我有点卡住了,也许有人可以提供帮助。我希望在某些字段发生变化时计算出“总计”。
我在excel中制作了一个原型来说明:
因此,无论何时更改价格或数量,都会重新计算总成本,并且还应更新摘要,包括“最终总计”。我已经使用了绑定并且它们不起作用,除非首次创建摘要项目,然后finalTotal字段不会重新计算。
我有两个类,一个名为Product,其中包含属性productName
,priceEach
,quantity
,productTotal
。每当设置priceEach
或quantity
属性时,都会调用calculateTotal()
方法来更新productTotal
。
这是代码:
import javafx.beans.property.*;
import javafx.beans.property.SimpleFloatProperty;
import javafx.beans.property.StringProperty;
public class Product {
private final StringProperty productName;
private final FloatProperty priceEach;
private final IntegerProperty quantity;
private FloatProperty productTotal;
public Product(){
this.productName = new SimpleStringProperty("Product Name");
this.priceEach = new SimpleFloatProperty(0);
this.quantity = new SimpleIntegerProperty(0);
this.productTotal = new SimpleFloatProperty(0);
}
public Product(String name, float priceEach, int quantity){
this.productName = new SimpleStringProperty(name);
this.priceEach = new SimpleFloatProperty(priceEach);
this.quantity = new SimpleIntegerProperty(quantity);
this.productTotal = calculateProductTotal();
}
private FloatProperty calculateProductTotal() {
return new SimpleFloatProperty(priceEach.get()*quantity.get());
}
public void setProductName(String name){
productName.set(name);
}
public void setPriceEach(float price){
priceEach.set(price);
productTotal = calculateProductTotal();
}
public void setQuantity(int number){
quantity.set(number);
productTotal = calculateProductTotal();
}
public String getProductName(){ return productName.get(); }
public float getPriceEach(){ return priceEach.get(); }
public int getQuantity(){ return quantity.get(); }
public float getProductTotal(){ return productTotal.get(); }
public StringProperty productNameProperty() { return productName;}
public FloatProperty priceEachProperty() { return priceEach;}
public IntegerProperty quantityProperty() { return quantity;}
public FloatProperty productTotalProperty() { return productTotal;}
@Override
public String toString(){
return " Product: " + getProductName() +
", Price: " + getPriceEach() +
", Quantity: " + getQuantity() +
", Total cost: " + getProductTotal();
}
}
我还有一个Summary类,它有两个属性,它们单向绑定到Products类中的相应属性。这就是问题所在。
import javafx.beans.property.*;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
public class Summary {
private FloatProperty finalTotal;
public ObservableList<Item> itemsSummary = FXCollections.observableArrayList();
public Summary(){
finalTotal=new SimpleFloatProperty(0);
}
public Item add()
{
Item newItem = new Item();
itemsSummary.add(newItem);
newItem.productTotalProperty().addListener((obs, oldAmount, newAmount) -> {
System.out.println("Item total changed from "+oldAmount+" to "+newAmount);
calculateTotal();
System.out.println("Final total: "+finalTotal);
});
return newItem;
}
public class Item{
private final StringProperty productName;
private FloatProperty productTotal;
public Item(){
this.productName = new SimpleStringProperty("");
this.productTotal = new SimpleFloatProperty(-1);
}
public void setProductName(String name) { productName.set(name); }
public void setProductTotal(float total) { productTotal.set(total); }
public String getProductName() { return productName.get(); }
public float getProductTotal() { return productTotal.get(); }
public StringProperty productNameProperty() { return productName;}
public FloatProperty productTotalProperty() { return productTotal;}
}
private void calculateTotal(){
float runningTotal=0;
for (Item i: itemsSummary )
runningTotal+= i.getProductTotal();
finalTotal.set(runningTotal);
}
@Override
public String toString(){
String output= "";
for(Item i: itemsSummary){
String pn = i.getProductName();
float pt = i.getProductTotal();
output = output +"\n"+ String.format("Product: %s, Product cost: %.2f", pn, pt);
}
return output+
"\nFinal total: " + finalTotal.getValue();
}
}
正如您所看到的,我有一个内部类Item包含数据(名称和小计)。我已经为newItem.productTotalProperty()
