast.makeText(HomeActivity.this, "Logout Berhasil", Toast.LENGTH_SHORT).show();
                
                // Kembali ke Layar Login
                startActivity(new Intent(HomeActivity.this, MainActivity.class));
                finish(); // Tutup layar Home ini
            }
        });
    }
}

<!-- activity_artikel.xml -->
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/layoutRoot"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:padding="32dp"
    android:gravity="center">

    <TextView
        android:id="@+id/tvJudul"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Layar Pengaturan Tema"
        android:textSize="20sp"
        android:textStyle="bold"
        android:layout_marginBottom="24dp" />

    <Switch
        android:id="@+id/switchTheme"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Aktifkan Mode Gelap" />

</LinearLayout>

package com.example.sharedpref;

import android.content.SharedPreferences;
import android.graphics.Color;
import android.os.Bundle;
import android.widget.CompoundButton;
import android.widget.Switch;
import android.widget.TextView;
import android.view.View;
import androidx.appcompat.app.AppCompatActivity;

public class ArtikelActivity extends AppCompatActivity {

    private static final String KEY_DARK_MODE = "is_dark_mode";

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

        Switch switchTheme = findViewById(R.id.switchTheme);

        // 1. PROSES BACA DATA DARI LOKER PRIVAT
        // Ingat, panggil getPreferences(), BUKAN getSharedPreferences()
        SharedPreferences prefLokal = getPreferences(MODE_PRIVATE);
        
        // Baca data boolean. Default-nya false (Mode Terang)
        boolean isDark = prefLokal.getBoolean(KEY_DARK_MODE, false);
        
        // Terapkan ke UI
        switchTheme.setChecked(isDark);
        terapkanTemaKeLayar(isDark);

        // 2. PROSES TULIS DATA SAAT SWITCH DIGESER
        switchTheme.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
                
                // Terapkan fungsi ganti warna background
                terapkanTemaKeLayar(isChecked);

                // Simpan ke Loker Privat secara permanen
                SharedPreferences.Editor editor = prefLokal.edit();
                editor.putBoolean(KEY_DARK_MODE, isChecked);
                editor.apply(); 
            }
        });
    }

    // Fungsi bantuan untuk merubah warna background
    private void terapkanTemaKeLayar(boolean isDark) {
        View root = findViewById(R.id.layoutRoot);
        TextView tvJudul = findViewById(R.id.tvJudul);
        Switch swTheme = findViewById(R.id.switchTheme);

        if (isDark) {
            root.setBackgroundColor(Color.parseColor("#121212")); // Gelap
            tvJudul.setTextColor(Color.WHITE);
            swTheme.setTextColor(Color.WHITE);
        } else {
            root.setBackgroundColor(Color.parseColor("#FFFFFF")); // Terang
            tvJudul.setTextColor(Color.BLACK);
            swTheme.setTextColor(Color.BLACK);
        }
    }
}