Android Tutorial Chapter 1 - Getting Started

ActivityMethods.java

protected void onCreate(...) {
  super.onCreate(savedInstanceState);

  TextView tv = new TextView(this);
  tv.setTextSize(40);
  tv.setText("blah");
  
  setContentView(tv); // adds tv as the root view of the activity's layout
}

AndroidManifest-declaringParent.xml

<application ...>
  ...
  <activity
    android:name="com...ExampleActivity"
    android:label="@string/title_activity_example"
    androidparentActivityName="com...ParentActivity">
    <!-- for 4.0 and lower -->
    <meta-data
      android:name="android.support.PARENT_ACTIVITY"
      android:value="com...ParentActivity" />
  </activity>
</application>

IntentPassing.java

/*
 * Using id
 */
EditText txt = (EditText) findViewById(R.id.edit_message);

/*
 * Starting another activity
 */
public final static String EXTRA_MESSAGE = "com.mycompany.firstapp.MESSAGE";
Intent intent = new Intent(this, RecipientClass.class);
intent.putExtra(EXTRA_MESSAGE, message);
startActivity(intent);

/*
 * Receiving the Intent (RecipientClass)
 */
protected void onCreate(...) {
  Intent intent = getIntent();
  String message = intent.getStringExtra(SenderActivity.EXTRA_MESSAGE);
}

SampleActivity.java

/*
 * Sample Activity
 */
public Class SampleActivity extends ActionBarActivity {
  // key methods to override
  // - onCreate() : declare essential properties to retain through pause-stop-resume lifecycle.
  // - onCreateView() : return View (or null in case there's no UI)
  // - onPause() : commit all changes
  
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_example);
    
    if (savedInstanceState == null) {
      getSupportFragmentManager().beginTransaction()
        .add(R.id.container, new PlacehoderFragment()).commit();
    }
  }
  
  @Override
  public boolean onOptionsItemSelected(MenuItem item) {
    // handles action bar item clicks.
    // Home/Up buttons are automatically handled so long as you specify a parent activity in AndroidManifest.xml
    int id = item.getItemId();
    if (id == R.id.action_settings) { return true; }
    return super.onOptionsItemSelected(item);
  }
  
  // placeholder fragment
  public static class PlaceholderFragment extends Fragment {
    public PlaceholderFragment() {}
    
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
      View rootView = inflater.inflate(R.layout.fragment_example, container, false);
      return rootView;
    }
  }
}