다른 Activity 시작하기

Starting Another Activity   다른 액티비티 시작하기

 

Previous                     Next

 

This lesson teaches you to  이 단원에서는 다음을 가르칩니다

1.       Respond to the Send Button               Send 버튼에 응답하기

2.       Build an Intent                                       Intent 빌드 하기

3.       Create the Second Activity                  두 번째 액티비티 만들기

4.       Receive the Intent                                 Intent 수신하기

5.       Display the Message                            메시지 표시하기

You should also read

·        Installing the SDK

After completing the previous lesson, you have an app that shows an activity (a single screen) with a text field and a button. In this lesson, you’ll add some code to MainActivity that starts a new activity when the user clicks the Send button.
앞선 단원(previous lesson)을 완료하면, 텍스트 필드(text field)와 단추(button)를 가진 한 activity(단일 화면)를 표시하는 app을 갖게 됩니다. 이 단원에서는 사용자가 Send(전송) 버튼을 클릭하면 새로운 activity를 시작하는 MainActivity.java 파일에 약간의 코드를 추가합니다.

Respond to the Send Button                       Send 버튼에 응답하기

1.       In Android Studio, from the res/layout directory, edit the content_main.xml file.
안드로이드 스튜디오의 res/layout 디렉토리에 있는 content_main.xml 파일을 편집하십시오.

2.       To the <Button> element, add the android:onClick attribute.
<Button>엘리먼트에 android:onClick속성을 추가하십시오.

res/layout/content_main.xml

 

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/button_send"
    android:onClick="sendMessage" />

 

The android:onClick attribute’s value, "sendMessage", is the name of a method in your activity that the system calls when the user clicks the button.
android:onClick 속성 값인 "sendMessage"는 사용자가 버튼을 클릭하면 시스템이 호출하는 activity안의 메소드 이름 입니다.

3.       In the java/com.example.hans.myapplication directory, open the MainActivity.java file.
java/com.example.hans.myapplication 디렉토리에서, MainActivity.java 파일을 여십시오.

4.       Within the MainActivity class, add the sendMessage() method stub shown below.
MainActivity 클래스 안에, 아래의 sendMessage() 메소드 stub를 추가하십시오.

java/com.example.hans.myapplication/MainActivity.java

/** Called when the user clicks the Send button  사용자가 Send 버튼을 클릭하면 호출됨 */
public void sendMessage(View view) {
    // Do something in response to button  버튼에 대한 응답으로 무엇인가를 함
}

In order for the system to match this method to the method name given to android:onClick, the signature must be exactly as shown. Specifically, the method must:
시스템이 이 메소드를 android:onClick에 부여된 메소드 이름과 매칭시켜야 하기 때문에, 아래처럼 signature가 정확 해야 합니다. 특히 메소드는 다음과 같아야 합니다:

o   Be public                                                              public 이어야 함

o   Have a void return value                                        리턴값이 void 이어야 함

o   Have a View as the only parameter (this will be the View that was clicked)   유일한 패러미터로 View를 가져야 함(this는 클릭되었던 View가 될 것임)

Next, you’ll fill in this method to read the contents of the text field and deliver that text to another activity.
다음에, text field의 컨텐츠를 읽도록 하기 위하여 이 메소드 안을 채우면, 해당 text를 다른 activity로 배달할 것입니다.

Build an Intent           Intent 빌드 하기

 

1.   In MainActivity.java, inside the sendMessage() method, create an Intent to start an activity called DisplayMessageActivity with the following code:
MainActivity.java의 sendMessage() 메소드 안에, 다음 코드를 가진 DisplayMessageActivity란 이름의 액티비티를 시작시키기 위한 Intent를 만드십시오:

java/com.example.hans.myapplication/MainActivity.java

public void sendMessage(View view) {
  Intent intent = new Intent(this, DisplayMessageActivity.class);
}

 

Intents

An Intent is an object that provides runtime binding between separate components (such as two activities). The Intent represents an app’s "intent to do something." You can use intents for a wide variety of tasks, but most often they’re used to start another activity. For more information, see Intents and Intent Filters.
Intent는 별개 구성요소(예, 2개의 activity) 간 런타임 바인딩을 제공하는 객체입니다. Intent는 "뭔가를 수행하고자 하는 app의 의도" 입니다. 다양한 작업 용도로 사용할 수 있지만, 다른 activity를 시작하는 용도로 가장 많이 사용됩니다. 자세한 내용은 Intents와 Intent Filters를 참조하십시오.

