获取存储卡路径的接口大家都很熟悉,一般是通过 Environment 接口来获取:
File sdcardRoot = Environment.getExternalStorageDirectory();
偶尔开发中会遇到需要获取外置存储卡的接口,一般是 TF小卡,网上有很多方法,但都不是完全准确的方法.
下面提供一个准确获取外置存储卡路径的方法.
原理:
Android 4.0 版本中谷歌其实已经加入了对多张存储卡的支持,而且支持代码相当完善.但其获取多存储卡路径和状态的三个接口却标注了@hide,所以在Android标准SDK中没有这三个方法.
这些接口在Android源代码中位置如下:
frameworks/base/core/java/android/os/storage/StorageManager.java
StorageManager类中,以下三个接口都被标注为@hide:
getVolumePaths()
返回全部存储卡路径, 包括已挂载的和未挂载的.
即: 有外置存储卡卡槽的机器,即使未插入外置存储卡,其路径也会被这个接口列出.
要判断某个挂载点的状态,可以用第三个接口.
getVolumeList()
返回全部 StorageVolume 类的数组,这个类也是 @hide 的.
该类提供了更详细的关于每个挂载点的信息.具体有什么信息,请继续向下看.
getVolumeState(String mountPoint)
返回某个挂载点代表的存储卡的状态. 即 Environment 中的几个常量(未全部列出):
Environment.MEDIA_REMOVED
Environment.MEDIA_MOUNTED
上面第一个和第二个方法都返回数组,都是数组第一个为主存储卡,第二个是副存储卡(如果该机型支持的话).
一般主存储卡就是手机内建的存储卡.不过也有厂商自己开发了存储卡切换功能,这时候主存储卡可能会被设为外置存储卡.这个不展开.
如果手机支持插入外置卡,那么无论有无TF卡插入卡槽,上面返回的数组长度是固定的.没有TF卡插入时,其状态即为 Environment.MEDIA_REMOVED.
所以要操作外置存储卡前,要先检查其状态是否在 Environment.MEDIA_MOUNTED 或 Environment.MEDIA_MOUNTED_READ_ONLY 的状态.
另1: 当然数组中也有可能不只两个元素.比如很多手机都支持OTG功能,就是用USB线连接U盘到手机的功能,这时上面方法返回的数组就会有三个元素,一般第三个元素就是 USB OTG.和外置存储卡一样,是否有U盘插入, OTG 都会在数组里被返回的.
另2: 一般能上市的4.0以上的手机,上面那几个接口肯定是有的.没有的话,就过不了谷歌的兼容性测试(CTS),就上不了市. 而且一般也没谁蛋疼会去改这几个接口.
那么问题来了, SDK 访问不到的方法,知道又有何用呢.
嗯,小明同学说的对,可以用反射.
简单的获取外置存储卡路径的方法:
import java.lang.reflect.Method;
import android.os.storage.StorageManager;
// 获取主存储卡路径
public String getPrimaryStoragePath() {
try {
StorageManager sm = (StorageManager) getSystemService(STORAGE_SERVICE);
Method getVolumePathsMethod = StorageManager.class.getMethod("getVolumePaths", null);
String[] paths = (String[]) getVolumePathsMethod.invoke(sm, null);
// first element in paths[] is primary storage path
return paths[0];
} catch (Exception e) {
Log.e(TAG, "getPrimaryStoragePath() failed", e);
}
return null;
}
// 获取次存储卡路径,一般就是外置 TF 卡了. 不过也有可能是 USB OTG 设备...
// 其实只要判断第二章卡在挂载状态,就可以用了.
public String getSecondaryStoragePath() {
try {
StorageManager sm = (StorageManager) getSystemService(STORAGE_SERVICE);
Method getVolumePathsMethod = StorageManager.class.getMethod("getVolumePaths", null);
String[] paths = (String[]) getVolumePathsMethod.invoke(sm, null);
// second element in paths[] is secondary storage path
return paths.length <= 1 ? null : paths[1];
} catch (Exception e) {
Log.e(TAG, "getSecondaryStoragePath() failed", e);
}
return null;
}
// 获取存储卡的挂载状态. path 参数传入上两个方法得到的路径
public String getStorageState(String path) {
try {
StorageManager sm = (StorageManager) getSystemService(STORAGE_SERVICE);
Method getVolumeStateMethod = StorageManager.class.getMethod("getVolumeState", new Class[] {String.class});
String state = (String) getVolumeStateMethod.invoke(sm, path);
return state;
} catch (Exception e) {
Log.e(TAG, "getStorageState() failed", e);
}
return null;
}
获取关于存储卡的更详细的信息:
在原理那节提到了 StorageVolume 可以提供更详细的存储卡信息.这里当然还是要用反射.
