編輯：關於Android編程
以前的Android(4.1之前的版本)中，SDcard跟路徑通過“/sdcard”或者“/mnt/sdcard”來表示存儲卡，而在Jelly Bean系統中修改為了“/storage/sdcard0”，以後可能還會有多個SDcard的情況。
目前為了保持和之前代碼的兼容，sdcard路徑做了link映射。
為了使您的代碼更加健壯並且能夠兼容以後的Android版本和新的設備，請通過Environment.getExternalStorageDirect
Environment.getExternalStorageDirectory().getPath()當外置sd卡不存在的情況下，這條語句是獲取的內置sd卡的路徑。外置sd卡存在，獲取是外置sd卡。獲取出來的值是/storage/sdcard0
public static String getSoftwareStorageDirectory() {
Map sysInfo=System.getenv();
//獲取外置的sd卡
String sd_defult = sysInfo.get("SECONDARY_STORAGE");
return sd_defult;
}
獲取出來的值是/storage/sdcard1，看序號一個是0，一個是1。我在網上看到有人說，這種獲取方法，在api23中將不存在，我還沒驗證，沒有相應 的機子測試，以及查看api23的源碼。就是這個字段在API 23版本中 SECONDARY_STORAGE 被移除。這種獲取方法也是類似於源碼獲取方式。
調試時候Map
{ANDROID_SOCKET_zygote=9,
SECONDARY_STORAGE=/storage/sdcard1,
ANDROID_STORAGE=/storage, ANDROID_BOOTLOGO=1,
EXTERNAL_STORAGE=/storage/sdcard0,
ANDROID_ASSETS=/system/app,
ASEC_MOUNTPOINT=/mnt/asec,
PATH=/sbin:/vendor/bin:/system/sbin:/system/bin:/system/xbin,
LOOP_MOUNTPOINT=/mnt/obb,
BOOTCLASSPATH=/system/framework/core.jar:/system/framework/core-junit.jar:
/system/framework/bouncycastle.jar:/system/framework/ext.jar:/system/framework/framework.jar:
/system/framework/telephony-common.jar:/system/framework/mms-common.jar:
/system/framework/android.policy.jar:/system/framework/services.jar:
/system/framework/apache-xml.jar:/system/framework/mediatek-common.jar:
/system/framework/mediatek-framework.jar:/system/framework/secondary-framework.jar:
/system/framework/CustomProperties.jar:/system/framework/mediatek-telephony-common.jar:
/system/framework/mediatek-op.jar,
ANDROID_DATA=/data,
ANDROID_PROPERTY_WORKSPACE=8,49664,
ANDROID_ROOT=/system,
LD_LIBRARY_PATH=/vendor/lib:/system/lib}
api17源碼，部分源碼Environment
private static final String ENV_EXTERNAL_STORAGE = "EXTERNAL_STORAGE";
private static final String ENV_EMULATED_STORAGE_SOURCE = "EMULATED_STORAGE_SOURCE";
private static final String ENV_EMULATED_STORAGE_TARGET = "EMULATED_STORAGE_TARGET";
private static final String ENV_MEDIA_STORAGE = "MEDIA_STORAGE";
public UserEnvironment(int userId) {
// See storage config details at http://source.android.com/tech/storage/
String rawExternalStorage = System.getenv(ENV_EXTERNAL_STORAGE);
String rawEmulatedStorageTarget = System.getenv(ENV_EMULATED_STORAGE_TARGET);
String rawMediaStorage = System.getenv(ENV_MEDIA_STORAGE);
if (TextUtils.isEmpty(rawMediaStorage)) {
rawMediaStorage = "/data/media";
}
if (!TextUtils.isEmpty(rawEmulatedStorageTarget)) {
// Device has emulated storage; external storage paths should have
// userId burned into them.
final String rawUserId = Integer.toString(userId);
final File emulatedBase = new File(rawEmulatedStorageTarget);
final File mediaBase = new File(rawMediaStorage);
// /storage/emulated/0
mExternalStorage = buildPath(emulatedBase, rawUserId);
// /data/media/0
mMediaStorage = 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
mExternalStorage = new File(rawExternalStorage);
// /data/media
mMediaStorage = new File(rawMediaStorage);
}
mExternalStorageAndroidObb = buildPath(mExternalStorage, DIRECTORY_ANDROID, "obb");
mExternalStorageAndroidData = buildPath(mExternalStorage, DIRECTORY_ANDROID, "data");
mExternalStorageAndroidMedia = buildPath(mExternalStorage, DIRECTORY_ANDROID, "media");
}
在上面的源碼當中String sdcardPath = System.getenv("EXTERNAL_STORAGE"); 獲取也是外置sd卡。
可是在源碼中也是沒有看到String extSdcardPath = System.getenv("SECONDARY_STORAGE"); 。SECONDARY_STORAGE這個變量是沒有，我也納悶，怎麼也可以使用。這就有點疑問了。
獲取外置sd卡是否存在的源碼
/**
* Gets the current state of the primary "external" storage device.
