当没有互联网可用的数据从数据库中获取数据时，我的应用程序工作正常，但问题是每次它在数据库中插入相同的数据，因此数据将显示多次帮助我如何将数据库限制为仅保护数据库中的唯一数据
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>();
String URL, URL2;
String SelectMenuAPI;
String _response;
String status;
GridView gridview;
private DbHelper mHelper;
private SQLiteDatabase dataBase;
private boolean isUpdate;
int IOConnect = 0;
// flag for Internet connection status
Boolean isInternetPresent = false;
// Connection detector class
ConnectionDetector cd;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mHelper=new DbHelper(this);
cd = new ConnectionDetector(getApplicationContext());
dataBase=mHelper.getWritableDatabase();
gridview = (GridView) findViewById(R.id.gridview);
cla = new CategoryListAdapter3(MainActivity.this);
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();
}
gridview.setOnItemClickListener(new OnItemClickListener() {
public void onItemClick(AdapterView<?> arg0, View arg1,
int position, long arg3) {
// TODO Auto-generated method stub
Intent iMenuList = new Intent(MainActivity.this,
Subcategory.class);
iMenuList.putExtra("Category_ID", Category_ID.get(position));
iMenuList.putExtra("Category_name", Category_name.get(position));
startActivity(iMenuList);
}
});
}
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.aaaa/_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();
}
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_ID)));
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();
}
数据库类
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, "+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);
}
}