Item added to the Recycler view every time orientation of the device is changed

Question

I have a shopping list app that has a bug, when the orientation of the device is changed (Portret to Landscape or the opposite) new item is added. For example, if I have one shopping item like this:

and after I change the orientation of the device it is duplicated:

and if I keep changing the orientation they keep duplicating. How can I avoid it without the need to set the orientation to portret only?

This is my code in MainActivity:

public class MainActivity extends AppCompatActivity {
public static boolean ifLongPress = false;
private Toolbar mToolbar;
private RecyclerView mRecyclerView;
public static ArrayList<String> shoppingListItems;
private SharedPreferences mSharedPreferences;
private SharedPreferences.Editor mEditor;
private TextView mEmptyTextView;
private int arrayListSizeDefaultValue = 0;
private ShoppingListAdapter adapter;
private ActionButton actionButton;
private MaterialDialog addItemdialog = null;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    mEmptyTextView = (TextView)findViewById(R.id.list_empty);
    mEmptyTextView.setVisibility(View.INVISIBLE);
    mSharedPreferences = getPreferences(MODE_PRIVATE);
    mEditor = mSharedPreferences.edit();

    actionButton = (ActionButton)findViewById(R.id.buttonFloat);
    actionButton.setButtonColor(getResources().getColor(R.color.ColorPrimary));
    actionButton.setButtonColorPressed(getResources().getColor(R.color.ColorPrimaryDark));
    actionButton.setImageDrawable(ResourcesCompat.getDrawable(getResources(), R.drawable.fab_plus_icon,null));
    actionButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            buildAlertDialog();
        }
    });
    mToolbar = (Toolbar)findViewById(R.id.tool_bar);
    setSupportActionBar(mToolbar);
    mRecyclerView = (RecyclerView)findViewById(R.id.recyclerView);
    if(shoppingListItems == null){
          shoppingListItems = new ArrayList<>();
    }

    //read the array lists
    readShoppingItems();

    adapter = new ShoppingListAdapter(this,shoppingListItems,mSharedPreferences,mEditor);
    mRecyclerView.addItemDecoration(new SimpleDividerItemDecoration(getApplicationContext()));
    mRecyclerView.setAdapter(adapter);
    LinearLayoutManager linearLayoutManager = new LinearLayoutManager(this);
    mRecyclerView.setLayoutManager(linearLayoutManager);

    mRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
        @Override
        public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
            super.onScrollStateChanged(recyclerView, newState);
            actionButton.setHideAnimation(ActionButton.Animations.SCALE_DOWN);
            actionButton.hide();
            if (newState == RecyclerView.SCROLL_STATE_IDLE) {
                actionButton.setShowAnimation(ActionButton.Animations.SCALE_UP);
                actionButton.show();
            }
        }
    });

    //check weather to show the empty text view
    isListEmpty();

}

private void readShoppingItems() {
    int size = mSharedPreferences.getInt(Constants.ARRAY_LIST_SIZE_KEY, arrayListSizeDefaultValue);
    for(int i = 0;i< size;i++){
        shoppingListItems.add(mSharedPreferences.getString(Constants.ARRAY_LIST_ITEM_KEY + i,null));
    }
}

private void saveShoppingItems() {
    //save array list
    mEditor.putInt(Constants.ARRAY_LIST_SIZE_KEY, shoppingListItems.size());
    for (int i =0;i<shoppingListItems.size();i++){
        mEditor.putString(Constants.ARRAY_LIST_ITEM_KEY + i,shoppingListItems.get(i));
    }
    mEditor.apply();
    adapter.notifyDataSetChanged();
}

private void buildAlertDialog() {
    final int[] choosenQuantity = {1};
    final String[] str = {""};
    final MaterialDialog.Builder addItemBuilder = new MaterialDialog.Builder(this);
    addItemBuilder.title("Add Item");
    addItemBuilder.widgetColor(getResources().getColor(R.color.ColorPrimaryDark));
    addItemBuilder.inputMaxLength(30, R.color.material_blue_grey_950);
    addItemBuilder.content("Quantity:" + choosenQuantity[0]);
    addItemBuilder.inputType(InputType.TYPE_CLASS_TEXT);
    addItemBuilder.autoDismiss(true);
    addItemBuilder.input("add shopping item", "", new MaterialDialog.InputCallback() {
        @Override
        public void onInput(MaterialDialog dialog, CharSequence input) {
            str[0] = input.toString().trim();
            //add it to shoppingListItems and save to sharedPreferences
            if (str[0].length() != 0) {
                if (choosenQuantity[0] > 1) {
                    shoppingListItems.add(str[0] + " (" + choosenQuantity[0] + ")");
                } else {
                    shoppingListItems.add(str[0]);
                }
                saveShoppingItems();
                isListEmpty();
                dialog.dismiss();
            } else {
                Toast.makeText(MainActivity.this, "no item description!", Toast.LENGTH_LONG).show();
            }

