我有一个以JSON响应的API。当我单击一个按钮时，我很容易解析JSON并在ListView中实现它。问题是当我打开我的应用程序时
再次，数据再次出现在ListView中。
以下是我的代码 -
Monday.java：
package com.example.reema.datatab2;
import android.app.ProgressDialog;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import android.widget.Toast;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
/**
* Created by reema on 30-Jan-17.
*/
public class Monday extends Fragment {
private String TAG = Monday.class.getSimpleName();
DatabaseHandler databaseHandler;
static boolean isDataLoaded = false;
private ProgressDialog pDialog;
ArrayList<HashMap<String, String>> mondayList;
ListView listview;
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View v=inflater.inflate(R.layout.monday,container,false);
mondayList= new ArrayList<>();
listview =(ListView)v.findViewById(R.id.lstmonday);
new GetContacts().execute();
return v;
}
class GetContacts extends AsyncTask<Void, Void, Void> {
@Override
protected Void doInBackground(Void... params) {
databaseHandler = new DatabaseHandler(getActivity());
HttpHandler sh = new HttpHandler();
String url = "My link here";
String jsonStr = sh.makeServiceCall(url);
Log.e(TAG, "Responce from url:" + jsonStr);
if(isDataLoaded == false) {
if (jsonStr != null) {
try {
JSONObject jsonObj = new JSONObject(jsonStr);
JSONArray Monday = jsonObj.getJSONArray("Monday");
for (int i = 0; i < Monday.length(); i++) {
JSONObject c = Monday.getJSONObject(i);
String SubjectName = c.getString("SubjectName");
String StandardName;
if (c.isNull("StandardName")) {
StandardName = null;
} else {
StandardName = c.getString("StandardName");
}
String DivisionName;
if (c.isNull("DivisionName")) {
DivisionName = null;
} else {
DivisionName = c.getString("DivisionName");
}
String StartTime = c.getString("StartTime");
String EndTime = c.getString("EndTime");
String LectureNoId;
if (c.isNull("DivisionName") && (c.isNull("StandardName"))) {
LectureNoId = null;
} else {
LectureNoId = c.getString("LectureNoId");
}
databaseHandler.addMonday(new People(LectureNoId, SubjectName, StandardName, DivisionName, StartTime, EndTime));
/* HashMap<String, String> monday = new HashMap<>();
monday.put("LectureNoId",LectureNoId);
monday.put("SubjectName", SubjectName);
monday.put("StandardName", StandardName);
monday.put("DivisionName", DivisionName);
monday.put("StartTime", StartTime);
monday.put("EndTime", EndTime);
mondayList.add(monday);*/
}
} catch (final JSONException e) {
Log.e(TAG, "Json parsing error: " + e.getMessage());
getActivity().runOnUiThread(new Runnable() {
public void run() {
Toast.makeText(getActivity().getApplicationContext(),
"Json parsing error: " + e.getMessage(),
Toast.LENGTH_LONG)
.show();
}
});
}
}
}
else {
Log.e(TAG, "Couldn't get json from server.");
getActivity().runOnUiThread(new Runnable() {
@Override
public void run() {
Toast.makeText(getActivity().getApplicationContext(),
"Couldn't get json from server. Check LogCat for possible errors!",
Toast.LENGTH_LONG)
.show();
}
});
}
return null;
}
protected void onPreExecute () {
super.onPreExecute();
// Showing progress dialog
pDialog = new ProgressDialog(getActivity());
pDialog.setMessage("Please wait...");
pDialog.setCancelable(false);
pDialog.show();
}
protected void onPostExecute(Void result) {
super.onPostExecute(result);
if (pDialog.isShowing())
pDialog.dismiss();
List<People>monday = databaseHandler.getAllMonday();
for(People p : monday) {
HashMap<String, String> mondayhash = new HashMap<>();
mondayhash.put("LectureNoId",p.getLectureNoId());
mondayhash.put("SubjectName", p.getSubjectName());
mondayhash.put("StandardName", p.getStandardName());
mondayhash.put("DivisionName", p.getDivisionName());
mondayhash.put("StartTime", p.getStartTime());
mondayhash.put("EndTime", p.getEndTime());
mondayList.add(mondayhash);
}
ListAdapter adapter = new SimpleAdapter(
getActivity(), mondayList,
R.layout.custom_list, new String[]{"SubjectName", "StandardName",
"DivisionName","StartTime","EndTime"}, new int[]{R.id.SubjectName,
R.id.StandardName, R.id.DivisionName,R.id.StartTime,R.id.EndTime});
isDataLoaded=true;
databaseHandler.deleteMonday();
listview.setAdapter(adapter);
}
}
}
Databasehandler.java：
