为什么在初始化后添加View会抛出NLP但不会在初始化期间使用afterburner.fx

Question

我正在使用afterburner.fx http://afterburner.adam-bien.com/

它像宣传的那样工作。我可以将多个fxml文件添加到中央/主要＆＃34;视图＆＃34;。

但是如果我想稍后添加另一个fxml / presenter，例如，使用不同navigationPane上的按钮将另一个fxml添加到mainAnchorPane。 然后它抛出NullPointerException。

public class MainscenePresenter implements Initializable {

    @FXML
    AnchorPane breadcrumbAnchor;

    @FXML
    AnchorPane navigationAnchor;

    //--------------------------------------------------------
    @FXML
    private AnchorPane mainAnchorPane; //ADD NEW ATPANE HERE

    private AtPresenter atPresenter;
    private AtView atView;

    //--------------------------------------------------------
    @Override
    public void initialize(URL url, ResourceBundle rb) {

        //add BreadCrumBar WORKS
        BreadcrumbbarView breadcrumbbarView = new BreadcrumbbarView();
        breadcrumbbarView.getViewAsync(breadcrumbAnchor.getChildren()::add);

        //add DFD  WORKS
        DfdView dfdView = new DfdView();
        Parent view2 = dfdView.getView();
        this.mainAnchorPane.getChildren().add(view2);

        //add Navigation  WORKS
        NavigationView navigationView = new NavigationView();
        Parent view = navigationView.getView();
        navigationAnchor.getChildren().add(view);

        //add AT
        this.atView = new AtView();
        this.atPresenter = (AtPresenter) this.atView.getPresenter();

        //ADDING AT VIEW LIKE THIS WORKS <=========================
        this.showAt();

    }

    void showAt() {
        this.mainAnchorPane.getChildren().add(this.atView.getView()); // <== NLP here if invoked with buttonAt
    }

    public void buttonAt() {
        //ADDING AT VIEW LIKE THIS(Button on different Presenter) DOES NOT WORK => NLP
        this.showAt();
    }
}



public class NavigationPresenter implements Initializable {

@FXML
Button atNavButton;

@Inject
MainscenePresenter mainscene;

private ResourceBundle resources = null;

@Override
public void initialize(URL location, ResourceBundle resources) {
    this.resources = resources;
}

@FXML
void showDfdScene(ActionEvent event) {
    mainscene.buttonAt();
}
}

似乎我不了解JavaFX的一些中心机制！无法命名，查找它！

为什么在这种情况下抛出NullPointerException而不是durin初始化？

Caused by: java.lang.NullPointerException
at abc.abc.app.mainscene.MainscenePresenter.showAt(MainscenePresenter.java:107)
at abc.abc.app.mainscene.MainscenePresenter.buttonAt(MainscenePresenter.java:112)
at abc.abc.app.navigation.NavigationPresenter.showDfdScene(NavigationPresenter.java:41)
... 58 more

Answer 1

Afterburner.fx是JavaFX的依赖注入框架。它提供的主要功能是能够将对象注入到加载FXML文件时创建的控制器/演示者中（通过实例化FXMLView的子类）。实例化FXMLView时发生的基本过程是：

1. 创建相应演示者的新实例
2. 检查演示者以查找任何@Inject - 带注释的字段
3. 对于每个@Inject - 注释字段，如果注入器缓存中存在该类型的实例，则将其设置为该字段的值。否则，将创建该类型的新实例并将其放置在缓存中，并将其设置为字段的值。

这里要注意的要点是，演示者本身的处理方式与其依赖关系不同。如果您尝试（如在您的代码中）将一个演示者注入另一个演示者，将专门为注入目的创建一个演示者类的实例：这将不同于加载FXML文件时创建的实例，因此它不会注入任何@FXML个字段。这就是为什么你得到一个空指针异常：{`1}}在``MainScenePresenter mainAnchorPane NavigationPresenter`中为空。

一位主持人提到另一位主持人通常是个坏主意：它会在两位主持人之间产生不必要的联系。相反，您应该将模型注入两个表示您想要在它们之间共享的状态的演示者。在你的情况下，你可能会有像

这样的东西

that is injected into the

现在在演示者中，

public class ViewState {

    private final BooleanProperty atShowing = new SimpleBooleanProperty();

    public BooleanProperty atShowingProperty() {
        return atShowing ;
    }

    public final boolean isAtShowing() {
        return atShowingProperty().get();
    }

    public final void setAtShowing(boolean atShowing) {
        atShowingProperty().set(atShowing);
    }
}

和

public class MainscenePresenter implements Initializable {

    @Inject
    private ViewState viewState ;

    @FXML
    AnchorPane breadcrumbAnchor;

    @FXML
    AnchorPane navigationAnchor;

    //------------------------------------------------------
    @FXML
    private AnchorPane mainAnchorPane; //ADD NEW ATPANE HERE

    private AtPresenter atPresenter;
    private AtView atView;

    //------------------------------------------------------
    @Override
    public void initialize(URL url, ResourceBundle rb) {

        //add BreadCrumBar WORKS
        BreadcrumbbarView breadcrumbbarView = new BreadcrumbbarView();
        breadcrumbbarView.getViewAsync(breadcrumbAnchor.getChildren()::add);

        //add DFD  WORKS
        DfdView dfdView = new DfdView();
        Parent view2 = dfdView.getView();
        this.mainAnchorPane.getChildren().add(view2);

        //add Navigation  WORKS
        NavigationView navigationView = new NavigationView();
        Parent view = navigationView.getView();
        navigationAnchor.getChildren().add(view);

        //add AT
        this.atView = new AtView();
        this.atPresenter = (AtPresenter) this.atView.getPresenter();

        this.viewState.atShowingProperty().addListener((obs, wasShowing, isNowShowing) -> {
            if (isNowShowing) {
                this.mainAnchorPane.getChildren().remove(this.atView.getView());
            } else {
                this.mainAnchorPane.getChildren().add(this.atView.getView());
            }
        });
    }      
}