Note: The reference to DisplayMessageActivity will raise an error if you’re using an IDE such as Android Studio because the class doesn’t exist yet. Ignore the error for now; you’ll create the class soon.
주: 안드로이드 스튜디오와 같은 IDE를 사용할 때 DisplayMessageActivity에 대한 참조는 오류를 발생시키는데, 그 이유는 아직 클래스가 존재하지 않기 때문입니다. 이제 오류를 무시하고; 클래스를 만드십시오.

The constructor used here takes two parameters: 여기 사용된 생성자는 2개의 패러미터를 갖고 있습니다:

o  A Context as its first parameter (this is used because the Activity class is a subclass of Context)
그 첫 패러미터인 Context(Activity 클래스가 Context의 하위클래스 이기 때문에 this가 사용됨)

o  The Class of the app component to which the system should deliver the Intent (in this case, the activity that should be started)
시스템이 Intent (이 경우, 시작되어야 할 activity)를 배달해야 하는 app 구성요소의 Class

Android Studio indicates that you must import the Intent class. 안드로이드 스튜디오는 Intent 클래스를 import 해야 함을 가리킵니다.

2.       At the top of the file, import the Intent class: 파일의 맨 위에, Intent 클래스가 자동으로 import 되어 있습니다:

java/com.example.hans.myapplication/MainActivity.java

import android.content.Intent;

Tip: In Android Studio, press Alt + Enter (option + return on Mac) to import missing classes.
팁: 안드로이드 스튜디어에서, 빠진 클래스들을 import 하려면 Alt + Enter를 누르십시오 (option + return on Mac)

3.       Inside the sendMessage() method, use findViewById() to get the EditText element.
sendMessage() 메소드 안에서, EditText 엘리먼트를 얻기 위하여 findViewById()를 사용하십시오.

java/com.example.hans.myapplication/MainActivity.java

public void sendMessage(View view) {
  Intent intent = new Intent(this, DisplayMessageActivity.class);
  EditText editText = (EditText) findViewById(R.id.edit_message);
}

4.      At the top of the file, import the EditText class.            파일 꼭대기에, EditText class가 자동으로 import 되어 있습니다.
import android.widget.EditText;

In Android Studio, press Alt + Enter (option + return on Mac) to import missing classes.

Android Studio에서, 빠진 클래스들을 import 하려면 Alt + Enter를 누르십시오 (option + return on Mac)

5.       Assign the text to a local message variable, and use the putExtra() method to add its text value to the intent.
local message 변수에 텍스트를 할당하고, intent에 텍스트 값을 추가하기 위하여 putExtra() 메소드를 사용하십시오.

java/com.example.hans.myapplication/MainActivity.java

public void sendMessage(View view) {
  Intent intent = new Intent(this, DisplayMessageActivity.class);
  EditText editText = (EditText) findViewById(R.id.edit_message);
  String message = editText.getText().toString();
  intent.putExtra(EXTRA_MESSAGE, message);
}

An Intent can carry data types as key-value pairs called extras. The putExtra() method takes the key name in the first parameter and the value in the second parameter.
Intent는 extras로 불리는 키-값 쌍으로 데이터 타입을 운반할 수 있습니다. putExtra() method는 첫째 패러미터 안에 키 이름을 취하고, 두 번째 패러미터 안에 값을 취합니다.

6.       At the top of the MainActivity class, add the EXTRA_MESSAGE definition as follows:
MainActivity 클래스의 꼭대기에, 다음과 같이 EXTRA_MESSAGE 정의(definition)를 추가하십시오:

java/com.example.hans.myapplication/MainActivity.java

public class MainActivity extends AppCompatActivity {
    public final static String EXTRA_MESSAGE = "com.example.hans.myapplication.MESSAGE";
    ...
}

For the next activity to query the extra data, you should define the key for your intent's extra using a public constant. It's generally a good practice to define keys for intent extras using your app's package name as a prefix. This ensures the keys are unique, in case your app interacts with other apps.
엑스트라 데이터를 조회하기 위한 다음 액티비티와 관련하여, public 상수를 사용하여 intent의 엑스트라에 대한 키를 정의해야 합니다. 접두사로 앱의 패키지 이름을 사용하여, intent 엑스트라에 대한 키를 정의하는 것은 일반적으로 좋은 습관입니다. 이렇게 하면 앱이 다른 앱과 상호 작용하는 경우, 키의 유일성을 보장합니다.

