Android 應用界面開發筆記 Service

Service

- A service is a application component that can perform long-run operations in the background and does not provide a user interface. 
- A service is not a separate process, nor a thread 

2 forms: start; bind

* Service not newed as a service file needs to be declared in Manifest
service較之activity有更高優先級，並且可以在後臺運行，不需要界面

-新建Service 可以new a service (系統會自動在manifest裏註冊，enabled, exported included), 自己new一個service class需要手動在manifest裏註冊

onStart() 已棄用，由onStartCommand() 代替

@Override
public int onStartCommand(Intent intent, int flags, int startId) {
    Log.i(TAG, "onStartCommand");
    return super.onStartCommand(intent, flags, startId);

}

-新建一個MusicServiceActivity，裏面包含Start和Stop兩個按鈕
create an activity, implements OnClickListener()
在onClick()

設置兩個按鈕的點擊事件：
            public class MusicServiceActivity extends Activity implements View.OnClickListener{

    private Button mStartButton;
    private Button mStopButton;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.music_service_activity);
        mStartButton = (Button)findViewById(R.id.start);
        mStopButton = (Button)findViewById(R.id.stop);
        
        mStartButton.setOnClickListener(this);
        mStartButton.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        switch (v.getId()){
            case R.id.start:
                break;
            case R.id.stop:
                break;
        }
            
    }
}

自帶startService() 和 stopService() 功能

  @Override
  public void onClick(View v) {
      switch (v.getId()){
          case R.id.start:
              startService(new Intent(MusicServiceActivity.this,MusicService.class));
              break;
          case R.id.stop:
              stopService(new Intent(MusicServiceActivity.this,MusicService.class));
              break;
      }

  }

Run the project, "start" "stop" buttons clicked, no response

- go to service file, set TAG 

@Override
public int onStartCommand(Intent intent, int flags, int startId) {
Log.i(TAG, "onStartCommand"); //Q: 這句LOG的位置如果放在下面這句後面會提示"unreachable statement"
return super.onStartCommand(intent, flags, startId);

}

再次run之後運行停止，發現問題，activity未註冊

03-21 07:23:52.494 396-396/naomi.edna.weekfourservice E/AndroidRuntime: android.content.ActivityNotFoundException: Unable to find explicit activity class {naomi.edna.weekfourservice/naomi.edna.weekfourservice.MusicServiceActivity}; have you declared this activity in your AndroidManifest.xml?

------26th March update

to change the font of the codes, -file-settings-editor-colors & fonts - font - click "save as", then create your own preference 

* onCreate()方法裏面含兩個參數--TBD 

在service下面放進去音樂之後，start() 音樂，.mp3 未關聯，文件的關聯可以通過file-settings-editor-file type來修改

--後來才知道，其實音樂文件關聯，文件名全改成小寫就可以解決問題

--manifest如果重複註冊，會error 

kill adb.exe 快捷鍵 ctrl + shift + A 

Service life cycle:

startService() - onCreate() - onStartCommand() - ServiceRunning - onDestroy() [unbounded service]

bindService() - onCreate() - onBind() - Clients are bound to Service - onUnbind() - onDestroy() [bounded]

bind/unbind - to replace start n stop 

helps to interact/communicate with service - activity 

->iBinder, create an inner class 

->lifecycle - a bound service can only be destroyed before unbind. 

---------------補充閱讀---------------

//  processes vs. threads  

http://developer.android.com/guide/components/processes-and-threads.html

// Thread 

http://developer.android.com/reference/java/lang/Thread.html

// App Manifest intro: 
http://developer.android.com/guide/topics/manifest/manifest-intro.html


//found some general answers on Quora, asking about how to become an Android developer from scratch, resources provided, could be useful: 

https://www.quora.com/How-do-I-get-started-with-Android-application-development?redirected_qid=4510292