Android实现简易记事本

public class MainActivity extends AppCompatActivity implements View.OnClickListener {
 private EditText subject;
 private EditText body;
 private EditText date;
 private Button chooseDate;
 private Button add;
 private Button query;
 private ListView result;
 private LinearLayout title;
 private MyDataBaseHelper mMyDataBaseHelper;
 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main);
 initView();
 }
 private void initView() {
 //控件初始化
 subject=(EditText)findViewById(R.id.subject);
 body=(EditText)findViewById(R.id.body);
 date=(EditText)findViewById(R.id.date);
 chooseDate=(Button)findViewById(R.id.chooseDate);
 add=(Button)findViewById(R.id.add);
 query=(Button)findViewById(R.id.query);
 result=(ListView)findViewById(R.id.result);
 title=(LinearLayout)findViewById(R.id.title);
 //选择日期，添加，查询的监听事件
 chooseDate.setOnClickListener(this);
 add.setOnClickListener(this);
 query.setOnClickListener(this);
 //查询情况默认隐藏，只有点击查询时才有效果
 title.setVisibility(View.INVISIBLE);
 }
 @Override
 public void onClick(View v) {
 //创建数据库
 mMyDataBaseHelper=new MyDataBaseHelper(MainActivity.this,"memento.db",null,1);
 SQLiteDatabase sqLiteDatabase=mMyDataBaseHelper.getReadableDatabase();
 //获取输入框的内容
 String strSubject=subject.getText().toString().trim();
 String strBody=body.getText().toString().trim();
 String strDate=date.getText().toString().trim();
 switch (v.getId()){
 case R.id.chooseDate:
 Calendar calendar=Calendar.getInstance();
 //选择时间，并将时间设置在date中
 new DatePickerDialog(MainActivity.this, new DatePickerDialog.OnDateSetListener() {
  @Override
  public void onDateSet(DatePicker view, int year, int month, int dayOfMonth) {
  date.setText(year+"-"+month+"-"+dayOfMonth);
  }
 },calendar.get(Calendar.YEAR),calendar.get(Calendar.MONTH),calendar.get(Calendar.DAY_OF_MONTH)).show();
 break;
 case R.id.add:
 //添加内容到数据库中，添加方法是add
 title.setVisibility(View.INVISIBLE);
 add(sqLiteDatabase,strSubject,strBody,strDate);
 Toast.makeText(this, "success!", Toast.LENGTH_SHORT).show();
 result.setAdapter(null);
 break;
 case R.id.query:
 //查询时显示结果设置为visible
 title.setVisibility(View.VISIBLE);
 //查询的结果保存在cursor中
 Cursor cursor=query(sqLiteDatabase,strSubject,strBody,strDate);
 SimpleCursorAdapter simpleCursorAdapter=new SimpleCursorAdapter(MainActivity.this,R.layout.result,cursor,new String[]{"_id", "subject", "body", "date"},
  new int[]{R.id.memento_num, R.id.memento_subject, R.id.memento_body, R.id.memento_date});
 //为listview添加适配器
 result.setAdapter(simpleCursorAdapter);
 break;
 }
 }
 //添加数据到数据库中的方法
 public void add(SQLiteDatabase sqLiteDatabase,String subject,String body,String date){
 sqLiteDatabase.execSQL("Insert into memento_tb values(null,?,?,?)",new String[]{subject,body,date});
 //初始设置为空
 this.subject.setText("");
 this.body.setText("");
 this.date.setText("");
 }
 //查询的方法，返回值为cursor
 public Cursor query(SQLiteDatabase sqLiteDatabase, String subject, String body, String date){
 Cursor cursor = sqLiteDatabase.rawQuery(
 "select * from memento_tb where subject like ? and body like ? and date like ? ",
 new String[]{"%" + subject + "%", "%" + body + "%",
  "%" + date + "%"});//对表的查询（insert的操作）
 return cursor;
 }
 protected void onDestroy() {
 super.onDestroy();
 if (mMyDataBaseHelper != null) {
 mMyDataBaseHelper.close();
 }
 }
}

public class MyDataBaseHelper extends SQLiteOpenHelper {
 //创建数据库的语句
 final String CREATE_TABLE_SQL =
 "create table memento_tb(_id integer primary " +
  "key autoincrement,subject,body,date)"; //建表
 public MyDataBaseHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
 super(context, name, factory, version);
 }
 //执行建表的操作
 @Override
 public void onCreate(SQLiteDatabase db) {
 db.execSQL(CREATE_TABLE_SQL);
 }
 @Override
 public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
 System.out.println("---------" + oldVersion + "------->" + newVersion);
 }
}