7.       In the sendMessage() method, to finish the intent, call the startActivity() method, passing it the Intent object created in step 1.
sendMessage() 메소드에서, intent를 종료하려면, startActivity() 메소드를 호출해서, 그것을 스텝1에서 생성된 Intent 객체로 보내십시오.

With this new code, the complete sendMessage() method that's invoked by the Send button now looks like this:
이 새 코드를 가진, Send 버튼이 인보크한 완전한 sendMessage() method는 아래와 같습니다:

java/com.example.hans.myapplication/MainActivity.java

/** Called when the user clicks the Send button */
public void sendMessage(View view) {
    Intent intent = new Intent(this, DisplayMessageActivity.class);
    EditText editText = (EditText) findViewById(R.id.edit_message);
    String message = editText.getText().toString();
    intent.putExtra(EXTRA_MESSAGE, message);
    startActivity(intent);
}

The system receives this call and starts an instance of the Activity specified by the Intent. Now you need to create the DisplayMessageActivity class in order for this to work.
시스템이 this call을 수신하면 Intent가 규정한 Activity의 인스턴스가 시작됩니다. 이제 this가 작동하도록 하기 위하여 DisplayMessageActivity 클래스를 만들어야 합니다.

Create the Second Activity          두 번째 액티비티 만들기

All subclasses of Activity must implement the onCreate() method. This method is where the activity receives the intent with the message, then renders the message. Also, the onCreate() method must define the activity layout with the setContentView() method. This is where the activity performs the initial setup of the activity components.
Activity의 모든 하위클래스는 onCreate() 메소드를 구현해야 합니다. 이 메소드는, 액티비티가 메시지를 가진 intent를 수신하고, 그런 다음 메시지를 렌더링 하는 곳입니다. 또한, onCreate() method는 setContentView () 메소드를 가진 액티비티 레이아웃을 정의해야 합니다. 이것은 액티비티가 액티비티 구성요소의 초기 설정을 수행하는 곳입니다.

 

Create a new activity using Android Studio

Figure 1. The new activity wizard in Android Studio.         안드로이드 스튜디오 내의 신규 액티비티 마법사

Android Studio includes a stub for the onCreate() method when you create a new activity.
Android Studio에는 신규 액티비티를 만들 때 onCreate() method에 대한 stub가 포함됩니다.

1.       In Android Studio, in the java directory, select the package, com.mycompany.myfirstapp, right-click, and select New > Activity > Blank Activity.
Android Studio의, java directory에서, 패키지 com.example.hans.myapplication을 선택한 다음, right-click하고, New > Activity > Blank Activity를 선택하십시오.

2.       In the Choose options window, fill in the activity details:

o   Activity Name: DisplayMessageActivity

o   Layout Name: activity_display_message

o   Title: DisplayMessageActivity

o   Hierarchical Parent: com.mycompany.myfirstapp.MainActivity

o   Package name: com.example.hans.myapplication

Click Finish.

3.       Open the DisplayMessageActivity.java file.  DisplayMessageActivity.java file을 여십시오.

The class already includes an implementation of the required onCreate() method. You will update the implementation of this method later. It also includes an implementation of onOptionsItemSelected(), which handles the app bar's Up behavior. Keep these two methods as they are for now.
요구되는 onCreate() method 구현이 이미 클래스에 포함되어 있습니다. 후에 이 메소드 구현을 업데이트될 것입니다. 이것에는 onOptionsItemSelected()의 구현도 포함되어 있는데, 이것은 app bar의 Up behavior를 처리합니다. Keep these two methods as they are for now.

4.       Remove the onCreateOptionsMenu() method.             onCreateOptionsMenu() method를 제거하십시오.

You won't need it for this app.  이 앱에는 이것이 필요없습니다.

If you're developing with Android Studio, you can run the app now, but not much happens. Clicking the Send button starts the second activity, but it uses a default "Hello world" layout provided by the template. You'll soon update the activity to instead display a custom text view.
안드로이드 스튜디오로 개발하는 경우, 이제 앱을 실행할 수 있지만, 많이는 실행하지 않습니다. 보내기 버튼을 클릭하면 두 번째 액티비티가 시작되지만, 템플릿이 제공하는 기본 "Hello World" 레이아웃을 사용합니다. 곧 대신 사용자 정의 텍스트보기를 표시 할 수 있는 Activity을 업데이트합니다.

