CS 185C/286 - Lecture 5

Cay S. Horstmann

Lecture 5 Quiz 1

Put your answer into Piazza.

What is NOT true about RSS parser code example in Android Recipes Section 3.8?

1. If the author had used the same trick as we did in the homework, the startElement method would have been shorter.
2. The channel element must be handled in the startElement method.
3. The title element must be handled in the endElement method.
4. The inItem flag is necessary.

Lecture 5 Quiz 2

What is NOT true about the XML pull parser implementation of the RSS parser code?

1. It is longer than the SAX implementation.
2. Its structure is more aligned with the structure of the data to be parsed.
3. Unlike the RSS parser, the pull parser checks that the document is valid.
4. The statement

   if (parser.getEventType() != XmlPullParser.START_TAG) {
       continue;
   }

   is necessary.

Today's Lecture/Lab

• Menus
• Local storage

Menus

• In the olden days, Android phones had a dedicated menu key.
• It was pretty nice for those people who understood menus. Push the key, and you get a menu of options that make sense on the current screen.
• Apparently, that's too complicated. Nowadays, the most common actions should go in the action bar.
• Not enough room? Put the rest into the overflow.
• Legacy menus also end up in an overflow at the bottom of the screen (next to Back, Home, Recent apps)
• See here for the exact compatibility rules.

Programming Menus

• Add menu items to resource:

  <item android:id="@+id/new_game"
            android:icon="@drawable/ic_new_game"
            android:title="@string/menu_new_game"
            android:showAsAction="ifRoom"/>

• Override onCreateOptionsMenu and “inflate” menu (i.e. read from XML):

  @Override public boolean onCreateOptionsMenu(Menu menu) {
      getMenuInflater().inflate(R.menu.my_menu, menu);
      return true;
  }

• React to menu selection:

  @Override public boolean onOptionsItemSelected(MenuItem item) {
     if (item.getItemId() == R.id.menu_new_game) { ...; return true; }
  	 else if (...) ...
  	 else return false;
  }

Contextual Menus

• The menus we discussed are called "options menus"
• Show up in the action bar or, with older Androids, somewhere when the menu button is pushed
• Menu items should apply to the current activity
• Contextual menu applies to single item within activity
• Commonly activated through long press
• Can show up as floating menus or action mode
  
• Also have more specialized PopupMenu—see your reading assignment

Storage Options

• Preferences, similar to Windows registry
• Internal storage: private file system
• External Storage: shared file system (ex. SD card)
• SQLite database
• Network connection: save on server

File Storage

• Get base directory for your app with getFilesDir, getCacheDir, or getExternalFilesDir, getExternalStoragePublicDirectory
• Then just use normal java.io library calls:

  File file = new File(context.getCacheDir(), filename);
  ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream(file)); 
  out.writeObject(object);
  out.close();

• Cache dir may get emptied if low resources, but you are still responsible for not overflowing it

SQLite

• Widely used open source project
• Embedded database: runs in-process, uses normal file system
• Uses standard SQL commands. (Don't know SQL? Programming Android Ch. 9 has a quick summary.)
• Use when you have more data than you want to hold in memory
• Use for long-term storage
• You need to bridge O/R mismatch
• Can debug database with sqlite3 ADK tool

Server Communication

• Default/AndroidHttpClient (don't use) and HttpUrlConnection (standard Java)
• See Android Recipes Section 3.6
• Remember—all this needs to happen in a separate thread
• And someone needs to write the server ☺

Reading Before Next Class

• Android Menu Guide
• Storage Options

Lab

• Bring your laptop to the lab
• You will work with a buddy
• One of you writes code, the other types up answers
• Switch roles each lab
• Submit lab work to git

Menu Items

1. Continue with the code from the solution to homework 2.
2. Add a menu with menu items to show correct responses, and one to hide them. What's the XML?
3. Add a menu handler. Set or clear a Boolean flag showCorrectResponses. What's the code?
4. Now you need to actually make it happen. Somewhere, where you populate the list, respect the flag. Where is that?
5. How do you get the list to repopulate when the flag changes?

Saving State

• We want to save the answers of the user so far.
• Quick hack: Just serialize the Quiz object.
• In which lifecycle method should that be done?
• Write the code for saving the object to quiz.ser in the cache directory. What is your code? (NB. Also remember to make the Quiz class implement Serializable.)
• To test this, click on the Back button until you leave the app. Where can you find the file? How big is it? (Hint: Run adb shell from the command line and look inside /data/data.)
• Now we need to deserialize when the app starts again. If it fails (e.g. on the first try), read from the web. In which method?
• What is your code?
• First check that your app comes up again when you relaunch it from the app screen. How can you tell?
• Now pause the app again and clear the cache. How did you do that?
• What happens when you relaunch your app?