Monthly Archives: February 2011

Android – Hidding the status and title bar of your application

Android

An Android application provides a titlebar. The Android platform provides a statusbar.

If you desire to hide them you can do this either via code or via the theme setting in your “AndroidManifest.xml”.

To hide the titlebar of your application you can use the predefined style android:theme=”@android:style/Theme.NoTitleBar”. If you also want to hide the statusbar of your application use android:theme=”@android:style/Theme.NoTitleBar.Fullscreen”. For example in my Android development tutorial :

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
      package="de.vogella.android.temperature"
      android:versionCode="1"
      android:versionName="1.0">
    <application android:icon="@drawable/icon" android:label="@string/app_name">
        <activity android:name=".Convert"
                  android:label="@string/app_name"
                   android:theme="@android:style/Theme.NoTitleBar.Fullscreen" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

    </application>
    <uses-sdk android:minSdkVersion="9" />

</manifest>

Give the following result.

You can archive the same via coding. Here is a corresponding snippet.

	@Override
	public void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		// hide titlebar of application
		// must be before setting the layout
		requestWindowFeature(Window.FEATURE_NO_TITLE);
		// hide statusbar of Android
		// could also be done later
		getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
				WindowManager.LayoutParams.FLAG_FULLSCREEN);
		setContentView(R.layout.main);
		text = (EditText) findViewById(R.id.EditText01);

	}

For more about Android Themes and Styles please see Android Themes.

I hope this helps. You can follow me on Twitter here.

Registering for Android Intents – Being a crappy browser

Android, Eclipse,

One of the most powerful concepts of Android Development is that you can send asynchronously messages to other activities and services via Intents. The standard case is that you specify the intent you want to call and then Android starts the corresponding activity.

You can also register yourself to existing events. For example if you writing an browser application you can register yourself in “AndroidManifest.mf” via the following intent filter as a browser.

  <application android:icon="@drawable/icon" android:label="@string/app_name">
        <activity android:name=".BrowserActivitiy"
                  android:label="@string/app_name">
            <intent-filter>
                <action android:name="android.intent.action.VIEW" />
                <category android:name="android.intent.category.DEFAULT" />
                <data android:scheme="http"/> 
            </intent-filter>
        </activity>

    </application>

If you install this application and open an URL in another application you should get a popup asking which application should be opened. As now two application have registered for the same intent the user have to choose which one should be used.

Once your activity is called you can use getIntent() to access the intent. The method getActivity() provides you the action and getData() let you access the data which was pasted. In this example we will simply read the HTML data and load it into a text view.

For more information please see Android Intents and Android Networking.

Disassemble Android dex files

Android,

The Android platform cames with a handy disassembler tool, called “dexdump”. You find this in your Android SDK installation directory in the folder”platform-tools”.

This allows you to create the Dalvik Virtual Machine bytecode from a dex file. If you are using Eclipse you can for example use the Navigator view to see the “bin” directory. This directory contains the file “classes.dex”. This is a dalvik executable generated from the compiled classes. To see the bytecode of this file, run: 

dexdump -d ~vogella/Desktop/classes.dex | less

This will show you the Dalvik Bytecode. To compile the Dalvik Bytecode to Java source code there are no official tools. You can use http://code.google.com/p/dex2jar/ to compile to jar files and continue your path from there. Thanks to Bernhard Merkle for the tip with dex2jar.

How to compile LibreOffice on Ubuntu

Other

LibreOffice tries to do what OpenOffice.org never managed well. It tries to make code contributions easy and tries to grow the developer community.

One important thing to attract new developer is to make it easy to compile the code. I think LibreOffice makes it really easy, at least on Ubuntu. Here is the sequence of commands which you need on a Ubuntu 10.04 version.

sudo apt-get build-dep openoffice.org 
sudo apt-get install libgnome-vfsmm-2.6-dev

git clone git://anongit.freedesktop.org/libreoffice/bootstrap libo
cd libo
./autogen.sh --without-junit
make
make dev-install

After some time you find a runable installation of libreoffice in “install/program” directory. Start for example the writer with “./swriter”

I think that is pretty easy and I hope that the LibreOffice team will be successful in attracting new developers. Good luck to the project!

Using Android Wakelock – Staying up all night long

Android

One of the think you as an Android developer should properly not do is prevent the Android system from shutting down certain components to save energy.

But sometimes you need to prevent the system from sleeping, e.g. during an important update or a critical download. If you choose to do so here is how you can aquire a WakeLock:


PowerManager pm = (PowerManager) getSystemService(Context.POWER_SERVICE);
PowerManager.WakeLock wakeLock = pm.newWakeLock(
		pm.SCREEN_DIM_WAKE_LOCK, "My wakelook");
// This will make the screen and power stay on
// This will release the wakelook after 1000 ms
wakeLock.acquire(1000);

// Alternative you can request and / or  release the wakelook via:
// wakeLock.acquire(); wakeLock.release();

Again, you most likely do not want to do this. Acquiring a wakelock interferes with the power management of the system and might surprise your users.

Google App Engine and sending Emails

Web,

One of the nice things in the Google App Engine is that is it very easy to work with emails. You can send out and receive emails in your servlets.

Lets demonstrate this by defining an application which allows the user to give some feedback. The backend servlet should receive this input and send out an email to the admin of the application.

For this we create a new App Engine project “de.vogella.gae.feedback” and create a simple form.

<!DOCTYPE html>
<html>
 <head>
  <meta charset="utf-8"> 
  <title>A form</title>
 </head>
 <body>
 <form action="feedback" method="post">
 
  <!-- Simple text field -->
 <label for="name">Name </label> 
 <input type="text" name="name"/>
 <br/>
 
  <!-- Email -->
 <label for="email">Email </label> 
 <input type="email" name="email"/>
 <br/>
 

  <!-- Textarea -->
 <label for="description">Description </label> 
 <textarea  name="description" cols="50" rows="5">Type your comment here</textarea>
 <br/>
 
 
 <input type="submit" name="submit" value="Send Request"/>
 </form>
 </body>
</html>

Then we define a Servlet under the URL /feedback which will receive the input from the form and send out an email.

 package de.vogella.gae.feedback;

import java.io.IOException;
import java.util.Properties;

import javax.mail.Message;
import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@SuppressWarnings("serial")
public class FeedbackServlet extends HttpServlet {

	@Override
	protected void doPost(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		String name = req.getParameter("name");
		String description = req.getParameter("description");
		String email = req.getParameter("email");
		Properties props = new Properties();
		Session session = Session.getDefaultInstance(props, null);

		String msgBody = name + "\n" + description + "\n" + email;

		try {
			Message msg = new MimeMessage(session);
			msg.setFrom(new InternetAddress("your_admin@googlemail.com",
					"Your admin"));
			msg.addRecipient(Message.RecipientType.TO, new InternetAddress(
					"your_email@example.com", "Your name
			msg.setSubject("Feedback");
			msg.setText(msgBody);
			Transport.send(msg);

		} catch (Exception e) {
			resp.setContentType("text/plain");
			resp.getWriter().println("Something went wrong. Please try again.");
			throw new RuntimeException(e);
		}

		resp.setContentType("text/plain");
		resp.getWriter().println(
				"Thank you for your feedback. An Email has been send out.");
	}
}

You have to make sure that the from email is the admin of the application otherwise you will receive an “Unauthorized Sender” Exception. If you deploy your application, access index.html, enter some data and press submit the person maintained in your recipient should receive an email with the feedback.

You find an example how to receive email in my Google App Engine Tutorial. You should also follow me on Twitter.