Q-2: Rotate & Blink Animation OR Android Shared Preferences (5 Marks)

Questions

a) Write a code to demonstrate the use of 'rotate' and 'blink' animation in android application. (5 marks)

b) Write a note on android shared preferences. (5 marks)

Answers

a) Rotate and Blink Animation Implementation

Step 1: Create Animation XML Files

res/anim/rotate_animation.xml:

<?xml version="1.0" encoding="utf-8"?>
<set xmlns:android="http://schemas.android.com/apk/res/android">
    <rotate
        android:fromDegrees="0"
        android:toDegrees="360"
        android:pivotX="50%"
        android:pivotY="50%"
        android:duration="2000"
        android:repeatMode="restart"
        android:repeatCount="infinite" />
</set>

res/anim/blink_animation.xml:

<?xml version="1.0" encoding="utf-8"?>
<set xmlns:android="http://schemas.android.com/apk/res/android">
    <alpha
        android:fromAlpha="1.0"
        android:toAlpha="0.0"
        android:duration="600"
        android:repeatMode="reverse"
        android:repeatCount="infinite" />
</set>

Step 2: Layout XML

activity_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:gravity="center"
    android:padding="16dp">

    <ImageView
        android:id="@+id/rotateImage"
        android:layout_width="100dp"
        android:layout_height="100dp"
        android:src="@drawable/ic_star"
        android:layout_marginBottom="32dp" />

    <TextView
        android:id="@+id/blinkText"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Blinking Text"
        android:textSize="20sp"
        android:textStyle="bold"
        android:layout_marginBottom="32dp" />

    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal">

        <Button
            android:id="@+id/btnStartRotate"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Start Rotate"
            android:layout_marginEnd="16dp" />

        <Button
            android:id="@+id/btnStartBlink"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Start Blink"
            android:layout_marginEnd="16dp" />

        <Button
            android:id="@+id/btnStop"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Stop All" />
    </LinearLayout>
</LinearLayout>

Step 3: MainActivity Java Code

public class MainActivity extends AppCompatActivity {
    private ImageView rotateImage;
    private TextView blinkText;
    private Button btnStartRotate, btnStartBlink, btnStop;
    private Animation rotateAnimation, blinkAnimation;

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

        // Initialize views
        rotateImage = findViewById(R.id.rotateImage);
        blinkText = findViewById(R.id.blinkText);
        btnStartRotate = findViewById(R.id.btnStartRotate);
        btnStartBlink = findViewById(R.id.btnStartBlink);
        btnStop = findViewById(R.id.btnStop);

        // Load animations
        rotateAnimation = AnimationUtils.loadAnimation(this, R.anim.rotate_animation);
        blinkAnimation = AnimationUtils.loadAnimation(this, R.anim.blink_animation);

        // Set click listeners
        btnStartRotate.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                startRotateAnimation();
            }
        });

        btnStartBlink.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                startBlinkAnimation();
            }
        });

        btnStop.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                stopAllAnimations();
            }
        });
    }

    private void startRotateAnimation() {
        if (rotateImage != null) {
            rotateImage.startAnimation(rotateAnimation);
            Toast.makeText(this, "Rotate animation started", Toast.LENGTH_SHORT).show();
        }
    }

    private void startBlinkAnimation() {
        if (blinkText != null) {
            blinkText.startAnimation(blinkAnimation);
            Toast.makeText(this, "Blink animation started", Toast.LENGTH_SHORT).show();
        }
    }

    private void stopAllAnimations() {
        if (rotateImage != null) {
            rotateImage.clearAnimation();
        }
        if (blinkText != null) {
            blinkText.clearAnimation();
        }
        Toast.makeText(this, "All animations stopped", Toast.LENGTH_SHORT).show();
    }
}

Alternative: Programmatic Animation Creation

// Create rotate animation programmatically
private Animation createRotateAnimation() {
    RotateAnimation rotate = new RotateAnimation(
        0f, 360f,
        Animation.RELATIVE_TO_SELF, 0.5f,
        Animation.RELATIVE_TO_SELF, 0.5f
    );
    rotate.setDuration(2000);
    rotate.setRepeatMode(Animation.RESTART);
    rotate.setRepeatCount(Animation.INFINITE);
    return rotate;
}

// Create blink animation programmatically
private Animation createBlinkAnimation() {
    AlphaAnimation blink = new AlphaAnimation(1.0f, 0.0f);
    blink.setDuration(600);
    blink.setRepeatMode(Animation.REVERSE);
    blink.setRepeatCount(Animation.INFINITE);
    return blink;
}

b) Android Shared Preferences

Definition

SharedPreferences is a lightweight storage mechanism in Android used to store small amounts of primitive data (key-value pairs) persistently across app sessions.