Create the activity without Android Studio                  안드로이드 스튜디오 없이 액티비티 만들기

If you're using a different IDE or the command line tools, do the following:

1.       Create a new file named DisplayMessageActivity.java in the project's src/ directory, next to the originalMainActivity.java file.
Create a new file named DisplayMessageActivity.java in the project's src/ directory, next to the originalMainActivity.java file.

2.       Add the following code to the file:

public class DisplayMessageActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_display_message);

        if (savedInstanceState == null) {
            getSupportFragmentManager().beginTransaction()
                .add(R.id.container, new PlaceholderFragment()).commit();
        }
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle app bar item clicks here. The app bar
        // automatically handles clicks on the Hans/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    /**
     * A placeholder fragment containing a simple view.
     */
    public static class PlaceholderFragment extends Fragment {

        public PlaceholderFragment() { }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                  Bundle savedInstanceState) {
              View rootView = inflater.inflate(R.layout.fragment_display_message,
                      container, false);
              return rootView;
        }
    }
}

Note: If you are using an IDE other than Android Studio, your project does not contain theactivity_display_message layout that's requested by setContentView(). That's OK because you will update this method later and won't be using that layout.

3.       To your strings.xml file, add the new activity's title as follows:

<resources>
    ...
    <string name="title_activity_display_message">My Message</string>
</resources>

4.       In your manifest file, AndroidManifest.xml, within the Application element, add the <activity> element for your DisplayMessageActivity class, as follows:

<application ... >
    ...
    <activity
        android:name="com.mycompany.myfirstapp.DisplayMessageActivity"
        android:label="@string/title_activity_display_message"
        android:parentActivityName="com.mycompany.myfirstapp.MainActivity" >
        <meta-data
            android:name="android.support.PARENT_ACTIVITY"
            android:value="com.mycompany.myfirstapp.MainActivity" />
    </activity>
</application>

The android:parentActivityName attribute declares the name of this activity's parent activity within the app's logical hierarchy. The system uses this value to implement default navigation behaviors, such as Up navigation on Android 4.1 (API level 16) and higher. You can provide the same navigation behaviors for older versions of Android by using the Support Library and adding the <meta-data> element as shown here.
android:parentActivityName 속성은 앱의 논리적 계층 내부에서의 이 Activity의 부모 Activity의 이름을 선언합니다. 이 시스템은 안드로이드 4.1 (API 레벨 16) 이상 최대 탐색과 같은 기본 탐색 동작을 구현하기 위해이 값을 사용합니다. Support Library를 사용하여 다음과 같이 <meta-data> 요소를 추가하여 안드로이드의 이전 버전에 대해 동일한 탐색 동작을 제공 할 수 있습니다.

Note: Your Android SDK should already include the latest Android Support Library, which you installed during the Adding SDK Packages step. When using the templates in Android Studio, the Support Library is automatically added to your app project (you can see the library's JAR file listed under Android Dependencies). If you're not using Android Studio, you need to manually add the library to your project—follow the guide for setting up the Support Library then return here.
참고: 안드로이드 SDK는 이미 추가 SDK 패키지 단계에서 설치한 최신 안드로이드 지원 라이브러리를 포함해야 합니다. 안드로이드 스튜디오에서 템플릿을 사용하는 경우, 지원 라이브러리가 자동으로 앱 프로젝트에 추가됩니다(라이브러리의 JAR 파일은 안드로이드 종속성 아래에 나열 볼 수 있습니다). 안드로이드 스튜디오를 사용하지 않는 경우, 수동으로에 라이브러리를 추가할 필요가 여기에 반환 지원 라이브러리를 forsetting 가이드를 프로젝트 수행합니다.

If you're using a different IDE than Android Studio, don't worry that the app won't yet compile. You'll soon update the activity to display a custom text view.
If you're using a different IDE than Android Studio, don't worry that the app won't yet compile. You'll soon update the activity to display a custom text view

Receive the Intent      Intent 수신하기

Every Activity is invoked by an Intent, regardless of how the user navigated there. You can get the Intent that started your activity by calling getIntent() and retrieve the data contained within the intent.
모든 Activity는 사용자가 거기를 네비게이트하는 방법과 관련없이, Intent에 의하여 인보크됩니다. You can get the Intent that started your activity by calling getIntent() and retrieve the data contained within the intent.

