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。