为了便于调用,写了一个基于反射的代理类,将 StorageVolume 信息全部暴露出来. 这些信息包括:
isPrimary() - 是否主存储卡
isRemovable() - 是否可移除. 内建存储卡肯定返回 false, 外置TF卡肯定返回 true
isEmulated() - 4.0 谷歌采用 fuse 文件系统后, 多数 Android 机的内建存储卡其实就都是虚拟的了.不过同学们知道这信息也没什么用处.
allowMassStorage() - 是否支持传统的大容量存储模式,就是早期那个黑底绿机器人举个USB的那个界面. 如上,用 fuse 的手机很少有支持这个功能的. 现在都用 MTP 了.
getMaxFileSize() - 获取磁盘最大可用容量.注意这个不一定就和磁盘容量完全相等,有的厂商会预留比如50MB出来作为最后阈值: 存储卡真全满了后果还是很严重的.
getMtpReserveSpace() - 同上, MTP 模式下的最大可用容量.这个一般厂商好像都会预留一些空间出来,防止用户用 MTP 填满磁盘.
此类没有太多可说的,就是反射反射再反射而已.不再一一解释了,直接贴代码:
package com.lx.mystalecode.utils;
import android.content.Context;
import android.os.storage.StorageManager;
import java.io.File;
import java.lang.reflect.Array;
import java.lang.reflect.Method;
/**
*
* author: liuxu
* date: 2014-10-27
*
* There are some useful methods in StorageManager, like:
* StorageManager.getVolumeList()
* StorageManager.getVolumeState()
* StorageManager.getVolumePaths()
* But for now these methods are not visible in SDK (marked as \@hide).
* one requirement for these methods is to get secondary storage or
* OTG disk info.
*
* here we use java reflect mechanism to retrieve these methods and data.
*
* Demo: ActivityStorageUtilsDemo
*/
public final class StorageManagerHack {
private StorageManagerHack() {
}
public static StorageManager getStorageManager(Context cxt) {
StorageManager sm = (StorageManager)
cxt.getSystemService(Context.STORAGE_SERVICE);
return sm;
}
/**
* Returns list of all mountable volumes.
* list elements are RefStorageVolume, which can be seen as
* mirror of android.os.storage.StorageVolume
* return null on error.
* @param cxt
* @return
*/
public static RefStorageVolume[] getVolumeList(Context cxt) {
if (!isSupportApi()) {
return null;
}
StorageManager sm = getStorageManager(cxt);
if (sm == null) {
return null;
}
try {
Class[] argTypes = new Class[0];
Method method_getVolumeList =
StorageManager.class.getMethod("getVolumeList", argTypes);
Object[] args = new Object[0];
Object array = method_getVolumeList.invoke(sm, args);
int arrLength = Array.getLength(array);
RefStorageVolume[] volumes = new
RefStorageVolume[arrLength];
for (int i = 0; i < arrLength; i++) {
volumes[i] = new RefStorageVolume(Array.get(array, i));
}
return volumes;
} catch (Exception e) {
e.printStackTrace();
return null;
}
}
/**
* Returns list of paths for all mountable volumes.
* return null on error.
*/
public static String[] getVolumePaths(Context cxt) {
if (!isSupportApi()) {
return null;
}
StorageManager sm = getStorageManager(cxt);
if (sm == null) {
return null;
}
try {
Class[] argTypes = new Class[0];
Method method_getVolumeList =
StorageManager.class.getMethod("getVolumePaths", argTypes);
Object[] args = new Object[0];
Object array = method_getVolumeList.invoke(sm, args);
int arrLength = Array.getLength(array);
String[] paths = new
String[arrLength];
for (int i = 0; i < arrLength; i++) {
paths[i] = (String) Array.get(array, i);
}
return paths;
} catch (Exception e) {
e.printStackTrace();
return null;
}
}
/**
* Gets the state of a volume via its mountpoint.
* return null on error.
*/
public static String getVolumeState(Context cxt, String mountPoint) {
if (!isSupportApi()) {
return null;
}
StorageManager sm = getStorageManager(cxt);
if (sm == null) {
return null;
}
try {
Class[] argTypes = new Class[1];
argTypes[0] = String.class;
Method method_getVolumeList =
StorageManager.class.getMethod("getVolumeState", argTypes);
Object[] args = new Object[1];
args[0] = mountPoint;
Object obj = method_getVolumeList.invoke(sm, args);
String state = (String) obj;
return state;
} catch (Exception e) {
e.printStackTrace();
return null;
}
}
/**
* Get primary volume of the device.
