Android

Stephen M. Reaves

2023-09-25

Notes about Lesson 6 of CS-6300

Summary

What is Android?
Basic Architecture
App Components
Android Activity Lifecycle

What is Android?

OS for mobile devices

Based on Linux

Basic Architecture

App Components

Android apps are collections of components of different types:

Activity
Service
Content Provider
Broadcast Receiver

All four are connected by intents and tied together by the manifest

Activity

Single screen with a UI

Independent units that work together to form a cohesive whole

Can be invoked by other applications

Service

App component that performs a (usually) long-running operation in the background.

Like music playing service or download service

Content Providers

Provides structured interface to a set of data.

SQLite content provider gives basic CRUD

Content providers can also be used to share data with other applications

Like Address Book

Broadcast Receiver

System/Application event handler

Intents

Abstract description of an operation to be performed

Action
Data

Allows for runtime-binding of decoupled applications

Binding modes:

Direct (Activity)
Direct (Service)
Broadcast

Manifests

Keeps android app together

XML file that declares components of app

<!-- @REF [Example android manifest](https://developer.android.com/guide/topics/manifest/manifest-intro)-->
<?xml version="1.0" encoding="utf-8"?>
<manifest
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:versionCode="1"
    android:versionName="1.0">

    <!-- Beware that these values are overridden by the build.gradle file -->
    <uses-sdk android:minSdkVersion="15" android:targetSdkVersion="26" />

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">

        <!-- This name is resolved to com.example.myapp.MainActivity
             based on the namespace property in the build.gradle file -->
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

        <activity
            android:name=".DisplayMessageActivity"
            android:parentActivityName=".MainActivity" />
    </application>
</manifest>

Simplified

<?xml version="1.0" encoding="utf-8"?>
<manifest>
  <uses-sdk ... />
  <uses-feature ... />
  <uses-permission ... />

  <application>
    <activity />
    <service />
    <provider />
    <receiver />
  </application>
</manifest>