Developing for Android

To start with, it’s worth taking a few minutes to read Google’s Android design philosophy at http://code.google.com/android/toolbox/philosophy.html.

• Fast
• Responsive
• Secure
• Seamless

One of the keys to writing efficient Android code is to not carry over assumptions from desktop and server environments to embedded devices.

• An application must respond to any user action, such as a key press or screen touch, within 5 seconds.
  
• A Broadcast Receiver must return from its onReceive handler within 10 seconds.
  

• Consider requiring permissions for any services you create or broadcasts you transmit.
  
• Take special care when accepting input to your application from external sources such as the Internet, SMS messages, or instant messaging (IM).
  
• Be cautious when your application may expose access to lower-level hardware.
  

In this example, you’ll be creating a new Android application from scratch. This simple example creates a new to-do list application using native Android View controls. It’s designed to illustrate the basic steps involved in starting a new project.

1. Start by creating a new Android project. Within Eclipse, select File ➪ New ➪ Project …, then choose Android (as shown in Figure 2-9) before clicking Next.
2. In the dialog box that appears (shown in Figure 2-10), enter the details for your new project. The “Application name” is the friendly name of your application, and the “Activity name” is the name of your Activity subclass. With the details entered, click Finish to create your new project.
3. Take this opportunity to set up debug and run configurations by selecting Run ➪ Open Debug Dialog … and then Run ➪ Open Run Dialog …, creating a new configuration for each, specifying the Todo_List project. You can leave the launch actions as Launch Default Activity or explicitly set them to launch the new ToDoList Activity, as shown in Figure 2-11.
4. Now decide what you want to show the users and what actions they’ll need to perform. Design a user interface that will make this as intuitive as possible.
   In this example, we want to present users with a list of to-do items and a text entry box to add new ones. There’s both a list and a text entry control (View) available from the Android libraries. The preferred method for laying out your UI is using a layout resource fi le. Open the main.xml layout file in the res/layout project folder, as shown in Figure 2-12.
5. Modify the main layout to include a ListView and an EditText within a LinearLayout. It’s important to give both the EditText and ListView controls IDs so you can get references to them in code.
   <?xml version=”1.0” encoding=”utf-8”?>
   <LinearLayout xmlns:android=”http://schemas.android.com/apk/res/android”
   android:orientation=”vertical”
   android:layout_width=”fill_parent”
   android:layout_height=”fill_parent”>
   <EditText
   android:id=”@+id/myEditText”
   android:layout_width=”fill_parent”
   android:layout_height=”wrap_content”
   android:text=”New To Do Item”
   />
   <ListView
   android:id=”@+id/myListView”
   android:layout_width=”fill_parent”
   android:layout_height=”wrap_content” />
6. With your user interface defined, open the ToDoList.java Activity class from your project’s source folder. In this example, you’ll make all your changes by overriding the onCreate method. Start by inflating your UI using setContentView and then get references to the ListView and EditText using findViewById.
   public void onCreate(Bundle icicle) {
   // Inflate your view
   setContentView(R.layout.main);
   // Get references to UI widgets
   ListView myListView = (ListView)findViewById(R.id.myListView);
   final EditText myEditText = (EditText)findViewById(R.id.myEditText);
   }
7. Still within onCreate, defi ne an ArrayList of Strings to store each to-do list item. You can bind a ListView to an ArrayList using an ArrayAdapter, so create a new ArrayAdapter instance to bind the to-do item array to the ListView.
   public void onCreate(Bundle icicle) {
   setContentView(R.layout.main);
   ListView myListView = (ListView)findViewById(R.id.myListView);
   final EditText myEditText = (EditText)findViewById(R.id.myEditText);
   // Create the array list of to do items
   final ArrayList<String> todoItems = new ArrayList<String>();
   // Create the array adapter to bind the array to the listview
   final ArrayAdapter<String> aa;
   aa = new ArrayAdapter<String>(this,
   android.R.layout.simple_list_item_1,
   todoItems);
   // Bind the array adapter to the listview.
   myListView.setAdapter(aa);
   }
8. The final step to make this to-do list functional is to let users add new to-do items. Add an onKeyListener to the EditText that listens for a “D-pad center button” click before adding the contents of the EditText to the to-do list array and notifying the ArrayAdapter of the change. Then clear the EditText to prepare for another item.
   public void onCreate(Bundle icicle) {
   setContentView(R.layout.main);
   ListView myListView = (ListView)findViewById(R.id.myListView);
   final EditText myEditText = (EditText)findViewById(R.id.myEditText);
   final ArrayList<String> todoItems = new ArrayList<String>();
   final ArrayAdapter<String> aa;
   aa = new ArrayAdapter<String>(this,
   android.R.layout.simple_list_item_1,
   todoItems);
   myListView.setAdapter(aa);
   myEditText.setOnKeyListener(new OnKeyListener() {
   public boolean onKey(View v, int keyCode, KeyEvent event) {
   if (event.getAction() == KeyEvent.ACTION_DOWN)
   if (keyCode == KeyEvent.KEYCODE_DPAD_CENTER)
   {
   todoItems.add(0, myEditText.getText().toString());
   aa.notifyDataSetChanged();
   myEditText.setText(“”);
   return true;
   }
   return false;
   }
   });
   }
9. Run or debug the application, and you’ll see a text entry box above a list, as shown in Figure 2-13.
10. You’ve now finished your first “real” Android application. Try adding breakpoints to the code to test the debugger and experiment with the DDMS perspective.
    

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