我有两项活动，一项是UserActivity，另一项是CartActivity我正在显示产品列表UserActivity。单击按钮后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，并且我在该购物车图标上有一个textview显示购物车计数器的自定义布局。每当我单击按钮时，该计数器就会更新AddtoCart。现在我继续CartActivity从购物车中删除一些产品。当我现在按返回按钮返回时UserActivity，计数器文本视图不会更新。
我已经阅读了几种在按下后退时进行更新的方法，如此处Back button and refresh previous activity的问题中给出的。答案中给出的两种方法是通过覆盖OnResume()方法UserActivity或通过启动结果活动。
我想当我按下后退按钮并将其从 Counter 中的原始产品数量中减去并更新文本视图时，我需要传递一个名为DeleteCounterfromCartActivity的变量。UserActivityTextView
这是的部分代码，UserActivity我只有在单击按钮时才调用此代码中更新购物车计数器的功能。onActivityResult()我也从上面给出的 SO question 链接的答案中尝试了 in的代码。它不工作：
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));
}
}
});
}
这是代码CartActivity：
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;
}
}
当我使用在两个活动中都被注释掉的代码时，即使用 start 活动作为结果方法时，会发生这种情况：当我单击删除按钮时，项目被删除但CartActivity自动关闭。UserActivity即使购物车中有产品，带有计数器文本的视图也会显示为“0”值。
请告诉我您需要从代码中获得的任何其他信息。欢迎在删除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CartActivity。任何帮助表示赞赏。