private DBManager mgr; private ListView listView;
@Override
public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main);
listView = (ListView) findViewById(R.id.listView); //初始化DBManager
mgr = new DBManager(this); }
@Override
protected void onDestroy() { }
public void add(View view) {
ArrayList
Person person1 = new Person(\Person person2 = new Person(\Person person3 = new Person(\Person person4 = new Person(\Person person5 = new Person(\
persons.add(person1); persons.add(person2); persons.add(person3); persons.add(person4); persons.add(person5);
mgr.add(persons); super.onDestroy();
//应用的最后一个Activity关闭时应释放DB mgr.closeDB();
}
public void update(View view) { }
public void delete(View view) { }
public void query(View view) { }
public void queryTheCursor(View view) {
List
ArrayList SimpleAdapter adapter = new SimpleAdapter(this, list, new String[]{\ HashMap map.put(\list.add(map); Person person = new Person(); person.age = 30; mgr.deleteOldPerson(person); Person person = new Person(); person.name = \person.age = 30; mgr.updateAge(person); String>>(); String>(); person.info); android.R.layout.simple_list_item_2, int[]{android.R.id.text1, android.R.id.text2}); listView.setAdapter(adapter); { } } Cursor c = mgr.queryTheCursor(); startManagingCursor(c); //托付给activity根据自己的生命 周期去管理Cursor的生命周期 CursorWrapper cursorWrapper = new CursorWrapper(c) { }; //确保查询结果中有\列 SimpleCursorAdapter adapter = new cursorWrapper, new String[]{\ @Override public String getString(int columnIndex) { } //将简介前加上年龄 if (getColumnName(columnIndex).equals(\ } return super.getString(columnIndex); int age = getInt(getColumnIndex(\return age + \ super.getString(columnIndex); SimpleCursorAdapter(this, android.R.layout.simple_list_item_2, \ ListView listView = (ListView) listView.setAdapter(adapter); findViewById(R.id.listView); 这里需要注意的是SimpleCursorAdapter的应用，当我们使用这个适配器时，我们必须先得到一个Cursor对象，这里面有几个问题：如何管理Cursor的生命周期，如果包装Cursor，Cursor结果集都需要注意什么。 如果手动去管理Cursor的话会非常的麻烦，还有一定的风险，处理不当的话运行期间就会出现异常，幸好Activity为我们提供了startManagingCursor(Cursor cursor)方法，它会根据Activity的生命周期去管理当前的Cursor对象，下面是该方法的说明： [java]view plaincopyprint? 1. /** 2. * This method allows the activity to take care of managing the gi ven 3. * {@link Cursor}'s lifecycle for you based on the activity's life cycle. 4. * That is, when the activity is stopped it will automatically cal l 5. * {@link Cursor#deactivate} on the given Cursor, and when it is l ater restarted 6. * it will call {@link Cursor#requery} for you. When the activity is 7. * destroyed, all managed Cursors will be closed automatically. 8. * 9. * @param c The Cursor to be managed. 10. * 11. * @see #managedQuery(android.net.Uri , String[], String, String[] , String) 12. * @see #stopManagingCursor 13. */ /** * This method allows the activity to take care of managing the given * {@link Cursor}'s lifecycle for you based on the activity's lifecycle. * That is, when the activity is stopped it will automatically call * {@link Cursor#deactivate} on the given Cursor, and when it is later restarted * it will call {@link Cursor#requery} for you. When the activity is * destroyed, all managed Cursors will be closed automatically. * * @param c The Cursor to be managed. * * @see #managedQuery(android.net.Uri , String[], String, String[], String) * @see #stopManagingCursor */ 文中提到，startManagingCursor方法会根据Activity的生命周期去管理当前的Cursor对象的生命周期，就是说当Activity停止时他会自动调用Cursor的deactivate方法，禁用游标，当Activity重新回到屏幕时它会调用Cursor的requery方法再次查询，当Activity摧毁时，被管理的Cursor都会自动关闭释放。 如何包装Cursor：我们会使用到CursorWrapper对象去包装我们的Cursor对象，实现我们需要的数据转换工作，这个CursorWrapper实际上是实现了Cursor接口。我们查询获取到的Cursor其实是Cursor的引用，而系统实际返回给我们的必然是Cursor接口的一个实现类的对象实例，我们用CursorWrapper包装这个实例，然后再使用SimpleCursorAdapter将结果显示到列表上。 Cursor结果集需要注意些什么：一个最需要注意的是，在我们的结果集中必须要包含一个“_id”的列，否则SimpleCursorAdapter就会翻脸不认人，为什么一定要这样呢？因为这源于SQLite的规范，主键以“_id”为标准。解决办法有三：第一，建表时根据规范去做；第二，查询时用别名，例如：SELECT id AS _id FROM person；第三，在CursorWrapper里做文章： [java]view plaincopyprint? 1. CursorWrapper cursorWrapper = new CursorWrapper(c) { 2. @Override 3. public int getColumnIndexOrThrow(String columnName) throws Illegal ArgumentException { 4. if (columnName.equals(\5. return super.getColumnIndex(\6. } 7. return super.getColumnIndexOrThrow(columnName); 8. } 9. }; CursorWrapper cursorWrapper = new CursorWrapper(c) { @Override public int getColumnIndexOrThrow(String columnName) if (columnName.equals(\ } return return super.getColumnIndex(\ throws IllegalArgumentException { super.getColumnIndexOrThrow(columnName); }; } 如果试图从CursorWrapper里获取“_id”对应的列索引，我们就返回查询结果里“id”对应的列索引即可。 最后我们来看一下结果如何：