Topics

Tab layout
ViewPager2
SharedPreferences.md

1. TabLayout

TabLayout is a UI component from the Material Design library that displays a series of tabs horizontally — typically used for navigating between different views or fragments.

For example:

| Home | Profile | Settings |

Each tab represents a different screen or section. When the user clicks a tab, you show a new content area (like a fragment).

It is part of:

com.google.android.material.tabs.TabLayout

Requirements

To use TabLayout, you must include the Material Components dependency in your build.gradle:

implementation 'com.google.android.material:material:1.12.0'

Then, in XML layout files, always use the full tag:

<com.google.android.material.tabs.TabLayout
    android:id="@+id/tabLayout"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"/>

Structure Overview

Typically, you use TabLayout with:

ViewPager (old) or ViewPager2 (new)
Fragments or custom layouts
TabItem (optional helper tag for static tabs)

Typical structure:

<LinearLayout
    android:orientation="vertical"
    ...>

    <com.google.android.material.tabs.TabLayout
        android:id="@+id/tabLayout"
        ... />

    <androidx.viewpager2.widget.ViewPager2
        android:id="@+id/viewPager"
        ... />

</LinearLayout>

Creating multiple Tabs

(a) `<com.google.android.material.tabs.TabLayout>`

This is the main container of all tabs.

(b) `<com.google.android.material.tabs.TabItem>`

This represents a single tab (used only when tabs are static, not dynamic).

Example:

<com.google.android.material.tabs.TabLayout
    android:id="@+id/tabLayout"
    android:layout_width="match_parent"
    android:layout_height="wrap_content">

    <com.google.android.material.tabs.TabItem
        android:text="Home" />

    <com.google.android.material.tabs.TabItem
        android:text="Profile" />

    <com.google.android.material.tabs.TabItem
        android:text="Settings" />

</com.google.android.material.tabs.TabLayout>

Key Attributes of `TabLayout`

Let’s explore the important attributes you can use in XML.

Attribute	Description	Example
`app:tabMode`	Controls how tabs are displayed. Options: `fixed` (equal width), `scrollable` (scrolls horizontally).	`app:tabMode="scrollable"`
`app:tabGravity`	Controls tab alignment. Options: `fill`, `center`.	`app:tabGravity="fill"`
`app:tabIndicatorColor`	Sets the color of the underline (indicator).	`app:tabIndicatorColor="@color/blue"`
`app:tabIndicatorHeight`	Height of the underline indicator.	`app:tabIndicatorHeight="3dp"`
`app:tabTextColor`	Default text color for unselected tabs.	`app:tabTextColor="@color/gray"`
`app:tabSelectedTextColor`	Text color for selected tab.	`app:tabSelectedTextColor="@color/black"`
`app:tabIconTint`	Tint for tab icons.	`app:tabIconTint="@color/white"`
`app:tabBackground`	Background drawable for each tab.	`app:tabBackground="@drawable/tab_selector"`
`app:tabRippleColor`	Ripple effect color when clicked.	`app:tabRippleColor="@color/purple_200"`
`app:tabIndicatorFullWidth`	Whether indicator spans full width or just text width.	`app:tabIndicatorFullWidth="false"`

Adding Tabs Dynamically in Java

You can also create tabs programmatically:

TabLayout tabLayout = findViewById(R.id.tabLayout);

tabLayout.addTab(tabLayout.newTab().setText("Home"));
tabLayout.addTab(tabLayout.newTab().setText("Profile"));
tabLayout.addTab(tabLayout.newTab().setText("Settings"));

To listen for tab changes:

tabLayout.addOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
    @Override
    public void onTabSelected(TabLayout.Tab tab) {
        Toast.makeText(getApplicationContext(), "Selected: " + tab.getText(), Toast.LENGTH_SHORT).show();
    }

    @Override
    public void onTabUnselected(TabLayout.Tab tab) { }

    @Override
    public void onTabReselected(TabLayout.Tab tab) { }
});

Linking with `ViewPager2`

If you want each tab to show a different fragment (most common case):

Step 1 — XML

<LinearLayout
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <com.google.android.material.tabs.TabLayout
        android:id="@+id/tabLayout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

    <androidx.viewpager2.widget.ViewPager2
        android:id="@+id/viewPager"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"/>
</LinearLayout>

Step 2 — Java code

TabLayout tabLayout = findViewById(R.id.tabLayout);
ViewPager2 viewPager = findViewById(R.id.viewPager);

