Arraylist在Android中自行清除

Question

我有一個asynctask，它從本地Sqlite數據庫獲取數據並將其顯示給用戶。 如果sqlite中沒有該數據，則將對服務器進行網絡調用以檢索服務器端數據。

問題是，當我調用數據庫並獲取數據時，我將其添加到列表中。 我檢查列表的大小，它顯示了內容。

然后，當我嘗試通知arraylist適配器時，它顯示列表大小為0，而未進行任何clear（）調用

文件如下：

包com.example.project.recommendedapp.AsyncTasks;

// SuggestionsGetterAsync start ---------------------------------------------- -------------------------------------------------- ----------------

public class SuggestionsGetterAsync extends AsyncTask<String,Void,Void> {

private String queryString;
private WeakReference<Activity> weakReference;
private Activity localReference;
private Fragment localFragment;
private ArrayList<Suggestions> localSuggestionsList;

double latitude,longitude;

String cityName;

int request_counter_in_fragment;

public SuggestionsGetterAsync(Activity passedReference, Fragment passedFragment, ArrayList<Suggestions> localSuggestionsList,int request_counter_in_fragment,double ...coordinates){
    weakReference=new WeakReference<Activity>(passedReference);
    localReference=weakReference.get();
    localFragment=passedFragment;
    this.localSuggestionsList=localSuggestionsList;

    latitude=coordinates[0];
    longitude=coordinates[1];

    this.request_counter_in_fragment=request_counter_in_fragment;
}

@Override
protected Void doInBackground(String... params) {
    queryString=params[0];

    cityName=params[1];

    if(localReference!=null && !localReference.isDestroyed() && !localReference.isFinishing()) {
        localReference.runOnUiThread(new Runnable() {
            @Override
            public void run() {
                localSuggestionsList.clear();
                ((LocalFragmentInteractionInterface)localFragment).notifyAdapter();
            }
        });

        //cancel the call to avoid load if it is a previously dispatched useless servelet
        if(((GetRequestCounterFromFragment)localFragment).getRequestDispatchedCounter()!=request_counter_in_fragment){
            this.cancel(true);
            return null;
        }
    }

    if(localReference!=null && !localReference.isDestroyed() && !localReference.isFinishing() && !queryString.equals("")){


        //cancel the call to avoid load if it is a previously dispatched useless servelet
        if(((GetRequestCounterFromFragment)localFragment).getRequestDispatchedCounter()!=request_counter_in_fragment){
            this.cancel(true);
            return null;
        }

        LocalDatabaseHelper localDatabaseHelper = LocalDatabaseHelper.getInstance(localReference);

        localSuggestionsList=localDatabaseHelper.getLocalSearchSuggestions(queryString);

        Log.d("FragmentCreate","localSuggestionsList size after db call is "+localSuggestionsList.size()); // prints ok and shows that the list has values

    }

    Log.d("FragmentCreate","localSuggestionsList size now is"+localSuggestionsList.size()); // prints ok and shows that the list has values

    if (localSuggestionsList.size()==0) {
        //basically first query the local cache, if nothing is found locally, go fetch the data from the server
        //put the fetched results inside the local database
        try {
            //String serveleturl = "http://192.168.1.7:8080/Servelet/SearchSuggestionsServelet?latitude="+latitude+"&longitude="+longitude+"&cityName="+cityName+"&queryString="+URLEncoder.encode(queryString,"UTF-8");
            String serveleturl = "http://kushan.dynu.com:8080/Servelet/SearchSuggestionsServelet?cityName="+URLEncoder.encode(cityName,"UTF-8")+"&queryString="+(queryString.equals("")?null:URLEncoder.encode(queryString,"UTF-8"));

            OkHttpClient client = new OkHttpClient.Builder()
                    .connectTimeout(30000, TimeUnit.MILLISECONDS)
                    .readTimeout(30000,TimeUnit.MILLISECONDS)
                    .retryOnConnectionFailure(false)
                    .build();

            Request request = new Request.Builder()
                    .url(serveleturl)
                    .build();

            Response response = client.newCall(request).execute();

            switch (response.code()){

                case 444:
                    if((localReference!=null && !localReference.isDestroyed() && !localReference.isFinishing()) && (((GetRequestCounterFromFragment)localFragment).getRequestDispatchedCounter()==request_counter_in_fragment) && !isCancelled()) {
                        localReference.runOnUiThread(new Runnable() {
                            @Override
                            public void run() {
                                ((LocalFragmentInteractionInterface)localFragment).setErrorText("No search results found",false);
                            }
                        });
                    }

                    break;

                case 222:
                    if((localReference!=null && !localReference.isDestroyed() && !localReference.isFinishing()) && (((GetRequestCounterFromFragment)localFragment).getRequestDispatchedCounter()==request_counter_in_fragment) && !isCancelled()) {
                        localReference.runOnUiThread(new Runnable() {
                            @Override
                            public void run() {
                                ((LocalFragmentInteractionInterface)localFragment).setErrorText("Hide the errortext",true);
                            }
                        });
                    }

