使用数据库实现对数据的存储。
以下上一个小样例，写日记。
效果例如以下：
当LIstView中没有数据显示时，我们须要告诉用户没有数据.
方法有二:
1.
activity继承ListActivity，在布局文件里例如以下编写：
<TextView
android:id="@id/android:empty"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="你好懒啊。还没開始写日记呢" />
<ListView
<span style="white-space:pre"> </span> android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/android:list"/> 2.
<span style="white-space:pre"> </span>if(adapter.isEmpty()&&textView==null){
textView = new TextView(MainActivity.this);
textView.setText("主人非常懒，什么也没留下");
textView.setVisibility(View.GONE);
((ViewGroup) listView.getParent()).addView(textView);
listView.setEmptyView(textView);
}else{
listView.setAdapter(simpleCursorAdapter);
}数据库的使用（安卓本身自带SQLite，假设想使用其它的数据库，那就得使用Web Server）：
继承SQLiteOpenHelper。
public DBHelper(Context context) //数据库的名字，数据库的版本号 public void onCreate(SQLiteDatabase db)////创建数据库 public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion)//更新数据库
详细代码例如以下：
cn.edu.bzu.diary.activity
MainActivity.java
public class MainActivity extends Activity {
ListView listView;
Cursor diaries;//游标
TextView textView = null;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
listView = (ListView) findViewById(R.id.listview);
refreshList();
this.registerForContextMenu(listView);
}
/**
* 刷新Adapter
*/
public void refreshList(){
DiaryDao diaryDao = new DiaryDao(this);
diaries = diaryDao.getAllDairies();
SimpleCursorAdapter simpleCursorAdapter = new SimpleCursorAdapter(
MainActivity.this, R.layout.item, diaries, new String[] { "title",
"created" }, new int[] { R.id.title, R.id.created });
if(simpleCursorAdapter.isEmpty()&&textView==null){
textView = new TextView(MainActivity.this);
textView.setText("主人非常懒，什么也没留下");
textView.setVisibility(View.GONE);
((ViewGroup) listView.getParent()).addView(textView);
listView.setEmptyView(textView);
}else{
listView.setAdapter(simpleCursorAdapter);
}
}
@Override
public void onCreateContextMenu(ContextMenu menu, View v,
ContextMenuInfo menuInfo) {
menu.setHeaderTitle("操作");
menu.add(0, 1, Menu.NONE, "编辑");
menu.add(0, 2, Menu.NONE, "删除");
super.onCreateContextMenu(menu, v, menuInfo);
}
@Override
public boolean onContextItemSelected(MenuItem item) { // onContextItemSelected
AdapterContextMenuInfo menuInfo = (AdapterContextMenuInfo) item
.getMenuInfo();
switch (item.getItemId()) {
case 1:
Intent intent = new Intent();
Bundle bundle = new Bundle();
bundle.putInt("id", (int)menuInfo.id);
intent.putExtras(bundle);
intent.setClass(MainActivity.this, DiaryEditAcitivity.class);
startActivity(intent);
break;
case 2:
DiaryDao dao = new DiaryDao(MainActivity.this);
dao.delete((int) menuInfo.id);//menuInfo.id与数据库的ID一致
refreshList();
break;
}
return super.onContextItemSelected(item);
}
/**
* 在退出日记加入中。利用生命周期刷新Adapter
*/
@Override
protected void onResume() {
super.onResume();
refreshList();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
/**
* 通过菜单进入“日记加入页面”
*/
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case R.id.save:
Intent intent = new Intent();
intent.setClass(MainActivity.this, DiaryAddAcitivity.class);
startActivity(intent);
break;
}
return super.onOptionsItemSelected(item);
}
}
public class DiaryAddAcitivity extends Activity {
DiaryDao diaryDao = new DiaryDao(DiaryAddAcitivity.this);
Button button;
EditText editText,editText2;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.diaryadd_acitivity);
editText = (EditText) findViewById(R.id.et_diaryadd);//标题
editText2 = (EditText) findViewById(R.id.et02_diaryadd);//内容
button = (Button) findViewById(R.id.but);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.diary_add_acitivity, menu);
return true;
}
public void click(View view){
String title = editText.getText().toString();
String content = editText2.getText().toString();
Diary diary = new Diary(title, content, Tool.dateChange(new Date()));
DiaryDao diaryDao = new DiaryDao(this);
diaryDao.save(diary);
finish();
}
}
DiaryEditAcitivity.java
public class DiaryEditAcitivity extends Activity {
DiaryDao diaryDao = new DiaryDao(DiaryEditAcitivity.this);
Button button;
EditText editText,editText2;
int id ;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.diaryadd_acitivity);
editText = (EditText) findViewById(R.id.et_diaryadd);//标题
editText2 = (EditText) findViewById(R.id.et02_diaryadd);//内容
button = (Button) findViewById(R.id.but);
Bundle bundle = this.getIntent().getExtras();
if(bundle!=null){
id = bundle.getInt("id");
Diary diary = diaryDao.getDiaryById(id);
editText.setText(diary.getTitle());
editText2.setText(diary.getContent());
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.diary_add_acitivity, menu);
return true;
}
public void click(View view){
String title = editText.getText().toString();
String content = editText2.getText().toString();
Diary diary = new Diary(title, content, Tool.dateChange(new Date()));
diary.setId(id);
DiaryDao diaryDao = new DiaryDao(this);
diaryDao.update(diary);
finish();
}
}
cn.edu.bzu.diary.dao
DiaryDao.javapublic class DiaryDao {
private DBHelper dbHelper;
private SQLiteDatabase sqLiteDatabase;
public DiaryDao(Context context) {
dbHelper = new DBHelper(context);
}
/**
* 加入日记
* @param diary
*/
public void save(Diary diary) {
String sql = "insert into diary(title,content,created) values(?,?,?)";
sqLiteDatabase = dbHelper.getWritableDatabase();
sqLiteDatabase.execSQL(
sql,
new String[] { diary.getTitle(), diary.getContent(),
diary.getDatetime() });
}
/**
* 依据id删除日记
*
* @param id
* 日记的id号
*/
public void delete(Integer id) {
sqLiteDatabase = dbHelper.getWritableDatabase();// 得到的是同一个数据库实例
sqLiteDatabase.execSQL("delete from diary where _id=?