* @param cxt
* @return RefStorageVolume can be seen as mirror of
* android.os.storage.StorageVolume
*/
public static RefStorageVolume getPrimaryVolume(Context cxt) {
RefStorageVolume[] volumes = getVolumeList(cxt);
if (volumes == null) {
return null;
}
for (RefStorageVolume volume : volumes) {
try {
if (volume.isPrimary()) {
return volume;
}
} catch (Exception e) {
e.printStackTrace();
return null;
}
}
return null;
}
/**
* see if SDK version of current device is greater
* than 14 (IceCreamSandwich, 4.0).
*/
private static boolean isSupportApi() {
int osVersion = android.os.Build.VERSION.SDK_INT;
boolean avail = osVersion >= 14;
return avail;
}
/**
* this class can be seen as mirror of android.os.storage.StorageVolume :
* Description of a storage volume and its capabilities, including the
* filesystem path where it may be mounted.
*/
public static class RefStorageVolume {
private static final int INIT_FLAG_STORAGE_ID = 0x01 << 0;
private static final int INIT_FLAG_DESCRIPTION_ID = 0x01 << 1;
private static final int INIT_FLAG_PATH = 0x01 << 2;
private static final int INIT_FLAG_PRIMARY = 0x01 << 3;
private static final int INIT_FLAG_REMOVABLE = 0x01 << 4;
private static final int INIT_FLAG_EMULATED = 0x01 << 5;
private static final int INIT_FLAG_ALLOW_MASS_STORAGE = 0x01 << 6;
private static final int INIT_FLAG_MTP_RESERVE_SPACE = 0x01 << 7;
private static final int INIT_FLAG_MAX_FILE_SIZE = 0x01 << 8;
private int mInitFlags = 0x00;
private int mStorageId;
private int mDescriptionId;
private File mPath;
private boolean mPrimary;
private boolean mRemovable;
private boolean mEmulated;
private boolean mAllowMassStorage;
private int mMtpReserveSpace;
/** Maximum file size for the storage, or zero for no limit */
private long mMaxFileSize;
private Class class_StorageVolume =
Class.forName("android.os.storage.StorageVolume");
private Object instance;
private RefStorageVolume(Object obj) throws ClassNotFoundException {
if (!class_StorageVolume.isInstance(obj)) {
throw new IllegalArgumentException(
"obj not instance of StorageVolume");
}
instance = obj;
}
public void initAllFields() throws Exception {
getPathFile();
getDescriptionId();
getStorageId();
isPrimary();
isRemovable();
isEmulated();
allowMassStorage();
getMaxFileSize();
getMtpReserveSpace();
}
/**
* Returns the mount path for the volume.
* @return the mount path
* @throws Exception
*/
public String getPath() throws Exception {
File pathFile = getPathFile();
if (pathFile != null) {
return pathFile.toString();
} else {
return null;
}
}
public File getPathFile() throws Exception {
if ((mInitFlags & INIT_FLAG_PATH) == 0) {
Class[] argTypes = new Class[0];
Method method = class_StorageVolume.getDeclaredMethod(
"getPathFile", argTypes);
Object[] args = new Object[0];
Object obj = method.invoke(instance, args);
mPath = (File) obj;
mInitFlags &= INIT_FLAG_PATH;
}
return mPath;
}
/**
* Returns a user visible description of the volume.
* @return the volume description
* @throws Exception
*/
public String getDescription(Context context) throws Exception {
int resId = getDescriptionId();
if (resId != 0) {
return context.getResources().getString(resId);
} else {
return null;
}
}
public int getDescriptionId() throws Exception {
if ((mInitFlags & INIT_FLAG_DESCRIPTION_ID) == 0) {
Class[] argTypes = new Class[0];
Method method = class_StorageVolume.getDeclaredMethod(
"getDescriptionId", argTypes);
Object[] args = new Object[0];
Object obj = method.invoke(instance, args);
mDescriptionId = (Integer) obj;
mInitFlags &= INIT_FLAG_DESCRIPTION_ID;
}
return mDescriptionId;
}
public boolean isPrimary() throws Exception {
if ((mInitFlags & INIT_FLAG_PRIMARY) == 0) {
Class[] argTypes = new Class[0];
Method method = class_StorageVolume.getDeclaredMethod(
"isPrimary", argTypes);
Object[] args = new Object[0];
Object obj = method.invoke(instance, args);
mPrimary = (Boolean) obj;
mInitFlags &= INIT_FLAG_PRIMARY;
}
return mPrimary;
}
/**
* Returns true if the volume is removable.
* @return is removable
*/
public boolean isRemovable() throws Exception {
if ((mInitFlags & INIT_FLAG_REMOVABLE) == 0) {
Class[] argTypes = new Class[0];
Method method = class_StorageVolume.getDeclaredMethod(
"isRemovable", argTypes);
Object[] args = new Object[0];
Object obj = method.invoke(instance, args);
mRemovable = (Boolean) obj;
mInitFlags &= INIT_FLAG_REMOVABLE;
}
return mRemovable;
}
/**
* Returns true if the volume is emulated.
