android技巧（五）一个异步+接口回调的例子

public class DataBaseUtils {
    // 当前数据库地址
    private String DB_PATH;
    // 备份后数据库保存地址
    private String DB_BACKUP_PATH;
    private Context context;
    private MessageShow ms;
    // 备份成功状态
    private final int BACKUP_OK = 1;
    // 备份失败状态
    private final int BACKUP_FAIL = -1;
    // 恢复成功状态
    private final int RECOVER_OK = 2;
    // 恢复失败状态
    private final int RECOVER_FAIL = -2;

    public interface MessageShow{

        public void onPepare();
        public void onSuccess();
        public void onFail();

    }

    public DataBaseUtils(Context context) {
        this.context = context;
    }

    /**
     * @Title: doDataBackUp
     * @Description: TODO(数据备份)
     * @param
     * @return void 返回类型
     * @author [email protected]/273219
     * @throws
     */
    public void doDataBackUp(String DB_PATH, String DB_BACKUP_PATH,MessageShow ms) {
        this.DB_PATH = DB_PATH;
        this.DB_BACKUP_PATH = DB_BACKUP_PATH;
        this.ms=ms;
        new BackUpTask().execute();
    }

    /**
     * @ClassName: BackUpTask
     * @Description: TODO(数据库备份异步任务)
     * @author [email protected]/273219
     * @date 2015-12-25 上午11:10:58
     *
     */
    @TargetApi(Build.VERSION_CODES.CUPCAKE)
    class BackUpTask extends AsyncTask<String, Void, Integer> {

        @Override
        protected void onPreExecute() {
            // TODO Auto-generated method stub
            super.onPreExecute();
            if(ms!=null) {
                ms.onPepare();
            }
        }

        @Override
        protected Integer doInBackground(String... params) {
            // TODO Auto-generated method stub

            // 默认路径 /data/data/(包名)/databases/*.db
            File dbFile = context.getDatabasePath(DB_PATH);
            File exportDir = new File(DB_BACKUP_PATH);
            int result = 0;
            if (!exportDir.exists()) {
                exportDir.mkdirs();
            }
            File backup = new File(exportDir, dbFile.getName());
            try {
                backup.createNewFile();
                fileCopy(dbFile, backup);
                result = BACKUP_OK;
            } catch (Exception e) {
                Log.e("backup_error", e.getMessage());
                result = BACKUP_FAIL;
            }

            return result;

        }

        @Override
        protected void onPostExecute(Integer result) {
            // TODO Auto-generated method stub
            super.onPostExecute(result);
            switch (result) {
                case BACKUP_OK:
                    if(ms!=null) {
                        ms.onSuccess();
                    }
                    break;

                case BACKUP_FAIL:
                    if(ms!=null) {
                        ms.onFail();
                    }
                    break;
            }
        }

    }

    /**
     * @Title: fileCopy
     * @Description: TODO(文件拷贝方法)
     * @param @param dbFile
     * @param @param backup
     * @param @throws IOException 设定文件
     * @return void 返回类型
     * @author [email protected]/273219
     * @throws
     */
    private void fileCopy(File dbFile, File backup) throws IOException {
        // TODO Auto-generated method stub
        FileChannel inChannel = new FileInputStream(dbFile).getChannel();
        FileChannel outChannel = new FileOutputStream(backup).getChannel();
        try {
            inChannel.transferTo(0, inChannel.size(), outChannel);
        } catch (IOException e) {
            // TODO Auto-generated catch block
            Log.e("fileCopy_error", e.getMessage());
        } finally {
            if (inChannel != null) {
                inChannel.close();
            }
            if (outChannel != null) {
                outChannel.close();
            }
        }
    }
}

调用DataBaseUtils中的doDataBackUp(String DB_PATH, String DB_BACKUP_PATH,MessageShow ms) 方法

public class MainActivity extends Activity {
       private String DB_BACKUP_PATH=Environment.getExternalStorageDirectory()+"/feng_contactsBackup";
       private String DATABASE_PATH=Environment.getExternalStorageDirectory() + "/ttttest.db";

       @Override
       protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            DatabaseUtils bru=new DatabaseUtils(MainActivity.this);
            bru.doDataBackUp(DB_PATH, DB_BACKUP_PATH,new MessageShow() {

                @Override
                public void onSuccess() {
                    // TODO Auto-generated method stub
                Toast.makeText(MainActivity.this,"success", Toast.LENGTH_LONG).show();
                }
                @Override
                public void onPepare() {
                    // TODO Auto-generated method stub
                Toast.makeText(MainActivity.this,"Pepare", Toast.LENGTH_LONG).show();
                }
                @Override
                public void onFail() {
                    // TODO Auto-generated method stub
                Toast.makeText(MainActivity.this,"Fail", Toast.LENGTH_LONG).show();
                }
            });

        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            Log.e("DB_ERROR", "Get bean dao error cause by " + e.getMessage());
        }
}
}

对整个异步回调使用的理解：

1.class   A,class   B   
  2.class   A实现接口callback
  3.class   B拥有一个参数为callback接口类型的函数bMethod(callback cb)
  4.class   A运行时调用class   B中的函数bMethod(callback cb),以自身传入参数   
  5.class   B已取得A，就可以随时回调A所实现的callback接口中的方法