",
new Object[] { id });
}
/**
* 更新日记
*
* @param diary
*/
public void update(Diary diary) {
sqLiteDatabase = dbHelper.getWritableDatabase();// 得到的是同一个数据库实例
sqLiteDatabase.execSQL(
"update diary set title=?,content=?,created=? where _id=?",
new Object[] { diary.getTitle(), diary.getContent(),
diary.getDatetime(), diary.getId() });
}
/**
* 返回一个游标。也能够使用凝视部分。返回一个List集合（使用SimpleAdapter），在这里使用游标，主要是由于
* AdapterContextMenuInfo中的ID是和数据库中一致的
* @return cursor
*/
public Cursor getAllDairies() {
//Diary diary = null;
//List<Diary> diaries = new ArrayList<Diary>();
sqLiteDatabase = dbHelper.getReadableDatabase();
Cursor cursor = sqLiteDatabase.rawQuery("select * from diary ", null);
/*
* while(cursor.moveToNext()){ String title =
* cursor.getString(cursor.getColumnIndex("title")); String content =
* cursor.getString(cursor.getColumnIndex("content")); String created =
* cursor.getString(cursor.getColumnIndex("created")); diary = new
* Diary(title, content, created); diaries.add(diary); }
*/
return cursor;
}
/**
* 获取记录总数
*/
public long count() {
long count = 0;
sqLiteDatabase = dbHelper.getReadableDatabase();
Cursor cursor = sqLiteDatabase.rawQuery("select count(*) from diary ",
null);
cursor.moveToFirst();
count = cursor.getLong(0);
return count;
}
public Diary getDiaryById(int id) {
sqLiteDatabase = dbHelper.getWritableDatabase();
Diary diary = null;
Cursor cursor = sqLiteDatabase.rawQuery(
"select * from diary where _id= ?", new String[] { id + "" });
if (cursor.moveToFirst()) {
String title = cursor.getString(cursor.getColumnIndex("title"));
String content = cursor.getString(cursor.getColumnIndex("content"));
String created = cursor.getString(cursor.getColumnIndex("created"));
diary = new Diary(title, content, created);
}
return diary;
}
}
cn.edu.bzu.diary.db
DBHelper.javapublic class DBHelper extends SQLiteOpenHelper{
public static final String DATABASE_NAME="diary.db";
public static final int VERSION = 1;
//数据库的名字。数据库的版本号
public DBHelper(Context context) {
super(context, DATABASE_NAME, null, VERSION);
// TODO Auto-generated constructor stub
}
//创建数据库，字段：id（主键），title，content，created。
@Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
db.execSQL("create table diary(_id integer primary key autoincrement,title varchar(20),content varchar(1000),created)");
}
//用于数据库的更新
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
}
}
cn.edu.bzu.diary.entity
Diary.javapublic class Diary {
private Integer id;
private String title;
private String content;
private String datetime;
public Diary(){
}
public Diary(String title,String content,String datetime){
this.title = title;
this.content = content;
this.datetime = datetime;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public String getContent() {
return content;
}
public void setContent(String content) {
this.content = content;
}
public String getDatetime() {
return datetime;
}
public void setDatetime(String datetime) {
this.datetime = datetime;
}
@Override
public String toString() {
return "Diary [title=" + title + ", content=" + content + ", datetime="
+ datetime + "]";
}
}
cn.edu.bzu.diary.tools
public class Tool {
/**
* 时间显示样式
* @param date
* @return
*/
public static String dateChange(Date date){
SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy年MM月dd日 hh时:mm分:ss秒");
return simpleDateFormat.format(date);
}
}代码下载地址