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Backing up and restoring your database

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rutura edited this page Apr 17, 2017 · 1 revision
  • Your database is actually a file somewhere in the internal storage of your app on the android system
  • Backing up means copying your database file to a location in the external storage so the user for example remove the sd card and store a db backup on her pc or whatever.
  • This example contains a bit of database logic code but just focus on storing the existing db file
  • We use AsyncTask to handle the backing up and restoring on the background thread *We do the backing up and restoring as shown below:
@Override
    protected Integer doInBackground(String... params) {
        //Get a reference to the database
        File dbFile = mContext.getDatabasePath("foodDb.db");
        //Get a reference to the directory location for the backup
        File exportDir =
                new File(Environment.getExternalStorageDirectory(), "myAppBackups");

        Log.d(MainActivity.LOGTAG," Database will be backed up in :"+ exportDir.getAbsolutePath());

        if (!exportDir.exists()) {
            exportDir.mkdirs();
        }
        File backup = new File(exportDir, dbFile.getName());
        //Check the required operation
        String command = params[0];
        if(command.equals(COMMAND_BACKUP)) {
        //Attempt file copy
            Log.d(MainActivity.LOGTAG,"Attempting to copy file :"+dbFile.getAbsolutePath() +
            " to "+backup.getAbsolutePath());
            if(dbFile.exists())
            {
                Log.d(MainActivity.LOGTAG,"The source file exits");
            }else
            {
                Log.d(MainActivity.LOGTAG,"The source DOES NOT exits");
            }

            try {
                backup.createNewFile();
                fileCopy(dbFile, backup);
                return BACKUP_SUCCESS;
            } catch (IOException e) {
                return BACKUP_ERROR;
            }
        } else if(command.equals(COMMAND_RESTORE)) {
        //Attempt file copy
            try {
                if(!backup.exists()) {
                    return RESTORE_NOFILEERROR;
                }
                dbFile.createNewFile();
                fileCopy(backup, dbFile);
                return RESTORE_SUCCESS;
            } catch (IOException e) {
                return BACKUP_ERROR;
            }
        } else {
            return BACKUP_ERROR;
        }
    }
  • You fire up the backup process like this:
   Log.d(LOGTAG,"Backing up database");
                if( Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED) ) {
                    BackupTask task = new BackupTask(MainActivity.this);
                    task.setCompletionListener(MainActivity.this);
                    task.execute(BackupTask.COMMAND_BACKUP);
                    Log.d(LOGTAG,"Started the backup process.");
                }else
                {
                    Log.d(LOGTAG,"Could not find a mountable external storage.");
                }
  • and the restoring process like this:
   if( Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED) ) {
                    BackupTask task = new BackupTask(MainActivity.this);
                    task.setCompletionListener(MainActivity.this);
                    task.execute(BackupTask.COMMAND_RESTORE);
                    Log.d(LOGTAG,"Started backup restore process.");
                }else
                {
                    Log.d(LOGTAG,"Could not find a mountable external storage.");
                }
  • The AsyncTask informs the caller on the status of its work through the callBack interface methods it calls :
   @Override
    protected void onPostExecute(Integer result) {
        switch(result) {
            case BACKUP_SUCCESS:
                Log.d(MainActivity.LOGTAG," BackupTask:Backup success");
                if(listener != null) {
                    listener.onBackupComplete();
                }
                break;
            case RESTORE_SUCCESS:
                Log.d(MainActivity.LOGTAG," BackupTask:Restore success");
                if(listener != null) {
                    listener.onRestoreComplete();
                }
                break;
            case RESTORE_NOFILEERROR:
                Log.d(MainActivity.LOGTAG," BackupTask:Restore_No_File_Error");
                if(listener != null) {
                    listener.onError(RESTORE_NOFILEERROR);
                }
                break;
            default:
                Log.d(MainActivity.LOGTAG," BackupTask:Backup Error");
                if(listener != null) {
                    listener.onError(BACKUP_ERROR);
                }
        }
    }
  • and the caller Activity implements them to listen in:
    public class MainActivity extends AppCompatActivity implements BackupTask.CompletionListener {

    ...

    @Override
    public void onBackupComplete() {
        Toast.makeText(this, "Backup Complete", Toast.LENGTH_SHORT).show();
    }

    @Override
    public void onRestoreComplete() {
        Toast.makeText(this, "Restore Complete", Toast.LENGTH_SHORT).show();
    }

    @Override
    public void onError(int errorCode) {
        if(errorCode == BackupTask.RESTORE_NOFILEERROR) {
            Toast.makeText(this, "No Backup Found to Restore",
                    Toast.LENGTH_SHORT).show();
        } else {
            Toast.makeText(this, "Error During Operation: "+errorCode,
                    Toast.LENGTH_SHORT).show();
        }

    }
}
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