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Download Android APP Fundamental By Shinping R. Wang CSIE Dept. of Da‐yeh University
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Android APP Fundamental By Shinping R. Wang CSIE Dept. of Da‐yeh University Reference The following discussion is excerpted from 1. Android Developer: Application Fundamentals http://developer.android.com/guide/topics/fundamentals.ht ml Application Fundamentals Android application Android applications consist of Java + xml + resource. The tools from Android SDK build the final .apk package. APK stands for Android package that an archive. Application Fundamentals Android application An Android Package file (.apk) is per application for Android-powered devices or AVD. Application Fundamentals Android application Once installed on a device, each Android application runs as a process and lives in its own security sandbox. Application Fundamentals Android application security sandbox ? Each application runs as an individual user to the hosting Linux system, with its own unique Linux user ID. the ID is used only by the system and is unknown to the application, with all files of it protected by the assigned the user ID. Application Fundamentals Android application Each process runs on its own virtual machine (VM), isolates from others such that system and apps are Secure and Easy of porting APP to different platform Application Fundamentals Android application Principle of least privilege each application, by default, has access only to the components that it requires to do its work and no more. Application Fundamentals Android application An application can starts others app/service when components of these app/service is required through intent. Sharing resources, and An app has to have multiple entry points!! Application Fundamentals Android application Shuts down the process when it's no longer needed or when the system must recover memory for other applications i.e. garbage collected (GC). You don’t have to specifically shut down an app, the system will do it for you when it is required. Application Fundamentals Android application Resources sharing between processes/applications and system services can be achieved by Arranging two applications to share the same Linux user ID, and share the same VM (the applications must also be signed with the same certificate). With permissions granted at install time to access device data such as the user's contacts, SMS messages, the mountable storage (SD card), camera, Bluetooth, and more. Application Fundamentals Core framework components Application framework components are the essential building blocks of an Android application. Application Fundamentals Core framework components Four different types of application components Activities Services Content Providers Broadcast Receivers Each with its own purpose, must be named inside the AndroidManfest.xml so that the system know theirs’ existence before running the app. Application Fundamentals core framework components Activities An activity represents a single screen with a user interface and each application can consist more than one activities. Application Fundamentals core framework components Activities For example, an email application might have Activities for listing of new emails, compose an email, reading emails. Although the activities work together to form a cohesive user experience in the email application, each one is independent of the others. Application Fundamentals core framework components Activities The activities of an App work together to form a cohesive user experience in the email application, however each activity is independent of the others. Implication, a camera App (if it is allowed) can invoke send mail activity from an email App to mail picture to others. Each activity may has its’ own entry point. Application Fundamentals core framework components Activities An activity is implemented as a subclass of Activity and you can learn more about it in the Activities developer guide. Application Fundamentals core framework components Services A service is a component that runs in the background to perform long-term operations or to perform work for remote processes. It does not provide a user interface. Application Fundamentals core framework components Services For example, a service might be Playing music in the background, Fetching data over the network, and etc.. Without blocking user form accessing other activities. Application Fundamentals core framework components Services Another component, such as an activity, can start the service and let it run or bind to it in order to interact with it. Application Fundamentals core framework components Services A service is implemented as a subclass of Service and you can learn more about it in the Services developer guide. Application Fundamentals core framework components Content providers A content provider manages a shared set of application data in A file system, A SQLite database, On the web, or any other persistent storage location your application can access. Application Fundamentals core framework components Content providers Through the content provider, other applications can query or even modify the data (if the content provider allows it). A means of provide security. Application Fundamentals core framework components Content providers For example, user's contact information Can be shared by phone and email through content provider. Application Fundamentals core framework components Content providers A content provider is implemented as a subclass of ContentProvider and must implement a standard set of APIs that enable other applications to perform transactions. For more information, see the Content Providers developer guide. Application Fundamentals core framework components Broadcast receivers is a component that responds to system-wide broadcast announcements or a "gateway" to other components and intended to do a very minimal amount of work such as initiating a service to perform some work based on the event. Application Fundamentals core framework components Broadcasting could originate either from the system the screen has turned off, the battery is low, or a picture was captured. An Application to let other applications know that some data has been downloaded to the device and is available for them to use. Application Fundamentals core framework components Broadcast receivers A broadcast receiver is implemented as a subclass of BroadcastReceiver and each broadcast is delivered as an Intent object. For more information, see the BroadcastReceiver class. Application Fundamentals core framework components A unique aspect of the Android system design is that any application can start another application’s component. Android applications don't have a single entry point (there's no main() function, for example). Application Fundamentals core framework components For example, An App can invokes activity play of the application Music The Camera application (process) will be started, the activity Application Fundamentals core framework components For security measure, app can not activate a component in another application in arbitrary. Three of the four component types—activities, services, and broadcast receivers—are activated by an asynchronous message called an intent. Application Fundamentals Activating Components intents bind individual components (of the same or different applications) to each other at runtime, work likes messengers that request an action from other components, are created with Intent objects, which defines a message to activate either a specific component or a specific type of component, and can be either explicit or implicit, respectively. Application Fundamentals Activating Components For activities and services, an intent defines the action to perform (for example, to "view" or "send" something) and may specify the URI of the data to act on. Action + data For example, request of “showing” some specific “image.” Application Fundamentals Activating Components For broadcast receivers, the intent simply defines the announcement being broadcast for example, a broadcast to