GreenDao 学习笔记 1

简介

就是这样一个简单的效果，可以通过输入框添加记录，点击列表项时则会删除对应的记录。

准备

https://github.com/greenrobot/greenDAO

到这里下载其中的 DaoExample 子项目，并运行。

我另外写了个 Activity ，实践下 GreenDao 的基本运用。

代码和分析

listview_item.xml

<TextView xmlns:android="http://schemas.android.com/apk/res/android"
          android:layout_width="match_parent"
          android:layout_height="40dp"
          android:gravity="center_vertical"
          android:textSize="18dp"
          android:paddingLeft="8dp"/>

listView 的项，就是一个 TextView。

ListViewAdapter.java

public class ListViewAdapter extends BaseAdapter {

    private List<Note> noteList = new ArrayList<Note>();

    private LayoutInflater layoutInflater;

    public ListViewAdapter(Activity activity) {

        layoutInflater = activity.getLayoutInflater();
    }

    @Override
    public int getCount() {

        return noteList.size();
    }

    @Override
    public Object getItem(int position) {

        return null;
    }

    @Override
    public long getItemId(int position) {

        return 0;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {

        TextView textView = (TextView) layoutInflater.inflate(R.layout.listview_item, parent, false);
        String text = noteList.get(position).getText();
        textView.setText(text);
        return textView;
    }

    public List<Note> getNoteList(){

      return noteList;
    }

}

my_activity.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:orientation="vertical"
              android:layout_width="match_parent"
              android:layout_height="match_parent">

    <LinearLayout android:layout_width="match_parent"
                  android:layout_height="50dp"
                  android:orientation="horizontal">

        <EditText android:id="@+id/etNote"
                  android:layout_weight="1" android:layout_width="0dp"
                  android:layout_height="match_parent"/>

        <Button android:id="@+id/btnAdd"
                android:layout_width="wrap_content"
                android:layout_height="match_parent"
                android:text="添加"/>

    </LinearLayout>

    <ListView android:id="@+id/lvNote"
              android:layout_width="match_parent"
              android:layout_height="0dp" android:layout_weight="1"/>

</LinearLayout>

一个输入框，一个按钮，一个列表。

MyActivity.java

public class MyActivity extends Activity implements View.OnClickListener, AdapterView.OnItemClickListener {

    private EditText etNote;

    private SQLiteDatabase db;

    private NoteDao noteDao;

    private ListViewAdapter listViewAdapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.my_activity);

        etNote = (EditText) findViewById(R.id.etNote);
        findViewById(R.id.btnAdd).setOnClickListener(this);

        DaoMaster.DevOpenHelper helper = new DaoMaster.DevOpenHelper(this, "notes-db", null);
        db = helper.getWritableDatabase();

        DaoMaster daoMaster = new DaoMaster(db);
        DaoSession daoSession = daoMaster.newSession();
        noteDao = daoSession.getNoteDao();

        ListView listView = (ListView) findViewById(R.id.lvNote);
        listViewAdapter = new ListViewAdapter(this);
        listView.setAdapter(listViewAdapter);
        listView.setOnItemClickListener(this);

        refreshListView();
    }

    @Override
    public void onClick(View v) {

        String text = etNote.getText().toString();
        if (!text.equals("")) {
            Note note = new Note(null, text, null, null);
            noteDao.insert(note);
            refreshListView();
        }
    }

    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {

        Long keyToDelete = listViewAdapter.getNoteList().get(position).getId();
        noteDao.deleteByKey(keyToDelete);
        refreshListView();
    }

    private void refreshListView() {

        List<Note> dataFromDb = getDataFromDb();
        List<Note> listViewData = listViewAdapter.getNoteList();
        listViewData.clear();
        listViewData.addAll(dataFromDb);
        listViewAdapter.notifyDataSetChanged();
    }

    private List<Note> getDataFromDb() {

        Cursor cursor = db.query(noteDao.getTablename(), noteDao.getAllColumns(), null, null, null, null, null);
        List<Note> noteList = new ArrayList<Note>();
        while (cursor.moveToNext()) {
            Long id = (cursor.getLong(cursor.getColumnIndex(NoteDao.Properties.Id.columnName)));
            String text = (cursor.getString(cursor.getColumnIndex(NoteDao.Properties.Text.columnName)));
            Note note = new Note(id, text, null, null);
            noteList.add(note);
        }

        return noteList;
    }

}

这样一来，对 GreenDao 就算有了个初步的印象了。

但还是有些问题：

1. 我没有看到 db.close 或 cursor.close 的语句，是不需要吗？

2. 操作数据库应该是开启 worker 线程的，使用 NoteDao 时曾抛出异常：

不能在非 UI 线程修改 UI，这真是很奇怪的事情，我又不可能在 NoteDao 的方法中刷新列表。