*
* @see #getExternalStorageDirectory()
*/
public static String getExternalStorageState() {
try {
IMountService mountService = IMountService.Stub.asInterface(ServiceManager
.getService("mount"));
final StorageVolume primary = getPrimaryVolume();
return mountService.getVolumeState(primary.getPath());
} catch (RemoteException rex) {
Log.w(TAG, "Failed to read external storage state; assuming REMOVED: " + rex);
return Environment.MEDIA_REMOVED;
}
}
一些映射關系
private static StorageVolume getPrimaryVolume() {
if (sPrimaryVolume == null) {
synchronized (sLock) {
if (sPrimaryVolume == null) {
try {
IMountService mountService = IMountService.Stub.asInterface(ServiceManager
.getService("mount"));
final StorageVolume[] volumes = mountService.getVolumeList();
sPrimaryVolume = StorageManager.getPrimaryVolume(volumes);
} catch (Exception e) {
Log.e(TAG, "couldn't talk to MountService", e);
}
}
}
}
return sPrimaryVolume;
}
那麼，在android上是怎麼判斷的。
/**
* getExternalStorageState() returns MEDIA_CHECKING if the media is present and being disk-checked
* 要獲取SD卡首先要確認SD卡是否裝載
* @return
*/
public boolean getExternalStorageState(){
return Environment.getExternalStorageState().equals(Environment.MEDIA_CHECKING);
}
判斷是都可以讀寫
/**
* getExternalStorageState() returns MEDIA_MOUNTED
* if the media is present and mounted at its mount point with read/write access.
* 要獲取SD卡是否可以讀寫
* @return
*/
public boolean getExternalStorageStateMOUNTED(){
return Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED);
}
這裡判斷讀寫跟判斷是都存在是有歧義的，我測試時候，沒有放sd卡，判斷讀寫是可以的，可是外置sd卡根本不存在。寫程序時候是不是先要判斷存在，再判斷能不能讀寫。
還有一個問題就是，既然外置sd卡不存在時候Environment.getExternalStorageDirectory().getPath()這條語句獲取的是內置的sd卡，那麼判斷是否是內置sd卡的讀寫呢？
方法一
/**
* 獲取外置SD卡路徑
*
* @return 應該就一條記錄或空
*/
public List getExtSDCardPath() {
List lResult = new ArrayList();
try {
Runtime rt = Runtime.getRuntime();
Process proc = rt.exec("mount");
InputStream is = proc.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
String line;
//rootfs / rootfs ro,relatime 0 0
while ((line = br.readLine()) != null) {
if (line.contains("extSdCard")) {
String[] arr = line.split(" ");
String path = arr[1];
File file = new File(path);
if (file.isDirectory()) {
lResult.add(path);
}
}
}
isr.close();
} catch (Exception e) {
}
return lResult;
}
//獲取外置存儲卡的根路徑，如果沒有外置存儲卡，則返回null
public String getExtSDCardPath2() {
String sdcard_path = null;
String sd_default = Environment.getExternalStorageDirectory()
.getAbsolutePath();
if (sd_default.endsWith("/")) {
sd_default = sd_default.substring(0, sd_default.length() - 1);
}
// 得到路徑
try {
Runtime runtime = Runtime.getRuntime();
Process proc = runtime.exec("mount");
InputStream is = proc.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
String line;
BufferedReader br = new BufferedReader(isr);
//rootfs / rootfs ro,relatime 0 0
while ((line = br.readLine()) != null) {
if (line.contains("secure"))
continue;
if (line.contains("asec"))
continue;
if (line.contains("fat") && line.contains("/mnt/")) {
String columns[] = line.split(" ");
if (columns != null && columns.length > 1) {
if (sd_default.trim().equals(columns[1].trim())) {
continue;
}
sdcard_path = columns[1];
}
} else if (line.contains("fuse") && line.contains("/mnt/")) {
String columns[] = line.split(" ");
if (columns != null && columns.length > 1) {
if (sd_default.trim().equals(columns[1].trim())) {
continue;
}
sdcard_path = columns[1];
}
}
}
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return sdcard_path;
}
我用機子測試時候，獲取出來的值都是//rootfs / rootfs ro,relatime 0 0
根本沒有想要的。
manifest權限
最後總結一下
Environment.getExternalStorageDirect
不過app應用來說是需要固定一個路徑的。
我現在使用的是
public String getSoftwareStorageDirectory() {
String strDirectory;
Map sysInfo=System.getenv();
String sd_defult = sysInfo.get("SECONDARY_STORAGE");
if (!CheckDirectoryExists(sd_defult))
{
sd_defult = Environment.getExternalStorageDirectory().getPath();
}
return strDirectory;
}
//判斷檢出目錄是否存在
private boolean CheckDirectoryExists(String fileName) {
if (fileName == null || fileName.length()<=0) {
return false;
}
File temFile = new File(fileName);
File[] childFiles = null;
if (temFile != null)
childFiles = temFile.listFiles();
if (childFiles == null) {
return false;
}
//目錄是否可以寫
File testFile = new File(temFile, "com_testDir");
if (!testFile.exists()) {
if (!testFile.mkdir()) {
return false;
}
testFile.delete();
}
return true;
}
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