Format SD card in Android

问题:

Things should be simple, but as most of the time, in Android, aren't. I need to format the SD card if the user selects the option in my app. Don't ask me why I need to do this if it's already in the OS... not practical but it's a requirement that I need to implement. As you may know, there is an option in Settings \ Storage \ Erase SD Card. I took a look at the froyo source code and it's something like:

final IMountService service =
         IMountService.Stub.asInterface(ServiceManager.getService("mount"));
        if (service != null) {
            new Thread() {
                public void run() {
                try {
                        service.formatVolume(Environment.getExternalStorageDirectory().toString());
                    } catch (Exception e) {
                        // Intentionally blank - there's nothing we can do here
                    Log.w("MediaFormat", "Unable to invoke IMountService.formatMedia()");
                    }
                }
            }.start();
        } else {
            Log.w("MediaFormat", "Unable to locate IMountService");
        }

It uses android.os.storage.IMountService and android.os.ServiceManager and I don't seem to have access to it. So, as I see it I could recursively search every file and delete it but that would be "not on my taste"... or I could start the screen from Erase SD card to the user.

Any help is more then welcome, as I am stuck.

回答1:

First of all, I think that you may need to umount .android_secure filesystem before formatting SD card, whatever your approach may be.

Then,

Try including following permissions in your app:

1) MOUNT_FORMAT_FILESYSTEMS - http://developer.android.com/reference/android/Manifest.permission.html#MOUNT_FORMAT_FILESYSTEMS

2) MOUNT_UNMOUNT_FILESYSTEMS - http://developer.android.com/reference/android/Manifest.permission.html#MOUNT_UNMOUNT_FILESYSTEMS

Android Settings app already uses the 2nd permission.

================================================================================

When you perform a build of AOSP or any other distribution code, IMountService.java file gets generated automatically. It contains following function which actually sends formatting commands to vold daemon I guess.:

private static class Proxy implements android.os.storage.IMountService
{
  private android.os.IBinder mRemote;
  Proxy(android.os.IBinder remote)
  {
    mRemote = remote;
  }

  public android.os.IBinder asBinder()
  {
    return mRemote;
  }

  // **** A LOT OF OTHER CODE IS HERE.....

  public int formatVolume(java.lang.String mountPoint) throws android.os.RemoteException
  {
    android.os.Parcel _data = android.os.Parcel.obtain();
    android.os.Parcel _reply = android.os.Parcel.obtain();
    int _result;
    try {
      _data.writeInterfaceToken(DESCRIPTOR);
      _data.writeString(mountPoint);
      mRemote.transact(Stub.TRANSACTION_formatVolume, _data, _reply, 0);
      _reply.readException();
      _result = _reply.readInt();
    }
    finally {
      _reply.recycle();
      _data.recycle();
    }
    return _result;
  }
}

回答2:

I can't find again the question here on SO, but It had a working solution. So all credit goes to that guy ;)

public void wipeMemoryCard() {
        File deleteMatchingFile = new File(Environment
                .getExternalStorageDirectory().toString());
        try {
            File[] filenames = deleteMatchingFile.listFiles();
            if (filenames != null && filenames.length > 0) {
                for (File tempFile : filenames) {
                    if (tempFile.isDirectory()) {
                        wipeDirectory(tempFile.toString());
                        tempFile.delete();
                    } else {
                        tempFile.delete();
                    }
                }
            } else {
                deleteMatchingFile.delete();
            }
        } catch (Exception e) {
            Utils.log(e.getMessage());
        }
    }

    private static void wipeDirectory(String name) {
        File directoryFile = new File(name);
        File[] filenames = directoryFile.listFiles();
        if (filenames != null && filenames.length > 0) {
            for (File tempFile : filenames) {
                if (tempFile.isDirectory()) {
                    wipeDirectory(tempFile.toString());
                    tempFile.delete();
                } else {
                    tempFile.delete();
                }
            }
        } else {
            directoryFile.delete();
        }
    }