Android Applications Development

Editor's Notes

• #21: Platform VersionAPI Level Android 4.419KITKAT Android 4.318JELLY_BEAN_MR2 Android 4.2, 4.2.217JELLY_BEAN_MR1 Android 4.1, 4.1.116JELLY_BEAN Android 4.0.3, 4.0.415ICE_CREAM_SANDWICH_MR1 Android 4.0, 4.0.1, 4.0.214ICE_CREAM_SANDWICH Android 3.213HONEYCOMB_MR2 Android 3.1.x12HONEYCOMB_MR1 Android 3.0.x11HONEYCOMB Android 2.3.4 Android 2.3.310GINGERBREAD_MR1 Android 2.3.2 Android 2.3.1 Android 2.39GINGERBREAD Android 2.2.x8FROYO Android 2.1.x7ECLAIR_MR1 Android 2.0.16ECLAIR_0_1 Android 2.05ECLAIR Android 1.64DONUT Android 1.53CUPCAKE Android 1.12BASE_1_1 Android 1.01BASE
• #35: As of this writing, Android Studio is still in Early Access Preview and Eclipse ADT Bundle have caused issues some plug-ins
• #44: Just an example on how it should and be like. Consistent, consistent, consistent!
• #45: What are DIPs? A virtual pixel unit that you should use when defining UI layout, to express layout dimensions or position in a density-independent way. The density-independent pixel is equivalent to one physical pixel on a 160 dpi screen, which is the baseline density assumed by the system for a "medium" density screen. At runtime, the system transparently handles any scaling of the dp units, as necessary, based on the actual density of the screen in use. The conversion of dp units to screen pixels is simple: px = dp * (dpi / 160). For example, on a 240 dpi screen, 1 dp equals 1.5 physical pixels. You should always use dp units when defining your application's UI, to ensure proper display of your UI on screens with different densities.
• #48: Go make a sample UI with TextView saying “Hello World!” in XML
• #60: class SampleBaseAdapter extends BaseAdapter { private LayoutInflater layoutInflater; private final String[] listItems = new String[] { "Item 1", "Item 2", "Item 3" }; public SampleBaseAdapter() {} public SampleBaseAdapter(Context context) { layoutInflater = LayoutInflater.from(context); } @Override public int getCount() { return listItems.length; } @Override public Object getItem(int position) { return listItems[position]; } @Override public long getItemId(int position) { return listItems[position].hashCode(); } @Override public View getView(int position, View convertView, ViewGroup parent) { ViewHolder viewHolder; if (convertView == null) { convertView = layoutInflater.inflate( android.R.layout.simple_list_item_1, null); viewHolder = new ViewHolder(); viewHolder.titleText = (TextView) convertView .findViewById(android.R.id.text1); convertView.setTag(viewHolder); } else { viewHolder = (ViewHolder) convertView.getTag(); } viewHolder.titleText.setText(listItems[position]); return convertView; } class ViewHolder { TextView titleText; } } ViewHolder or make a custom View
• #62: Make sample form!
• #63: Make sample form!
• #77: <?xml version="1.0" encoding="utf-8"?><resources>    <plurals name="numberOfSongsAvailable">        <item quantity="one">Znaleziono jedną piosenkę.</item>        <item quantity="few">Znaleziono %d piosenki.</item>        <item quantity="other">Znaleziono %d piosenek.</item>    </plurals></resources> int count = getNumberOfsongsAvailable();Resources res = getResources();String songsFound = res.getQuantityString(R.plurals.numberOfSongsAvailable, count, count) Resources res = getResources();String text = String.format(res.getString(R.string.welcome_messages), username, mailCount); <string name="welcome_messages">Hello, %1$s! You have %2$d new messages.</string>
• #104: package com.safeway.sampleserviceusage; import android.app.Activity; import android.content.ComponentName; import android.content.Context; import android.content.Intent; import android.content.ServiceConnection; import android.os.Bundle; import android.os.IBinder; import android.view.Menu; import android.view.MenuItem; public class MainActivity extends Activity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); bindService(new Intent(this, SampleService.class), serviceConnection , Context.BIND_AUTO_CREATE); } @Override public boolean onCreateOptionsMenu(Menu menu) { // Inflate the menu; this adds items to the action bar if it is present. getMenuInflater().inflate(R.menu.main, menu); return true; } @Override public boolean onOptionsItemSelected(MenuItem item) { switch (item.getItemId()) { case R.id.action_settings: if (sampleService != null) { sampleService.showMessage("Hello " + System.currentTimeMillis()); } return true; default: return super.onOptionsItemSelected(item); } } private SampleService sampleService; private ServiceConnection serviceConnection = new ServiceConnection() { @Override public void onServiceDisconnected(ComponentName name) { sampleService = null; } @Override public void onServiceConnected(ComponentName name, IBinder service) { sampleService = ((SampleService.SampleBinder) service).getService(); } }; }
• #131: Disadvantages of using Java threads in Android If you use Java threads you have to handle the following requirements Synchronization with the main thread if you post back results to the user interface No default for canceling the thread No default thread pooling No default for handling configuration changes in Android
• #137: Cancelling a task A task can be cancelled at any time by invoking cancel(boolean). Invoking this method will cause subsequent calls to isCancelled() to return true. After invoking this method,onCancelled(Object), instead of onPostExecute(Object) will be invoked after doInBackground(Object[]) returns. To ensure that a task is cancelled as quickly as possible, you should always check the return value of isCancelled() periodically from doInBackground(Object[]), if possible (inside a loop for instance.)
• #138: Cancelling a task A task can be cancelled at any time by invoking cancel(boolean). Invoking this method will cause subsequent calls to isCancelled() to return true. After invoking this method,onCancelled(Object), instead of onPostExecute(Object) will be invoked after doInBackground(Object[]) returns. To ensure that a task is cancelled as quickly as possible, you should always check the return value of isCancelled() periodically from doInBackground(Object[]), if possible (inside a loop for instance.)
• #140: Scheduling messages is accomplished with the post(Runnable), postAtTime(Runnable, long), postDelayed(Runnable, long), sendEmptyMessage(int), sendMessage(Message),sendMessageAtTime(Message, long), and sendMessageDelayed(Message, long) methods. The post versions allow you to enqueue Runnable objects to be called by the message queue when they are received; the sendMessage versions allow you to enqueue a Message object containing a bundle of data that will be processed by the Handler's handleMessage(Message)method (requiring that you implement a subclass of Handler).
• #154: standard – multiple instances singleTop – can have multiple instances, but if target is on top, will create nothing singleTask – creates a new task, similar to singleTop singleInstance - similar to singleTask, but only one, and only one, can exist