Group items tagged

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().

We compared these findings with that of our tests of Apple's mobile Safari browser on the iPhone 4. The results show that the Android device delivers significantly faster JavaScript execution than the iPhone, scoring over three times better on V8 and almost twice as fast on SunSpider

To find your minimum width and height in density-independent pixels (dp), use this formula: (number of cells * 74) - 2

how often the App Widget framework should request an update from the AppWidgetProvider by calling the onUpdate() method

exactly on time

Additionally, you can feel free to use the Search bar selection mechanism as a replacement for tabs since it’s really just a fast pivot on a data set. If you have more than 3 data sets, tabs become problematic since no more than 3 can be onscreen at once. For example, look at how we implemented the Profile switching mechanism below:

The good news for developers is you get this highly functional contacts feature for free if users choose to sync contact information into your app

The good news for developers is you get this highly functional contacts feature for free if users choose to sync contact information into your app. QuickContact for Android provides instant access to a contact's information and communication modes.

市场调研公司尼尔森最近发布了 ”App Playbook“，他们调查了 4200 名在过去 1 个月中下载应用的人

2009 年第四季度，21% 美国无线用户拥有智能手机，这一数字高于上一季度的 19%，大幅高于 2008 年底的 14%。 14% 的移动用户在 30 天内下载过一个应用。 应用程序平均数量：智能手机：22，功能手机：10 BlackBerry: 10 iPhone:37 Android: 22 Palm: 14 Windows Mobile: 13

Facebook, Google Maps and Weather Channel 是跨平台间最受欢迎的应用 iPhones: Facebook (58%), iTunes (48%), Google Maps (47%) Android: Google Maps (67%), Facebook (50%), Weather Channel (38%) Blackberry: Facebook (51%), Google Maps(34%), Weather Channel (28%)

Their conclusion is that Android 2.1′s new speech-to-text thing works, just about, although there’s a delay of a few seconds while the phone crunches your spoken words and tries to get the gist of what you’re saying – and a few errors sneak in, particularly when dealing with those smaller words we tend to hurry over. Basically, it looks like you have an awkward choice to make – speak your messages then spend a bit of time awkwardly tidying up the few errors that will inevitably sneak in, or carry on as normal with traditional text input methods.

When onReceive() returns

by the system at any time

> Now I just want to update the GUI from this method. > Can I somehow call a method in PushEndpointDemo.java? No, for two reasons: 1. Because C2DMReceiver is a manifest-registered BroadcastReceiver and therefore has no access to any activities 2. There might not be an activity, since you have no control over the timing of when the C2DM message is received (e.g., the user pressed BACK, the user pressed HOME) > Do I need a Broadcast Intent to do this? Possibly. -- If you want to update an activity or else ignore the message, have C2DMReceiver send out a private broadcast, picked up by a receiver registered via registerReceiver() in the activity -- If you want to update an activity or else raise a notification, have C2DMReceiver send out an ordered broadcast, as described here: http://commonsware.com/blog/2010/08/11/activity-notification-ordered-... -- If you want to update a database, call startActivity() on an IntentService, and have it do the database I/O, plus possibly broadcast an Intent to update an activity/raise a notification.

The density of a screen is important because, other things being equal, a UI element (such as a button) whose height and width are defined in terms of screen pixels will appear larger on the lower density screen and smaller on the higher density screen.

The density-independent pixel is equivalent to one physical pixel on a 160 dpi screen, the baseline density assumed by the platform (as described later in this document). At run time, the platform transparently handles any scaling of the dip units needed, based on the actual density of the screen in use. The conversion of dip units to screen pixels is simple: pixels = dips * (density / 160). For example, on 240 dpi screen, 1 dip would equal 1.5 physical pixels. Using dip units to define your application's UI is highly recommended, as a way of ensuring proper display of your UI on different screens.

