我想使用 SQLite 计算购物车中产品的总价。当我使用 Settext() 在 textview 中设置价格时，它不会返回总和值。这是 DBhelper 类中的 gettotalprice 方法。
public int getTotalExpenses()
{
int total = 0;
SQLiteDatabase database = this.getReadableDatabase();
Cursor cursor = database.rawQuery("SELECT SUM("+ OrderContract.OrderEntry.COLUMN_PRICE + ") FROM " + OrderContract.OrderEntry.TABLE_NAME, null);
if (cursor.moveToFirst())
{
total = cursor.getInt(4);
}
while (cursor.moveToNext());
return total;
}
OrderProvider 类：
package com.example.myapp;
import android.content.ContentProvider;
import android.content.ContentUris;
import android.content.ContentValues;
import android.content.UriMatcher;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.net.Uri;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
public class OrderProvider extends ContentProvider {
// this constant is needed in order to define the path of our modification in the table
public static final int ORDER=100;
public DBHelper mhelper;
public static UriMatcher sUriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
static {
sUriMatcher.addURI(OrderContract.CONTENT_AUTHORITY,OrderContract.PATH,ORDER);
}
@Override
public boolean onCreate() {
mhelper = new DBHelper(getContext());
return true;
}
@Override
public Cursor query( Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
SQLiteDatabase database = mhelper.getReadableDatabase();
Cursor cursor;
int match = sUriMatcher.match(uri);
switch (match){
case ORDER:
cursor = database.query(OrderContract.OrderEntry.TABLE_NAME, projection, selection, selectionArgs, null,null, sortOrder);
break;
default:
throw new IllegalArgumentException("CANT QUERY");
}
cursor.setNotificationUri(getContext().getContentResolver(),uri);
return cursor;
}
@Override
public String getType(Uri uri) {
return null;
}
@Override
public Uri insert(Uri uri, ContentValues values) {
int match = sUriMatcher.match(uri);
switch (match) {
case ORDER:
return insertCart(uri, values);
default:
throw new IllegalArgumentException("Cant insert data");
}
}
private Uri insertCart(Uri uri, ContentValues values) {
String name = values.getAsString(OrderContract.OrderEntry.COLUMN_NAME);
if(name == null){
throw new IllegalArgumentException("Name is Required");
}
String quantity = values.getAsString(OrderContract.OrderEntry.COLUMN_QUANTITY);
if(quantity == null){
throw new IllegalArgumentException("Quantity is Required");
}
String price = values.getAsString(OrderContract.OrderEntry.COLUMN_PRICE);
if(price == null){
throw new IllegalArgumentException("Price is Required");
}
//insert values into order
SQLiteDatabase database = mhelper.getWritableDatabase();
long id = database.insert(OrderContract.OrderEntry.TABLE_NAME, null, values);
if(id == 0){
return null;
}
getContext().getContentResolver().notifyChange(uri,null);
return ContentUris.withAppendedId(uri,id);
}
@Override
public int delete(Uri uri, String selection, String[] selectionArgs) {
//delete data once order is made
int rowsDeleted;
SQLiteDatabase database = mhelper.getWritableDatabase();
int match = sUriMatcher.match(uri);
switch (match) {
case ORDER:
rowsDeleted = database.delete(OrderContract.OrderEntry.TABLE_NAME, selection, selectionArgs);
break;
default:
throw new IllegalArgumentException("Cannot delete");
}
if (rowsDeleted!=0) {
getContext().getContentResolver().notifyChange(uri, null);
}
return rowsDeleted;
}
@Override
public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
return 0;
}
}
OrderContract 类：
public class OrderContract {
public OrderContract() {
}
//content authority requires package name
public static final String CONTENT_AUTHORITY = "com.example.myapp";
public static final Uri BASE_URI = Uri.parse(("content://" +CONTENT_AUTHORITY));
//same as table name
public static final String PATH = "orders" ;
public static abstract class OrderEntry implements BaseColumns{
public static final Uri CONTENT_URI = Uri.withAppendedPath(BASE_URI,PATH);
public static final String TABLE_NAME = "orders" ;
public static final String _ID = BaseColumns._ID ;
public static final String COLUMN_NAME = "name" ;
public static final String COLUMN_QUANTITY = "quantity" ;
public static final String COLUMN_PRICE = "price" ;
}
}
购物车活动：
sofaname=findViewById(R.id.sofaname);
sofaprice=findViewById(R.id.sofaprice);
sofadesc=findViewById(R.id.sofadesc);
plusquantity = findViewById(R.id.addquantity);
minusquantity = findViewById(R.id.subquantity);
quantitynumber = findViewById(R.id.quantity);
addtocart = findViewById(R.id.addtocart);
