5.5.2. Overridden Activity Method onCreate
Overridden Activity method onCreate (Fig. 5.19) calls setContentView (line 36) to set MainActivity’s GUI. Android chooses the activity_main.xml file from the res/layout folder if the app is running in portrait orientation or res/layout-large-land if the app is running on a tablet in landscape orientation.
32 @Override
33 protected void onCreate(Bundle savedInstanceState)
34 {
35 super.onCreate(savedInstanceState);
36 setContentView(R.layout.activity_main);
37
38 // set default values in the app's SharedPreferences
39 PreferenceManager.setDefaultValues(this, R.xml.preferences, false);
40
41 // register listener for SharedPreferences changes
42 PreferenceManager.getDefaultSharedPreferences(this).
43 registerOnSharedPreferenceChangeListener(
44 preferenceChangeListener);
45
46 // determine screen size
47 int screenSize = getResources().getConfiguration().screenLayout &
48 Configuration.SCREENLAYOUT_SIZE_MASK;
49
50 // if device is a tablet, set phoneDevice to false
51 if (screenSize == Configuration.SCREENLAYOUT_SIZE_LARGE ||
52 screenSize == Configuration.SCREENLAYOUT_SIZE_XLARGE )
53 phoneDevice = false; // not a phone-sized device
54
55 // if running on phone-sized device, allow only portrait orientation
56 if (phoneDevice)
57 setRequestedOrientation(
58 ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);
59 } // end method onCreate
60
Fig. 5.19 | MainActivity overridden Activity method onCreate.
Setting the Default Preference Values and Registering a Change Listener
When you install and launch the app for the first time, line 39 sets the app’s default preferences by calling PreferenceManager method setDefaultValues—this creates and initializes the app’s SharedPreferences file using the default values that you specified in preferences.xml. The method requires three arguments:
• the preferences’ Context—the Activity (this) for which you are setting the default preferences
• the resource ID for the preferences XML file (R.xml.preferences) that you created in Section 5.4.10
• a boolean indicating whether the default values should be reset each time method setDefaultValues is called—false indicates that the default preference values should be set only the first time this method is called.
Each time the user changes the app’s preferences, MainActivity should call QuizFragment’s methods updateGuessRows or updateRegions (based on which preference changed) to reconfigure the quiz. MainActivity registers an OnSharedPreferenceChangedListener (lines 42–44) so that it will be notified each time a preference changes. PreferenceManager method getDefaultSharedPreferences returns a reference to the SharedPreferences object representing the app’s preferences, and SharedPreferences method registerOnSharedPreferenceChangeListener registers the listener, which is defined in Section 5.5.6.
Configuring a Phone Device for Portrait Orientation
Lines 47–53 determine whether the app is running on a tablet or a phone. Inherited method getResources returns the app’s Resources object (package android.content.res) that can be used to access an app’s resources and determine information about the app’s environment. Resources method getConfiguration returns a Configuration object (package android.content.res) that contains public instance variable screenLayout, which you can use to determine the device’s screen-size category. To do so, first you combine the value of screenLayout with Configuration.SCREENLAYOUT_SIZE_MASK using the bitwise AND (&) operator. Then, you compare the result to the Configuration constants SCREENLAYOUT_SIZE_LARGE and SCREENLAYOUT_SIZE_XLARGE (lines 51–52). If either is a match, the app is running on a tablet-sized device. Finally, if the device is a phone, lines 57–58 call inherited Activity method setRequestedOrientation to force the app to display MainActivity in only portrait orientation.