下面是我的源代码我的问题是如何从服务器更新数据库第一次应用程序在数据库中插入值 formserver 现在在服务器更新数据库一段时间后应用程序如何知道服务器更改数据库现在需要更新数据库？
public class MainActivity extends Activity {
CategoryListAdapter3 cla;
static ArrayList<String> Category_ID = new ArrayList<String>();
static ArrayList<String> Category_name = new ArrayList<String>();
static ArrayList<String> Category_image = new ArrayList<String>();
private DbHelper mHelper;
private SQLiteDatabase dataBase;
private boolean isUpdate;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mHelper=new DbHelper(this);
dataBase=mHelper.getWritableDatabase();
isInternetPresent = cd.isConnectingToInternet();
// check for Internet status
if (isInternetPresent) {
// Internet Connection is Present
// make HTTP requests
new TheTask().execute();
} else {
// Internet connection is not present
// Ask user to connect to Internet
displayData();
}
void clearData() {
Category_ID.clear();
Category_name.clear();
Category_image.clear();
}
public class TheTask extends AsyncTask<Void, String, String> {
@Override
protected void onPreExecute() {
super.onPreExecute();
}
@Override
protected String doInBackground(Void... arg0) {
SelectMenuAPI = "http://www.xyz/_webservices/mobile_api.php?response=getmaincategories";
clearData();
URL = SelectMenuAPI;
URL2 = URL.replace(" ", "%20");
try {
Log.i("url", "" + URL2);
HttpClient client = new DefaultHttpClient();
HttpGet request = new HttpGet(URL2);
HttpResponse response = client.execute(request);
HttpEntity resEntity = response.getEntity();
_response = EntityUtils.toString(resEntity);
} catch (Exception e) {
e.printStackTrace();
// IOConnect = 1;
}
return _response;
}
@Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
try {
JSONObject json2 = new JSONObject(result);
status = json2.getString("Status");
if (status.equals("1")) {
JSONArray school2 = json2.getJSONArray("data");
//
for (int i = 0; i < school2.length(); i++) {
JSONObject object = school2.getJSONObject(i);
String id = object.getString("category_id");
String name =object.getString("name");
String image_path = object.getString("image_path");
dataBase=mHelper.getWritableDatabase();
ContentValues values=new ContentValues();
values.put(DbHelper.KEY_MYID,id);
values.put(DbHelper.KEY_FNAME,name);
values.put(DbHelper.KEY_LNAME,image_path );
System.out.println("");
if(isUpdate)
{
//update database with new data
dataBase.update(DbHelper.TABLE_NAME, values, DbHelper.KEY_ID+"="+id, null);
}
else
{
//insert data into database
dataBase.insert(DbHelper.TABLE_NAME, null, values);
}
//close database
dataBase.close();
}
else {
}
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
displayData();
}
}
private void displayData() {
dataBase = mHelper.getWritableDatabase();
Cursor mCursor = dataBase.rawQuery("SELECT * FROM "
+ DbHelper.TABLE_NAME, null);
Category_ID.clear();
Category_name.clear();
Category_image.clear();
if (mCursor.moveToFirst()) {
do {
Category_ID.add(mCursor.getString(mCursor.getColumnIndex(DbHelper.KEY_MYID)));
Category_name.add(mCursor.getString(mCursor.getColumnIndex(DbHelper.KEY_FNAME)));
Category_image.add(mCursor.getString(mCursor.getColumnIndex(DbHelper.KEY_LNAME)));
} while (mCursor.moveToNext());
}
gridview.setAdapter(cla);
mCursor.close();
}
public class DbHelper extends SQLiteOpenHelper {
static String DATABASE_NAME="userdata";
public static final String TABLE_NAME="user";
public static final String KEY_FNAME="fname";
public static final String KEY_LNAME="lname";
public static final String KEY_ID="id";
public static final String KEY_MYID="myid";
public DbHelper(Context context) {
super(context, DATABASE_NAME, null, 1);
}
@Override
public void onCreate(SQLiteDatabase db) {
String CREATE_TABLE="CREATE TABLE "+TABLE_NAME+" ("+KEY_ID+" INTEGER PRIMARY
KEY,"+KEY_MYID+" TEXT UNIQUE NOT NULL, "+KEY_FNAME+" TEXT, "+KEY_LNAME+" BLOB)";
db.execSQL(CREATE_TABLE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("DROP TABLE IF EXISTS "+TABLE_NAME);
onCreate(db);
}
}