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Creating objects ahead of time is an important optimization. Views are redrawn very frequently, and many drawing objects require expensive initialization. Creating drawing objects within your onDraw() method significantly reduces performance and can make your UI appear sluggish.

If your view doesn't need special control over its size, you only need to override one method: onSizeChanged().

When you switch orientations, Android will create a new View. You're probably getting crashes because your background thread is trying to change the state on the old one. (It may also be having trouble because your background thread isn't on the UI thread) I'd suggest making that mHandler volatile and updating it when the orientation changes.

I’ve run into the following generalized question a lot recently: I have an event that occurs in the background. I want to update my activity, if the activity is on the screen. Otherwise, I want to raise a Notification.

Hence, the recipe for the activity-or-Notification pattern is: Define an action string you will use when the event occurs that you want to go to the activity or notification (e.g., com.commonsware.java.packages.are.fun.EVENT). Dynamically register a BroadcastReceiever in your activity, with an IntentFilter set up for the aforementioned action string and with a positive priority (the default priority for a filter is 0). This receiver should then have the activity do whatever it needs to do to update the UI based on this event. The receiver should also call abortBroadcast() to prevent others from getting it. Be sure to register the receiver in onStart() or onResume() and unregister the receiver in the corresponding onStop or onPause() method. Register in your manifest a BroadcastReceiver, with an <intent-filter> set up for the aforementioned action string. This receiver should raise the Notification. In your service (e.g., an IntentService), when the event occurs, call sendOrderedBroadcast(). And that’s it. If the activity is on-screen, its receiver will be registered, so it will get the event, process it, and cancel the broadcast. If the activity is not on-screen, its receiver will not be registered, so the event will go to the default handler, in the form of your manifest-registered BroadcastReceiver, which will raise the Notification.

A facility for the application to tell the system about something it wants to be doing in the background

A facility for an application to expose some of its functionality to other applications.

I haven't looked in details at the 3 other approaches but I know that a big difference between what I do in Shelves and what I've seen done in other places is how user interaction is handled. Shelves listens to scroll events on the ListView and tries to identify taps vs scrolls vs fling to always give priority to the UI. For instance, when you touch the screen to stop a fling, Shelves starts loading images, but does so only after a very short delay so that if you are touching the screen to fling some more, the fling animation won't stutter because of the extra work load. But that's details.

In my_button we define 4 states (as a button has 4 states: not pressed and not focused, pressed and focused, pressed and not focused, not pressed and focused) with each of those states having their own drawable.

Spinner s2 = (Spinner) findViewById(R.id.spinner2);Cursor cur = managedQuery(People.CONTENT_URI, PROJECTION, null, null);     SimpleCursorAdapter adapter2 = new SimpleCursorAdapter(this,    android.R.layout.simple_spinner_item, // Use a template                                          // that displays a                                          // text view    cur, // Give the cursor to the list adatper    new String[] {People.NAME}, // Map the NAME column in the                                         // people database to...    new int[] {android.R.id.text1}); // The "text1" view defined in                                     // the XML template                                         adapter2.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);s2.setAdapter(adapter2);

Removing the window's background can be achieved very easily by using a custom theme. To do so, first create a file called res/values/theme.xml containing the following:

<resources>    <style name="Theme.NoBackground" parent="android:Theme">        <item name="android:windowBackground">@null</item>    </style></resources>

You then need to apply the theme to your activity by adding the attribute android:theme="@style/Theme.NoBackground" to your <activity /> or <application /> tag. This trick comes in very handy for any app that uses a MapView, a WebView or any other full screen opaque view.