是否可以重新加载相同的fxml/controller实例？

Question

我有一个用于总体设置窗口的主窗口，其中包含一个listview和所有设置类别。窗口的右侧有一个Anchorpane，用于在从列表中选择每个类别时为每个类别加载单独的FXML文件。

当一个用户选择一个类别，我需要他们能够编辑右边的设置，切换到另一个类别，并作出更多的改变。然而，如果他们回到第一类，那里所做的改变会持续下去。

我的明显问题是，每次用户更改类别时，FXMLLoader都会重新加载FXML文件和控制器，将其中的所有控件重置为它们的默认值。

研究：

我找到的唯一解决这个问题的答案是如何在不重新加载FXML文件的情况下使用javafx应用程序控制器？。它提到了对FXML控制器使用单例，但没有解决每次都重新加载FXML文件本身的问题。

如果有人能指出这类设置菜单的基本示例，我会很高兴。

Answer 1

基本上有三种方法可以做到这一点：

1. 定义一个表示数据的模型(设置)，并创建它的单个实例。每次重新加载FXML文件，并将单个实例传递给控制器。将UI中的数据与模型中的数据绑定。这样，当您重新加载FXML时，它将使用相同的数据进行更新。（这是我的首选选项。）
2. 只创建一次控制器。每次重新加载FXML文件，每次设置相同的控制器。让initialize()方法从本地存储的字段或模型更新UI。重新加载FXML文件时，@FXML-注释字段将被替换，并调用initialize()方法，用现有数据更新新控件。（这感觉有点做作。从道义上讲，任何名为initialize()的方法只应该执行一次。但是，这是完全可行的。）
3. 加载每个FXML文件一次并缓存UI（可能还有控制器）。然后当用户在列表视图中选择某些内容时，只需显示已经加载的视图。这可能是最简单的，但在内存中的开销要大一些，因为您要一直将所有视图保存在内存中。

假设您有一个模型，它可能如下所示：

public class Settings {

    private final UserInfo userInfo ;
    private final Preferences prefs ;
    private final Appearance appearance ;

    public Settings(UserInfo userInfo, Preferences prefs, Appearance appearance) {
        this.userInfo = userInfo ;
        this.prefs = prefs ;
        this.appearance = appearance ;
    }

    public Settings() {
        this(new UserInfo(), new Preferences(), new Appearance());
    }

    public UserInfo getUserInfo() {
        return userInfo ;
    }

    public Preferences getPreferences() {
        return prefs ;
    }

    public Appearance getAppearance() {
       return appearance ;
    }
}

和

public class UserInfo {

    private final StringProperty name = new SimpleStringProperty() ;
    private final StringProperty department = new SimpleStringProperty() ;
    // etc...

    public StringProperty nameProperty() {
        return name ;
    }

    public final String getName() {
        return nameProperty().get();
    }

    public final void setName(String name) {
        nameProperty().set(name);
    }

    // etc...
}

（对于首选项、外观等类似）

public class UserInfoController {

    private final UserInfo userInfo ;

    @FXML
    private TextField name ;
    @FXML
    private ComboBox<String> department ;

    public UserInfoController(UserInfo userInfo) {
        this.userInfo = userInfo ;
    }

    public void initialize() {
        name.textProperty().bindBidirectional(userInfo.nameProperty());
        department.valueProperty().bindBidirectional(userInfo.departmentProperty());
    }
}

public class MainController {

    @FXML
    private BorderPane root ;
    @FXML
    private ListView<String> selector ;

    private Settings settings = new Settings() ; // or pass in from somewhere else..

    public void initialize() {
        selector.getSelectionModel().selectedItemProperty().addListener((obs, oldSelection, newSelection) -> {
            if ("User Information".equals(newSelection)) {
                loadScreen("UserInfo.fxml", new UserInfoController(settings.getUserInfo()));
            } else if ("Preferences".equals(newSelection)) {
                loadScreen("Preferences.fxml", new PreferencesController(settings.getPreferences()));
            } else if ("Appearance".equals(newSelection)) {
                loadScreen("Appearance.fxml", new AppearanceController(settings.getAppearance()));
            } else {
                root.setCenter(null);
            }
    }

    private void loadScreen(String resource, Object controller) {
        try {
            FXMLLoader loader = new FXMLLoader(getClass().getResource(resource));
            loader.setController(controller);
            root.setCenter(loader.load());
        } catch (IOException exc) {
            exc.printStackTrace();
            root.setCenter(null);
        }
    }
}

public class UserInfoController {

    @FXML
    private TextField name ;
    @FXML
    private ComboBox<String> department ;

    private final StringProperty nameProp = new SimpleStringProperty();
    private final ObjectProperty<String> departmentProp = new SimpleObjectProperty();

    public StringProperty nameProperty() {
        return nameProp;
    }

    public final String getName() {
        return nameProperty().get();
    }

    public final void setName(String name) {
        nameProperty().set(name);
    }

    public ObjectProperty<String> departmentProperty() {
        return departmentProp ;
    }

    public final String getDepartment() {
        return departmentProperty().get();
    }

    public final void setDepartment(String department) {
        departmentProperty().set(department);
    }

    public void initialize() {
        // initialize controls with data currently in properties, 
        // and ensure changes to controls are written back to properties:
        name.textProperty().bindBidirectional(nameProp);
        department.valueProperty().bindBidirectional(departmentProp);
    }
}