        }
    });
    addItemBuilder.negativeText("Cancel");
    addItemBuilder.callback(new MaterialDialog.ButtonCallback() {
        @Override
        public void onNegative(MaterialDialog dialog) {
            super.onNegative(dialog);
            dialog.dismiss();
        }
    });
    addItemBuilder.neutralText("Add Quantity");
    addItemBuilder.callback(new MaterialDialog.ButtonCallback() {
        @Override
        public void onNeutral(final MaterialDialog dialog) {
            super.onNeutral(dialog);
            addItemBuilder.autoDismiss(false);
            MaterialDialog.Builder quantityDialogBuilder = new MaterialDialog.Builder(MainActivity.this);
            quantityDialogBuilder.title("Add Quantity");
            quantityDialogBuilder.negativeText("CANCEL").callback(new MaterialDialog.ButtonCallback() {
                @Override
                public void onNegative(MaterialDialog dialog) {
                    super.onNegative(dialog);
                    addItemBuilder.autoDismiss(true);
                }
            });
            quantityDialogBuilder.items(R.array.Quantaty_array);
            quantityDialogBuilder.itemsCallback(new MaterialDialog.ListCallback() {
                @Override
                public void onSelection(MaterialDialog dialog, View view, int which, CharSequence text) {
                    choosenQuantity[0] = which + 1;
                    addItemdialog.setContent("Quantity:" + choosenQuantity[0]);
                    addItemBuilder.autoDismiss(true);
                }
            });
            quantityDialogBuilder.cancelListener(new DialogInterface.OnCancelListener() {
                @Override
                public void onCancel(DialogInterface dialog) {
                    addItemBuilder.autoDismiss(true);
                }
            });
            quantityDialogBuilder.show();
        }
    });
    addItemdialog = addItemBuilder.build();
    addItemdialog.show();
}
 @Override
protected void onResume() {
    super.onResume();
    isListEmpty();
}
 private void isListEmpty() {
    if (mRecyclerView.getAdapter().getItemCount() == 0) {
        mEmptyTextView.setVisibility(View.VISIBLE);
    }
    else {
        mEmptyTextView.setVisibility(View.INVISIBLE);
    }
}

And this is the code in my Adapter:

public class ShoppingListAdapter extends RecyclerView.Adapter<ShoppingListAdapter.ShoppingListViewHolder> {
private ArrayList<String> mItems;
private Context mContext;
private SharedPreferences mSharedPreferences;
private SharedPreferences.Editor mEditor;
private MaterialDialog addItemdialog;

public ShoppingListAdapter(Context context, ArrayList<String> items, SharedPreferences preferences,SharedPreferences.Editor editor) {
    mItems = items;
    mContext = context;
    mSharedPreferences = preferences;
    mEditor = editor;
}

@Override
public ShoppingListViewHolder onCreateViewHolder(ViewGroup viewGroup, int position) {
    View view = LayoutInflater.from(mContext).inflate(R.layout.shopping_list_item,viewGroup,false);
    ShoppingListViewHolder viewHolder = new ShoppingListViewHolder(view);

    return viewHolder;
}

@Override
public void onBindViewHolder(ShoppingListViewHolder shoppingListViewHolder, int position) {
    shoppingListViewHolder.bindShoppingList(mItems.get(position));
}

@Override
public int getItemCount() {
    return mItems.size();
}

public class ShoppingListViewHolder extends RecyclerView.ViewHolder implements CompoundButton.OnCheckedChangeListener, View.OnLongClickListener{
    public TextView mShoppingListItem;
    public CheckBox mCheckBox;

    public ShoppingListViewHolder(View itemView) {
        super(itemView);
        mShoppingListItem = (TextView) itemView.findViewById(R.id.shoppingListItem);
        mCheckBox = (CheckBox) itemView.findViewById(R.id.shoppingListCheckBox);
        mCheckBox.setOnCheckedChangeListener(this);
        itemView.setOnLongClickListener(this);
    }

    public void bindShoppingList(String item){
        mShoppingListItem.setText(item);
        mCheckBox.setChecked(false);
    }


    @Override
    public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
        if(isChecked){
            mItems.remove(getAdapterPosition());
            saveShoppingItems();
            notifyItemRemoved(getAdapterPosition());
        }
    }

    private void saveShoppingItems() {
        //save array list
        mEditor.putInt(Constants.ARRAY_LIST_SIZE_KEY, mItems.size());
        for (int i =0;i<mItems.size();i++){
            mEditor.putString(Constants.ARRAY_LIST_ITEM_KEY + i,mItems.get(i));
        }
        mEditor.apply();
    }

    @Override
    public boolean onLongClick(View v) {
        final int selectedItem = getAdapterPosition();
        String itemToBeEdited = mSharedPreferences.getString(Constants.ARRAY_LIST_ITEM_KEY + selectedItem, null);
        //check if the selected item has added quantity and if yes -> remove space+(number)
        String formatted ="";
        int itemSavedQuantity = 1;
        if(itemToBeEdited.length()-4>0 && (itemToBeEdited.charAt(itemToBeEdited.length()-1)==')')){
            //get the save quantity
            itemSavedQuantity = Integer.parseInt(itemToBeEdited.charAt(itemToBeEdited.length()-2)+"");
            //format the string by removing the space + (number)
            formatted = itemToBeEdited.substring(0, itemToBeEdited.length() - 4);