// always "this" even if fragment or activity as we have two constructors (or keep one acc to req)
ViewPagerAdapter adapter = new ViewPagerAdapter(this);     
viewPager.setAdapter(adapter);

new TabLayoutMediator(tabLayout, viewPager,
    (tab, position) -> {
        switch (position) {
            case 0:
                tab.setText("Home");
                break;
            case 1:
                tab.setText("Profile");
                break;
            case 2:
                tab.setText("Settings");
                break;
        }
    }
).attach();

Step 3 — Adapter Class

public class ViewPagerAdapter extends FragmentStateAdapter {

    // --- Used by Activity ---
    public ViewPagerAdapter(@NonNull FragmentActivity fragmentActivity) {
        super(fragmentActivity); 
        // Android says: "Okay, I'll attach tabs to the Activity."
    }

    // --- Used by Fragment ---
    public ViewPagerAdapter(@NonNull Fragment fragment) {
        super(fragment); 
        // Android says: "Okay, I'll attach tabs as children of this Fragment."
    }

    @NonNull
    @Override
    public Fragment createFragment(int position) {
        switch (position) {
            case 0: return new HomeFragment();
            case 1: return new ProfileFragment();
            case 2: return new SettingsFragment();
            default: return new HomeFragment();
        }
    }

    @Override
    public int getItemCount() {
        return 3;
    }
}

This allows swiping between tabs and auto-sync between ViewPager2 and TabLayout.

Related Concepts

Concept	Explanation
ViewPager / ViewPager2	Component that allows swiping between pages (fragments or layouts). Used with `TabLayout`.
Fragment	Each tab’s content is often a fragment (small portion of UI).
TabLayoutMediator	A bridge between `TabLayout` and `ViewPager2` to keep them in sync.
Material Components	`TabLayout` belongs to Material library, so it follows Material Design principles.
Custom Tabs	You can create custom tab views with icons, badges, or layouts.

Example of custom tab:

TabLayout.Tab tab = tabLayout.newTab();
tab.setCustomView(R.layout.custom_tab);
tabLayout.addTab(tab);

Common Customizations

✅ Add icons:

tabLayout.getTabAt(0).setIcon(R.drawable.ic_home);

✅ Add badges:

tabLayout.getTabAt(1).getOrCreateBadge().setNumber(5);

✅ Change indicator style (XML):

app:tabIndicatorGravity="bottom"
app:tabIndicatorFullWidth="false"
app:tabIndicatorColor="@color/red"

Common Mistakes to Avoid

Mistake	Explanation
Forgetting to use `TabLayoutMediator` with `ViewPager2`	Without it, tab selection won’t sync.
Using old `ViewPager` (deprecated)	Use `ViewPager2` for modern apps.
Not adding Material dependency	The TabLayout class won’t be found.
Mixing static `<TabItem>` with dynamic `addTab()`	Choose one approach.

`ViewPager` / `ViewPager2`

Normally, ViewPager2 is the engine that:

Manages which fragment is visible right now.
Automatically handles swiping gestures (left ↔ right).
Synchronizes with TabLayout (through TabLayoutMediator).
Automatically destroys and restores fragments efficiently.

So, when you swipe → it changes page. When you tap a tab → it automatically scrolls to the matching page.

What if we don’t use `ViewPager`?

Totally valid. Without ViewPager, TabLayout is just a visual bar — a UI component that can show tabs and detect which one you clicked. 👉 But it doesn’t know what content to display on its own.

That means:

You can still listen for tab selection events.
You must manually switch the content (e.g., replace Fragments or change layouts) yourself.

✅ It will work — just no automatic swiping or automatic fragment handling.

How to do it manually (without ViewPager)

Let’s say we have three fragments:

HomeFragment
ProfileFragment
SettingsFragment

Step 1 — XML

<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <com.google.android.material.tabs.TabLayout
        android:id="@+id/tabLayout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>

    <FrameLayout
        android:id="@+id/frameContainer"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>
</LinearLayout>

Step 2 — Java (manual fragment switching)

TabLayout tabLayout = findViewById(R.id.tabLayout);

// Add tabs
tabLayout.addTab(tabLayout.newTab().setText("Home"));
tabLayout.addTab(tabLayout.newTab().setText("Profile"));
tabLayout.addTab(tabLayout.newTab().setText("Settings"));