ImageSlider imageSlider = findViewById(R.id.sofaslider1);
List<SlideModel> slideModels = new ArrayList<>();
slideModels.add(new SlideModel(R.drawable.card14));
slideModels.add(new SlideModel(R.drawable.card6));
slideModels.add(new SlideModel(R.drawable.card7));
imageSlider.setImageList(slideModels,false);
imageSlider.setClickable(false);
DB = new DBHelper(Sofa1.this);
String Name = DB.getProductNamePrice("SELECT F_Name FROM Furniture WHERE F_Type = 'Sofa';");
String Price = DB.getProductNamePrice("SELECT F_Price FROM Furniture WHERE F_Type = 'Sofa';");
String Desc = DB.getProductNamePrice("SELECT F_Description FROM Furniture WHERE F_Type = 'Sofa';");
sofaname.setText(Name);
sofaprice.setText(Price);
sofadesc.setText(Desc);
plusquantity.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if(quantity<5){
//sofaprice
int baseprice= Integer.parseInt(sofaprice.getText().toString());
quantity++;
displayquantity();
totalprice = baseprice * quantity;
String setnewprice = (String.valueOf(totalprice));
sofaprice.setText(setnewprice);
}
}
});
minusquantity.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
int baseprice=0;
String Price = DB.getProductNamePrice("SELECT F_Price FROM Furniture WHERE F_Type = 'Sofa';");
baseprice = Integer.parseInt(Price);
if(quantity>1) {
quantity--;
displayquantity();
totalprice = baseprice * quantity;
String setnewprice = (String.valueOf(totalprice));
sofaprice.setText(setnewprice);
}
}
});
addtocart.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent =new Intent(Sofa1.this,Cart.class);
startActivity(intent);
// once this button is clicked we want to save our values in the database and send those values
// right away to summary activity where we display the order info
SaveCart();
totalamount = (TextView) findViewById(R.id.total);
int totalAmount = DB.getTotalExpenses();
totalamount.setText(String.valueOf(totalAmount));
}
});
}
private boolean SaveCart() {
String name = sofaname.getText().toString();
String price = sofaprice.getText().toString();
String quantity = quantitynumber.getText().toString();
ContentValues values = new ContentValues();
values.put(OrderContract.OrderEntry.COLUMN_NAME,name);
values.put(OrderContract.OrderEntry.COLUMN_PRICE,price);
values.put(OrderContract.OrderEntry.COLUMN_QUANTITY,quantity);
if(mcurrentcarturi == null){
Uri newUri = getContentResolver().insert(OrderContract.OrderEntry.CONTENT_URI, values);
if(newUri == null){
Toast.makeText(this, "Failed to add to cart", Toast.LENGTH_SHORT).show();
}else{
Toast.makeText(this, "Product added to cart", Toast.LENGTH_SHORT).show();
}
}
hasallrequiredvalues = true;
return hasallrequiredvalues;
}
private void displayquantity() {
quantitynumber.setText(String.valueOf(quantity));
}
@Override
public @NotNull Loader<Cursor> onCreateLoader(int id, Bundle args) {
String[] projection = {OrderContract.OrderEntry._ID,
OrderContract.OrderEntry.COLUMN_NAME,
OrderContract.OrderEntry.COLUMN_PRICE,
OrderContract.OrderEntry.COLUMN_QUANTITY};
return new CursorLoader(this, mcurrentcarturi, projection, null, null, null);
}
@Override
public void onLoadFinished(@NotNull Loader<Cursor> loader, Cursor cursor) {
if(cursor==null || cursor.getCount() < 1){
return;
}
if(cursor.moveToFirst()){
int name = cursor.getColumnIndex(OrderContract.OrderEntry.COLUMN_NAME);
int price = cursor.getColumnIndex(OrderContract.OrderEntry.COLUMN_PRICE);
int quantity = cursor.getColumnIndex(OrderContract.OrderEntry.COLUMN_QUANTITY);
String nameofsofa = cursor.getString(name);
String priceofsofa = cursor.getString(price);
String quantityofsofa = cursor.getString(quantity);
sofaname.setText(nameofsofa);
sofaprice.setText(priceofsofa);
quantitynumber.setText(quantityofsofa);
}
}
@Override
public void onLoaderReset(@NotNull Loader<Cursor> loader) {
sofaname.setText("");
sofaprice.setText("");
quantitynumber.setText("");
}
答案 0 :(得分：0)
因为您的查询有效
SELECT SUM(price) FROM orders;
只会返回一列，因此使用 total = cursor.getInt(4); 应该会导致异常，因为该列越界，只有 1 列并且它的索引将为 0。
因此尝试更改为使用 :-
public int getTotalExpenses()
{
int total = 0;
SQLiteDatabase database = this.getReadableDatabase();
Cursor cursor = database.rawQuery("SELECT SUM("+ OrderContract.OrderEntry.COLUMN_PRICE + ") FROM " + OrderContract.OrderEntry.TABLE_NAME, null);
if (cursor.moveToFirst())
{
total = cursor.getInt(0); //<<<<<<<<<< CHANGED
}
//while (cursor.moveToNext()); //<<<<<<<<<< COMMENTED OUT NOT NEEDED
cursor.close(); //<<<<<<<<<< ADDED should always close cursor when finished with them
return total;
}