当我进入应用程序更深处的不同活动并按向上按钮返回原始活动时，不会显示使用 sqlite 存储的应用程序中保存的数据。
这是由 listactivity 膨胀的 listfragment。
请注意，我将查询放在 onCreate 中，以便在返回活动时再次执行它。
package com.example.sample;
import java.util.ArrayList;
import android.app.Activity;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Build;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;
import com.actionbarsherlock.app.SherlockListFragment;
/**
* A list fragment representing a list of Courses. This fragment also supports
* tablet devices by allowing list items to be given an 'activated' state upon
* selection. This helps indicate which item is currently being viewed in a
* {@link CourseDetailFragment}.
* <p>
* Activities containing this fragment MUST implement the {@link Callbacks}
* interface.
*/
public class CourseListFragment extends SherlockListFragment {
SQLiteDatabase db;
DbHelper dbHelper;
boolean bool = false;
private static String courseName;
ArrayList<String> courseItems;
ArrayAdapter<String> adapter;
/**
* The serialization (saved instance state) Bundle key representing the
* activated item position. Only used on tablets.
*/
private static final String STATE_ACTIVATED_POSITION = "activated_position";
/**
* The fragment's current callback object, which is notified of list item
* clicks.
*/
private Callbacks mCallbacks = sDummyCallbacks;
/**
* The current activated item position. Only used on tablets.
*/
private int mActivatedPosition = ListView.INVALID_POSITION;
/**
* A callback interface that all activities containing this fragment must
* implement. This mechanism allows activities to be notified of item
* selections.
*/
public interface Callbacks {
/**
* Callback for when an item has been selected.
*/
public void onItemSelected(String id);
}
/**
* A dummy implementation of the {@link Callbacks} interface that does
* nothing. Used only when this fragment is not attached to an activity.
*/
private static Callbacks sDummyCallbacks = new Callbacks() {
@Override
public void onItemSelected(String id) {
}
};
/**
* Mandatory empty constructor for the fragment manager to instantiate the
* fragment (e.g. upon screen orientation changes).
*/
public CourseListFragment() {
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
dbHelper = new DbHelper(getActivity());
db = dbHelper.getReadableDatabase();
courseItems = new ArrayList<String>();
int layout = (Build.VERSION.SDK_INT >= 11) ? android.R.layout.simple_list_item_activated_1
: android.R.layout.simple_list_item_1;
adapter = new ArrayAdapter<String>(getActivity(), layout, courseItems);
// TODO: replace with a real list adapter.
setListAdapter(adapter);
if (bool) {
String[] projection = { DbHelper.COURSE_NAME };
Cursor c = db.query(DbHelper.TABLE_NAME, projection, null, null,
null, null, null);
c.moveToFirst();
while (c.moveToNext()) {
courseName = c
.getString(c.getColumnIndex(DbHelper.COURSE_NAME));
courseItems.add(courseName);
}
c.close();
adapter.notifyDataSetChanged();
}
}
@Override
public void onViewCreated(View view, Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
// Restore the previously serialized activated item position.
if (savedInstanceState != null
&& savedInstanceState.containsKey(STATE_ACTIVATED_POSITION)) {
setActivatedPosition(savedInstanceState
.getInt(STATE_ACTIVATED_POSITION));
}
}
public void addCourse() {
String[] projection = { DbHelper.COURSE_NAME };
Cursor c = db.query(DbHelper.TABLE_NAME, projection, null, null, null,
null, null);
c.moveToFirst();
while (c.moveToNext()) {
courseName = c.getString(c.getColumnIndex(DbHelper.COURSE_NAME));
courseItems.add(courseName);
}
c.close();
adapter.notifyDataSetChanged();
bool = true;
}
@Override
public void onAttach(Activity activity) {
super.onAttach(activity);
// Activities containing this fragment must implement its callbacks.
if (!(activity instanceof Callbacks)) {
throw new IllegalStateException(
"Activity must implement fragment's callbacks.");
}
mCallbacks = (Callbacks) activity;
}
@Override
public void onDetach() {
super.onDetach();
// Reset the active callbacks interface to the dummy implementation.
mCallbacks = sDummyCallbacks;
}
@Override
public void onListItemClick(ListView listView, View view, int position,
long id) {
super.onListItemClick(listView, view, position, id);
// Notify the active callbacks interface (the activity, if the
// fragment is attached to one) that an item has been selected.
mCallbacks.onItemSelected(null);
}
@Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
if (mActivatedPosition != ListView.INVALID_POSITION) {
// Serialize and persist the activated item position.
outState.putInt(STATE_ACTIVATED_POSITION, mActivatedPosition);
}
}
/**
* Turns on activate-on-click mode. When this mode is on, list items will be
* given the 'activated' state when touched.