后来呢

public class MainController {

    @FXML
    private BorderPane root ;
    @FXML
    private ListView<String> selector ;

    private UserInfoController userInfoController = new UserInfoController();
    private PreferencesController preferencesController = new PreferencesController();
    private AppearanceController appearanceController = new AppearanceController();

    public void initialize() {
        // initialize controllers with data if necessary...

        selector.getSelectionModel().selectedItemProperty().addListener((obs, oldSelection, newSelection) -> {
        selector.getSelectionModel().selectedItemProperty().addListener((obs, oldSelection, newSelection) -> {
            if ("User Information".equals(newSelection)) {
                loadScreen("UserInfo.fxml", userInfoController);
            } else if ("Preferences".equals(newSelection)) {
                loadScreen("Preferences.fxml", preferencesController);
            } else if ("Appearance".equals(newSelection)) {
                loadScreen("Appearance.fxml", appearanceController);
            } else {
                root.setCenter(null);
            }
        }
    }

    private void loadScreen(String resource, Object controller) {
        // as before...
    }
}

这是因为当FXML文件重新加载时，您不创建新的控制器，控制器中的initialize方法使用已经存在的数据更新控件。（请注意调用bindbiredicion方法的方式。）

第三个选项可以在主控制器中实现，也可以在主fxml文件中实现。要在控制器中实现它，您基本上要做

public class MainController {

    @FXML
    private BorderPane root ;
    @FXML
    private ListView<String> selector ;

    private Parent userInfo ;
    private Parent prefs;
    private Parent appearance;

    // need controllers to get data later...

    private UserInfoController userInfoController ;
    private PreferencesController prefsController ;
    private AppearanceController appearanceController ;

    public void initialize() throws IOException {

        FXMLLoader userInfoLoader = new FXMLLoader(getClass().getResource("userInfo.fxml));
        userInfo = userInfoLoader.load();
        userInfoController = userInfoLoader.getController();

        FXMLLoader prefsLoader = new FXMLLoader(getClass().getResource("preferences.fxml));
        prefs = prefsLoader.load();
        prefsController = prefsLoader.getController();

        FXMLLoader appearanceLoader = new FXMLLoader(getClass().getResource("appearance.fxml));
        appearance = appearanceLoader.load();
        appearanceController = appearanceLoader.getController();

        // configure controllers with data if needed...

        selector.getSelectionModel().selectedItemProperty().addListener((obs, oldSelection, newSelection) -> {
            if ("User Information".equals(newSelection)) {
                root.setCenter(userInfo);
            } else if ("Preferences".equals(newSelection)) {
                root.setCenter(prefs); 
            } else if ("Appearance".equals(newSelection)) {
                root.setCenter(prefs);
            } else {
                root.setCenter(null);
            }
        }
    }
}

<!-- imports etc omitted -->
<BorderPane xmlns="http://javafx.com/javafx/8.0.111" xmlns:fx="http://javafx.com/fxml/1"
    fx:controller="com.example.MainController">

    <left>
        <ListView fx:id="selector" />
    </left>

    <fx:define>
        <fx:include fx:id="userInfo" source="UserInfo.fxml" >
    </fx:define>

    <fx:define>
        <fx:include fx:id="prefs" source="Preferences.fxml" >
    </fx:define>

    <fx:define>
        <fx:include fx:id="appearance" source="Appearance.fxml" >
    </fx:define>

</BorderPane>

的FXML-injection规则是，用指定的fx:id（例如UserInfo)注入所包含的FMXL文件的根（例如UserInfo)，当“controller”追加到fx:id（例如UserInfoController)时，将这些所包含文件的控制器（“嵌套控制器”）注入到具有给定名称的字段中。所以主控制器现在看起来像

public class MainController {

    @FXML
    private BorderPane root ;
    @FXML
    private ListView<String> selector ;

    @FXML
    private Parent userInfo ;
    @FXML
    private Parent prefs;
    @FXML
    private Parent appearance;

    // need controllers to get data later...

    @FXML
    private UserInfoController userInfoController ;
    @FXML
    private PreferencesController prefsController ;
    @FXML
    private AppearanceController appearanceController ;

    public void initialize() {

        // configure controllers with data if needed...

        selector.getSelectionModel().selectedItemProperty().addListener((obs, oldSelection, newSelection) -> {
            if ("User Information".equals(newSelection)) {
                root.setCenter(userInfo);
            } else if ("Preferences".equals(newSelection)) {
                root.setCenter(prefs); 
            } else if ("Appearance".equals(newSelection)) {
                root.setCenter(prefs);
            } else {
                root.setCenter(null);
            }
        }
    }
}