我目前正在建立一个库存，用户应该可以在商品概览/主要活动中点击“购买”按钮，这会将商品的数量减少1。 我已经在另一个活动（所选项目的详细视图）中完成了这项任务，但我似乎无法在主要活动中完成它。
以下是完整的源代码：https://github.com/Fedor98/InventoryApp/tree/master/app/src/main
DetailActivity.java （其中一切正常）
/**
* Displays details of item that wes selected in the CatalogActivity.
*/
public class DetailActivity extends AppCompatActivity implements LoaderManager.LoaderCallbacks<Cursor> {
/** Tag for the log messages */
public static final String LOG_TAG = DetailActivity.class.getSimpleName();
/**
* Identifier for the inventory data loader
*/
private static final int EXISTING_INVENTORY_LOADER = 0;
/** Content URI for the existing item */
private Uri mCurrentItemUri;
/** TextView to show item's name */
private TextView mNameTextView;
/** TextView to show item's price */
private TextView mPriceTextView;
/** TextView to show item's quantity */
private TextView mQuantityTextView;
/** TextView to show item's supplier */
private TextView mSupplierTextView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_detail);
// Examine the intent that was used to launch this activity,
// We're creating a new item.
Intent intent = getIntent();
mCurrentItemUri = intent.getData();
// Change app bar to say "View Item details"
setTitle(getString(R.string.detail_activity_title_detail_item));
// Initialize a loader to read the item data from the database
// and display the current values in the editor
getLoaderManager().initLoader(EXISTING_INVENTORY_LOADER, null, this);
// Find all relevant views that we will need to read info from
mNameTextView = (TextView) findViewById(R.id.name);
mPriceTextView = (TextView) findViewById(R.id.price);
mQuantityTextView = (TextView) findViewById(R.id.quantity);
mSupplierTextView = (TextView) findViewById(R.id.supplier);
// Find the Button which will increase the item's quantity by 1
Button increaseButton = (Button) findViewById(R.id.increase_button);
// Setup the item click listener
increaseButton.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
int quantity = Integer.parseInt(mQuantityTextView.getText().toString());
quantity = quantity + 1;
ContentValues values = new ContentValues();
values.put(InventoryEntry.COLUMN_ITEM_QUANTITY, quantity);
int rowsAffected = getContentResolver().update(mCurrentItemUri, values, null, null);
// Show a toast message depending on whether or not the increasement was successful.
if (rowsAffected == 0) {
// If no rows were affected, then there was an error with the update.
Toast.makeText(DetailActivity.this, "Error with increasing quantity",
Toast.LENGTH_SHORT).show();
} else {
// Otherwise, the update was successful and we can display a toast.
Toast.makeText(DetailActivity.this, "Quantity increased by 1",
Toast.LENGTH_SHORT).show();
}
}
});
// Find the Button which will decrease the item's quantity by 1
Button decreaseButton = (Button) findViewById(R.id.decrease_button);
// Setup the item click listener
decreaseButton.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
int quantity = Integer.parseInt(mQuantityTextView.getText().toString());
if (quantity > 0) {
quantity = quantity - 1;
ContentValues values = new ContentValues();
values.put(InventoryEntry.COLUMN_ITEM_QUANTITY, quantity);
int rowsAffected = getContentResolver().update(mCurrentItemUri, values, null, null);
// Show a toast message depending on whether or not the decreasement was successful.
if (rowsAffected == 0) {
// If no rows were affected, then there was an error with the update.
Toast.makeText(DetailActivity.this, "Error with decreasing quantity",
Toast.LENGTH_SHORT).show();
} else {
// Otherwise, the update was successful and we can display a toast.
Toast.makeText(DetailActivity.this, "Quantity decreased by 1",
Toast.LENGTH_SHORT).show();
}
} else {
Toast.makeText(DetailActivity.this,
"Cannot set quantity to a value lower than 0",
Toast.LENGTH_SHORT).show();
}
}
});
}
[...]
