Question

我遇到了一个奇怪的问题，/storage/udisk/sda4/和/mnt/media_rw/udisk/sda4/应该表示android中的相同文件夹，但代码如下：

File sdcard = new File("/mnt/media_rw/udisk/sda4");

Log.d(LOG_TAG, "sdcard: " + sdcard 
                + ", exists: " + sdcard.exists());            // return false

sdcard = new File("/storage/udisk/sda4");

Log.d(LOG_TAG, "sdcard: " + sdcard 
                + ", exists: " + sdcard.exists());            // return true

我得到不同的结果，为什么会这样？

ll /mnt/media_rw/udisk/返回drwxrwx--- media_rw media_rw 1970-01-01 00:00 sda4

ll /storage/udisk返回drwxrwx--x root sdcard_r 1970-01-01 00:00 sda4

Answer 1

/ mnt / media_rw / udisk / sda4 是已安装的存储设备。并且它有更多访问权限（permission-771）
/ storage / udisk / sda4 是软存储（权限-751）

使用 / mnt / media_rw / udisk / sda4 以获得更好的访问权限

Answer 2

你可以尝试这个代码，我希望这个工作

import java.io.File;
import java.util.ArrayList;
import java.util.Scanner;
import android.os.Build;
import android.os.Environment;
import android.util.Log;

public class StorageOptions {
private static ArrayList<String> mMounts = new ArrayList<String>();
private static ArrayList<String> mVold = new ArrayList<String>();

public static String[] labels;
public static String[] paths;
public static int count = 0;
private static final String TAG = StorageOptions.class.getSimpleName();

public static void determineStorageOptions() {
    readMountsFile();

    readVoldFile();

    compareMountsWithVold();

    testAndCleanMountsList();

    setProperties();
 }

 private static void readMountsFile() {
    /*
     * Scan the /proc/mounts file and look for lines like this:
     * /dev/block/vold/179:1 /mnt/sdcard vfat
     * rw,dirsync,nosuid,nodev,noexec,
     * relatime,uid=1000,gid=1015,fmask=0602,dmask
     * =0602,allow_utime=0020,codepage
     * =cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
     * 
     * When one is found, split it into its elements and then pull out the
     * path to the that mount point and add it to the arraylist
     */

    // some mount files don't list the default
    // path first, so we add it here to
    // ensure that it is first in our list
    mMounts.add("/mnt/sdcard");

    try {
        Scanner scanner = new Scanner(new File("/proc/mounts"));
        while (scanner.hasNext()) {
            String line = scanner.nextLine();
            if (line.startsWith("/dev/block/vold/")) {
                String[] lineElements = line.split(" ");
                String element = lineElements[1];

                // don't add the default mount path
                // it's already in the list.
                if (!element.equals("/mnt/sdcard"))
                    mMounts.add(element);
            }
        }
    } catch (Exception e) {
        // Auto-generated catch block

        e.printStackTrace();
    }

    for(String p:mMounts)
    {
        Log.i("storage", p);
    }
  }

  private static void readVoldFile() {
    /*
     * Scan the /system/etc/vold.fstab file and look for lines like this:
     * dev_mount sdcard /mnt/sdcard 1
     * /devices/platform/s3c-sdhci.0/mmc_host/mmc0
     * 
     * When one is found, split it into its elements and then pull out the
     * path to the that mount point and add it to the arraylist
     */

    // some devices are missing the vold file entirely
    // so we add a path here to make sure the list always
    // includes the path to the first sdcard, whether real
    // or emulated.
    mVold.add("/mnt/sdcard");

    try {
        Scanner scanner = new Scanner(new File("/system/etc/vold.fstab"));
        while (scanner.hasNext()) {
            String line = scanner.nextLine();
            if (line.startsWith("dev_mount")) {
                String[] lineElements = line.split(" ");
                String element = lineElements[2];

                if (element.contains(":"))
                    element = element.substring(0, element.indexOf(":"));

                // don't add the default vold path
                // it's already in the list.
                if (!element.equals("/mnt/sdcard"))
                    mVold.add(element);
            }
        }


    } catch (Exception e) {
        // Auto-generated catch block

        e.printStackTrace();
    }
  }

  private static void compareMountsWithVold() {
    /*
     * Sometimes the two lists of mount points will be different. We only
     * want those mount points that are in both list.
     * 
     * Compare the two lists together and remove items that are not in both
     * lists.
     */

    for (int i = 0; i < mMounts.size(); i++) {
        String mount = mMounts.get(i);
        if (!mVold.contains(mount))
            mMounts.remove(i--);
    }

    // don't need this anymore, clear the vold list to reduce memory
    // use and to prepare it for the next time it's needed.
    mVold.clear();
  }

  private static void testAndCleanMountsList() {
    /*
     * Now that we have a cleaned list of mount paths Test each one to make
     * sure it's a valid and available path. If it is not, remove it from
     * the list.
     */

    for (int i = 0; i < mMounts.size(); i++) {
        String mount = mMounts.get(i);
        File root = new File(mount);
        if (!root.exists() || !root.isDirectory() || !root.canWrite())
            mMounts.remove(i--);
    }
  }

  @SuppressWarnings("unchecked")
  private static void setProperties() {
    /*
     * At this point all the paths in the list should be valid. Build the
     * public properties.
     */
    Constants.mMounts = new ArrayList<String>();
    ArrayList<String> mLabels = new ArrayList<String>();

    int j = 0;
    if (mMounts.size() > 0) {
        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.GINGERBREAD)
            mLabels.add("Auto");
        else if (Build.VERSION.SDK_INT < Build.VERSION_CODES.HONEYCOMB) {
            if (Environment.isExternalStorageRemovable()) {
                mLabels.add("External SD Card 1");
                j = 1;
            } else
                mLabels.add("Internal Storage");
        } else {
            if (!Environment.isExternalStorageRemovable()
                    || Environment.isExternalStorageEmulated())
                mLabels.add("Internal Storage");
            else {
                mLabels.add("External SD Card 1");
                j = 1;
            }
        }

        if (mMounts.size() > 1) {
            for (int i = 1; i < mMounts.size(); i++) {
                mLabels.add("External SD Card " + (i + j));
            }
        }
    }

    labels = new String[mLabels.size()];
    mLabels.toArray(labels);

    paths = new String[mMounts.size()];
    mMounts.toArray(paths);
    Constants.mMounts = (ArrayList<String>) mMounts.clone();
    Constants.mLabels = (ArrayList<String>) mLabels.clone();
    count = Math.min(labels.length, paths.length);

    // don't need this anymore, clear the mounts list to reduce memory
    // use and to prepare it for the next time it's needed.
    mMounts.clear();

  }
 }

此代码可帮助您查找所有SD卡和外部存储路径

我得到了三星手机的路径 enter image description here

Android中的“/ storage / udisk / sda4 /”和“/ mnt / media_rw / udisk / sda4 /”有什么区别？

2 个答案: