Unit 1: Android app development practice

• The syllabus names Eclipse with the Android Development Tools (ADT) plug-in; ADT was discontinued in 2015 and Android Studio (which bundles the SDK, emulator and Gradle build system) is now the official IDE.

• Physical device: enable Developer options and USB debugging, connect by USB or Wi-Fi pairing; the device appears in the run target list.

xml<!-- res/layout/activity_main.xml: ConstraintLayout adapts to width -->
<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent" android:layout_height="match_parent">
    <Button android:id="@+id/btnStart" android:text="@string/start"
        android:layout_width="0dp" android:layout_height="wrap_content"
        app:layout_constraintStart_toStartOf="parent" app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintTop_toTopOf="parent" android:layout_margin="16dp"/>
</androidx.constraintlayout.widget.ConstraintLayout>

• Create res/layout-land and res/layout-sw600dp versions of the same file for landscape and tablets; Android picks the best match. Test on phone, tablet and rotated emulators.

java// Alert dialog with a single-choice list
String[] courses = getResources().getStringArray(R.array.courses);
new AlertDialog.Builder(this)
    .setTitle("Choose course")
    .setSingleChoiceItems(courses, -1, (d, which) -> chosen = courses[which])
    .setPositiveButton("OK", (d, w) -> Toast.makeText(this, chosen, Toast.LENGTH_SHORT).show())
    .show();

// Custom dialog with its own layout
Dialog dlg = new Dialog(this);
dlg.setContentView(R.layout.dialog_login);
EditText user = dlg.findViewById(R.id.etUser);
dlg.findViewById(R.id.btnOk).setOnClickListener(v -> { /* validate */ dlg.dismiss(); });
dlg.show();

xml<!-- res/values/arrays.xml -->
<resources>
    <string-array name="courses">
        <item>BCA</item><item>B.Sc IT</item><item>BBA</item><item>MBA</item>
    </string-array>
</resources>

java// Custom list row: image + title + subtitle
public class CourseAdapter extends ArrayAdapter<Course> {
    public CourseAdapter(Context c, List<Course> list) { super(c, 0, list); }
    @Override public View getView(int pos, View row, ViewGroup parent) {
        if (row == null) row = LayoutInflater.from(getContext()).inflate(R.layout.row_course, parent, false);
        Course c = getItem(pos);
        ((TextView) row.findViewById(R.id.tvTitle)).setText(c.name);
        ((TextView) row.findViewById(R.id.tvSeats)).setText(c.seats + " seats");
        ((ImageView) row.findViewById(R.id.ivIcon)).setImageResource(c.icon);
        return row;
    }
}

javaSpinner sp = findViewById(R.id.spCourse);
ArrayAdapter<CharSequence> ad = ArrayAdapter.createFromResource(this, R.array.courses,
        android.R.layout.simple_spinner_item);
ad.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
sp.setAdapter(ad);
sp.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
    public void onItemSelected(AdapterView<?> p, View v, int pos, long id) { selected = p.getItemAtPosition(pos).toString(); }
    public void onNothingSelected(AdapterView<?> p) { }
});

javapublic class StudentDB extends SQLiteOpenHelper {
    public StudentDB(Context c) { super(c, "students.db", null, 1); }
    public void onCreate(SQLiteDatabase db) {
        db.execSQL("CREATE TABLE student(_id INTEGER PRIMARY KEY AUTOINCREMENT, name TEXT, course TEXT, marks INTEGER)");
    }
    public void onUpgrade(SQLiteDatabase db, int o, int n) { db.execSQL("DROP TABLE IF EXISTS student"); onCreate(db); }

    public long add(String name, String course, int marks) {
        ContentValues cv = new ContentValues();
        cv.put("name", name); cv.put("course", course); cv.put("marks", marks);
        return getWritableDatabase().insert("student", null, cv);
    }
    public int update(long id, int marks) {
        ContentValues cv = new ContentValues(); cv.put("marks", marks);
        return getWritableDatabase().update("student", cv, "_id=?", new String[]{String.valueOf(id)});
    }
    public int delete(long id) {
        return getWritableDatabase().delete("student", "_id=?", new String[]{String.valueOf(id)});
    }
    public Cursor all() {
        return getReadableDatabase().rawQuery("SELECT * FROM student ORDER BY name", null);
    }
}

javaCursor c = db.all();
SimpleCursorAdapter adapter = new SimpleCursorAdapter(this, android.R.layout.simple_list_item_2, c,
        new String[]{"name", "course"}, new int[]{android.R.id.text1, android.R.id.text2}, 0);
ListView lv = findViewById(R.id.lvStudents);
lv.setAdapter(adapter);
lv.setOnItemLongClickListener((p, v, pos, id) -> {    // id is the _id column
    db.delete(id);
    adapter.changeCursor(db.all());                   // refresh
    return true;
});

• A cursor used with SimpleCursorAdapter must have an _id column.

java// Manifest: <uses-permission android:name="android.permission.READ_CONTACTS"/>
if (checkSelfPermission(Manifest.permission.READ_CONTACTS) != PackageManager.PERMISSION_GRANTED) {
    requestPermissions(new String[]{Manifest.permission.READ_CONTACTS}, 1);
    return;
}
Cursor c = getContentResolver().query(ContactsContract.CommonDataKinds.Phone.CONTENT_URI,
        null, null, null, ContactsContract.CommonDataKinds.Phone.DISPLAY_NAME + " ASC");
List<String> list = new ArrayList<>();
while (c.moveToNext()) {
    list.add(c.getString(c.getColumnIndexOrThrow(ContactsContract.CommonDataKinds.Phone.DISPLAY_NAME)) + "  " +
             c.getString(c.getColumnIndexOrThrow(ContactsContract.CommonDataKinds.Phone.NUMBER)));
}
c.close();

• Updating contacts needs WRITE_CONTACTS and ContentProviderOperation batches. Browser bookmarks: the old public Browser bookmarks provider was removed in Android 6.0, so modern labs practise the same provider pattern with contacts, the call log or MediaStore instead.

xml<GridView android:id="@+id/gvCourses"
    android:layout_width="match_parent" android:layout_height="wrap_content"
    android:numColumns="auto_fit" android:columnWidth="140dp"
    android:verticalSpacing="8dp" android:horizontalSpacing="8dp"/>

• Install the SDK and IDE; create emulators for a phone and a tablet.
• Hello app; activity life-cycle logging with Logcat.
• Layout supporting portrait, landscape and tablet sizes.
• Alert dialog, single and multiple choice dialogs, date picker, custom login dialog.
• String array in a Spinner and ListView; custom list with images.
• SQLite database with SQLiteOpenHelper: insert, update, delete, view.
• Display records with SQLiteDatabase and Cursor in a ListView.
• Read contacts with run-time permission.
• CRUD app with GridView and ListView display.