But in practice, you will notice that the AsyncTask is limited to 10 threads. This number is hardcoded somewhere in the Android SDK so we cannot change this. In this case it’s a limitation we cannot live with, because often more than 10 images are loaded at the same time.

I’ve shown you how to improve performance of a ListView in three different ways: By loading images in a seperate thread By reusing rows in the list By caching views within a row

As part of my job, I ran into memory leaks issues in Android applications and they are most of the time due to the same mistake: keeping a long-lived reference to a Context.

There are two easy ways to avoid context-related memory leaks. The most obvious one is to avoid escaping the context outside of its own scope. The example above showed the case of a static reference but inner classes and their implicit reference to the outer class can be equally dangerous. The second solution is to use the Application context. This context will live as long as your application is alive and does not depend on the activities life cycle. If you plan on keeping long-lived objects that need a context, remember the application object. You can obtain it easily by calling Context.getApplicationContext() or Activity.getApplication().

In summary, to avoid context-related memory leaks, remember the following: Do not keep long-lived references to a context-activity (a reference to an activity should have the same life cycle as the activity itself) Try using the context-application instead of a context-activity Avoid non-static inner classes in an activity if you don't control their life cycle, use a static inner class and make a weak reference to the activity inside. The solution to this issue is to use a static inner class with a WeakReference to the outer class, as done in ViewRoot and its W inner class for instance A garbage collector is not an insurance against memory leaks

The android:inputType attribute has three pieces: The class is the overall interpretation of characters. The currently supported classes are text (plain text), number (decimal number), phone (phone number), and datetime (a date or time). The variation is a further refinement on the class. In the attribute you will normally specify the class and variant together, with the class as a prefix. For example, textEmailAddress is a text field where the user will enter something that is an e-mail address (foo@bar.com) so the key layout will have an '@' character in easy access, and numberSigned is a numeric field with a sign. If only the class is specified, then you get the default/generic variant. Additional flags can be specified that supply further refinement. These flags are specific to a class. For example, some flags for the text class are textCapSentences, textAutoCorrect, and textMultiline.

    <EditText android:id="@+id/edtInput"        android:layout_width="0dip"        android:layout_height="wrap_content"        android:layout_weight="1"        android:inputType="textShortMessage|textAutoCorrect|textCapSentences|textMultiLine"        android:imeOptions="actionSend|flagNoEnterAction"        android:maxLines="4"        android:maxLength="2000"        android:hint="@string/compose_hint"/>

Moreover I am not one of top developers nor any of my apps have been promoted by Android Market. I am just an one among of thousands of Android developers with not to well known apps. And what may be really surprising all my apps are free as Google do not allow developers from my country (Poland) to sell apps via Android Market!

So keep in mind these facts: None of my apps has been ever promoted in Top of Android Market I am providing only free apps (mostly due of Android Market limitations) Even if I would be able to sell apps I would not use it as main income source… (I believe that you still can make more from ads…)

X-Ray Scanner (over 268 000 downloads) Cracked Screen (over 182 000 downloads) Virtual Drums (over 20 000 downloads) Daily Beauty Tips (over 11 000 downloads) Don’t push it (over 6 500 downloads) WP Stats (over 4 000 downloads)

So the basic idea is: launch an AsyncTask making your service call, show a nifty progress dialog while the task thread is running, and have the task’s result be posted back to your activity once it completes. Cool, but what if the user decides to rotate the screen while your task is running? Or a phone call comes in, interrupting your app, and Android decides to kill it? Both these actions will effectively terminateyour activity, and recreate it when resuming (yes, a screen rotation kills your activity, very clever, isn’t it?). Unfortunately, any AsyncTask that was still running now holds a stale reference to your activity, because the restarted activity will be an entirely different object in memory (and it will go through onCreate(), as if the activity had started for the first time). I’m not entirely sure whether AsyncTask will actually post back the data to the old activity object (if it was a weak reference, it may already have been garbage collected), but in any case, your “new” activity will never see it, because it’s a different instance.