android 4.0 取内外置SD卡新特性
private StorageManager mStorageManager = null;

protected String mSDCardPath = null;
protected boolean mSDCardMounted = true;
protected boolean mSDCard2Mounted = false;
protected String mSDCardPath = null;
protected String mSDCard2Path = null;


mStorageManager = (StorageManager)getSystemService(Context.STORAGE_SERVICE);
String[] storagePathList = mStorageManager.getVolumePaths();
if (storagePathList != null) {
Log.d(TAG, "StorgaeList size: " + storagePathList.length);
if (storagePathList.length >= 2) {
mSDCardPath = storagePathList[0];
mSDCard2Path = storagePathList[1];
} else if (storagePathList.length == 1){
mSDCardPath = storagePathList[0];
}
}

Log.d(TAG, "SDCard path: " + mSDCardPath); //取出来的/mnt/sdcard
Log.d(TAG, "SDCard2 path: " + mSDCard2Path);//取出来的应该是/mnt/sdcard

mSDCardMounted = checkSDCardMount(mSDCardPath);
mSDCard2Mounted = checkSDCardMount(mSDCard2Path);
Log.d(TAG, "SDCard state in onCreate: " + mSDCardMounted);
Log.d(TAG, "SDCard2 state in onCreate: " + mSDCard2Mounted);

//判断sdcard是否挂载上，返回值为true证明挂载上了，否则不存在
protected boolean checkSDCardMount(String mountPoint) {
if(mountPoint == null){
return false;
}
String state = null;
state = mStorageManager.getVolumeState(mountPoint);
return Environment.MEDIA_MOUNTED.equals(state);
}

所说的4.0新特性是指针对android2.3来说的，android2.3判断内外置sdcard将在下篇文章“android 2.3 取内外置SD卡”带过，以稍作完善。