                    JSONArray suggestionsArray = new JSONArray(response.body().string());

                    if(suggestionsArray.length()!=0){
                        try{

                            if(localReference!=null && !localReference.isDestroyed() && !localReference.isFinishing()){

                                LocalDatabaseHelper localDatabaseHelper = LocalDatabaseHelper.getInstance(localReference);

                                localDatabaseHelper.putSuggestions(suggestionsArray);

                            }

                        }catch (Exception e){
                            Log.e("FragmentCreate","Error saving the suggestion inside db",e);
                        }
                    }

                    for(int i=0;i<suggestionsArray.length();i++){
                        if(((GetRequestCounterFromFragment)localFragment).getRequestDispatchedCounter()==request_counter_in_fragment) {
                            localSuggestionsList.add(new Suggestions(suggestionsArray.getJSONObject(i)));
                        }else{
                            return null;
                        }
                    }


                    break;

                default:
                    if((localReference!=null && !localReference.isDestroyed() && !localReference.isFinishing()) && (((GetRequestCounterFromFragment)localFragment).getRequestDispatchedCounter()==request_counter_in_fragment) && !isCancelled()) {
                        localReference.runOnUiThread(new Runnable() {
                            @Override
                            public void run() {
                                ((LocalFragmentInteractionInterface)localFragment).setErrorText("No search results found",false);
                            }
                        });
                    }
                    break;

            }

            response.close();

        }catch (Exception e){
            if((localReference!=null && !localReference.isDestroyed() && !localReference.isFinishing()) && (((GetRequestCounterFromFragment)localFragment).getRequestDispatchedCounter()==request_counter_in_fragment) && !isCancelled()) {
                localReference.runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        ((LocalFragmentInteractionInterface)localFragment).setErrorText("Check your Internet connection or try again after some time",false);
                    }
                });
            }
        }
    }else{
        if (localReference!=null && !localReference.isDestroyed() && !localReference.isFinishing()) {
            localReference.runOnUiThread(new Runnable() {
                @Override
                public void run() {
                    Log.d("FragmentCreate","before postExecute the size of the list is "+localSuggestionsList.size()); // prints size as zero for no reason
                    ((LocalFragmentInteractionInterface)localFragment).setErrorText("Hide the errortext",true);
                }
            });
        }
    }

    return null;
}




@Override
public void onPostExecute(Void voided){

    if((localReference!=null && !localReference.isDestroyed() && !localReference.isFinishing()) && (((GetRequestCounterFromFragment)localFragment).getRequestDispatchedCounter()==request_counter_in_fragment)) {
        Log.d("FragmentCreate","request counter in asynctask ="+request_counter_in_fragment+" queryString is =  "+queryString+" "+localSuggestionsList.size()); // prints size as zero for no reason
        ((LocalFragmentInteractionInterface) localFragment).notifyAdapter();

        if(queryString.equals("")){
            ((LocalFragmentInteractionInterface)localFragment).setErrorText("",true);
        }

    }


    weakReference=null;
    localReference=null;
    localFragment=null;
    queryString=null;
    localSuggestionsList=null;
}

@Override
public void onCancelled(){
    Log.d("FragmentCreate","AsyncTaskCancelled");
}



}

從sqlite返回列表的函數如下：

public ArrayList<Suggestions> getLocalSearchSuggestions(String searchString) throws SQLiteException{

    //localSuggestionsList.clear();
    ArrayList<Suggestions> localSuggestionsList = new ArrayList<>();

    SQLiteDatabase db = this.getReadableDatabase();

    String sql = "SELECT "+TableAndColumnNames.SEARCH_RESULTS_DATA+" FROM "+TableAndColumnNames.SEARCH_RESULTS_TABLE_NAME+" WHERE "+TableAndColumnNames.SEARCH_RESULTS_SUGGESTION+" LIKE '%"+searchString+"%' limit 20";

    Cursor c = db.rawQuery(sql,null);

    JSONObject suggestionObject;

    if(c!=null){

        if(c.moveToFirst()){
            do{

                try{
                    //Log.d("FragmentCreate",c.getString(0)+" found in suggestion");
                    suggestionObject = new JSONObject(c.getString(0));
                    localSuggestionsList.add(new Suggestions(suggestionObject));
                }catch (JSONException je){
                    Log.d("FragmentCreate","Data got corrupted for searched list");
                }

            }while(c.moveToNext());
        }

        c.close();
    }

    return localSuggestionsList;

}

Answer 1

if(localReference!=null && !localReference.isDestroyed() && !localReference.isFinishing()) {
    localReference.runOnUiThread(new Runnable() {
        @Override
        public void run() {
            localSuggestionsList.clear();
            ((LocalFragmentInteractionInterface)localFragment).notifyAdapter();
        }
    });

    //cancel the call to avoid load if it is a previously dispatched useless servelet
    if(((GetRequestCounterFromFragment)localFragment).getRequestDispatchedCounter()!=request_counter_in_fragment){
        this.cancel(true);
        return null;
    }
}

在這里您清除列表並通知適配器

Answer 2

首先檢查您的數據庫數據更新與否。