Introducing Android in Java

Encode QR Code ISO/IEC18004 in Java Introducing Android

The Linux environment is complete, including process management. You can launch and kill applications directly from the shell on the Android platform, but this is a developer s debugging task, not something the average Android handset user is likely to carry out. It s nice to have this option for troubleshooting application issues. It s a relatively recent phenomenon to be able to touch the metal of a mobile phone in this way. For more in-depth exploration of the Linux foundations of Android, see chapter 13.

Let s look at a simple Android application consisting of a single Activity, with one View. The Activity collects data (a street address) and creates an Intent to find this address. The Intent is ultimately dispatched to Google Maps. Figure 1.7 is a screen shot of the application running on the emulator. The name of the application is Where Do You Live.

As we previously stated, the AndroidManifest.xml file contains the descriptors for the application components of the application. This application contains a single Activity named AWhereDoYouLive. The application s AndroidManifest.xml file is shown in the following listing.

< xml version="1.0" encoding="utf-8" > <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.msi.manning.unlockingandroid"> <application android:icon="@drawable/icon"> <activity android:name=".AWhereDoYouLive" android:label="@string/app_name"> <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> </application> <uses-permission android:name="android.permission.INTERNET" /> </manifest>

package com.msi.manning.unlockingandroid; // imports omitted for brevity public class AWhereDoYouLive extends Activity { @Override public void onCreate(Bundle icicle) { super.onCreate(icicle); setContentView(R.layout.main); final EditText addressfield = (EditText) findViewById(R.id.address); final Button button = (Button) findViewById(R.id.launchmap); button.setOnClickListener(new Button.OnClickListener() public void onClick(View view) { try { String address = addressfield.getText().toString(); address = address.replace(' ', '+'); Intent geoIntent = new Intent Prepare (android.content.Intent.ACTION_VIEW, Intent Uri.parse("geo:0,0 q=" + address)); startActivity(geoIntent); } catch (Exception e) {

} } }); } }

In this example application, the setContentView method creates the primary UI, which is a layout defined in main.xml in the /res/layout directory. The EditText view collects information, which in this case is an address. The EditText view is a text box or edit box in generic programming parlance. The findViewById method connects the resource identified by R.id.address to an instance of the EditText class. A Button object is connected to the launchmap UI element, again using the findViewById method. When this button is clicked, the application obtains the entered address by invoking the getText method of the associated EditText B. When the address has been retrieved from the UI, we need to create an Intent to find the entered address. The Intent has a VIEW action, and the data portion represents a geographic search query C. Finally, the application asks Android to perform the Intent, which ultimately results in the mapping application displaying the chosen address. The startActivity method is invoked, passing in the prepared Intent. Resources are precompiled into a special class known as the R class, as shown in listing 1.8. The final members of this class represent UI elements. You should never modify the R.java file manually; it s automatically built every time the underlying resources change. (We ll cover Android resources in greater depth in chapter 3.)

/* AUTO-GENERATED FILE. DO NOT MODIFY. * * This class was automatically generated by the * aapt tool from the resource data it found. It * should not be modified by hand. */ package com.msi.manning.unlockingandroid; public final class R { public static final class attr { } public static final class drawable { public static final int icon=0x7f020000; } public static final class id { public static final int address=0x7f050000; public static final int launchmap=0x7f050001; } public static final class layout { public static final int main=0x7f030000; } public static final class string { public static final int app_name=0x7f040000; } }

Figure 1.7 shows the sample application in action. Someone looked up the address of the White House; the result shows the White House pinpointed on the map.