Android：AsyncTask

public class MainActivity extends Activity implements OnClickListener {

private ORMLiteDatabaseHelper mDatabaseHelper;
private Dao<MyClass, Integer> mClassDao;
private Dao<Student, Integer> mStudentDao;
private boolean temp;
ListView list_view;
EditText edit;
Object ob;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

list_view = (ListView) findViewById(R.id.list_view);
Button create = (Button) findViewById(R.id.create);
Button query = (Button) findViewById(R.id.query);
edit = (EditText) findViewById(R.id.edit);

create.setOnClickListener(this);
query.setOnClickListener(this);

}

@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.create:
temp = true;
MyAsyncTask mAsyncTask = new MyAsyncTask();
mAsyncTask.execute();//执行语句

break;
case R.id.query:
Integer id = Integer.parseInt(edit.getText().toString());
temp = false;
if (id <= 3 && id >= 1) {
MyAsyncTask mTask = new MyAsyncTask();
mTask.execute(id);
}else{
Toast.makeText(this, "班级不存在", Toast.LENGTH_SHORT).show();
}
break;

default:
break;
}
}

public class MyAsyncTask extends AsyncTask {

public MyAsyncTask() {

}
//doInBackground 繁琐事件多数在这里执行处理
@Override
protected List<Student> doInBackground(Object... params) {

if (temp) {
create();
return null;
} else {
ForeignCollection<Student> student = query((Integer) params[0]);
List<Student> result = new ArrayList<Student>();
for (Student stu : student) {
result.add(stu);
}
return result;
}

}
//onPostExecute 可直接设置UI界面
@Override
protected void onPostExecute(Object result) {

if (result == null) {
Toast.makeText(MainActivity.this, "创建数据库成功", Toast.LENGTH_SHORT).show();
} else {
Toast.makeText(MainActivity.this, "查询成功", Toast.LENGTH_SHORT).show();

List<Student> list = (List<Student>) result;
list_view.setAdapter(new ArrayAdapter(MainActivity.this, android.R.layout.simple_list_item_1, list));
}
}
}

public void create() {

mDatabaseHelper = ORMLiteDatabaseHelper.getInstance(this);
mClassDao = mDatabaseHelper.getClassDao();
mStudentDao = mDatabaseHelper.getStudentDao();

for (int i = 1; i < 4; i++) {

MyClass myclass = new MyClass();

myclass.myclass_id = i;
myclass.name = i + "班";

try {
mClassDao.createIfNotExists(myclass);
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
String[] studentName = { "王二", "张三", "李四", "刘五", "赵六" };
String[] studentSex = { "男", "女" };
Random rand = new Random();
for (int j = 0; j < 5; j++) {

Student stu = new Student();

stu.student_id = j;
stu.name = studentName[rand.nextInt(5)];
stu.age = 18 + j;
stu.sex = studentSex[rand.nextInt(2)];

stu.mclass = myclass;

try {
mStudentDao.createIfNotExists(stu);
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}

public ForeignCollection<Student> query(Integer id) {
try {
MyClass mclass = mClassDao.queryForId(id);

ForeignCollection<Student> student = mclass.student;

return student;
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return null;
}

}