Unit 2: UI widgets and data storage

xml<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:padding="16dp"
    android:layout_width="match_parent" android:layout_height="match_parent">
    <TextView android:text="Student name" android:textSize="18sp"
        android:layout_width="wrap_content" android:layout_height="wrap_content"/>
    <EditText android:id="@+id/etName" android:hint="Enter name" android:inputType="textPersonName"
        android:layout_width="match_parent" android:layout_height="wrap_content"/>
    <Button android:id="@+id/btnGreet" android:text="Greet"
        android:layout_width="wrap_content" android:layout_height="wrap_content"/>
</LinearLayout>

javaEditText et = findViewById(R.id.etName);
Button b = findViewById(R.id.btnGreet);
b.setOnClickListener(v -> Toast.makeText(this, "Hello " + et.getText(), Toast.LENGTH_SHORT).show());

• Other controls: CheckBox, RadioButton in a RadioGroup, Spinner, SeekBar, ProgressBar, ImageButton.

javaToggleButton tb = findViewById(R.id.tbWifi);          // or Switch / SwitchMaterial
tb.setOnCheckedChangeListener((btn, on) -> img.setImageResource(on ? R.drawable.bulb_on : R.drawable.bulb_off));

ImageView img = findViewById(R.id.imgLogo);
img.setImageResource(R.drawable.sbs_logo);
img.setScaleType(ImageView.ScaleType.CENTER_CROP);

• Toast: a short message that fades automatically; Snackbar: a message with an optional action at the bottom of the screen.

javaNotificationCompat.Builder nb = new NotificationCompat.Builder(this, "fees")
        .setSmallIcon(R.drawable.ic_notify)
        .setContentTitle("Fee reminder")
        .setContentText("Semester fee is due on 15 October")
        .setAutoCancel(true);
NotificationManagerCompat.from(this).notify(1, nb.build());

javanew AlertDialog.Builder(this)
    .setTitle("Delete record")
    .setMessage("Are you sure?")
    .setPositiveButton("Yes", (d, w) -> deleteRecord())
    .setNegativeButton("No", null)
    .show();

• Dialog types: AlertDialog (with list, single or multiple choice), DatePickerDialog, TimePickerDialog, custom dialogs with their own layout, and DialogFragment.

javaString[] courses = {"BCA", "B.Sc IT", "MBA"};
ListView lv = findViewById(R.id.lvCourses);
lv.setAdapter(new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, courses));
lv.setOnItemClickListener((p, v, pos, id) -> Toast.makeText(this, courses[pos], Toast.LENGTH_SHORT).show());

• RecyclerView recycles row views with a ViewHolder and is preferred for long lists.

javapublic void onMapReady(GoogleMap map) {
    LatLng sbs = new LatLng(30.90, 75.85);                 // Ludhiana (approximate)
    map.addMarker(new MarkerOptions().position(sbs).title("SBS Ludhiana"));
    map.moveCamera(CameraUpdateFactory.newLatLngZoom(sbs, 14));
}

• Location sources: GPS (accurate, outdoors, more battery), network (Wi-Fi and cell towers), fused provider (combines them efficiently).

• Stores small key–value data (settings, login flags) in an XML file private to the app.

javaSharedPreferences sp = getSharedPreferences("settings", MODE_PRIVATE);
sp.edit().putString("user", "riya").putBoolean("darkMode", true).apply();   // save
String user = sp.getString("user", "guest");                              // read with default

javatry (FileOutputStream fos = openFileOutput("notes.txt", MODE_PRIVATE)) {
    fos.write("Lab 5 completed".getBytes());
}
try (BufferedReader br = new BufferedReader(new InputStreamReader(openFileInput("notes.txt")))) {
    String line = br.readLine();
}

• SQLite: a lightweight, serverless, file-based relational database built into Android — ideal for structured app data such as student records or expenses. Details are in Unit 4.

javaAnimation fade = AnimationUtils.loadAnimation(this, R.anim.fade_in);   // view animation
logo.startAnimation(fade);

ImageView iv = findViewById(R.id.ivRun);                                // drawable animation
iv.setBackgroundResource(R.drawable.run_frames);
((AnimationDrawable) iv.getBackground()).start();