添加了一个监听器,但这只在构造新Item时才起作用:当产品的字段发生更改时,其实例的总数会更新,但对Summary对象的绑定会停止工作,所以它的所有领域都没有改变。
以下是测试驱动程序代码:
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
public class BindingsPrototypeTestDriver {
public static void main(String[] args)
{
Product A = new Product("Pencil", 1.50f, 300);
Product B = new Product("Eraser", 0.50f, 200);
Product C = new Product("Paper", 4.95f, 100);
ObservableList<Product> products = FXCollections.observableArrayList();
products.add(A);
products.add(B);
products.add(C);
Summary summary = new Summary();
for(Product p: products)
{
Summary.Item summaryItem = summary.add();
summaryItem.productNameProperty().bind(p.productNameProperty());
summaryItem.productTotalProperty().bind(p.productTotalProperty());
}
for(Product p: products){ System.out.println(p.toString()); }
System.out.println(summary.toString());
C.setQuantity(200);
for(Product p: products){ System.out.println(p.toString()); }
System.out.println(summary.toString());
}
}
这是输出:
run:
Item total changed from -1.0 to 450.0
Final total: FloatProperty [value: 450.0]
Item total changed from -1.0 to 100.0
Final total: FloatProperty [value: 550.0]
Item total changed from -1.0 to 494.99997
Final total: FloatProperty [value: 1045.0]
Product: Pencil, Price: 1.50, Quantity: 300, Total cost: 450.00
Product: Eraser, Price: 0.50, Quantity: 200, Total cost: 100.00
Product: Paper, Price: 4.95, Quantity: 100, Total cost: 495.00
Product: Pencil, Product cost: 450.00
Product: Eraser, Product cost: 100.00
Product: Paper, Product cost: 495.00
Final total: 1045.0
Product: Pencil, Price: 1.50, Quantity: 300, Total cost: 450.00
Product: Eraser, Price: 0.50, Quantity: 200, Total cost: 100.00
Product: Paper, Price: 4.95, Quantity: 200, Total cost: 990.00
Product: Pencil, Product cost: 450.00
Product: Eraser, Product cost: 100.00
Product: Paper, Product cost: 495.00
Final total: 1045.0
如您所见,当“Paper”实例的数量更改为200时,所有内容都会在Product实例中正确更新,但不会在摘要中...
我做错了什么?
答案 0 :(得分:2)
您的代码存在一些问题。
您遇到的问题是您使用的productTotal
属性不会更新,但每次更新时都会替换为新的属性对象。您的Product
课程的用户无法知道这一点。实际上,用户希望属性getter总是返回相同的实例(并且你也期望也是这样)。
为了简单起见,不是创建新属性,而是为旧属性分配新值,或者只使用Bindings
类:
public class Product {
private final StringProperty productName;
private final FloatProperty priceEach;
private final IntegerProperty quantity;
private final FloatProperty productTotal;
public Product(){
this("Product Name", 0, 0);
}
public Product(String name, float priceEach, int quantity){
this.productName = new SimpleStringProperty(name);
this.priceEach = new SimpleFloatProperty(priceEach);
this.quantity = new SimpleIntegerProperty(quantity);
this.productTotal = new SimpleFloatProperty();
this.productTotal.bind(Bindings.multiply(this.quantity, this.priceEach));
}
public void setPriceEach(float price){
priceEach.set(price);
}
...
Summary
class Item
类。您已经有Product
课程。将数据存储在内存中两次并没有多大意义。你也依靠外部代码为你绑定价值......那个设计很差。itemsSummary
为public
而非final
,这意味着任何引用Summary
实例的人都可以更改值{{1} }实例没有被告知这一变化。这不是问题的唯一原因是您不能使用Summary
列表。实际上,您可以使用ObservableList
替换代码中的所有列表,但这不会有所作为。这就是我要做的事情:
ArrayList
itemsSummary
甚至final
并提供吸气剂private
在列表项目中添加/删除列表。ListChangeListener
s Product
这些修改使public class Summary {
private final FloatProperty finalTotal;
public final ObservableList<Product> itemsSummary;
private final ChangeListener<Number> itemTotalChangeListener = (observable, oldValue, newValue) -> {
calculateTotal();
};
public Summary() {
finalTotal = new SimpleFloatProperty(0);
itemsSummary = FXCollections.observableArrayList();
itemsSummary.addListener((ListChangeListener.Change<? extends Product> c) -> {
boolean modified = false;
while (c.next()) {
if (c.wasRemoved()) {
modified = true;
for (Product p : c.getRemoved()) {
p.productTotalProperty().removeListener(itemTotalChangeListener);
}
}
if (c.wasAdded()) {
modified = true;
for (Product p : c.getAddedSubList()) {
p.productTotalProperty().addListener(itemTotalChangeListener);
}
}
}
if (modified) {
calculateTotal();
}
});
}
...
方法中的代码更简单:
main