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天涯何處無幹話，何必要講實務話

SystemService

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 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
setShowRunningNotification(boolean show) 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
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