indicate the device battery is low includes only a known action string that indicates "battery is low”. Application Fundamentals Activating Components The content provider is not activated by intents, but by a request from a ContentResolver. The content resolver handles all direct transactions with the content provider. Application Fundamentals Activating Components The content resolver Is a layer of abstraction between the content provider and the component requesting information (for security consideration). Application Fundamentals Activating Components In all, there are separate methods for activating each type of component: For activity : by passing an Intent to startActivity() or startActivityForResult() (when you want the activity to return a result). For service: by passing an Intent to startService(). Or you can bind to the service by passing an Intent to bindService(). For broadcast : Intent to methods like sendBroadcast(), sendOrderedBroadcast(), or sendStickyBroadcast(). For content provider by calling query() on a ContentResolver. Application Fundamentals The Manifest File The Android application manifest file locates at the root directory of the .apk. has to be named as AndroidManifest.xml Application Fundamentals The Manifest File The AndroidManifest.xml does a number of things declaring the application's components, identifying any required user permissions, declaring the minimum API Level, declaring required hardware and software features, Specifying special API libraries, and more. Application Fundamentals Declaring components For example, a manifest file declares an activity as follows: <?xml version="1.0" encoding="utf-8"?> <manifest ... > <application android:icon="@drawable/app_icon.png" ... > <activity android:name="com.example.project.ExampleActivity" android:label="@string/example_label" ... > </activity> ... </application> </manifest> Application Fundamentals Declaring components Name of application components in XML as elements <activity> <service> <receiver> <provider> elements for activities elements for services elements for broadcast receivers elements for content providers <?xml version="1.0" encoding="utf-8"?> <manifest ... > <application android:icon="@drawable/app_icon.png" ... > <activity android:name="com.example.project.ExampleActivity" android:label="@string/example_label" ... > </activity> ... </application> </manifest> Application Fundamentals Declaring components You must declare Activities, services, and content providers in the manifest, or else they can never run. Broadcast receivers can be either declared and registered in the manifest or created dynamically in code. Application Fundamentals Declaring components For more about how to structure the manifest file for your application, see the The AndroidManifest.xml File documentation. Application Fundamentals Declaring component capabilities A component informs the system about which intents it can/willing to receive by defining intent filters in its manifest file. Application Fundamentals Declaring component capabilities An example Two set of intent filters have been given In the activity title_notes_list. When request action is sent by other components through an intent, the system will divert the request to here. <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.android.notepad"> <application android:icon="@drawable/app_notes" android:label="@string/app_name"> <provider class=".NotePadProvider" android:authorities="com.google.provider.NotePad" /> <activity class=".NotesList" android:label="@string/title_notes_list"> <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> <intent-filter> <action android:name="android.intent.action.VIEW" /> <action android:name="android.intent.action.EDIT" /> <action android:name="android.intent.action.PICK" /> <category android:name="android.intent.category.DEFAULT" /> <data android:mimeType="vnd.android.cursor.dir/vnd.google.note" /> </intent-filter> …. Application Fundamentals Declaring component capabilities A real example: NotePad from Android SDK The file consist of declaration of application(line 25), provider(line 28), and several activities(line 32-). Inside of each activity is the intent-filter that specifies groups of action to be taken when corresponding intent is received. Application Fundamentals Declaring component capabilities A real example: NotePad from Android SDK Line 113 gives the target SDK (its actually the API level) which is API 4, and minimum SDK which is 3. Application Fundamentals Declaring component capabilities An example an email application with an activity for composing a new email might declare an intent filter in its manifest entry to respond to "send" intents (in order to send email). An activity in your application can then create an intent with the “send” action (ACTION_SEND), which the system matches to the email application’s “send” activity and launches it when you invoke the intent with startActivity(). Application Fundamentals Declaring component capabilities There are two primary forms of intents you will use. Explicit Intents provides the exact class to be run as argument of the intent. Implicit Intents provides enough information for the system to determine which of the available components is best to run for that intent. (√) Application Fundamentals Declaring component capabilities For more about creating intent filters, see the Intents and Intent Filters document. Application Fundamentals Declaring application requirements In addition to the declaration of app’s components, it's important to define special features of your app in your manifest file. Doing this will prevent device that lack of these required features from installing your application from Google Play( formerly Android Market.) Application Fundamentals Declaring application requirements For example, if your application requires a camera and uses APIs introduced in Android 2.1 (API Level 7), you should declare these as requirements in your manifest file. Application Fundamentals Declaring application requirements Important device features that you should consider as you design and develop your application: Screen size and density Input configurations defined as the <uses-configuration> element. Device features (For more information, see the Supporting Multiple Screens document.) defined as the <supports-screens> element. defined as the <uses-feature> element. Platform Version defined as the <uses-sdk> element. Application Fundamentals Application Resources An Android application is composed of codes and resources such as images, audio files, animations, menus, styles, colors, layout of activity user interfaces, and possibly more. Application Fundamentals Application Resources SDK build tools (aapt) define a unique integer ID for most of resources that you include in your Android project, specifically the generated /gen/<packagename>/R.java. Application Fundamentals Application Resources app_notes.png Application Fundamentals Application Resources Application Fundamentals Application Resources The ID can be used to reference the resource from your application code or from other resources defined in XML. Application Fundamentals Application Resources Separating the resources from the code enables you to alternate resources for different device configurations while keeping code unchanged. Application Fundamentals Application Resources For example, Changing the value of hello in strings.xml without making any change to the code, will change the appearance of your application. Application Fundamentals Application Resources For example, Using different language for different location(nation) is a topic called localization and a topic that we will talk about in the future of this class. Android has a smart mechanism to chose proper language for your application as long as the resources is properly provided. Changing the value of hello in strings.xml without making any change to the code, will change the appearance of your application. Conclusion An android app consists of many parts Resources define how the app looks and feels, and code define how the app acts Eclipse and Android SDK pull everything together.