1.       In the java/com.mycompany.myfirstapp directory, edit the DisplayMessageActivity.java file.
In the java/com.mycompany.myfirstapp directory, edit the DisplayMessageActivity.java file

2.       In the onCreate() method, remove the following line:    onCreate() method 안에서 다음 라인을 제거하십시오.

  setContentView(R.layout.activity_display_message);

3.       Get the intent and assign it to a local variable.             Intent를 얻은 다음 그것을 로컬 변수에 할당하십시오.

Intent intent = getIntent();

4.       At the top of the file, import the Intent class.                파일 꼭대기에 Intent 클래스가 자동으로 import 되어 있습니다.

In Android Studio, press Alt + Enter (option + return on Mac) to import missing classes.

5.       Extract the message delivered by MainActivity with the getStringExtra() method.
getStringExtra() method로 MainActivity가 배달한 메시지를 추출하십시오.

String message = intent.getStringExtra(MainActivity.EXTRA_MESSAGE);

Display the Message                   메시지 표시하기

 

1.       In the onCreate() method, create a TextView object.

TextView textView = new TextView(this);

2.       Set the text size and message with setText().

textView.setTextSize(40);
textView.setText(message);

3.       Then add the TextView as the root view of the activity’s layout by passing it to setContentView().

setContentView(textView);

4.       At the top of the file, import the TextView class.

In Android Studio, press Alt + Enter (option + return on Mac) to import missing classes.

The complete onCreate() method for DisplayMessageActivity now looks like this:

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    // Get the message from the intent  intent로부터 메시지를 가져옵니다
    Intent intent = getIntent();
    String message = intent.getStringExtra(MainActivity.EXTRA_MESSAGE);

    // Create the text view text view를 만듭니다
    TextView textView = new TextView(this);
    textView.setTextSize(40);
    textView.setText(message);

    // Set the text view as the activity layout              액티비티 레이아웃으로 text view를 설정합니다
    setContentView(textView);
}

You can now run the app. When it opens, type a message in the text field, click Send, and the message appears on the second activity.
이제 앱을 가동할 수 있습니다. 이것이 열리면 텍스트 필드에 메시지를 타입하고, Send를 클릭하면, 두 번째 activity에 메시지가 나타납니다.

 

Figure 2. Both activities in the final app, running on Android 4.4.

That's it, you've built your first Android app!

To learn more, follow the link below to the next class.

 

Next class: Supporting Different Devices

 

public abstract class

Context

extends Object

 

java.lang.Object
↳	android.content.Context

 

Known Direct Subclasses ContextWrapper, MockContext ContextWrapper Proxying implementation of Context that simply delegates all of its calls to another Context.  MockContext A mock Context class.

 

