系統級的 Service，以 Notification 為例，取得的方法如下：
NotificationManager nm = (NotificationManager) getSystemService(NOTIFICATION_SERVICE)每個 Service 和 Class 名稱都有對應，這在[官方說明](http://developer.android.com/reference/android/content/Context.html#getSystemService(java.lang.String) getSystemService() 方法裡面都有寫。
條列如下：
| Class Name | Constant Name | Description | API Level |
|---|---|---|---|
| AccessibilityManager | ACCESSIBILITY_SERVICE | 4 | |
| AccountManager | ACCOUNT_SERVICE | 5 | |
| ActivityManager | ACTIVITY_SERVICE | 1 | |
| AlarmManager | ALARM_SERVICE | 1 | |
| AppOpsManager | APP_OPS_SERVICE | 19 | |
| AudioManager | AUDIO_SERVICE | 1 | |
| BluetoothAdapter | BLUETOOTH_SERVICE | 18 | |
| CaptioningManager | CAPTIONING_SERVICE | 19 | |
| ClipboardManager | CLIPBOARD_SERVICE | 1 | |
| ConnectivityManager | CONNECTIVITY_SERVICE | 1 | |
| ConsumerIrManager | CONSUMER_IR_SERVICE | 19 | |
| DevicePolicyManager | DEVICE_POLICY_SERVICE | 8 | |
| DisplayManager | DISPLAY_SERVICE | 17 | |
| framework:android:systemservice:downloadmanager | DOWNLOAD_SERVICE | 9 | |
| DropBoxManager | DROPBOX_SERVICE | 8 | |
| InputMethodManager | INPUT_METHOD_SERVICE | 3 | |
| InputManager | INPUT_SERVICE | 16 | |
| KeyguardManager | KEYGUARD_SERVICE | 1 | |
| LayoutInflater | LAYOUT_INFLATER_SERVICE | 1 | |
| LocationManager | LOCATION_SERVICE | 1 | |
| MediaRouter | MEDIA_ROUTER_SERVICE | 16 | |
| NfcManager | NFC_SERVICE | 10 | |
| NotificationManager | NOTIFICATION_SERVICE | 1 | |
| NsdManager | NSD_SERVICE | 16 | |
| PowerManager | POWER_SERVICE | 1 | |
| PrintManager | PRINT_SERVICE | 19 | |
| SearchManager | SEARCH_SERVICE | 1 | |
| SensorManager | SENSOR_SERVICE | 1 | |
| StorageManager | STORAGE_SERVICE | 9 | |
| TelephonyManager | TELEPHONY_SERVICE | 1 | |
| TextServicesManager | TEXT_SERVICES_MANAGER_SERVICE | 14 | |
| UiModeManager | UI_MODE_SERVICE | 8 | |
| UsbManager | USB_SERVICE | 12 | |
| UserManager | USER_SERVICE | 17 | |
| WallpaperService | WALLPAPER_SERVICE | 1 | |
| WifiP2pManager | WIFI_P2P_SERVICE | 14 | |
| WifiManager | WIFI_SERVICE | 1 | |
| WindowManager | WINDOW_SERVICE | 1 |
DownloadManager
DownloadManager 提供相關的 class 如下：
| Class Name | Description |
|---|---|
| DownloadManager | 下載管理器 |
| DownloadManager.Query | 查詢下載的訊息 |
| DownloadManager.Request | 請求下載的詳細內容 |
Start
首先要能下載，第一步是需要權限，在 AndroidManifest.xml加入以下權限：
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />DownloadManager 是系統層級的 Service，所以要在 Activity 下用 getSystemService() 取得
DownloadManager downloadManager = (DownloadManager) getSystemService(DOWNLOAD_SERVICE);再來是初始化 Request
String url = "http://www.example.com/file.zip";
DownloadManager.Request request = new DownloadManager.Request(url);
// 設定request
request.setTitle("Title");
request.setDescription("Description");
// 排程下載，並取得唯一碼
long downloadId = downloadManager.enqueue(request);設定 request 的 method 如下，下面每個 method 都可 chaining
| Method | Description |
|---|---|
| addRequestHeader(String header, String value) | 設定 HTTP 表頭 |
| setAllowedNetworkTypes(int flags) | 允許下載的網路型態為何，可以為 NETWORK_MOBILE和NETWORK_WIFI |
| setAllowedOverMetered(boolean allow) | 是否允許計量網路下載 |
| setAllowedOverRoaming(boolean allowed) | 是否允許漫遊時下載，預設是true |
| setDescription(CharSequence description) | 通知訊息裡的小字 |
| setDestinationInExternalFilesDir(Context context, String dirType, String subPath) | 設定檔案存放位置，使用系統的目錄 |
| setDestinationInExternalPublicDir(String dirType, String subPath) | 設定檔案存放位置，使用自定的目錄 |
| setDestinationUri(Uri uri) | 直接用 Uri 當存檔位置 |
| setMimeType(String mimeType) | 設定檔案的 MimeType。下載完成要開檔案時，即會用這個 MimeType 開啟 |
| setNotificationVisibility(int visibility) | 設定通知列是否顯示 Android Developer有說明傳入值為何 |
| deprecated in API level 11 | |
| setTitle(CharSequence title) | 通知訊息裡的標題 |
| setVisibleInDownloadsUi(boolean isVisible) | 是否要在系統的下載頁面出現 |
在 setNotificationVisibility() 時，設定成 VISIBILITY_HIDDEN 時，要記得加入權限：
<uses-permission android:name="android.permission.DOWNLOAD_WITHOUT_NOTIFICATION" />否則會出現錯誤訊息：
java.lang.SecurityException: Invalid value for visibility: 2