android - 每次更改设备方向时，项目都会添加到 Recycler View 中

Question

我有一个购物 list 应用程序有一个错误，当设备的方向改变时(Portret 到 Landscape 或相反)添加新项目。例如，如果我有一件这样的购物商品:

在我改变设备的方向后，它被复制了:

如果我不断改变方向，它们就会不断复制。我怎样才能避免它而无需将方向设置为仅 portret？

这是我在 MainActivity 中的代码:

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);
    }
}

这是我的适配器中的代码:

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

每次您更改屏幕的旋转时，您的 Activity 都会被销毁并重新创建。

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

因此，重要的是您只实例化您的对象一次，而不是在每次重新创建您的应用程序时都重新创建它们。然后将它们添加到您的列表中。

您需要使用 onSaveInstanceState并且，可能，onRestoreInstanceState