Android Hello World – Episode #1

Hello,

This is Pharid, Exclusive Author at Envato. ūüôā

This is my first blog’s post relating Android Tutorial.¬† Today I will teach you how to create your first Android “Hello World!” Application with Android Studio ( SDK ).

Before Starting our work, First we need to install Android Studio on our Laptop/PC. You can download it from Official site

Android Studio Download

I recommend you to use more than 4gb Internal Memory installed PC. Android Studio could reduce your speed of your laptop. ūüôĀ¬† We have to¬†sacrifice something at initial ). I also assume that you have a little bit working knowledge with Android studio.

So let us proceed to write a simple Android Application which will print “Hello World!”.

Create Android Application

The first step is to create a simple Android Application using Android studio. When you click on Android studio icon, it will show screen as shown below

Hello Android Wizard

You can start your application development by calling start a new android studio project. in a new installation frame should ask Application name, package information and location of the project.‚ąí

Hello Android Project

After entered application name, it going to be called select the form factors your application runs on, here need to specify Minimum SDK, in our tutorial, I have declared as API23: Android 6.0(Mashmallow) ‚ąí

Hello Android Project

The next level of installation should contain selecting the activity to mobile, it specifies the default layout for Applications.

Hello Android Project

At the final stage it going to be open development tool to write the application code.

Hello Android Project

Anatomy of Android Application

Before you run your app, you should be aware of a few directories and files in the Android project ‚ąí

 

Sr.No. Folder, File & Description
1 Java

This contains the .java source files for your project. By default, it includes an MainActivity.java source file having an activity class that runs when your app is launched using the app icon.

2 res/drawable-hdpi

This is a directory for drawable objects that are designed for high-density screens.

3 res/layout

This is a directory for files that define your app’s user interface.

4 res/values

This is a directory for other various XML files that contain a collection of resources, such as strings and colours definitions.

5 AndroidManifest.xml

This is the manifest file which describes the fundamental characteristics of the app and defines each of its components.

6 Build.gradle

This is an auto generated file which contains compileSdkVersion, buildToolsVersion, applicationId, minSdkVersion, targetSdkVersion, versionCode and versionName

Following section will give a brief overview of the important application files.

The Main Activity File

The main activity code is a Java file¬†MainActivity.java. This is the actual application file which ultimately gets converted to a Dalvik executable and runs your application. Following is the default code generated by the application wizard for¬†Hello World!¬†application ‚ąí

package com.example.helloworld;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

public class MainActivity extends AppCompatActivity {
   @Override
   protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
   }
}

Here, R.layout.activity_main refers to the activity_main.xml file located in the res/layout folder. The onCreate() method is one of many methods that are figured when an activity is loaded.

The Manifest File

Whatever component you develop as a part of your application, you must declare all its components in a¬†manifest.xml¬†which resides at the root of the application project directory. This file works as an interface between Android OS and your application, so if you do not declare your component in this file, then it will not be considered by the OS. For example, a default manifest file will look like as following file ‚ąí

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.helloworld">

   <application
      android:allowBackup="true"
      android:icon="@mipmap/ic_launcher"
      android:label="@string/app_name"
      android:supportsRtl="true"
      android:theme="@style/AppTheme">
      
      <activity android:name=".MainActivity">
         <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
         </intent-filter>
      </activity>
   </application>
</manifest>

Here <application>…</application> tags enclosed the components related to the application. Attribute¬†android:icon¬†will point to the application icon available under¬†res/drawable-hdpi. The application uses the image named ic_launcher.png located in the drawable folders

The <activity> tag is used to specify an activity and android:name attribute specifies the fully qualified class name of the Activity subclass and the android:label attributes specifies a string to use as the label for the activity. You can specify multiple activities using <activity> tags.

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by Counterflix

The¬†action¬†for the intent filter is named¬†android.intent.action.MAIN¬†to indicate that this activity serves as the entry point for the application. The¬†categoryfor the intent-filter is named¬†android.intent.category.LAUNCHER¬†to indicate that the application can be launched from the device’s launcher icon.

The¬†@string¬†refers to the¬†strings.xml¬†file explained below. Hence,¬†@string/app_name¬†refers to the¬†app_name¬†string defined in the strings.xml file, which is “HelloWorld”. Similar way, other strings get populated in the application.

Following is the list of tags which you will use in your manifest file to specify different Android application components ‚ąí

  • <activity>elements for activities
  • <service> elements for services
  • <receiver> elements for broadcast receivers
  • <provider> elements for content providers

The Strings File

The¬†strings.xml¬†file is located in the¬†res/values¬†folder and it contains all the text that your application uses. For example, the names of buttons, labels, default text, and similar types of strings go into this file. This file is responsible for their textual content. For example, a default strings file will look like as following file ‚ąí

<resources>
   <string name="app_name">HelloWorld</string>
   <string name="hello_world">Hello world!</string>
   <string name="menu_settings">Settings</string>
   <string name="title_activity_main">MainActivity</string>
</resources>

The Layout File

The¬†activity_main.xml¬†is a layout file available in¬†res/layout¬†directory, that is referenced by your application when building its interface. You will modify this file very frequently to change the layout of your application. For your “Hello World!” application, this file will have following content related to default layout ‚ąí

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
   xmlns:tools="http://schemas.android.com/tools"
   android:layout_width="match_parent"
   android:layout_height="match_parent" >
   
   <TextView
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_centerHorizontal="true"
      android:layout_centerVertical="true"
      android:padding="@dimen/padding_medium"
      android:text="@string/hello_world"
      tools:context=".MainActivity" />
      
</RelativeLayout>

This is an example of simple¬†RelativeLayout¬†which we will study in a separate chapter. The¬†TextView¬†is an Android control used to build the GUI and it have various attributes like¬†android:layout_width,¬†android:layout_height¬†etc which are being used to set its width and height etc.. The¬†@string¬†refers to the strings.xml file located in the res/values folder. Hence, @string/hello_world refers to the hello string defined in the strings.xml file, which is “Hello World!”.

Running the Application

Let’s try to run our¬†Hello World!¬†application we just created. I assume you had created your¬†AVD¬†while doing environment set-up. To run the app from Android studio, open one of your project’s activity files and click Run¬†Eclipse Run Icon¬†icon from the tool bar. Android studio installs the app on your AVD and starts it and if everything is fine with your set-up and application, it will display following Emulator window ‚ąí

Android Hello World

Congratulations!!! you have developed your first Android Application and now just keep following rest of the tutorial step by step to become a great Android Developer. All the very best.

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