binding - JavaFX 2 绑定

Question

我在绑定LabeltextProperty 时遇到问题，我希望使用双变量对文本进行格式化。
如果我执行以下操作，它可以工作（标签文本属性已更新），但这样我就无法按照我的意愿格式化文本。

label.textProperty().bind(model.doubleProperty().asString());

这样不起作用（标签文本属性未更新）：

StringBinding labelBinding = new StringBinding() {

        {
            bind(model.doubleProperty().asString());
        }

        @Override
        protected String computeValue() {
            if(model.getDouble() <= 0) {
                return "---";
            } else {
                return df1.format(model.getDouble());
            }
        }
    };
    label.textProperty().bind(labelBinding);

感谢您的帮助。

Answer 1

我找到了如何让它工作，但我真的不明白它是如何工作的。

StringBinding labelBinding = new StringBinding() { 

    { 
        bind(model.doubleProperty()); // don't call asString() here
    } 

    @Override 
    protected String computeValue() { 
        if(model.getDouble() <= 0) { 
            return "---"; 
        } else { 
            return df1.format(model.getDouble()); 
        } 
    } 
}; 
label.textProperty().bind(labelBinding); 

但这会产生编译错误

label.textProperty().bind(model.doubleProperty());      

Answer 2

假设您有以下“JavaFX-Bean”：

import javafx.beans.property.DoubleProperty;
import javafx.beans.property.SimpleDoubleProperty;
import javafx.beans.property.SimpleStringProperty;
import javafx.beans.property.StringProperty;

public class Employee {
    private final StringProperty lastname = new SimpleStringProperty();
    private final StringProperty firstname = new SimpleStringProperty();
    private final DoubleProperty salary = new SimpleDoubleProperty();

    /**
     * @return the lastname Property
     */
    public StringProperty lastnameProperty() {
        return lastname;
    }


    /**
     * @return the lastname String
     */
    public String getLastname() {
        return lastname.get();
    }

    /**
     * @param lastname the lastname to set
     */
    public void setLastname(final String lastname) {
        this.lastname.set(lastname);
    }

    /**
     * @return the firstname property
     */
    public StringProperty firstnameProperty() {
        return firstname;
    }


    /**
     * @return the firstname String
     */
    public String getFirstname() {
        return firstname.get();
    }

    /**
     * @param firstname the firstname to set
     */
    public void setFirstname(final String firstname) {
        this.firstname.set(firstname);
    }

    /**
     * @return the salary Property
     */
    public DoubleProperty salaryProperty() {
        return salary;
    }


    /**
     * @return the salary double
     */
    public double getSalary() {
        return salary.get();
    }

    /**
     * @param salary the salary to set
     */
    public void setSalary(final double salary) {
        this.salary.set(salary);
    }

}

现在在应用程序的启动方法中定义一个标签：

Label labaelSalary = new Label();

并将其与'JavaFX-Bean'的salaryProperty绑定：

labaelSalary.textProperty()
         .bind(emp.salaryProperty().asString("%.2f"));

添加一个按钮并设置此按钮的操作：

Button changeSalaryButton = new Button("Change Salary"); 
changeSalaryButton.setOnAction(new EventHandler<ActionEvent>() {
   @Override
   public void handle(final ActionEvent event) {
      double salary = Math.random() * 10000;
      emp.setSalary(salary);
   }
});

每次点击 Button 时，Employee 对象 emp 的薪水是随机设置的。labelSalary 的有界文本（属性）立即更改为显示emp Employee 对象的salary 属性的新值。下面是启动方法的代码：

@覆盖

public void start(final Stage primaryStage) {

   Employee emp = new Employee();
   emp.setFirstname("Fred");
   emp.setLastname("Las Frite");
   emp.setSalary(12.500);

   Label labelSalary = new Label();
   labelSalary.textProperty()
      .bind(emp.salaryProperty().asString("%.2f"));
   Button changeSalaryButton = new Button("OK");
   changeSalaryButton.setOnAction(new EventHandler<ActionEvent>() {

      @Override
      public void handle(final ActionEvent event) {
         double salary = Math.random() * 10000;
         emp.setSalary(salary);
      }
   });

   HBox hBox = new HBox(10, labelSalary, changeSalaryButton);
   hBox.setPadding(new Insets(20));
   hBox.setAlignment(Pos.CENTER);
   primaryStage.setScene(new Scene(hBox));
   primaryStage.setWidth(400);
   primaryStage.setHeight(600);
   primaryStage.show();
}