Question

我正在编写JavaFX应用程序。我用SceneBuilder 8.2创建了GUI。我已经放了一些ChoiceBox但是使用Java Type，而不是自定义Type。它运作良好。但是使用自定义Type，choiceBox没有实例化，为什么？代码下方：

public class PelController {
    //instanciation is OK
    @FXML
    private ChoiceBox<PeriodeEnum> fCalculInteret;

    //not instanciated at launch
   @FXML
    private ChoiceBox<DureeChoiceBoxElement> duree;

/**
     * Initializes the controller class. This method is automatically called
     * after the fxml file has been loaded.
     */
    @FXML
    private void initialize() {
//fCalculInteret is NOT NULL, automatically instantiated at startup.
fCalculInteret.valueProperty().bindBidirectional(pel.fCalculInteretProperty());
//duree is NULL causing NullPointerException
duree.valueProperty().get().dureeProperty().bindBidirectional(pel.dureeProperty());
    }
}

自定义类型：

public class DureeChoiceBoxElement extends ObservableValueBase<DureeChoiceBoxElement> {

    private IntegerProperty duree;

    public DureeChoiceBoxElement() {

    }

    public DureeChoiceBoxElement(int duree) {
        this.duree = new SimpleIntegerProperty(duree);
    }

    public IntegerProperty dureeProperty() {
        return duree;
    }

    public Integer getDuree() {
        return duree.getValue();
    }

    @Override
    public DureeChoiceBoxElement getValue() {
        // TODO Auto-generated method stub
        return new DureeChoiceBoxElement(duree.get());
    }

    public void setDuree(Integer duree) {
        this.duree.setValue(duree);
    }

    @Override
    public String toString() {
        return duree + " an";
    }

}

你能解释为什么这个NullPointer。感谢

Answer 1

duree.valueProperty().get().dureeProperty().bindBidirectional(pel.dureeProperty());        

                                 |                                    |

- ＆gt; Null可能来自|

嗯，似乎方法：

 public IntegerProperty dureeProperty() {
        return duree;
 }

返回null，因为默认的构造函数不初始化duree属性。

1）一种解决方案是将方法修改为：

//lazy
public IntegerProperty dureeProperty() {
       if(duree == null) //if duree has not been initialized
         duree = new SimpleIntegerProperty();
        return duree;
}

或2）您可以更改默认构造函数以初始化private IntegerProperty duree;属性，尽管解决方案1更好。

JavaFX自定义ChoiceBox在启动时未实例化

1 个答案: