Android 獲取SD卡路徑：
外置sd卡路徑，也許很多同學在平時的工作中并不會用到，因為現在很多機型都不支持外置sd卡(這也是Google目標)，所以并不用考慮外置sd卡的路徑問題。除了開發文件管理類的應用之外，其他應用使用 Enviroment 這個類中的一些靜態方法就能滿足需要。但也有一些特殊需求需要用到外置sd卡路徑，那怎么才能準確獲得外置sd卡的路徑呢？
方法一
//內置sd卡路徑String sdcardPath = System.getenv("EXTERNAL_STORAGE"); //內置sd卡路徑String sdcardPath = Environment.getExternalStorageDirectory().getAbsolutePath();//外置置sd卡路徑String extSdcardPath = System.getenv("SECONDARY_STORAGE");在Enviroment類的源碼中獲得sd卡路徑其實也是通過 System.getnv() 方法來實現的，如隱藏的方法:/** {@hide} */public static File getLegacyExternalStorageDirectory() { return new File(System.getenv(ENV_EXTERNAL_STORAGE));} 注：更詳細的內容還是去看Enviroment源碼。
另外要注意的是，在API 23版本中 SECONDARY_STORAGE 被移除。
方法二
private static String getStoragePath(Context mContext, boolean is_removale) { StorageManager mStorageManager = (StorageManager) mContext.getSystemService(Context.STORAGE_SERVICE); Class<?> storageVolumeClazz = null; try { storageVolumeClazz = Class.forName("android.os.storage.StorageVolume"); Method getVolumeList = mStorageManager.getClass().getMethod("getVolumeList"); Method getPath = storageVolumeClazz.getMethod("getPath"); Method isRemovable = storageVolumeClazz.getMethod("isRemovable"); Object result = getVolumeList.invoke(mStorageManager); final int length = Array.getLength(result); for (int i = 0; i < length; i++) { Object storageVolumeElement = Array.get(result, i); String path = (String) getPath.invoke(storageVolumeElement); boolean removable = (Boolean) isRemovable.invoke(storageVolumeElement); if (is_removale == removable) { return path; } } } catch (ClassNotFoundException e) { e.printStackTrace(); } catch (InvocationTargetException e) { e.printStackTrace(); } catch (NoSuchMethodException e) { e.printStackTrace(); } catch (IllegalAccessException e) { e.printStackTrace(); } return null;}通過反射的方式使用在sdk中被 隱藏 的類 StroageVolume 中的方法getVolumeList()，獲取所有的存儲空間（Stroage Volume），然后通過參數is_removable控制，來獲取內部存儲和外部存儲（內外sd卡）的路徑，參數 is_removable為false時得到的是內置sd卡路徑，為true則為外置sd卡路徑。
在API 23 Enviroment 類中的內部類 UserEnvironment 中有一方法getExternalDirs與此一樣，代碼如下：
public File[] getExternalDirs() { final StorageVolume[] volumes = StorageManager.getVolumeList(mUserId,StorageManager.FLAG_FOR_WRITE); final File[] files = new File[volumes.length]; for (int i = 0; i < volumes.length; i++) { files[i] = volumes[i].getPathFile(); } return files;}再看Enviroment的getExternalStorageDirectory方法實現：
public static File getExternalStorageDirectory() { throwIfUserRequired(); return sCurrentUser.getExternalDirs()[0];}可以看出，在API 23時，先是通過getExternalDirs()獲取到所有存儲空間的File[]數組，這個數組的第一個值：getExternalDirs()[0]，即為內置sd卡所在路徑。
而在API 23 之前的版本中，并沒有類似getExternalDirs()的方法通過StorageVolume直接獲得存儲空間(Storage Volume)，而時通過別的方式來實現的，看關鍵方法的源碼：
public static File getExternalStorageDirectory() { throwIfUserRequired(); return sCurrentUser.getExternalDirsForApp()[0];}這里的 getExternalDirsForApp() 和上面的 getExternalDirs() 的作用是一樣的，都是得到所有存儲空間的File[]數組。
public File[] getExternalDirsForApp() { return mExternalDirsForApp;}mExternalDirsForApp 是在 Enviroment 類中的內部類 UserEnvironment 的構造方法中初始化的，Enviroment#UserEnvironment構造函數源碼如下：
public UserEnvironment(int userId) { // See storage config details at http://source.android.com/tech/storage/ String rawExternalStorage = System.getenv(ENV_EXTERNAL_STORAGE); String rawEmulatedSource = System.getenv(ENV_EMULATED_STORAGE_SOURCE); String rawEmulatedTarget = System.getenv(ENV_EMULATED_STORAGE_TARGET); String rawMediaStorage = System.getenv(ENV_MEDIA_STORAGE); if (TextUtils.isEmpty(rawMediaStorage)) { rawMediaStorage = "/data/media"; } ArrayList<File> externalForVold = Lists.newArrayList(); ArrayList<File> externalForApp = Lists.newArrayList(); if (!TextUtils.isEmpty(rawEmulatedTarget)) { // Device has emulated storage; external storage paths should have // userId burned into them. final String rawUserId = Integer.toString(userId); final File emulatedSourceBase = new File(rawEmulatedSource); final File emulatedTargetBase = new File(rawEmulatedTarget); final File mediaBase = new File(rawMediaStorage); // /storage/emulated/0 externalForVold.add(buildPath(emulatedSourceBase, rawUserId)); externalForApp.add(buildPath(emulatedTargetBase, rawUserId)); // /data/media/0 mEmulatedDirForDirect = buildPath(mediaBase, rawUserId); } else { // Device has physical external storage; use plain paths. if (TextUtils.isEmpty(rawExternalStorage)) { Log.w(TAG, "EXTERNAL_STORAGE undefined; falling back to default"); rawExternalStorage = "/storage/sdcard0"; } // /storage/sdcard0 externalForVold.add(new File(rawExternalStorage)); externalForApp.add(new File(rawExternalStorage)); // /data/media mEmulatedDirForDirect = new File(rawMediaStorage); } // Splice in any secondary storage paths, but only for owner final String rawSecondaryStorage = System.getenv(ENV_SECONDARY_STORAGE); if (!TextUtils.isEmpty(rawSecondaryStorage) && userId == UserHandle.USER_OWNER) { for (String secondaryPath : rawSecondaryStorage.split(":")) { externalForVold.add(new File(secondaryPath)); externalForApp.add(new File(secondaryPath)); } } mExternalDirsForVold = externalForVold.toArray(new File[externalForVold.size()]); mExternalDirsForApp = externalForApp.toArray(new File[externalForApp.size()]); }也可以根據這個方法得到一個獲取所有存儲空間的路徑的方法getStorageDirectories()：
/** * Returns all available SD-Cards in the system (include emulated) * <p/> * Warning: Hack! Based on Android source code of version 4.3 (API 18) * Because there is no standard way to get it. * TODO: Test on future Android versions 4.4+ * * @return paths to all available SD-Cards in the system (include emulated) */ private static final Pattern DIR_SEPARATOR = Pattern.compile("/"); public List<String> getStorageDirectories() { // Final set of paths final ArrayList<String> rv = new ArrayList<String>(); // Primary physical SD-CARD (not emulated) final String rawExternalStorage = System.getenv("EXTERNAL_STORAGE"); // All Secondary SD-CARDs (all exclude primary) separated by ":" final String rawSecondaryStoragesStr = System.getenv("SECONDARY_STORAGE"); // Primary emulated SD-CARD final String rawEmulatedStorageTarget = System.getenv("EMULATED_STORAGE_TARGET"); if (TextUtils.isEmpty(rawEmulatedStorageTarget)) { // Device has physical external storage; use plain paths. if (TextUtils.isEmpty(rawExternalStorage)) { // EXTERNAL_STORAGE undefined; falling back to default. rv.add("/storage/sdcard0"); } else { rv.add(rawExternalStorage); } } else { // Device has emulated storage; external storage paths should have // userId burned into them. final String rawUserId; if (Build.VERSION.SDK_INT < Build.VERSION_CODES.JELLY_BEAN_MR1) { rawUserId = ""; } else { final String path = Environment.getExternalStorageDirectory().getAbsolutePath(); final String[] folders = DIR_SEPARATOR.split(path); final String lastFolder = folders[folders.length - 1]; boolean isDigit = false; try { Integer.valueOf(lastFolder); isDigit = true; } catch (NumberFormatException ignored) { } rawUserId = isDigit ? lastFolder : ""; } // /storage/emulated/0[1,2,...] if (TextUtils.isEmpty(rawUserId)) { rv.add(rawEmulatedStorageTarget); } else { rv.add(rawEmulatedStorageTarget + File.separator + rawUserId); } } // Add all secondary storages if (!TextUtils.isEmpty(rawSecondaryStoragesStr)) { // All Secondary SD-CARDs splited into array final String[] rawSecondaryStorages = rawSecondaryStoragesStr.split(File.pathSeparator); Collections.addAll(rv, rawSecondaryStorages); } rootmode = Sp.getBoolean("rootmode", false); if (rootmode) rv.add("/"); File usb = getUsbDrive(); if (usb != null && !rv.contains(usb.getPath())) rv.add(usb.getPath()); return rv; }public File getUsbDrive() { File parent; parent = new File("/storage"); try { for (File f : parent.listFiles()) { if (f.exists() && f.getName().toLowerCase().contains("usb") && f.canExecute()) { return f; } } } catch (Exception e) { } parent = new File("/mnt/sdcard/usbStorage"); if (parent.exists() && parent.canExecute()) return (parent); parent = new File("/mnt/sdcard/usb_storage"); if (parent.exists() && parent.canExecute()) return parent; return null; }綜上分析，通過方法一和方法二都可以正確的獲取內外sd卡路徑，但方法一會存在以下問題：
1、API>=23 時方法一無效（暫未測試）
2、有些廠商的Rom改動太多，對相關原生API的支持存在問題，這時方法一可能會存在問題。
3、其他一些情況造成的原因（基本與2差不多，是ROM等因素造成的）
所以，在使用時建議使用方法二來獲取內外置sd卡路徑，在API 23（Android 6.0）之前使用getStorageDirectories() 應該也是OK的。
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