// Show default fragment
getSupportFragmentManager().beginTransaction()
        .replace(R.id.frameContainer, new HomeFragment())
        .commit();

// Listen for tab changes
tabLayout.addOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
    @Override
    public void onTabSelected(TabLayout.Tab tab) {
        Fragment selected = null;
        switch (tab.getPosition()) {
            case 0:
                selected = new HomeFragment();
                break;
            case 1:
                selected = new ProfileFragment();
                break;
            case 2:
                selected = new SettingsFragment();
                break;
        }
        getSupportFragmentManager().beginTransaction()
                .replace(R.id.frameContainer, selected)
                .commit();
    }

    @Override
    public void onTabUnselected(TabLayout.Tab tab) { }

    @Override
    public void onTabReselected(TabLayout.Tab tab) { }
});

✅ You can now click tabs and see fragments change. ❌ But there’s no swipe gesture.

MINI WHATSAPP CHAT SYSTEM

We’ll make 3 fragments:

ChatsFragment
StatusFragment
CallsFragment

and an adapter (MainPagerAdapter) plus the MainActivity with full explanations.

1️⃣ Fragments

Each fragment just displays some sample data.

ChatsFragment.java

package com.example.whatsappclone;

import android.os.Bundle;
import androidx.fragment.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

public class ChatsFragment extends Fragment {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate a simple layout with text
        TextView textView = new TextView(getContext());
        textView.setText("This is the CHATS fragment\nUnread chat messages shown here.");
        textView.setTextSize(18);
        textView.setPadding(40, 100, 40, 100);
        return textView;
    }
}

StatusFragment.java

package com.example.whatsappclone;

import android.os.Bundle;
import androidx.fragment.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

public class StatusFragment extends Fragment {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        TextView textView = new TextView(getContext());
        textView.setText("This is the STATUS fragment\nFriends' statuses appear here.");
        textView.setTextSize(18);
        textView.setPadding(40, 100, 40, 100);
        return textView;
    }
}

CallsFragment.java

package com.example.whatsappclone;

import android.os.Bundle;
import androidx.fragment.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

public class CallsFragment extends Fragment {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        TextView textView = new TextView(getContext());
        textView.setText("This is the CALLS fragment\nRecent call logs appear here.");
        textView.setTextSize(18);
        textView.setPadding(40, 100, 40, 100);
        return textView;
    }
}

2️⃣ ViewPager2 Adapter

MainPagerAdapter.java

package com.example.whatsappclone;

import androidx.annotation.NonNull;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentActivity;
import androidx.viewpager2.adapter.FragmentStateAdapter;

// This adapter tells ViewPager2 which fragment to show for each position
public class MainPagerAdapter extends FragmentStateAdapter {

    public MainPagerAdapter(@NonNull FragmentActivity fragmentActivity) {
        super(fragmentActivity);
    }

    @NonNull
    @Override
    public Fragment createFragment(int position) {
        switch (position) {
            case 0:
                return new ChatsFragment();
            case 1:
                return new StatusFragment();
            case 2:
                return new CallsFragment();
            default:
                return new ChatsFragment();
        }
    }

    @Override
    public int getItemCount() {
        return 3; // total number of tabs/fragments
    }
}

3️⃣ Main Activity

MainActivity.java

package com.example.whatsappclone;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import com.google.android.material.tabs.TabLayout;
import com.google.android.material.tabs.TabLayoutMediator;
import androidx.viewpager2.widget.ViewPager2;
import com.google.android.material.badge.BadgeDrawable;

public class MainActivity extends AppCompatActivity {

    private TabLayout tabLayout;
    private ViewPager2 viewPager;

    // Example counts (can be dynamic)
    private int unreadChats = 5;
    private int missedCalls = 2;

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

        tabLayout = findViewById(R.id.tabLayout);
        viewPager = findViewById(R.id.viewPager);

        // Attach adapter to ViewPager2
        MainPagerAdapter adapter = new MainPagerAdapter(this);
        viewPager.setAdapter(adapter);

        // Add tabs manually (optional)
        tabLayout.addTab(tabLayout.newTab().setText("CHATS"));
        tabLayout.addTab(tabLayout.newTab().setText("STATUS"));
        tabLayout.addTab(tabLayout.newTab().setText("CALLS"));

        // Add badge directly (method 1)
        tabLayout.getTabAt(0).getOrCreateBadge().setNumber(unreadChats);

