官网：http://greenrobot.org/greendao/
GitHub：https://github.com/greenrobot/greenDAO
greendao.png
这是官网给出的GreenDao图解，通过图我们很清楚的知道GreenDao、java对象和SQLite数据的关系，而GreenDao的出现相当于为SQLite数据库和java对象搭建了一座桥梁。
言归正传，如此优秀的开源框架，我们来实践一下，下面的图是实践的效果图。
GreenDao.png
这里实现了数据库的增删改查操作。
项目添加GreenDao
1）、project--->build.gradle
GreenDao.png
2）、app—>build.gradle
GreenDao.png
greendao{ schemaVersion 1 //数据库版本号 daoPackage'com.lwj.greendao.gen'//存放dao的包名 targetGenDir'src/main/java' //存放的目录 } |
编写实体类
@Entity public class Student { @Id(autoincrement = true)//主键设置为自增的 private Long id; private String name; private int age; @Generated(hash = 352757281) public Student(Long id, String name, int age) { this.id = id; this.name = name; this.age = age; } @Generated(hash = 1556870573) public Student() { } public void setId(Long id) { this.id = id; } public void setName(String name) { this.name = name; } public void setAge(int age) { this.age = age; } public Long getId() { return id; } public String getName() { return name; } public int getAge() { return age; } } |
其中
@Generated(hash = 352757281) public Student(Long id, String name, int age) { this.id = id; this.name = name; this.age = age; } @Generated(hash = 1556870573) public Student() { } |
这两个构造不需要手动写，sync project一下自动生成的，包括生成greendao下的greendao配置信息。
GreenDao.png
初始化
初始化包括DaoMaster、DaoSession和建立数据库等信息。这里我建立一个管理类统一处理。
public class GreenDaoManager { private static GreenDaoManager mInstance = null; private DaoMaster mDaoMaster; private DaoSession mDaoSession; private DaoMaster.DevOpenHelper mHelper; private SQLiteDatabase db; private GreenDaoManager() { mHelper = new DaoMaster.DevOpenHelper(BaseApplication.getContext(), "student.db"); db = mHelper.getWritableDatabase(); mDaoMaster = new DaoMaster(db); mDaoSession = mDaoMaster.newSession(); } public static GreenDaoManager getInstance() { if (mInstance == null) { synchronized (GreenDaoManager.class) { if (mInstance == null) { mInstance = new GreenDaoManager(); } } } return mInstance; } public DaoSession getDaoSession() { return mDaoSession; } public SQLiteDatabase getDb() { return db; } public void setDaoMaster(DaoMaster daoMaster) { mDaoMaster = daoMaster; } public DaoSession getNewSession() { mDaoSession = mDaoMaster.newSession(); return mDaoSession; } } |
使用单例模式，不需要每次使用是GreenDao都初始化信息。
public class BaseApplication extends Application { private static Context mContext; @Override public void onCreate() { super.onCreate(); mContext = this; GreenDaoManager.getInstance(); } /** * 获取上下文 * * @return */ public static Context getContext() { return mContext; } public static BaseApplication getInstance() { return (BaseApplication) mContext; } } |
在Application的onCreate调用管理类的初始化就好了。
实践操作
xml文件：
<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" android:padding="20dp" tools:context="com.lwj.uiproject.GreenDaoDBActivity"> <LinearLayout android:layout_width="match_parent" android:layout_height="wrap_content" android:orientation="horizontal"> <EditText android:id="@+id/edit" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_weight="1"/> <Button android:id="@+id/add" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="add"/> <Button android:id="@+id/update" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="update"/> </LinearLayout> <ListView android:id="@+id/list_db" android:layout_width="match_parent" android:layout_height="match_parent" android:layout_marginTop="20dp"/> </LinearLayout> |
Activity:
public class GreenDaoDBActivity extends AppCompatActivity { private EditText mEditText; private Button mAdd; private Button mUpdate; private ListView mListView; private ListAdapter mAdapter; private List<String> datas = new ArrayList<>(); private StudentDao mDao; private static Long id = 1L; private Student updateInfo = null; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_green_dao_db); mDao = GreenDaoManager.getInstance().getDaoSession().getStudentDao(); initView(); initListenecr(); selectAll(); } private void initView() { mEditText = (EditText) this.findViewById(R.id.edit); mAdd = (Button) this.findViewById(R.id.add); mListView = (ListView) this.findViewById(R.id.list_db); mUpdate = (Button) this.findViewById(R.id.update); mAdapter = new ListAdapter(this, datas); mListView.setAdapter(mAdapter); } /** * 监听器初始化 */ private void initListenecr() { mAdd.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { String text = mEditText.getText().toString().trim(); Log.i("tag", text); insert(text); } }); mUpdate.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { update(); } }); mAdapter.setOnItemOnclickListener(new ListAdapter.OnItemOnclickListener() { @Override public void onClike(String text) { deleteAndUpdate(text); } }); } /** * 插入数据 * * @param text 插入数据 */ private void insert(String text) { try { Student s = new Student(id, text, 18); Long tagId = id; id++; mDao.insert(s); Log.i("tag", "插入成功"); mEditText.setText(""); selectById(tagId); } catch (Exception e) { e.printStackTrace(); Log.i("tag", "插入失败"); } } /** * 根据id查询数据 * * @param id */ private void selectById(Long id) { Student s = mDao.load(id); if (s != null) { datas.add(s.getName()); } mAdapter.notifyDataSetChanged(); } /** * 查询该表的所有数据 */ private void selectAll() { List<Student> mList = mDao.loadAll(); datas.clear(); for (Student student : mList) { datas.add(student.getName()); } mAdapter.notifyDataSetChanged(); } private void deleteAndUpdate(final String text) { List<Student> list = mDao.loadAll(); for (Student student : list) { if (student.getName().equals(text.trim())) { updateInfo = student; break; } } AlertDialog.Builder builder = new AlertDialog.Builder(this); //builder.setIcon(R.drawable.ic_launcher); builder.setTitle("选择"); // 指定下拉列表的显示数据 final String[] cities = {"删除", "修改"}; // 设置一个下拉的列表选择项 builder.setItems(cities, new DialogInterface.OnClickListener() { @Override public void onClick(DialogInterface dialog, int which) { if (which == 0) { delete(updateInfo); updateInfo = null; selectAll(); } else { mEditText.setText(updateInfo.getName()); } } }); builder.show(); } /** * 修改数据表的记录 */ private void update() { String text = mEditText.getText().toString().trim(); if (updateInfo != null) { try { updateInfo.setName(text); mDao.update(updateInfo); Log.i("tag", "修改成功"); updateInfo = null; mEditText.setText(""); selectAll(); } catch (Exception e) { e.printStackTrace(); Log.i("tag", "修改失败"); } } Log.i("tag", "没有找到合适的记录修改"); } /** * 删除 * * @param s */ private void delete(Student s) { try { mDao.delete(s); Log.i("tag", "删除成功"); } catch (Exception e) { e.printStackTrace(); Log.i("tag", "删除失败"); } } } |
对于增删改查的操作基本在文件已经注释好了，除了以上的方法来操作数据库，GreenDao还支持使用sql语句来操作数据库，这也是其强大的功能之一。支持对象实体间一对多，多对一的关系。虽然本文没有实践一对多的关系，但是读者可以自己去实践，相信也不会有太大的难度。
