Start an Activity

In ApiDemos, ApiDemos/Graphics/OpenGL ES/OpenGL ES 2.0 is a rotating triangle containing a green robot.

Here’s how I found the names of the package and the activity class I passed to the constructor for ComponentName The <manifest> element in the ApiDemos AndroidManifest.xml file contains the following attribute.

package="com.example.android.apis"

This <manifest> element contains an <application> element that contains hundreds of <activity> elements. One of them is

		<activity android:name=".graphics.GLES20Activity"
			android:label="Graphics/OpenGL ES/OpenGL ES 2.0"
			android:theme="@android:style/Theme.NoTitleBar"
			android:configChanges="orientation|keyboardHidden">

			<intent-filter>
				<action android:name="android.intent.action.MAIN"/>
				<category android:name="android.intent.category.SAMPLE_CODE"/>
			</intent-filter>

		</activity>

It seems redundant to repeat the package name in front of the class name in the arguments of the constructor of ComponentName. But if we don’t, startActivity concatenates the two names with a slash and throws the following exception.

Android.content.ActivityNotFoundException: Unable to find explicit activity class {com.example.android.apis/graphics.GLES20Activity}; have you declared this activity in your AndroidManifest.xml?

Source code in Start.zip

1. MainActivity.java
2. activity_main.xml. The TextView and RelativeLayout have id numbers.
3. strings.xml. The textView string resource contains a newline \n.
4. AndroidManifest.xml

Things to try

1. Why do we have to press the Android back button twice before we can get back to the original activity?


2. Deliberately misspell the class name by adding an x. Verify that the ActivityNotFoundException says

   android.content.ActivityNotFoundException:
   Unable to find explicit activity class
   {com.example.android.apis/com.example.android.apis.graphics.GLES20Activityx};
   have you declared this activity in your AndroidManifest.xml?
   



3. Try an Intent that will call a phone number. Genymotion said “Mobile network not available” until I changed the 212 to 911.

   				final Uri uri = Uri.parse("tel:2125551212");               //Uniform Resource Identifier
   				final Intent intent = new Intent(Intent.ACTION_CALL, uri); //vs. ACTION_DIAL.
   

   Add the following element immediately before the application element in AndroidManifest.xml. CALL_PHONE has an underscore. See Using Permissions.

   	<uses-permission android:name="android.permission.CALL_PHONE"/>
   

   Find the TCP port number that the Android Emulator would use to talk to telnet. It’s displayed at the top of the Emulator and defaults to 5554. (5555 for Genymotion). But just to make sure,

   netstat -a -f inet -p tcp     (Macintosh Terminal)
   
   netstat -an -f inet -p tcp | awk 'NR <= 2 || /5554/'
   Active Internet connections (including servers)
   Proto Recv-Q Send-Q  Local Address          Foreign Address        (state)
   tcp4       0      0  192.168.56.1.49448     192.168.56.101.5555    ESTABLISHED
   
   netstat -a -p TCP             (Windows cmd.exe)
   

   To give an Emulator console command, we must telnet to the Android Emulator. See Telephony Emulation and Emulating Phone Operations in the Eclipse DDMS Perspective. On Macintosh,

   telnet localhost 5554
   

   On Microsoft Windows, install PuTTY and launch putty.exe.
   Host Name: localhost
   Port: 5554
   Connection type: • Telnet (but it worked better when I chose • Raw)
   Open

   Android Console: type 'help' for a list of commands
   help
   
   Android console command help:
   
       help|h|?         print a list of commands
       event            simulate hardware events
       geo              Geo-location commands
       gsm              GSM related commands (Global System for Mobile Communications)
       cdma             CDMA related commands (Code Division Multiple Access)
       kill             kill the emulator instance
       network          manage network settings
       power            power related commands
       quit|exit        quit control session
       redir            manage port redirections
       sms              SMS related commands (Short Mesage Service)
       avd              control virtual device execution
       window           manage emulator window
       qemu             QEMU-specific commands (Quick Emulator)
       sensor           manage emulator sensors
   
   try 'help ' for command-specific help
   OK
   
   help gsm
   allows you to change GSM-related settings, or to make a new inbound phone call
   
   available sub-commands:
      gsm list             list current phone calls
      gsm call             create inbound phone call
      gsm busy             close waiting outbound call as busy
      gsm hold             change the state of an oubtound call to 'held'
      gsm accept           change the state of an outbound call to 'active'
      gsm cancel           disconnect an inbound or outbound phone call
      gsm data             modify data connection state
      gsm voice            modify voice connection state
      gsm status           display GSM status
      gsm signal           set sets the rssi and ber
   OK
   
   help gsm list
   'gsm list' lists all inbound and outbound calls and their state
   OK
   

   Launch the app and let it call (212) 555–1212. While the call is in progress,

   gsm list
   outbound to  2125551212 : active
   OK
   
   gsm cancel 2125551212
   (The emulator says CALL ENDED.)
   OK
   
   exit