java - 我必须在哪里初始化类成员变量JavaFX

Question

我正在通过 Java 中的场景构建器使用 JavaFX 和 JFoenix 制作一个应用程序，但我在类成员变量的初始化方面遇到了一些问题。这是我的代码

public class MessageApp extends Application {

    private AnchorPane mainLayout;
    private Stage primaryStage;
    private int i = 5;

    public void init() {
        i = 0;
    }

    public void start(Stage primaryStage) {
        try {
            FXMLLoader loader = new FXMLLoader();
            loader.setLocation(PeerApp.class.getResource("PeerApp.fxml"));
            mainLayout = loader.load();
        } catch (IOException e) {
            e.printStackTrace();
        }

        this.primaryStage = primaryStage;
        this.primaryStage.setTitle("Test");
        JFXDecorator decorator = new JFXDecorator(primaryStage, mainLayout);
        decorator.setCustomMaximize(true);
        Scene scene = new Scene(decorator, 600, 400);
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    @FXML
    private void clickSendMessage() {
        System.out.println("i = " + i);
    }

    public static void main(String[] args) {
        launch(args);
    }
}

这里的问题是，即使我在 init 函数或 start 函数中将 I 重置为 0，当我单击触发 的发送按钮时， clickSendMessage 函数，我的 println 打印“i = 5”。重置它的唯一方法是将 i = 0 放入 clickSendMessage 函数本身。

所以，在这种情况下，这不是一个大问题，但是如果我在声明期间没有初始化类成员变量，即使我在 init 或 中初始化它start 函数，当我单击发送按钮时，我的应用程序崩溃了，因为在这个阶段它仍然被视为 null，但我不知道为什么。

知道为什么吗？我必须在哪里初始化我的类成员变量？

编辑:

好吧，我尝试为我的 View 创建一个专用 Controller ，我的第一个问题似乎已经解决，一切都按预期初始化，但现在我的 ListView 每次添加 Contact 到我的列表，但以前就是这样。我不知道创建一个单独的 Controller 会破坏什么，你知道吗？

这是完整的代码

PeerApp.java

public class PeerApp extends Application {

    private AnchorPane mainLayout;
    private Stage primaryStage;

    public void start(Stage primaryStage) {
        try {
            FXMLLoader loader = new FXMLLoader();
            loader.setLocation(PeerApp.class.getResource("PeerApp.fxml"));
            mainLayout = loader.load();
        } catch (IOException e) {
            e.printStackTrace();
        }

        this.primaryStage = primaryStage;
        this.primaryStage.setTitle("Peer Messenger");
        JFXDecorator decorator = new JFXDecorator(primaryStage, mainLayout);
        decorator.setCustomMaximize(true);
        Scene scene = new Scene(decorator, 600, 400);
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    public static void main(String[] args) {
        launch(args);
    }
}

PeerAppController.java

public class PeerAppController {

    private PeerApplication peer = new PeerApplication("1234");
    private ObservableList<Contact> contacts;
    private ChangeListener<Contact> listener;
    private int i = 5;

    @FXML
    private JFXListView<Contact> contactList;
    @FXML
    private JFXButton addContactButton;
    @FXML
    private JFXTextArea messageTextArea;
    @FXML
    private GridPane chatGridPane;
    @FXML
    private JFXButton sendButton;

    @FXML
    public void initialize() {
        initPeer();
        initRootLayout();
        contacts = FXCollections.observableArrayList(Contact.extractor());

        contactList.setItems(contacts);

        listener = new ChangeListener<Contact>() {
            @Override
            public void changed(ObservableValue<? extends Contact> observable, Contact oldValue, Contact newValue) {
                chatGridPane.getChildren().clear();
                List<Message> conversation = contacts.get(contactList.getSelectionModel().getSelectedIndex()).getConversation();
                int i;

                i = 0;
                while (conversation.size() >= i + 1) {
                    Label messageLabel = new Label(conversation.get(i).getContent());
                    chatGridPane.addRow(i, messageLabel);
                    i++;
                }
            }
        };
        contactList.getSelectionModel().selectedItemProperty().addListener(listener);

        i = 0;
    }

    private void initPeer() {
        peer.init(EncryptionType.NONE, CompressionType.NONE);
        peer.getPeerDaemonPlug().setComListener(new ICommunicationListener() {
            @Override
            public void onDataReceived(String s) {
                Label labelMessage = new Label(s);
                GridPane.setHalignment(labelMessage, HPos.RIGHT);
                chatGridPane.addRow(getRowCount(chatGridPane) + 1, labelMessage);
                contacts.get(contactList.getSelectionModel().getSelectedIndex()).getConversation().add(new Message(s, false));
            }