Known Indirect Subclasses AbstractInputMethodService, AccessibilityService, AccountAuthenticatorActivity, ActionBarActivity, Activity, ActivityGroup, AliasActivity, AppCompatActivity, Application, BackupAgent, BackupAgentHelper, CameraPrewarmService, CarrierMessagingService, and 38 others. AbstractInputMethodService AbstractInputMethodService provides a abstract base class for input methods.  AccessibilityService An accessibility service runs in the background and receives callbacks by the system when AccessibilityEvents are fired.  AccountAuthenticatorActivity Base class for implementing an Activity that is used to help implement an AbstractAccountAuthenticator.  ActionBarActivity This class is deprecated. Use AppCompatActivity instead.   Activity An activity is a single, focused thing that the user can do.  ActivityGroup This class was deprecated in API level 13. Use the new Fragment and FragmentManager APIs instead; these are also available on older platforms through the Android compatibility package.   AliasActivity Stub activity that launches another activity (and then finishes itself) based on information in its component's manifest meta-data.  AppCompatActivity Base class for activities that use the support library action bar features.  Application Base class for those who need to maintain global application state.  BackupAgent Provides the central interface between an application and Android's data backup infrastructure.  BackupAgentHelper A convenient BackupAgent wrapper class that automatically manages heterogeneous data sets within the backup data, each identified by a unique key prefix.  CameraPrewarmService Extend this class to implement a camera prewarm service.  CarrierMessagingService A service that receives calls from the system when new SMS and MMS are sent or received.  CarrierService A service that exposes carrier-specific functionality to the system.  ChooserTargetService A service that receives calls from the system when the user is asked to choose a target for an intent explicitly by another app.  ConnectionService An abstract service that should be implemented by any apps which can make phone calls (VoIP or otherwise) and want those calls to be integrated into the built-in phone app.  CustomTabsService Abstract service class for implementing Custom Tabs related functionality.  DreamService Extend this class to implement a custom dream (available to the user as a "Daydream").  ExpandableListActivity An activity that displays an expandable list of items by binding to a data source implementing the ExpandableListAdapter, and exposes event handlers when the user selects an item.  FragmentActivity Base class for activities that want to use the support-based Fragment and Loader APIs.  HostApduService HostApduService is a convenience Service class that can be extended to emulate an NFC card inside an Android service component.  InCallService This service is implemented by any app that wishes to provide the user-interface for managing phone calls.  InputMethodService InputMethodService provides a standard implementation of an InputMethod, which final implementations can derive from and customize.  IntentService IntentService is a base class for Services that handle asynchronous requests (expressed as Intents) on demand.  IsolatedContext A mock context which prevents its users from talking to the rest of the device while stubbing enough methods to satify code that tries to talk to other packages.  JobService Entry point for the callback from the JobScheduler.  LauncherActivity Displays a list of all activities which can be performed for a given intent.  ListActivity An activity that displays a list of items by binding to a data source such as an array or Cursor, and exposes event handlers when the user selects an item.  MediaBrowserService Base class for media browse services.  MediaRouteProviderService Base class for media route provider services.  MidiDeviceService A service that implements a virtual MIDI device.  MockApplication A mock Application class.  MultiDexApplication Minimal MultiDex capable application.  MutableContextWrapper Special version of ContextWrapper that allows the base context to be modified after it is initially set.  NativeActivity Convenience for implementing an activity that will be implemented purely in native code.  NotificationCompatSideChannelService Abstract service to receive side channel notifications sent from NotificationManagerCompat.  NotificationListenerService A service that receives calls from the system when new notifications are posted or removed, or their ranking changed.  OffHostApduService OffHostApduService is a convenience Service class that can be extended to describe one or more NFC applications that are residing off-host, for example on an embedded secure element or a UICC.  PreferenceActivity This is the base class for an activity to show a hierarchy of preferences to the user.  PrintService This is the base class for implementing print services.  RecognitionService This class provides a base class for recognition service implementations.  RemoteViewsService The service to be connected to for a remote adapter to request RemoteViews.  RenamingDelegatingContext This is a class which delegates to the given context, but performs database and file operations with a renamed database/file name (prefixes default names with a given prefix).  Service A Service is an application component representing either an application's desire to perform a longer-running operation while not interacting with the user or to supply functionality for other applications to use.  SettingInjectorService Dynamically specifies the enabled status of a preference injected into the list of app settings displayed by the system settings app For use only by apps that are included in the system image, for preferences that affect multiple apps.  SpellCheckerService SpellCheckerService provides an abstract base class for a spell checker.  TabActivity This class was deprecated in API level 13. New applications should use Fragments instead of this class; to continue to run on older devices, you can use the v4 support library which provides a version of the Fragment API that is compatible down to DONUT.   TextToSpeechService Abstract base class for TTS engine implementations.  TvInputService The TvInputService class represents a TV input or source such as HDMI or built-in tuner which provides pass-through video or broadcast TV programs.  VoiceInteractionService Top-level service of the current global voice interactor, which is providing support for hotwording, the back-end of a VoiceInteractor, etc.  VoiceInteractionSessionService An active voice interaction session, initiated by a VoiceInteractionService.  VpnService VpnService is a base class for applications to extend and build their own VPN solutions.  WallpaperService A wallpaper service is responsible for showing a live wallpaper behind applications that would like to sit on top of it.

Class Overview

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Interface to global information about an application environment. This is an abstract class whose implementation is provided by the Android system. It allows access to application-specific resources and classes, as well as up-calls for application-level operations such as launching activities, broadcasting and receiving intents, etc.
애플리케이션 환경에 대한 글로벌 정보에 대한 Interface. Context는 안드로이드 시스템이 제공하는 구현인 추상 클래스 입니다. Context를 이용하면, activity시작, intent 방송 및 수신 등과 같은 애플리케이션-레벨 운영에 대한 up-call은 물론, 애플리케이션-특정 리소스 및 클래스에 대한 접근이 가능하게 됩니다.

Summary

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Constants
String	ACCESSIBILITY_SERVICE	Use with getSystemService(Class) to retrieve a AccessibilityManager for giving the user feedback for UI events through the registered event listeners.
String	ACCOUNT_SERVICE	Use with getSystemService(Class) to retrieve a AccountManager for receiving intents at a time of your choosing.
String	ACTIVITY_SERVICE	Use with getSystemService(Class) to retrieve a ActivityManager for interacting with the global system state.
String	ALARM_SERVICE	Use with getSystemService(Class) to retrieve a AlarmManager for receiving intents at a time of your choosing.