我有两个 Activity ，一个是 UserActivity，另一个是 CartActivity 我在 UserActivity 中显示产品列表。单击按钮 AddtoCart 我将产品添加到购物车。我面临这个问题:

当我添加单击按钮 AddtoCart 时，操作栏中有一个购物车图标，我有一个 textview 的自定义布局，在该购物车图标上显示购物车计数器。每当我单击 AddtoCart 按钮时，该计数器就会更新。现在我转到 CartActivity 并从购物车中删除一些产品。当我现在按下后退按钮返回到 UserActivity 时，计数器 TextView 不会更新。

我已经阅读了一些关于按下后退进行更新的方法，如此处的问题 Back button and refreshing previous activity 所示。 .答案中给出的两种方法是覆盖 UserActivity 的 OnResume() 方法或通过启动结果 Activity 。

我想当我按下后退按钮并从Counter TextView 中的原始产品数量并更新 TextView 。

这是 UserActivity 的部分代码，我只有在这段代码中有更新购物车计数器的功能，当我点击一个按钮时调用。 onActivityResult() 的代码也在评论中，我从上面给出的 SO 问题链接的答案中尝试过。不成功:

    public class UserActivity extends AppCompatActivity{
            private int cartindex = 0;
            private TextView counterTV = null;
            
            @Override
            protected void onCreate(Bundle savedInstanceState) {
                super.onCreate(savedInstanceState);
                setContentView(R.layout.activity_user);
              
                Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
                setSupportActionBar(toolbar);
            }
//    @Override
//    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
//        if (requestCode == 1) {
//
//            if(resultCode == RESULT_OK){
//                  Intent intent = getIntent();
//                  Integer deletecounter = intent.getIntExtra("DeleteCounter",0);
//                  if(deletecounter>0){
//                      UpdateCartCount(Integer.parseInt(counterTV.getText().toString())-deletecounter);
//                  }
//            }
//        }
//    }
            
        @Override
            public boolean onCreateOptionsMenu(Menu menu) {
                // Inflate the menu; this adds items to the action bar if it is present.
                getMenuInflater().inflate(R.menu.user, menu);
                final View menu_list = menu.findItem(R.id.action_hawk).getActionView();
                counterTV = (TextView) menu_list.findViewById(R.id.cartcounter);
                UpdateCartCount(cartindex);
                new MyMenuItemStuffListener(menu_hotlist, "Show message") {
                    @Override
                    public void onClick(View v) {
                        Intent intent= new  Intent(UserActivity.this,CartActivity.class);
                        intent.putExtra("ProductTitle",pname);
                        intent.putExtra("ProductUrl",purl);
                        intent.putExtra("ProductPrice",pprice);
                        intent.putExtra("BargainPrice",bargainprice);
                        UserActivity.this.startActivity(intent);
                    }
                };
                return true;
    }
    //Function to update cart count
            public void UpdateCartCount(final int new_number) {
                    cartindex = new_number;
                    if (counterTV == null) return;
                    runOnUiThread(new Runnable() {
                        @Override
                        public void run() {
                            if (new_number == 0)
                                counterTV.setVisibility(View.INVISIBLE);
                            else {
                                counterTV.setVisibility(View.VISIBLE);
                                counterTV.setText(Integer.toString(new_number));
                            }
                        }
                    });
                }

这是 CartActivity 的代码:

    public class CartActivity extends AppCompatActivity {
    
        private List<Product> mCartList;
        private ProductAdapter mProductAdapter;
        private static List<Product> cart;
        private static Integer deletecounter= 0;
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_cart);
            Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
            setSupportActionBar(toolbar);
            mCartList = getCart();
    
    
            Intent intent = getIntent();
            String ProductTitle = intent.getStringExtra("ProductTitle");
            String ProductUrl = intent.getStringExtra("ProductUrl");
            String ProductPrice = intent.getStringExtra("ProductPrice");
            String BargainPrice = intent.getStringExtra("BargainPrice");
            Product product = new Product(ProductTitle, ProductUrl, ProductPrice, BargainPrice);
            mCartList.add(product);
            // Make sure to clear the selections
            for (int i = 0; i < mCartList.size(); i++) {
                mCartList.get(i).selected = false;
            }
    
            // Create the list
            final ListView listViewCatalog = (ListView) findViewById(R.id.cart_list_view);
            mProductAdapter = new ProductAdapter(mCartList, getLayoutInflater(), true, CartActivity.this);
            listViewCatalog.setAdapter(mProductAdapter);
    
            listViewCatalog.setOnItemClickListener(new AdapterView.OnItemClickListener() {
    
                @Override
                public void onItemClick(AdapterView<?> parent, View view, int position,
                                        long id) {
    