* @return is removable
*/
public boolean isEmulated() throws Exception {
if ((mInitFlags & INIT_FLAG_EMULATED) == 0) {
Class[] argTypes = new Class[0];
Method method = class_StorageVolume.getDeclaredMethod(
"isEmulated", argTypes);
Object[] args = new Object[0];
Object obj = method.invoke(instance, args);
mEmulated = (Boolean) obj;
mInitFlags &= INIT_FLAG_EMULATED;
}
return mEmulated;
}
/**
* Returns the MTP storage ID for the volume.
* this is also used for the storage_id column in the media provider.
* @return MTP storage ID
*/
public int getStorageId() throws Exception {
if ((mInitFlags & INIT_FLAG_STORAGE_ID) == 0) {
Class[] argTypes = new Class[0];
Method method = class_StorageVolume.getDeclaredMethod(
"getStorageId", argTypes);
Object[] args = new Object[0];
Object obj = method.invoke(instance, args);
mStorageId = (Integer) obj;
mInitFlags &= INIT_FLAG_STORAGE_ID;
}
return mStorageId;
}
/**
* Returns true if this volume can be shared via USB mass storage.
* @return whether mass storage is allowed
*/
public boolean allowMassStorage() throws Exception {
if ((mInitFlags & INIT_FLAG_ALLOW_MASS_STORAGE) == 0) {
Class[] argTypes = new Class[0];
Method method = class_StorageVolume.getDeclaredMethod(
"allowMassStorage", argTypes);
Object[] args = new Object[0];
Object obj = method.invoke(instance, args);
mAllowMassStorage = (Boolean) obj;
mInitFlags &= INIT_FLAG_ALLOW_MASS_STORAGE;
}
return mAllowMassStorage;
}
/**
* Returns maximum file size for the volume, or zero if it is unbounded.
* @return maximum file size
*/
public long getMaxFileSize() throws Exception {
if ((mInitFlags & INIT_FLAG_MAX_FILE_SIZE) == 0) {
Class[] argTypes = new Class[0];
Method method = class_StorageVolume.getDeclaredMethod(
"getMaxFileSize", argTypes);
Object[] args = new Object[0];
Object obj = method.invoke(instance, args);
mMaxFileSize = (Long) obj;
mInitFlags &= INIT_FLAG_MAX_FILE_SIZE;
}
return mMaxFileSize;
}
/**
* Number of megabytes of space to leave unallocated by MTP.
* MTP will subtract this value from the free space it reports back
* to the host via GetStorageInfo, and will not allow new files to
* be added via MTP if there is less than this amount left free in the
* storage.
* If MTP has dedicated storage this value should be zero, but if MTP is
* sharing storage with the rest of the system, set this to a positive
* value
* to ensure that MTP activity does not result in the storage being
* too close to full.
* @return MTP reserve space
*/
public int getMtpReserveSpace() throws Exception {
if ((mInitFlags & INIT_FLAG_MTP_RESERVE_SPACE) == 0) {
Class[] argTypes = new Class[0];
Method method = class_StorageVolume.getDeclaredMethod(
"getMtpReserveSpace", argTypes);
Object[] args = new Object[0];
Object obj = method.invoke(instance, args);
mMtpReserveSpace = (Integer) obj;
mInitFlags &= INIT_FLAG_MTP_RESERVE_SPACE;
}
return mMtpReserveSpace;
}
@Override
public String toString() {
try {
final StringBuilder builder = new StringBuilder("RefStorageVolume [");
builder.append("mStorageId=").append(getStorageId());
builder.append(" mPath=").append(getPath());
builder.append(" mDescriptionId=").append(getDescriptionId());
builder.append(" mPrimary=").append(isPrimary());
builder.append(" mRemovable=").append(isRemovable());
builder.append(" mEmulated=").append(isEmulated());
builder.append(" mMtpReserveSpace=").append(getMtpReserveSpace());
builder.append(" mAllowMassStorage=").append(allowMassStorage());
builder.append(" mMaxFileSize=").append(getMaxFileSize());
builder.append("]");
return builder.toString();
} catch (Exception e) {
e.printStackTrace();
return null;
}
}
}
}
上面这个类收录在作者的 github 内:
https://github.com/liuxu0703/MyAndroidStaleCode/blob/master/app/src/main/java/com/lx/mystalecode/utils/StorageManagerHack.java
最后我想说,然并卵...
并没有好的方法获取外置存储卡完全的读写权限,即使获取了外置存储卡路径,也得按谷歌的规则玩,才能有限的操作外置存储卡.
所以我猜测,想拿到外置存储卡路径的各位同学,需求方面应该也是比较奇葩的吧...
这个悲伤的故事在这里就不展开了.