# 数据库初始化
DemoApplication累承担了DaoSession的初始化工作
~~~
public class DemoApplication extends Application {
public static final boolean ENCRYPTED = false;
private static DemoApplication youAppction;
private DaoSession daoSession;
@Override
public void onCreate() {
super.onCreate();
DaoMaster.DevOpenHelper helper = new DaoMaster.DevOpenHelper(this, ENCRYPTED ? "notes-db-encrypted" : "notes-db3");
Database db = ENCRYPTED ? helper.getEncryptedWritableDb("super-secret") : helper.getWritableDb();
daoSession = new DaoMaster(db).newSession();
}
public static DemoApplication getInstance() {
return youAppction;
}
public DaoSession getDaoSession() {
return daoSession;
}
}
~~~
# 以登录模块为例，讲解GreenDao的用法
~~~
UserDao noteDao=((DemoApplication)getApplication()).getDaoSession().getUserDao() if(noteDao.queryBuilder().where(UserDao.Properties.Password.eq(password),UserDao.Properties.Username.eq(username)).count()>0){
Log.i("登录成功","ok");
Toast.makeText(getApplicationContext(),"登录成功！",Toast.LENGTH_LONG).show();
Constant.Account account= Constant.getAccount();
account.setPhone(username);
account.setPassword(password);
startActivity(new Intent(LoginActivity.this,MainActivity.class));
}else {
Log.i("登录失败","密码错误");
Toast.makeText(getApplicationContext(),"登录失败！账号密码错误",Toast.LENGTH_LONG).show();
}
~~~
这段代码讲的是 如果 userdao对象，在数据库查询不到结果，就说明输入的账号密码信息错误，从而提示登录失败、密码错误的信息。
第一步先创建UserDao 对象
`UserDao noteDao=((DemoApplication)getApplication()).getDaoSession().getUserDao() `
第二步再编写数据库查询语句
~~~
noteDao.queryBuilder().where(UserDao.Properties.Password.eq(password),UserDao.Properties.Username.eq(username)).count()
~~~
count为0,说明输入的账号密码插叙匹配不到数据，count不为0，则说明账号密码正确。
# 以注册模块为例，讲解GreenDao的插入用法
~~~
User user=new User();
user.setUsername(username);
user.setPassword(password);
try {
noteDao.insert(user);
Log.i("注册成功","ok");
Toast.makeText(getApplicationContext(),"注册成功！",Toast.LENGTH_LONG).show();
Constant.Account account= Constant.getAccount();
account.setPhone(username);
account.setPassword(password);
startActivity(new Intent(LoginActivity.this,MainActivity.class));
}catch (Exception e){
Log.i("注册失败","手机号已存在");
Toast.makeText(getApplicationContext(),"注册失败！手机号已存在",Toast.LENGTH_LONG).show();
Log.e("注册失败信息",e.toString());
}
~~~
首先想明白自己要插入什么：User对象，因此第一步是先创建User对象
~~~
User user=new User();
user.setUsername(username);
user.setPassword(password);
~~~
其次使用userdao对象，插入user对象，插入的过程不一定会成功，失败会抛出异常，因此我们使用try{}cath语句进行拦截异常。
插入成功，给予注册成功的提示，插入失败，给予注册失败的提示即可。
