Unable to clear data in ArrayAdapter by using adapterName.clear()

Question

I'm using PreferenceFragment and I want that every time I change the value of a PreferenceScreen's widget the results should be displayed according to that in the ListView. Everything is working fine except when I change the value of any PreferenceScreen's widget instead of showing me a new list in the ListView it's adding the values in that same list. Apparently, adapter.clear() is not working.

Can anyone suggest how to make it work?

Here is my MainActivity:

public class MainActivity extends AppCompatActivity implements 
LoaderManager.LoaderCallbacks<String>, 
SharedPreferences.OnSharedPreferenceChangeListener{
private static final String TAG = "MainActivity";

private static final int LOADER_INIT_KEY = 0;

EditText titleTextView;
Button searchButton;
ListView listView;


String query = "";
private ArrayList<String> authorsList = new ArrayList<>();
private ArrayList<BooksDetails> booksDetails = new ArrayList<>();
private String title = null, id = null;

private CustomAdapter adapter;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main_layout);

    titleTextView = findViewById(R.id.author_textView);
    searchButton = findViewById(R.id.search);
    listView = findViewById(R.id.list_view);

    /**
     * this declaration is needed
     */
     adapter = new CustomAdapter(this, new ArrayList<BooksDetails>());

     final ListView listView = findViewById(R.id.list_view_in_main_layout);

     listView.setAdapter(adapter);

     // getting instance of SharedPreference and attaching listener to it
    SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(this);
    //  any change in the SharedPreference will get notified
    //  if user tweaks any settings
    sharedPreferences.registerOnSharedPreferenceChangeListener(this);

    //  Search button
    searchButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

            //  getting value from textView
            query = titleTextView.getText().toString();

            Log.d(TAG, "onClick: "+query);

            //  clearing the adapter
            adapter.clear();

            //  checking the network connection
            ConnectivityManager connectivityManager = (ConnectivityManager)getSystemService(CONNECTIVITY_SERVICE);
            assert connectivityManager != null;
            NetworkInfo networkInfo = connectivityManager.getActiveNetworkInfo();

            if(networkInfo != null && networkInfo.isConnected()) {
                if(query.length() != 0) {

                    getSupportLoaderManager().initLoader(LOADER_INIT_KEY, null, MainActivity.this);
                    closeKeyboard();
                    Log.d(TAG, "onClick: ");
                }
                else
                    Toast.makeText(MainActivity.this, "Enter a title", Toast.LENGTH_SHORT).show();
            }
            else{
                Toast.makeText(MainActivity.this, "Not connected to internet", Toast.LENGTH_SHORT).show();
            }
        }
    });
}

private void closeKeyboard(){
    //  hiding keyboard after the search
    InputMethodManager inputMethodManager = (InputMethodManager)getSystemService(Context.INPUT_METHOD_SERVICE);

    View focusedView = this.getCurrentFocus();
    if(focusedView != null) {
        try {
            assert inputMethodManager != null;

        inputMethodManager.hideSoftInputFromWindow(focusedView.getWindowToken(), InputMethodManager.HIDE_NOT_ALWAYS);
        }catch (AssertionError e){
            Log.e(TAG, "closeKeyboard: Assertion error is thrown inputMethodManager is null", e);
        }
    }
}

@NonNull
@Override
public android.support.v4.content.Loader onCreateLoader(int id, @Nullable Bundle args) {

    Log.d(TAG, "onCreateLoader: ");
    //  getting the SharedPreference which contains all the values of the Preference

    //  SharedPreference for maxResults
    SharedPreferences maxResultsSharedPreferences = PreferenceManager.getDefaultSharedPreferences(this);
    String maxResults = maxResultsSharedPreferences.getString(getString(R.string.settings_default_result_key),
            getString(R.string.settings_default_value_of_result));

    //  SharedPreference for OrderBy
    SharedPreferences orderBySharedPreference = PreferenceManager
    .getDefaultSharedPreferences(this);

    String orderByValue = orderBySharedPreference.getString(getString(R.string.settings_order_by_key),
            getString(R.string.settings_order_by_default));


    //  passing the minResults with query
    return new CustomLoader(this, query, maxResults, orderByValue);
}


@Override
public void onLoadFinished(@NonNull android.support.v4.content.Loader loader, String s) {
    Log.d(TAG, "onLoadFinished: ");

    //  clearing the adapter
    adapter.clear();

    //  after getting the raw json we are parsing it here
    try {
        JSONObject rootObject = new JSONObject(s);
        JSONArray itemsArray = rootObject.getJSONArray("items");

        for(int i = 0;i < itemsArray.length();i++){
            //  getting each object in the array itemsArray
            JSONObject booksInfo = itemsArray.getJSONObject(i);

            //  getting book id
            id = booksInfo.getString("id");

            //  getting the volumeInfo object
            JSONObject volumeInfo = booksInfo.getJSONObject("volumeInfo");

            //  getting title of the book
            title = volumeInfo.getString("title");
            //  getting the author

            JSONArray author = volumeInfo.getJSONArray("authors");

            //  getting all the members of author array
            for(int j = 0;j < author.length();j++){
                authorsList.add(author.getString(j));
            }

            if(title == null) {
                //  if no title matches
                titleTextView.setText("No title matches");
            }

            //   adding details in the ArrayList bookDetails
            booksDetails.add(new BooksDetails(id, title, authorsList.get(0)));

        }

        adapter.addAll(booksDetails);
    }
    catch(Exception e){
        Log.e(TAG, "onLoadFinished: exception in json parsing", e);
    }
}

@Override
public void onLoaderReset(@NonNull android.support.v4.content.Loader loader) {
    Log.d(TAG, "onLoaderReset: ");

    //  clearing the adapter
    adapter.clear();
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.settings_menu, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    if(item.getItemId() == R.id.action_settings){
        Intent intent = new Intent(this, SettingsActivity.class);
        startActivity(intent);
    }
    return super.onOptionsItemSelected(item);
}

@Override
public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {
    Log.d(TAG, "onSharedPreferenceChanged: ");

    if(key.equals(getString(R.string.settings_order_by_key)) || key.equals(getString(R.string.settings_default_result_key))){

        //  clearing the adapter
        adapter.clear();

        getSupportLoaderManager().restartLoader(LOADER_INIT_KEY, null, this);
    }
}

@Override
protected void onRestart() {
    super.onRestart();

    adapter.clear();
}

}

Answer 1

You need to reset you source list which you've passed to the adapter. because you placed initial code inside of onCreate method which has been called once while activity created.

Instead of adapter = new CustomAdapter(this, new ArrayList<BooksDetails>());

try this:

CustomAdapter adapter;
List<BooksDetails> srcList;

public void onCreate() {
srcList = new ArrayList<BookDetails>();
adapter = new CustomAdapter(this, srcList);
}

and when you need to clear your adapter try this

srcList().clear();
adapter.clear();
adapter.notifyDatasetChanged();