在过去的两天里，我遇到了一个小问题。让我先解释一下情况。我从我的服务器获取一些数据（当然是JSON对象），将它们存储在数据库中并在回收站视图中显示它们。
现在我想尝试一些有趣的事情。 Wifi关闭时应显示数据。我认为我不会有任何问题，因为从sqlite数据库读取的数据。但不知何故，在这种情况下，我的屏幕上没有显示任何内容。
这是我的代码：
AnnouncementsFragment
public class AnnouncementsFragment extends Fragment {
public String titleForSQLite;
public String imageForSQLite;
public String articleForSQLite;
public static final String TAG = "AelApp";
private ArrayList<AnnouncementsModel> listItemsList;
private static final String IMAGE_URL = "http://www.theo-android.co.uk/ael/cms/announcement_images/";
AnnouncementsModel item;
RecyclerView myList;
AnnouncementsDatabaseHandler dba;
Context mContext;
private ArrayList<AnnouncementsModel> dbAnnouncements = new ArrayList<>();
private AnnouncementsAdapter announcementsAdapter;
public static final String ANNOUNCMENT_TAG = "ANNOUNCEMENT_FRAGMENT";
public AnnouncementsFragment() {
// Required empty public constructor
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
getActivity().setTitle("Ανακοινώσεις");
View rootView = inflater.inflate(R.layout.fragment_announcements, container, false);
listItemsList = new ArrayList<>();
dba = new AnnouncementsDatabaseHandler(getActivity());
myList = (RecyclerView) rootView.findViewById(R.id.listview_announcements);
final LinearLayoutManager linearLayoutManager = new LinearLayoutManager(getActivity());
myList.setHasFixedSize(true);
myList.setLayoutManager(linearLayoutManager);
announcementsAdapter = new AnnouncementsAdapter(getActivity(), listItemsList);
myList.setAdapter(announcementsAdapter);
updateAnnouncementsList();
storingDataToSQlite();
return rootView;
}
public void updateAnnouncementsList() {
listItemsList.clear();
// Instantiate the RequestQueue.
RequestQueue queue = Volley.newRequestQueue(getActivity());
// Request a string response from the provided URL.
JsonArrayRequest jsObjRequest = new JsonArrayRequest(Request.Method.GET, URL.GET_ANNOUNCEMENTS, new Response.Listener<JSONArray>() {
@Override
public void onResponse(JSONArray response) {
Log.d(TAG, response.toString());
//hidePD();
// Parse json data.
// Declare the json objects that we need and then for loop through the children array.
// Do the json parse in a try catch block to catch the exceptions
try {
for (int i = 0; i < response.length(); i++) {
JSONObject post = response.getJSONObject(i);
item = new AnnouncementsModel();
item.setAnnouncement_title(post.getString("title"));
item.setAnnouncement_image(IMAGE_URL + post.getString("announcement_image"));
item.setAnnouncement_article(post.getString("article"));
listItemsList.add(item);
//Here I store the json strings.
titleForSQLite = post.getString("title");
imageForSQLite = post.getString("announcement_image");
articleForSQLite = post.getString("article");
}
} catch (JSONException e) {
e.printStackTrace();
}
// Update list by notifying the adapter of changes
announcementsAdapter.notifyDataSetChanged();
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
VolleyLog.d(TAG, "Error: " + error.getMessage());
//hidePD();
}
});
queue.add(jsObjRequest);
}
/*
* A method that add data in the SQlite database. It is found in AnnouncementsDatabaseHandler class
*/
public void storingDataToSQlite(){
AnnouncementsModel myAnnouncements = new AnnouncementsModel();
myAnnouncements.setAnnouncement_title(titleForSQLite);
myAnnouncements.setAnnouncement_title(imageForSQLite);
myAnnouncements.setAnnouncement_article(articleForSQLite);
dba.addAnnouncements(myAnnouncements);
fetchDataFromDB();
dba.close();
}
/*
* A method that reads data from the database. It is found in AnnouncementsDatabaseHandler class
*/
public void fetchDataFromDB() {
ArrayList<AnnouncementsModel> membersDB = dba.getAnnouncements();
for(int i=0; i<membersDB.size();i++){
String id = membersDB.get(i).getAnnouncement_id();
String mTitle = membersDB.get(i).getAnnouncement_title();
String mArticle = membersDB.get(i).getAnnouncement_article();
String image = membersDB.get(i).getAnnouncement_image();
AnnouncementsModel f = new AnnouncementsModel();
f.setAnnouncement_id(id);
f.setAnnouncement_title(mTitle);
f.setAnnouncement_article(mArticle);
f.setAnnouncement_image(image);
dbAnnouncements.add(f);
}
dba.close();
}
}
在我的webservice方法中，我从响应中提取json字符串。（也许我应该从ArrayList中读取字符串？）
//Here I store the json strings.