        // Add badge manually by creating a BadgeDrawable (method 2)
        BadgeDrawable callBadge = tabLayout.getTabAt(2).getOrCreateBadge();
        callBadge.setVisible(true);
        callBadge.setNumber(missedCalls);

        // Link TabLayout and ViewPager2 together using TabLayoutMediator
        new TabLayoutMediator(tabLayout, viewPager, (tab, position) -> {
            switch (position) {
                case 0:
                    tab.setText("CHATS");
                    break;
                case 1:
                    tab.setText("STATUS");
                    break;
                case 2:
                    tab.setText("CALLS");
                    break;
            }
        }).attach();

        // 1️⃣ If you want to control switching through ViewPager2
        //    e.g. user swipes → change tab automatically
        viewPager.registerOnPageChangeCallback(new ViewPager2.OnPageChangeCallback() {
            @Override
            public void onPageSelected(int position) {
                super.onPageSelected(position);

                // Example: remove badge when tab is viewed
                if (position == 0 && tabLayout.getTabAt(0).getBadge() != null)
                    tabLayout.getTabAt(0).removeBadge();
                if (position == 2 && tabLayout.getTabAt(2).getBadge() != null)
                    tabLayout.getTabAt(2).removeBadge();
            }
        });

        // 2️⃣ If you want to control switching through TabLayout listeners
        //    (use this if you want to handle tab clicks manually)
        tabLayout.addOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
            @Override
            public void onTabSelected(@NonNull TabLayout.Tab tab) {
                // When tab clicked, update ViewPager page
                viewPager.setCurrentItem(tab.getPosition());

                // Remove badge when that tab is opened
                if (tab.getBadge() != null)
                    tab.removeBadge();
            }

            @Override
            public void onTabUnselected(@NonNull TabLayout.Tab tab) {}

            @Override
            public void onTabReselected(@NonNull TabLayout.Tab tab) {}
        });
    }
}

4️⃣ Layout File

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <!-- Top Tab Layout -->
    <com.google.android.material.tabs.TabLayout
        android:id="@+id/tabLayout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:tabGravity="fill"
        app:tabMode="fixed" />

    <!-- ViewPager2 for swipe navigation -->
    <androidx.viewpager2.widget.ViewPager2
        android:id="@+id/viewPager"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</LinearLayout>

1️⃣ SharedPreferences

SharedPreferences is a lightweight key–value storage mechanism built into Android. It lets you store small pieces of data persistently — that is, data that remains available even after the app is closed or restarted.

You can think of it like a small dictionary or JSON file saved inside your app’s private storage.

Examples of what you might store:

User login state (e.g., logged in or not)
Username, email, or profile info
App settings (dark mode, language, sound on/off)
High score or last played level in a game

2️⃣ How SharedPreferences Works Internally

Internally, each SharedPreferences file is stored as an XML file in:

/data/data/<your_package_name>/shared_prefs/

Example:

/data/data/com.example.myapp/shared_prefs/user_prefs.xml

It stores data like:

<map>
    <string name="username">Abdul</string>
    <int name="score" value="95" />
    <boolean name="logged_in" value="true" />
</map>

3️⃣ Getting SharedPreferences

You can get a SharedPreferences instance in two main ways:

(a) Activity Context

SharedPreferences prefs = getSharedPreferences("MyPrefs", MODE_PRIVATE);

// Fragment
SharedPreferences prefs = requireActivity().getSharedPreferences("MyPrefs", Context.MODE_PRIVATE);

"MyPrefs" → file name (you can give any name)
MODE_PRIVATE → file is accessible only by your app (default mode)

(b) Application-wide default preferences

SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(this);

// Fragment
SharedPreferences defaultPrefs = PreferenceManager.getDefaultSharedPreferences(requireContext());

This is a global preference file for the whole app

(b) Using `PreferenceManager.getDefaultSharedPreferences(this)`

SharedPreferences  prefs  = PreferenceManager.getDefaultSharedPreferences(this);
prefs.edit().putString("username", "Abdul").apply();
prefs.edit().putBoolean("dark_mode", true).apply();

Now both values go inside the same single file:

<package_name>_preferences.xml

So everything is stored globally — all settings in one place..

4️⃣ Modes (Old versions concept)

Mode	Description
`MODE_PRIVATE`	Default; file only accessible by your app.
`MODE_APPEND`	Append new data to existing (rarely used).
`MODE_WORLD_READABLE`	Deprecated – used to allow other apps to read it.
`MODE_WORLD_WRITEABLE`	Deprecated – used to allow other apps to write it.

