Hello Android

Now we’re going to explore our first Android application which will be the famous Hello World application. We are going to explain the structure of an Android application and some of the basic concepts wee must understand

1. Open Eclipse and select from the menu File>New>Android Project, you’ll see a window like this.
2. Now there are several fields that appear here they are:
   Project Name: The Eclipse project name, the name of the folder that will hold the project files.
   Application Name:The name of the application that will appear on the phone.
   Package Name: The package name space, it sould be in the form of [abc].[xyz].
   Create Activity: the name of the basic activity class of your application. it’s optional to create.
   Min SDK Version: the minimum API level required by the application. You see in the Build Target list there is a list of the available SDK versions to use for the application and in front of each one the corresponding API level. You must ensure that you application API level is supported b the device.
3. Press Finish then press run and choose run as Android Application, the emulator will start, wait until the main screen appears, unlock by pressing the menu button then you should see something like this
   
   
   Notice: the emulator may take a long time to boot so please be patient.
   
4. Now go to the package explorer on the left bar of eclipse to your project
   
   
   
   folder navigate to src/[PackageName]/HelloAndroid.java this is the main activity class of your application. It should be like this:
   

   package mina.android.helloandroid;
   
   import android.app.Activity;
   import android.os.Bundle;
   
   public class HelloAndroid extends Activity {
   /** Called when the activity is first created. */
   @Override
   public void onCreate(Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);
   setContentView(R.layout.main);
   }
   }
   

   
   
5. We will explain what each line in this code means later but now let’s understand what each folder in our project contains.
   
6. The project contains the following folders
   
   
   
   

   Folder Name	Description	Required
   src	Contains all the source code (class files) for the project	Yes
   gen	Contains the R.java class file	Generated automatically
   Android 1.5	Its name changes according to the sdk version you use (1.5 here). Contains the Android API class files packed in android.jar files	Generated automatically
   assets	You can place any external resources (text files,images,…) in this folder. It’s much like the res file except it’s more like the file system where you put files that you want to access them as raw bytes	no
   res	Contains resources for the application	Yes
   drawable	Contains the images required for you application. You can add your own image files to this folder	No
   Layout	Contains the main.xml file that defines the view that construct the User Interface of the application	No
   Values	Contains other resources that can be used for your application such as string resources, styles or colors	No

   
   
7. So that was a quick look on the android project structure, in this post we will take a deeper look on the hello Android application.