Android Tutorial - Chapter 3 Activity

P1_AndroidManifest.xml

<!-- Declaring the main "launcher" activity -->
<activity android:name=".MainActivity" android:label="@string/app_name">
  <intent-filter>
    <action android:name="android.intent.action.MAIN" />
    <category android:name="android.intent.category.LAUNCHER" />
  </intent-filter>
</activity>

P1_CreateAndDestory.java

TextView mTextView; // text view in the layout

@Override
public void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  
  // set UI
  // e.g.: res/layout/main_activity.xml
  setContentView(R.layout.main_activity);
  
  // set up member variables
  mTextView = (TextView) findViewById(R.id.text_message);
  
  // version checking
  if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
    getActionBar().setHomeButtonEnabled(false);
  }
}

@Override
public void onDestroy() {
  super.onDestory(); // ALWAYS call this
  
  // TODO: destroy background threads (otherwise, this method overriding is often optional)
}

P2_PausingAndResuming.java

// 1. stop animations and other CPU-consuming actions
// 2. commit unsaved changes
// 3. release resources (receivers, handles, sockets..)
@Override
public void onPause() {
  super.onPause();  // always call this first
  if (mCamera != null) {
    m.Camera.release();
    m.Camera = null;
  }
}

// kind of counter-acts the onPause() method
@Override
public void onResume() {
  super.onResule();
  
  if (mCamera == null) {
    initializeCamera();
  }
}

P3_StopAndStart.java

// automated restoration usually does its job... i.e. don't need to implement
@Override
protected void onStop() {
  super.onStop(); //again, call this first. always.
  
  ContentValues values = new ContentValues();
  values.put(SOME_TITLE, getTitle());
  values.put(SOME_VALUE, getValue());
  
  getContentResolver().update(
    mUri,
    values,
    null,
    null
  )
}

// use onStart() to counter onStop(), rather than onRestart().... in most cases
@Override
protected void onStart() {
  super.onStart();
  
  if (!gpsEnabled) {
    enableGPS();
  }
}

P4_Recreating.java

// when system destroys an activity due to system contraints
@Override
public void onSaveInstanceState(Bundle savedInstanceState) {
  savedInstanceState.putInt(PLAYER_SCORE, mCurrentScore);
  super.onSaveInstanceState(savedInstanceState);  // always all it at the end
}

// restoration - option 1
@Override
protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  
  if (savedInstanceState != null) {
    mCurrentScore = savedInstanceState.getInt(PLAYER_SCORE);
  } else {
    // put default values..?
  }
}

// restoration - option2
// this method runs after onStart()
// this method runs ONLY if there's a saved state to restore
@Override
public void onRestoreInstanceState(Bundle savedInstanceState) {
  super.onRestoreInstanceState(savedInstanceState);
  mCurrentScore = savedInstanceState.getInt(PLAYER_SCORE);
}