Modern Android (post API 24) only uses MODE_PRIVATE.

5️⃣ Storing Data

You can’t write directly into SharedPreferences — you must use an Editor object.

Example:

SharedPreferences prefs = getSharedPreferences("MyPrefs", MODE_PRIVATE);
SharedPreferences.Editor editor = prefs.edit();

// Store values
editor.putString("username", "Abdul");
editor.putInt("score", 90);
editor.putBoolean("logged_in", true);

// Commit the changes
editor.apply();  // or editor.commit();

Difference:

Method	Description
`apply()`	Asynchronous (faster, no return value). Recommended.
`commit()`	Synchronous (returns boolean success). Slower, blocks UI.

6️⃣ Retrieving Data

SharedPreferences prefs = getSharedPreferences("MyPrefs", MODE_PRIVATE);

String user = prefs.getString("username", "Guest"); // default = "Guest"
int score = prefs.getInt("score", 0);               // default = 0
boolean isLogged = prefs.getBoolean("logged_in", false);

If the key doesn’t exist, the default value is returned.

7️⃣ Removing or Clearing Data

SharedPreferences prefs = getSharedPreferences("MyPrefs", MODE_PRIVATE);
SharedPreferences.Editor editor = prefs.edit();

editor.remove("username"); // removes specific key
editor.clear();             // clears all data
editor.apply();

Rmoving File from phone

boolean  deleted  = getApplicationContext().deleteSharedPreferences("MyPrefs");
if (deleted) {
    Log.d("Prefs", "SharedPreferences file deleted successfully!");
} else {
    Log.d("Prefs", "Failed to delete SharedPreferences file!");
}

Explanation:

"MyPrefs" is the same name you passed to getSharedPreferences("MyPrefs", MODE_PRIVATE).
This deletes the entire XML file (MyPrefs.xml) from the shared_prefs folder.
After this, the next time you call getSharedPreferences("MyPrefs", ...), a new empty file will be created automatically.
✅ Deletes entire file
✅ Safe, official method
⚠️ Works only on Android 7.0+

8️⃣ Checking if Key Exists

if (prefs.contains("username")) {
    // Key exists
}

`EncryptedSharedPreferences` (For Sensitive Data)

Introduced in AndroidX Security library.

SharedPreferences securePrefs = EncryptedSharedPreferences.create(
        "SecurePrefs",
        MasterKeys.getOrCreate(MasterKeys.AES256_GCM_SPEC),
        context,
        EncryptedSharedPreferences.PrefKeyEncryptionScheme.AES256_SIV,
        EncryptedSharedPreferences.PrefValueEncryptionScheme.AES256_GCM
);

Login & logout Example

🔹 Project Overview

We’ll have two activities:

LoginActivity —
- User enters name and password
- On login, we store:
  - "username"
  - "password"
  - "isLoggedIn" = true
- Then navigate to MainActivity.
MainActivity —
- Checks if user is logged in on startup.
- If not logged in, redirect back to LoginActivity.
- If logged in, show user info and a Logout button.
- On logout → remove preferences completely.

🔹 File 1 — LoginActivity.java

package com.example.sharedprefdemo;

import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import androidx.appcompat.app.AppCompatActivity;

public class LoginActivity extends AppCompatActivity {

    EditText etName, etPassword;
    Button btnLogin;

    // File name for local storage
    private static final String PREF_FILE = "UserPrefs";

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

        etName = findViewById(R.id.etName);
        etPassword = findViewById(R.id.etPassword);
        btnLogin = findViewById(R.id.btnLogin);

        // Step 1: Check if already logged in
        SharedPreferences prefs = getSharedPreferences(PREF_FILE, Context.MODE_PRIVATE);
        boolean isLoggedIn = prefs.getBoolean("isLoggedIn", false);

        if (isLoggedIn) {
            // User already logged in → skip login
            Intent intent = new Intent(LoginActivity.this, MainActivity.class);
            startActivity(intent);
            finish(); // close login screen
            return;
        }

        // Step 2: Handle login button
        btnLogin.setOnClickListener(v -> {
            String name = etName.getText().toString().trim();
            String password = etPassword.getText().toString().trim();

            if (name.isEmpty() || password.isEmpty()) {
                Toast.makeText(this, "Enter name and password", Toast.LENGTH_SHORT).show();
                return;
            }