titleForSQLite = post.getString("title");
imageForSQLite = post.getString("announcement_image");
articleForSQLite = post.getString("article");
接下来，我在数据库中添加了titleForSQLite，imageForSQLite，articleForSQLite。
public void storingDataToSQlite(){
AnnouncementsModel myAnnouncements = new AnnouncementsModel();
myAnnouncements.setAnnouncement_title(titleForSQLite);
myAnnouncements.setAnnouncement_title(imageForSQLite);
myAnnouncements.setAnnouncement_article(articleForSQLite);
dba.addAnnouncements(myAnnouncements);
fetchDataFromDB();
dba.close();
}
最后我读了它们
public void fetchDataFromDB() {
ArrayList<AnnouncementsModel> membersDB = dba.getAnnouncements();
for(int i=0; i<membersDB.size();i++){
String id = membersDB.get(i).getAnnouncement_id();
String mTitle = membersDB.get(i).getAnnouncement_title();
String mArticle = membersDB.get(i).getAnnouncement_article();
String image = membersDB.get(i).getAnnouncement_image();
AnnouncementsModel f = new AnnouncementsModel();
f.setAnnouncement_id(id);
f.setAnnouncement_title(mTitle);
f.setAnnouncement_article(mArticle);
f.setAnnouncement_image(image);
dbAnnouncements.add(f);
}
dba.close();
}
那么为什么我遇到了我之前描述的问题呢？由于所有内容都存储在数据库中，因此数据应该同时读取ON和OFF的情况，对吗？有什么想法吗？
这是我的sqlite db代码。
public class AnnouncementsDatabaseHandler extends SQLiteOpenHelper {
private final ArrayList<AnnouncementsModel> announcementsModelArrayList = new ArrayList<>();
public AnnouncementsDatabaseHandler(Context context) {
super(context, Constants.DATABASE_NAME, null, Constants.DATABASE_VERSION);
}
/*
* This callback method creates the database
*/
@Override
public void onCreate(SQLiteDatabase db) {
String CREATE_ANNOUNCEMENTS_TABLE = "CREATE TABLE IF NOT EXISTS " + AnnouncementsConstants.TABLE_NAME +
"(" + AnnouncementsConstants.KEY_ID + " INTEGER PRIMARY KEY, " + AnnouncementsConstants.ANNOUNCEMENT_TITLE+
" TEXT, " + AnnouncementsConstants.ANNOUNCEMENT_image + " TEXT, " + AnnouncementsConstants.ANNOUNCEMENT_article + " TEXT);";
db.execSQL(CREATE_ANNOUNCEMENTS_TABLE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int i, int i1) {
db.execSQL("DROP TABLE IF EXISTS " + AnnouncementsConstants.TABLE_NAME);
onCreate(db);
}
/*
*Add contents to table. Those contents are json strings that
*are retrieved from the server!
*/
public void addAnnouncements(AnnouncementsModel announcementsModel) {
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(AnnouncementsConstants.KEY_ID,announcementsModel.getAnnouncement_id());
values.put(AnnouncementsConstants.ANNOUNCEMENT_article, announcementsModel.getAnnouncement_title());
values.put(AnnouncementsConstants.ANNOUNCEMENT_image, announcementsModel.getAnnouncement_title());
values.put(AnnouncementsConstants.ANNOUNCEMENT_article, announcementsModel.getAnnouncement_article());
db.insertWithOnConflict(AnnouncementsConstants.TABLE_NAME, AnnouncementsConstants.KEY_ID, values,
SQLiteDatabase.CONFLICT_REPLACE);
db.close();
Log.d("Theo", "heeeey!data saved");
}
/*
* This method allows to read the stored data,and returns an
* array list.
*/
public ArrayList<AnnouncementsModel> getAnnouncements() {
String select_query = "SELECT * " + AnnouncementsConstants.TABLE_NAME;
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.query(Constants.TABLE_NAME, new String[]{
AnnouncementsConstants.KEY_ID, AnnouncementsConstants.ANNOUNCEMENT_TITLE, AnnouncementsConstants.ANNOUNCEMENT_article
,AnnouncementsConstants.ANNOUNCEMENT_image}, null, null, null, null,
Constants.KEY_ID + " DESC");
if (cursor.moveToFirst()) {
do {
AnnouncementsModel m = new AnnouncementsModel();
m.setAnnouncement_title(cursor.getString(cursor.getColumnIndex(AnnouncementsConstants.ANNOUNCEMENT_TITLE)));
m.setAnnouncement_image(cursor.getString(cursor.getColumnIndex(AnnouncementsConstants.ANNOUNCEMENT_image)));
m.setAnnouncement_article(cursor.getString(cursor.getColumnIndex(AnnouncementsConstants.ANNOUNCEMENT_article)));
m.setAnnouncement_id(cursor.getString(cursor.getColumnIndex(AnnouncementsConstants.KEY_ID)));
announcementsModelArrayList.add(m);
}while(cursor.moveToNext());
}
return announcementsModelArrayList;
}
谢谢，
西奥。
答案 0 :(得分：1)
答案 1 :(得分：0)
我认为您的选择查询错误
应该是
String select_query = "SELECT * from " + AnnouncementsConstants.TABLE_NAME;
从服务器
收到数据后，请调用以下方法表单进行循环storingDataToSQlite（）;
和fetchDataFromDB（）;在for循环结束后......或者如果数据已经存在，你也可以从oncreate调用这个方法
在Oncreate中添加以下代码
if(isOnline)
{
// get data from server
}else{
// fetch data from db
}
答案 2 :(得分：-2)
试试这个
public void fetchDataFromDB() {
ArrayList<AnnouncementsModel> membersDB = dba.getAnnouncements();
for(int i=0; i<membersDB.size();i++){
Cursor cursor = database.query(YOUR_TABLE_NAME,YOURCOLUMN_NAME[0],null, null, null, null, null, null);
if (cursor.moveToFirst()) {
while (!cursor.isAfterLast()) {
AnnouncementsModel f = new AnnouncementsModel();
f.setAnnouncement_id(cursor.getInt(cursor.getColumnIndex("this is db key for id")));
f.setAnnouncement_title(cursor.getString(cursor.getColumnIndex("title key")));
f.setAnnouncement_article(cursor.getString(cursor.getColumnIndex("article key")));
dbAnnouncements.add(f);
}
}
}
dba.close();
}