Android Mobile App Development Learning Guide

The programming language for mobile development on Android is very simple – Java. Google is now actively promoting Kotlin as a language that can replace Java. Applications are also written in C++.

The creation of a simple application consists of several stages:

• project in Android Studio;
• creating a user interface;
• adding activities, navigation and actions;
• test drive the application in the emulator.

Required tools

The first step is to install the Android Studio program . This is the official development environment (IDE) for Android and runs on Windows, macOS and Linux. Although you can use other environments besides Android Studio when developing programs for Android.

If the Android SDK and other components are not installed on your computer , Android Studio will automatically download them. The Android SDK is a programming environment that includes libraries, executables, scripts, documentation, etc.

The Android SDK compiles

the code along with any data and resources into an* .apk* file. It contains everything you need to install an application on an Android device.

It is useful to install an Android emulator as well in order to run and test applications. The emulator comes bundled with Android Studio .

When all the tools are installed, you can create your first project. But first, you need to understand the basic concepts.

What does an Android application consist of ? ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

An Android application has four components. Each component is an entry point through which a system or user can access.

1. Activity** (activity)** – the elements of an interactive user interface. One activity engages another and passes information about what the user intends to do through the Intent class. Activities are like web pages, and intents are like links between them. Application launch is the Main activity.
2. Service** (service,)** – a universal entry point to maintain the application in the background. This component performs long running operations or work for remote processes without a visual interface.
3. A broadcast receiver broadcasts intents from an application to multiple participants.
4. Acontent provider manages a common set of application data from the file system, SQLite database, internet, or other storage.

Now let’s try to make our own application for Android.

Building an Android app in Android Studio ~~~~~~~~~~~~~~~~~~~~~~~~

Step 1

Select the application name, company domain, project path and package name. We indicate whether to enable support for the optional programming languages ​​C ++ and Kotlin.

Step 2

We set one or more target platforms for the build. It uses SDK and AVD, Android virtual device manager. The tool allows you to install packages into the SDK that support multiple Android OS versions and multiple API (Application Programming Interface) levels.

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reference

The lower the Android version, the more devices on which the application will run. The higher the version, the richer the API functionality.

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Step 3

Select the main activity that will be launched when you click on the application icon, and give it a name.

Step 4

After a few minutes of building, Android Studio opens the IDE interface. There are three main points here.

If you select Android view from the drop-down menu, you will see the project files. For example, our main activity is named app> java> en.appbox.appboxapp> FullscreenActivity . When creating the project, we specified a full-screen activity instead of the Main activity.

Next, you can see the file app> res> layout> activity_fullscreen.xml . This is an XML layout file for the UI of our main activity.

Finally, the third important file app> manifests> AndroidManifest.xml describes the fundamental characteristics of the application and defines all its components.

Manifest content

<?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="en.appbox.appboxapp"> <application android:allowBackup="true" android:icon="@mipmap/ic_launcher" android:label="@string/app_name" android:roundIcon="@mipmap/ic_launcher_round" android:supportsRtl="true" android:theme="@style/AppTheme"> <activity android:name=".FullscreenActivity" android:configChanges="orientation|keyboardHidden|screenSize" android:label="@string/app_name" android:theme="@style/FullscreenTheme"> <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> </application> </manifest>

Run on a real device

The application we created is one activity that runs in full screen mode and has no graphical elements.

We run it on an Android device or in an emulator.

Smartphone or tablet to connect it to the USB-debugging mode, which is activated in the Settings developer in the menu settings .

To run the emulator in Android Studio click the button Run in the menu Run (the Shift + the F10). We select the appropriate device and OS version, portrait or landscape (landscape) orientation.

Android Studio will install the emulator and launch it.

Building a simple user interface

The user interface of an Android application is built through a hierarchy of layouts(layouts, ViewGroup objects) and widgets (View objects). Layouts control the layout of child widgets on the screen. The widgets themselves are directly UI components: buttons, text fields on the screen, etc.

The activity interface is created in Android Studio in the Layout Editor and is stored mostly in XML files.

1. Open the file app> res> layout> activity_fullscreen.xml .
2. Add widgets to the screen from the Palette by dragging the mouse.
3. For example, let’s take a text field (PlainText). This is an EditText widget where the user can enter text.
4. Add buttons and other necessary elements.

You can also drag buttons and other elements onto the screen.

Adding actions, activities and navigation

Let’s say we created an activity with a text box and a Submit button. After that, you need to write what exactly will happen when you click the “Send” button.

1. Go to the code app> java> FullscreenActivity .
2. Add the SendMessage () method to the FullscreenActivity class so that when the button is clicked, this method is called.
3. We create intents (Intent class) for moving from one activity to another, new activities, navigation and everything else that is necessary for the application.

And, of course, we start dreaming of how to monetize the application.

General rules for Android applications ~~~~~~~~~~~~~~~~~~~~~~~~

The Android application lives in its own sandbox, which obeys the Linux security rules:

1. Each application is a separate user on a multiuser Linux system.
2. By default, the system assigns each application a unique user ID that is unknown to the application; all files are accessible only to this user ID.
3. All processes have their own virtual machine (VM), so that the executable code is isolated from other applications.
4. By default, each application starts its own Linux process.

There are exceptions to the rules:

1. It is possible for two applications to have a common user ID so that they can share files with each other.
2. The application can request permission to access the user’s contacts, SMS, drive content, information from the camera and other data.