                    Product selectedProduct = mCartList.get(position);
                    if (selectedProduct.selected)
                        selectedProduct.selected = false;
                    else
                        selectedProduct.selected = true;
    
                    mProductAdapter.notifyDataSetInvalidated();
    
                }
            });
            FloatingActionButton Delete = (FloatingActionButton) findViewById(R.id.fab);
            delete.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    // Loop through and remove all the products that are selected
                    // Loop backwards so that the remove works correctly
    
                    for (int i = mCartList.size() - 1; i >= 0; i--) {
    
                        if (mCartList.get(i).selected) {
                            mCartList.remove(i);
                            deletecounter++;
                        }
                    }
// THIS IS THE CODE I USED TO RETURN DATA TO PREVIOUS ACTIVITY BUT UserActivity STARTS AUTOMATICALLY AFTER DELETION OF SELECTED PRODUCTS AS SOON AS I CLICK THE DELETE BUTTON EVEN WHEN THERE ARE PRODUCTS IN THE CART.
 //                  if(deletecounter!=0) {
//                    Intent i = new Intent(HawkActivity.this, UserActivity.class);
//                    startActivityForResult(i, 1);
//                    Intent returnIntent = new Intent();
//                    returnIntent.putExtra("DeleteCounter", deletecounter);
//                    setResult(RESULT_OK, returnIntent);
//                }
                    mProductAdapter.notifyDataSetChanged();
                    Snackbar.make(view,"Selected items deleted successfully",Snackbar.LENGTH_SHORT).show();
                }
            }
            );
        }
        public static List<Product> getCart() {
            if(cart == null) {
                cart = new Vector<Product>();
            }
    
            return cart;
        }
    }

当我使用在两个 Activity 中被注释掉的代码时，即使用 start Activity 作为结果方法时，会发生这种情况: 当我点击删除按钮时，项目被删除但 CartActivity 自动关闭。即使购物车中有产品，带有计数器 TextView 的 UserActivity 也显示为“0”值。

请告诉我您需要从代码中获得的任何其他信息。欢迎使用在删除 CartActivity 中的某些项目后按下后退按钮更新购物车计数器的任何其他方法。感谢您的帮助。

最佳答案

使用

invalidateOptionsMenu();

在 onActivityResult 中再次填充菜单。

你的 UserActivity 代码应该是这样的:

public class UserActivity extends AppCompatActivity {
    private int cartindex = 0;
    private TextView counterTV = null;

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

        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        if (requestCode == 1) {

            if (resultCode == RESULT_OK) {
                Intent intent = getIntent();
                Integer deletecounter = intent.getIntExtra("DeleteCounter",0);
                if (deletecounter>0) {
                    cartindex=Integer.parseInt(counterTV.getText().toString())-deletecounter;
                    invalidateOptionsMenu();
                }
            }
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.user, menu);
        final View menu_list = menu.findItem(R.id.action_hawk).getActionView();
        counterTV = (TextView) menu_list.findViewById(R.id.cartcounter);
        UpdateCartCount(cartindex);
        new MyMenuItemStuffListener(menu_hotlist, "Show message") {
            @Override
            public void onClick(View v) {
                Intent intent= new  Intent(UserActivity.this,CartActivity.class);
                intent.putExtra("ProductTitle",pname);
                intent.putExtra("ProductUrl",purl);
                intent.putExtra("ProductPrice",pprice);
                intent.putExtra("BargainPrice",bargainprice);
                UserActivity.this.startActivity(intent);
            }
        };
        return true;
    }

    //Function to update cart count
    public void UpdateCartCount(final int new_number) {
        cartindex = new_number;
        if (counterTV == null) return;
        runOnUiThread(new Runnable() {
            @Override
            public void run() {
                if (new_number == 0)
                    counterTV.setVisibility(View.INVISIBLE);
                else {
                    counterTV.setVisibility(View.VISIBLE);
                    counterTV.setText(Integer.toString(new_number));
                }
            }
        });
    }

    @Override
    protected void onRestart() {
        if (CartActivity.cart.size()!=0) {
            cartindex=CartActivity.cart.size(); 
            invalidateOptionsMenu();
            super.onRestart()
        }

关于java - 删除后按后退按钮更新购物车计数，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/34411960/