        }else{
            formatted = itemToBeEdited;
        }

        final String[] str = {""};
        final int[] userQuantityInput = {itemSavedQuantity};
        Toast.makeText(mContext, "Long Press", Toast.LENGTH_LONG).show();
        final MaterialDialog.Builder addItemBuilder = new MaterialDialog.Builder(mContext);
        addItemBuilder.title("Edit Item");
        addItemBuilder.widgetColor(mContext.getResources().getColor(R.color.ColorPrimaryDark));
        addItemBuilder.inputMaxLength(30, R.color.material_blue_grey_950);
        addItemBuilder.content("Quantity:" + userQuantityInput[0]);
        addItemBuilder.inputType(InputType.TYPE_CLASS_TEXT);
        addItemBuilder.autoDismiss(true);
        addItemBuilder.input("Edit shopping item", "", new MaterialDialog.InputCallback() {
            @Override
            public void onInput(MaterialDialog dialog, CharSequence input) {
                str[0] = input.toString().trim();
                //add it to shoppingListItems and save to sharedPreferences
                if (str[0].length() != 0) {
                    //save items
                    if (userQuantityInput[0] > 1) {
                        str[0] += " (" + userQuantityInput[0] + ")";
                    }
                    mEditor.putString(Constants.ARRAY_LIST_ITEM_KEY + selectedItem, str[0]);
                    mEditor.apply();
                    //clear the content
                    MainActivity.shoppingListItems.clear();
                    //read again content
                    readShoppingItems();
                    notifyDataSetChanged();
                    dialog.dismiss();
                    Toast.makeText(mContext, "Saved", Toast.LENGTH_LONG).show();
                } else {
                    Toast.makeText(mContext, "no item description!", Toast.LENGTH_LONG).show();
                }
            }
        });
        addItemBuilder.negativeText("Cancel");
        addItemBuilder.callback(new MaterialDialog.ButtonCallback() {
            @Override
            public void onNegative(MaterialDialog dialog) {
                super.onNegative(dialog);
                dialog.dismiss();
            }
        });
        addItemBuilder.neutralText("Edit Quantity");
        addItemBuilder.callback(new MaterialDialog.ButtonCallback() {
            @Override
            public void onNeutral(final MaterialDialog dialog) {
                super.onNeutral(dialog);
                addItemBuilder.autoDismiss(false);
                MaterialDialog.Builder quantityDialogBuilder = new MaterialDialog.Builder(mContext);
                quantityDialogBuilder.title("Edit Quantity");
                quantityDialogBuilder.negativeText("CANCEL").callback(new MaterialDialog.ButtonCallback() {
                    @Override
                    public void onNegative(MaterialDialog dialog) {
                        super.onNegative(dialog);
                        addItemBuilder.autoDismiss(true);
                    }
                });
                quantityDialogBuilder.items(R.array.Quantaty_array);
                quantityDialogBuilder.itemsCallback(new MaterialDialog.ListCallback() {
                    @Override
                    public void onSelection(MaterialDialog dialog, View view, int which, CharSequence text) {
                        userQuantityInput[0] = which + 1;
                        addItemdialog.setContent("Quantity:" + userQuantityInput[0]);
                        addItemBuilder.autoDismiss(true);
                    }
                });
                quantityDialogBuilder.cancelListener(new DialogInterface.OnCancelListener() {
                    @Override
                    public void onCancel(DialogInterface dialog) {
                        addItemBuilder.autoDismiss(true);
                    }
                });
                quantityDialogBuilder.show();
            }
        });
        addItemdialog = addItemBuilder.build();
        addItemdialog.getInputEditText().setText(formatted);
        addItemdialog.show();
        return true;
    }
}
private void readShoppingItems() {
    int size = mSharedPreferences.getInt(Constants.ARRAY_LIST_SIZE_KEY, 0);
    for(int i = 0;i< size;i++){
        MainActivity.shoppingListItems.add(mSharedPreferences.getString(Constants.ARRAY_LIST_ITEM_KEY + i, null));
    }
}

Answer 1

Every time you change the rotation of the screen your activity is destroyed and recreated.

Caution: Your activity will be destroyed and recreated each time the user rotates the screen. When the screen changes orientation, the system destroys and recreates the foreground activity because the screen configuration has changed and your activity might need to load alternative resources (such as the layout).
Recreating an Activity

So it's important you only instantiate your objects once, and not keep recreating them each time your app is recreated. Which then adds them to your list.

You need to use onSaveInstanceState and, possibly, onRestoreInstanceState

Answer 2

After

if(shoppingListItems == null){
    shoppingListItems = new ArrayList<>();
}

place

shoppingListItems.clear();