            // Save data in SharedPreferences
            SharedPreferences.Editor editor = prefs.edit();
            editor.putString("username", name);
            editor.putString("password", password);
            editor.putBoolean("isLoggedIn", true);
            editor.apply(); // save asynchronously

            Toast.makeText(this, "Login Successful", Toast.LENGTH_SHORT).show();

            // Move to main activity
            Intent intent = new Intent(LoginActivity.this, MainActivity.class);
            startActivity(intent);
            finish();
        });
    }
}

Explanation:

Uses getSharedPreferences("UserPrefs", MODE_PRIVATE) — private file per app.
Saves three fields:
- username
- password
- isLoggedIn
If already logged in, directly navigates to MainActivity.

🔹 File 2 — MainActivity.java

package com.example.sharedprefdemo;

import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.widget.Button;
import android.widget.TextView;

import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {

    TextView tvWelcome;
    Button btnLogout;
    private static final String PREF_FILE = "UserPrefs";

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

        tvWelcome = findViewById(R.id.tvWelcome);
        btnLogout = findViewById(R.id.btnLogout);

        SharedPreferences prefs = getSharedPreferences(PREF_FILE, Context.MODE_PRIVATE);

        // Step 1: Verify login status
        boolean isLoggedIn = prefs.getBoolean("isLoggedIn", false);

        if (!isLoggedIn) {
            // Not logged in → go back to login screen
            Intent intent = new Intent(MainActivity.this, LoginActivity.class);
            startActivity(intent);
            finish();
            return;
        }

        // Step 2: Retrieve stored user info
        String name = prefs.getString("username", "Unknown User");
        String password = prefs.getString("password", "N/A"); // only for demo

        tvWelcome.setText("Welcome, " + name + "\nPassword: " + password);

        // Step 3: Handle logout
        btnLogout.setOnClickListener(v -> {

            // Option 1: Clear all preferences (keeps empty file)
            // prefs.edit().clear().apply();

            // Option 2: Fully delete SharedPreferences file (recommended for full logout)
            getApplicationContext().deleteSharedPreferences(PREF_FILE);

            // Redirect back to login
            Intent intent = new Intent(MainActivity.this, LoginActivity.class);
            startActivity(intent);
            finish();
        });
    }
}

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Topics

1. TabLayout

Requirements

Structure Overview

Creating multiple Tabs

(a) <com.google.android.material.tabs.TabLayout>

(b) <com.google.android.material.tabs.TabItem>

Key Attributes of TabLayout

Adding Tabs Dynamically in Java

Linking with ViewPager2

Step 1 — XML

Step 2 — Java code

Step 3 — Adapter Class

Related Concepts

Common Customizations

Common Mistakes to Avoid

ViewPager / ViewPager2

What if we don’t use ViewPager?

How to do it manually (without ViewPager)

Step 1 — XML

Step 2 — Java (manual fragment switching)

MINI WHATSAPP CHAT SYSTEM

1️⃣ Fragments

ChatsFragment.java

StatusFragment.java

CallsFragment.java

2️⃣ ViewPager2 Adapter

MainPagerAdapter.java

3️⃣ Main Activity

MainActivity.java

4️⃣ Layout File

activity_main.xml

1️⃣ SharedPreferences

2️⃣ How SharedPreferences Works Internally

3️⃣ Getting SharedPreferences

(a) Activity Context

(b) Application-wide default preferences

(b) Using PreferenceManager.getDefaultSharedPreferences(this)

4️⃣ Modes (Old versions concept)

5️⃣ Storing Data

Example:

6️⃣ Retrieving Data

7️⃣ Removing or Clearing Data

Rmoving File from phone

8️⃣ Checking if Key Exists

EncryptedSharedPreferences (For Sensitive Data)

Login & logout Example

🔹 Project Overview

🔹 File 1 — LoginActivity.java

Explanation:

🔹 File 2 — MainActivity.java

(a) `<com.google.android.material.tabs.TabLayout>`

(b) `<com.google.android.material.tabs.TabItem>`

Key Attributes of `TabLayout`

Linking with `ViewPager2`

`ViewPager` / `ViewPager2`

What if we don’t use `ViewPager`?

(b) Using `PreferenceManager.getDefaultSharedPreferences(this)`

`EncryptedSharedPreferences` (For Sensitive Data)