*/
public void setActivateOnItemClick(boolean activateOnItemClick) {
// When setting CHOICE_MODE_SINGLE, ListView will automatically
// give items the 'activated' state when touched.
getListView().setChoiceMode(
activateOnItemClick ? ListView.CHOICE_MODE_SINGLE
: ListView.CHOICE_MODE_NONE);
}
public void setActivatedPosition(int position) {
if (position == ListView.INVALID_POSITION) {
getListView().setItemChecked(mActivatedPosition, false);
} else {
getListView().setItemChecked(position, true);
}
mActivatedPosition = position;
}
}
为 onoviewstaterestored 更新了编辑
package com.example.sample;
import java.util.ArrayList;
import android.app.Activity;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Build;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;
import com.actionbarsherlock.app.SherlockListFragment;
/**
* A list fragment representing a list of Courses. This fragment also supports
* tablet devices by allowing list items to be given an 'activated' state upon
* selection. This helps indicate which item is currently being viewed in a
* {@link CourseDetailFragment}.
* <p>
* Activities containing this fragment MUST implement the {@link Callbacks}
* interface.
*/
public class CourseListFragment extends SherlockListFragment {
SQLiteDatabase db;
DbHelper dbHelper;
boolean bool = false;
private static String courseName;
ArrayList<String> courseItems;
ArrayAdapter<String> adapter;
/**
* The serialization (saved instance state) Bundle key representing the
* activated item position. Only used on tablets.
*/
private static final String STATE_ACTIVATED_POSITION = "activated_position";
/**
* The fragment's current callback object, which is notified of list item
* clicks.
*/
private Callbacks mCallbacks = sDummyCallbacks;
/**
* The current activated item position. Only used on tablets.
*/
private int mActivatedPosition = ListView.INVALID_POSITION;
/**
* A callback interface that all activities containing this fragment must
* implement. This mechanism allows activities to be notified of item
* selections.
*/
public interface Callbacks {
/**
* Callback for when an item has been selected.
*/
public void onItemSelected(String id);
}
/**
* A dummy implementation of the {@link Callbacks} interface that does
* nothing. Used only when this fragment is not attached to an activity.
*/
private static Callbacks sDummyCallbacks = new Callbacks() {
@Override
public void onItemSelected(String id) {
}
};
/**
* Mandatory empty constructor for the fragment manager to instantiate the
* fragment (e.g. upon screen orientation changes).
*/
public CourseListFragment() {
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
dbHelper = new DbHelper(getActivity());
db = dbHelper.getReadableDatabase();
courseItems = new ArrayList<String>();
int layout = (Build.VERSION.SDK_INT >= 11) ? android.R.layout.simple_list_item_activated_1
: android.R.layout.simple_list_item_1;
adapter = new ArrayAdapter<String>(getActivity(), layout, courseItems);
// TODO: replace with a real list adapter.
setListAdapter(adapter);
}
@Override
public void onViewCreated(View view, Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
// Restore the previously serialized activated item position.
if (savedInstanceState != null
&& savedInstanceState.containsKey(STATE_ACTIVATED_POSITION)) {
setActivatedPosition(savedInstanceState
.getInt(STATE_ACTIVATED_POSITION));
}
}
@Override
public void onViewStateRestored(Bundle savedInstanceState) {
super.onViewStateRestored(savedInstanceState);
String[] projection = { DbHelper.COURSE_NAME };
Cursor c = db.query(DbHelper.TABLE_NAME, projection, null, null, null,
null, null);
c.moveToFirst();
while (c.moveToNext()) {
courseName = c.getString(c.getColumnIndex(DbHelper.COURSE_NAME));
courseItems.add(courseName);
}
c.close();
adapter.notifyDataSetChanged();
}
@Override
public void onAttach(Activity activity) {
super.onAttach(activity);
// Activities containing this fragment must implement its callbacks.
if (!(activity instanceof Callbacks)) {
throw new IllegalStateException(
"Activity must implement fragment's callbacks.");
}
mCallbacks = (Callbacks) activity;
}
@Override
public void onDetach() {
super.onDetach();
// Reset the active callbacks interface to the dummy implementation.
mCallbacks = sDummyCallbacks;
}
@Override
public void onListItemClick(ListView listView, View view, int position,
long id) {
super.onListItemClick(listView, view, position, id);
// Notify the active callbacks interface (the activity, if the
// fragment is attached to one) that an item has been selected.
mCallbacks.onItemSelected(null);
}
@Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
if (mActivatedPosition != ListView.INVALID_POSITION) {
// Serialize and persist the activated item position.
outState.putInt(STATE_ACTIVATED_POSITION, mActivatedPosition);
}
}
/**
* Turns on activate-on-click mode. When this mode is on, list items will be
* given the 'activated' state when touched.
*/
public void setActivateOnItemClick(boolean activateOnItemClick) {
// When setting CHOICE_MODE_SINGLE, ListView will automatically
// give items the 'activated' state when touched.
getListView().setChoiceMode(
activateOnItemClick ? ListView.CHOICE_MODE_SINGLE
: ListView.CHOICE_MODE_NONE);
}
public void setActivatedPosition(int position) {
if (position == ListView.INVALID_POSITION) {
getListView().setItemChecked(mActivatedPosition, false);
} else {
getListView().setItemChecked(position, true);
}
mActivatedPosition = position;
}
}