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// User clicked on a menu option in the app bar overflow menu
switch (item.getItemId()) {
// Respond to a click on the "Delete" menu option
case R.id.action_delete:
// Pop up confirmation dialog for deletion
showDeleteConfirmationDialog();
return true;
case R.id.action_shop:
purchaseItem();
return true;
}
return super.onOptionsItemSelected(item);
}
[...]
public void purchaseItem() {
int quantity = Integer.parseInt(mQuantityTextView.getText().toString());
if (quantity > 0) {
quantity = quantity - 1;
ContentValues values = new ContentValues();
values.put(InventoryEntry.COLUMN_ITEM_QUANTITY, quantity);
int rowsAffected = getContentResolver().update(mCurrentItemUri, values, null, null);
// Show a toast message depending on whether or not the purchase was successful.
if (rowsAffected == 0) {
// If no rows were affected, then there was an error with the update.
Toast.makeText(DetailActivity.this, "Error with purchasing product",
Toast.LENGTH_SHORT).show();
} else {
// Otherwise, the update was successful and we can display a toast.
Toast.makeText(DetailActivity.this, "Purchase was successful",
Toast.LENGTH_SHORT).show();
}
} else {
Toast.makeText(DetailActivity.this,
"Item sold out",
Toast.LENGTH_SHORT).show();
}
}
InventoryCursorAdapter.java （我需要最后的onClickListener与上面方法中的减少功能相同）
/**{@link InventoryCursorAdapter} is an adapter for a list or grid view
* that uses a {@link Cursor} of inventory data as its data source. This adapter knows
* how to create list items for each row of inventory data in the {@link Cursor}.
*/
public class InventoryCursorAdapter extends CursorAdapter {
/** Tag for the log messages */
public static final String LOG_TAG = DetailActivity.class.getSimpleName();
/** Content URI for the existing item */
private Uri mCurrentItemUri;
/**
* Constructs a new {@link InventoryCursorAdapter}.
*
* @param context The context
* @param c The cursor from which to get the data.
*/
public InventoryCursorAdapter(Context context, Cursor c) {
super(context, c, 0 /* flags */);
}
/**
* Makes a new blank list item view. No data is set (or bound) to the views yet.
*
* @param context app context
* @param cursor The cursor from which to get the data. The cursor is already
* moved to the correct position.
* @param parent The parent to which the new view is attached to
* @return the newly created list item view.
*/
@Override
public View newView(Context context, Cursor cursor, ViewGroup parent) {
// Inflate a list item view using the layout specified in list_item.xml
return LayoutInflater.from(context).inflate(R.layout.list_item, parent, false);
}
/**
* This method binds the inventory data (in the current row pointed to by cursor) to the given
* list item layout. For example, the name for the current item can be set on the name TextView
* in the list item layout.
*
* @param view Existing view, returned earlier by newView() method
* @param context app context
* @param cursor The cursor from which to get the data. The cursor is already moved to the
* correct row.
*/
@Override
public void bindView(View view, final Context context, Cursor cursor) {
// Find individual views that we want to modify in the list item layout
TextView nameTextView = (TextView) view.findViewById(R.id.name_catalog);
final TextView quantityTextView = (TextView) view.findViewById(R.id.quantity_catalog);
TextView priceTextView = (TextView) view.findViewById(R.id.price_catalog);
// Find the columns of item attributes that we're interested in
int nameColumnIndex = cursor.getColumnIndex(InventoryEntry.COLUMN_ITEM_NAME);
final int quantityColumnIndex = cursor.getColumnIndex(InventoryEntry.COLUMN_ITEM_QUANTITY);
int priceColumnIndex = cursor.getColumnIndex(InventoryEntry.COLUMN_ITEM_PRICE);
// Read the item attributes from the Cursor for the current item
String itemName = cursor.getString(nameColumnIndex);
String itemQuantity = cursor.getString(Integer.parseInt(Integer.toString(quantityColumnIndex)));
String itemPrice = cursor.getString(priceColumnIndex);
itemPrice = itemPrice + "€";
// Update the TextViews with the attributes for the current item
nameTextView.setText(itemName);
quantityTextView.setText(itemQuantity);
priceTextView.setText(itemPrice);
mCurrentItemUri = ContentUris.withAppendedId(InventoryEntry.CONTENT_URI, id);
// Find the Button which will decrease the item's quantity by 1
Button saleButton = (Button) view.findViewById(R.id.sale_button);
// Setup the item click listener
saleButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
提前感谢您的帮助。我很迷茫，从几天开始坐在这里，没有再进一步......