package com.example.reema.datatab2;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
import java.util.ArrayList;
import java.util.List;
public class DatabaseHandler extends SQLiteOpenHelper {
private static final int DATABASE_VERSION = 1;
private static final String DATABASE_NAME = "mondayManager";
private static final String Monday = "monday";
private static final String LectureNoId = "LectureNoId";
private static final String SubjectName = "SubjectName";
private static final String StandardName = "StandardName";
private static final String DivisionName = "DivisionName";
private static final String StartTime = "StartTime";
private static final String EndTime = "EndTime";
public DatabaseHandler(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
String monday = "CREATE TABLE " + Monday + "(" + LectureNoId + " TEXT,"
+ SubjectName + " TEXT," + StandardName + " TEXT," + DivisionName + " TEXT," + StartTime + " TEXT,"
+ EndTime + " TEXT" + ")";
db.execSQL(monday);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("DROP TABLE IF EXISTS Monday ");
db.execSQL("DROP TABLE IF EXISTS Tuesday" );
db.execSQL("DROP TABLE IF EXISTS Wensday" );
db.execSQL("DROP TABLE IF EXISTS Thursday");
db.execSQL("DROP TABLE IF EXISTS Friday");
db.execSQL("DROP TABLE IF EXISTS Saturday");
onCreate(db);
}
public void addMonday(People contact) {
if (!SearchExistingLectureID(contact.getLectureNoId(), Monday)) {
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(LectureNoId, contact.getLectureNoId());
values.put(SubjectName, contact.getSubjectName());
values.put(StandardName, contact.getStandardName());
values.put(DivisionName, contact.getDivisionName());
values.put(StartTime, contact.getStartTime());
values.put(EndTime, contact.getEndTime());
db.insert(Monday, null, values);
Log.d("db", "insert called");
db.close();
}
}
void deleteMonday()
{
SQLiteDatabase db = this.getWritableDatabase();
db.execSQL("delet from Monday");
}
public Boolean SearchExistingLectureID(String LectureID, String Table)
{
String selectQuery = "SELECT * FROM " + Table + " where LectureNoId = " +LectureID;
SQLiteDatabase db = this.getWritableDatabase();
Cursor cursor = db.rawQuery(selectQuery, null);
Boolean retValue = false;
//there is a chance of exceptoin if the lectureid is not found in db.
try {
if (cursor.getCount()>0 && cursor.moveToFirst()) {
String val = cursor.getString(1);
retValue = true;
}
}catch (Exception ex){
Log.d("error", ex.getMessage());
}
return retValue;
}
public List<People> getAllMonday() {
List<People> MondayList = new ArrayList<People>();
String selectQuery = "SELECT * FROM " + Monday;
SQLiteDatabase db = this.getWritableDatabase();
Cursor cursor = db.rawQuery(selectQuery, null);
if (cursor.moveToFirst()) {
do {
People contact = new People(cursor.getString(0),cursor.getString(1), cursor.getString(2), cursor.getString(3), cursor.getString(4), cursor.getString(5));
contact.setLectureNoId(cursor.getString(0));
contact.setSubjectName(cursor.getString(1));
contact.setStandardName(cursor.getString(2));
contact.setDivisionName(cursor.getString(3));
contact.setStartTime(cursor.getString(4));
contact.setEndTime(cursor.getString(5));
MondayList.add(contact);
} while (cursor.moveToNext());
}
return MondayList;
}
}
答案 0 :(得分：2)
if(databaseHandler.getRows()==0)
{
new GetContacts().execute(); //Calling
databaseHandler.addMethod();
}
else
{
}
方式
public int getRows()
{
String countQuery = "SELECT * FROM your_table_name";
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.rawQuery(countQuery, null);
int cnt = cursor.getCount();
cursor.close();
return cnt;
}
答案 1 :(得分：0)
将以下代码添加到您的DatabaseHandler
数据库清算方法：
public void removeAll()
{
SQLiteDatabase db = this.getWritableDatabase(); // helper is object extends SQLiteOpenHelper
db.delete(DatabaseHelper.TAB_USERS, null, null);
db.delete(DatabaseHelper.TAB_USERS_GROUP, null, null);
}
请致电
databaseHandler.removeAll();之前
databaseHandler.addMonday(new People(LectureNoId, SubjectName, StandardName, DivisionName, StartTime, EndTime));
在GetContacts AsyncTask。
这是因为您通过对数据库执行相同的数据来复制数据库。
致谢：请参阅this。
答案 2 :(得分：-1)
List<People>monday = databaseHandler.getAllMonday();
monday.clear;
for(People p : monday) {}
尝试这个我认为你应该清除数组