Key Characteristics

Persistent Storage: Data survives app restarts and device reboots
Key-Value Storage: Stores data as key-value pairs
Primitive Data Types: Supports boolean, int, long, float, String
XML Storage: Data stored in XML files in app's private directory
Thread-Safe: Safe for concurrent access

Creating and Accessing SharedPreferences

1. Get SharedPreferences Instance:

// Private to app
SharedPreferences sharedPref = getSharedPreferences("MyPrefs", Context.MODE_PRIVATE);

// Activity-specific
SharedPreferences sharedPref = getPreferences(Context.MODE_PRIVATE);

// Default shared preferences
SharedPreferences sharedPref = PreferenceManager.getDefaultSharedPreferences(this);

2. Writing Data:

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

// Store different data types
editor.putString("username", "john_doe");
editor.putInt("user_age", 25);
editor.putBoolean("is_logged_in", true);
editor.putFloat("app_version", 1.5f);
editor.putLong("last_login", System.currentTimeMillis());

// Commit changes
editor.apply(); // Asynchronous
// or
editor.commit(); // Synchronous

3. Reading Data:

SharedPreferences sharedPref = getSharedPreferences("MyPrefs", Context.MODE_PRIVATE);

// Read with default values
String username = sharedPref.getString("username", "default_user");
int age = sharedPref.getInt("user_age", 0);
boolean isLoggedIn = sharedPref.getBoolean("is_logged_in", false);
float version = sharedPref.getFloat("app_version", 1.0f);
long lastLogin = sharedPref.getLong("last_login", 0);

Complete Example: User Preferences

public class UserPreferences {
    private static final String PREF_NAME = "UserPrefs";
    private static final String KEY_USERNAME = "username";
    private static final String KEY_EMAIL = "email";
    private static final String KEY_IS_FIRST_TIME = "is_first_time";
    private static final String KEY_THEME = "theme";

    private SharedPreferences sharedPreferences;
    private SharedPreferences.Editor editor;
    private Context context;

    public UserPreferences(Context context) {
        this.context = context;
        sharedPreferences = context.getSharedPreferences(PREF_NAME, Context.MODE_PRIVATE);
        editor = sharedPreferences.edit();
    }

    // Save user data
    public void saveUserData(String username, String email) {
        editor.putString(KEY_USERNAME, username);
        editor.putString(KEY_EMAIL, email);
        editor.apply();
    }

    // Get username
    public String getUsername() {
        return sharedPreferences.getString(KEY_USERNAME, "");
    }

    // Get email
    public String getEmail() {
        return sharedPreferences.getString(KEY_EMAIL, "");
    }

    // Set first time user flag
    public void setFirstTimeUser(boolean isFirstTime) {
        editor.putBoolean(KEY_IS_FIRST_TIME, isFirstTime);
        editor.apply();
    }

    // Check if first time user
    public boolean isFirstTimeUser() {
        return sharedPreferences.getBoolean(KEY_IS_FIRST_TIME, true);
    }

    // Save theme preference
    public void saveTheme(String theme) {
        editor.putString(KEY_THEME, theme);
        editor.apply();
    }

    // Get theme
    public String getTheme() {
        return sharedPreferences.getString(KEY_THEME, "light");
    }

    // Clear all preferences
    public void clearPreferences() {
        editor.clear();
        editor.apply();
    }

    // Remove specific key
    public void removeKey(String key) {
        editor.remove(key);
        editor.apply();
    }
}

Usage in Activity

public class MainActivity extends AppCompatActivity {
    private UserPreferences userPrefs;

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

        userPrefs = new UserPreferences(this);

        // Check if first time user
        if (userPrefs.isFirstTimeUser()) {
            // Show welcome screen
            showWelcomeScreen();
            userPrefs.setFirstTimeUser(false);
        }

        // Load user data
        String username = userPrefs.getUsername();
        String email = userPrefs.getEmail();
        
        if (!username.isEmpty()) {
            // User is logged in
            loadUserProfile(username, email);
        }
    }

    private void saveUserLogin(String username, String email) {
        userPrefs.saveUserData(username, email);
    }

    private void logout() {
        userPrefs.clearPreferences();
        // Redirect to login screen
    }
}

Best Practices

Data Types: Only store primitive data types
Size Limitation: Don't store large amounts of data
Security: Don't store sensitive data (passwords, tokens)
apply() vs commit(): Use apply() for better performance
Key Management: Use constants for keys to avoid typos
Backup: Data is not backed up by default

Common Use Cases

User preferences and settings
App configuration
Login state
Theme preferences
First-time user flags
Simple caching of small data

Questions​

Answers​

a) Rotate and Blink Animation Implementation​

Step 1: Create Animation XML Files​

Step 2: Layout XML​

Step 3: MainActivity Java Code​

Alternative: Programmatic Animation Creation​

b) Android Shared Preferences​

Definition​

Key Characteristics​

Creating and Accessing SharedPreferences​

Complete Example: User Preferences​

Usage in Activity​

Best Practices​

Common Use Cases​