            @Override
            public void onStreamPacketCompleted(OutputStream outputStream) {
            }
        });
    }

    private void initRootLayout() {
        // Init the layout
        ColumnConstraints c1 = new ColumnConstraints();
        c1.setPercentWidth(100);

        sendButton = new JFXButton();
        contactList = new JFXListView<Contact>();
        chatGridPane = new GridPane();
        chatGridPane.setMaxSize(Double.MAX_VALUE, Double.MAX_VALUE);
        chatGridPane.getColumnConstraints().add(c1);
    }

    @FXML
    private void clickAddContact() {
        TextInputDialog dialog = new TextInputDialog("");
        dialog.setTitle("New Contact");
        dialog.setHeaderText("Add a new contact");
        dialog.setContentText("Enter the ID of your contact:");

        Optional<String> result = dialog.showAndWait();
        result.ifPresent(id -> {
            Contact c = new Contact(id);
            contacts.add(c);
            System.out.println(contactList.getItems().size());
        });
    }

    @FXML
    private void clickSendMessage() {
        // Not to be there

        String message = messageTextArea.getText();
        Label labelMessage = new Label(message);

        try {
            peer.sendRequest(sendDataToNode, new SendDataToNodeParam(contactList.getSelectionModel().getSelectedItem().toString(), message));
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        } catch (NoSuchPaddingException e) {
            i = 0;
            e.printStackTrace();
        } catch (IllegalBlockSizeException e) {
            i = 1;
            e.printStackTrace();
        } catch (InvalidAlgorithmParameterException e) {
            i = 2;
            e.printStackTrace();
        } catch (InvalidKeyException e) {
            i = 3;
            e.printStackTrace();
        } catch (BadPaddingException e) {
            i = 4;
            e.printStackTrace();
        } catch (IOException e) {
            i = 5;
            e.printStackTrace();
        }

        messageTextArea.setText("");
        GridPane.setHalignment(labelMessage, HPos.LEFT);
        chatGridPane.addRow(getRowCount(chatGridPane) + 1, labelMessage);
        contacts.get(contactList.getSelectionModel().getSelectedIndex()).getConversation().add(new Message(message, true));
        System.out.println("i = " + i);
    }

    private int getRowCount(GridPane pane) {
        int numRows = pane.getRowConstraints().size();
        for (int i = 0; i < pane.getChildren().size(); i++) {
            Node child = pane.getChildren().get(i);
            if (child.isManaged()) {
                Integer rowIndex = GridPane.getRowIndex(child);
                if(rowIndex != null){
                    numRows = Math.max(numRows,rowIndex+1);
                }
            }
        }
        return numRows;
    }

}

Contact.java

public class Contact {
    private StringProperty id;
    private List<Message> conversation;

    public Contact(String id) {
        this.id = new SimpleStringProperty(id);
        this.conversation = FXCollections.observableArrayList();
    }

    public static Callback<Contact, Observable[]> extractor() {
        return new Callback<Contact, Observable[]>() {
            @Override
            public Observable[] call(Contact param) {
                return new Observable[]{param.id};
            }
        };
    }

    @Override
    public String toString() {
        return String.format("%s", id.get());
    }

    public StringProperty getId() {
        return this.id;
    }

    public void setId(StringProperty id) {
        this.id = id;
    }

    public List<Message> getConversation() {
        return this.conversation;
    }
}

PeerApp.fxml

<AnchorPane prefHeight="400.0" prefWidth="600.0" xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1" fx:controller="PeerAppController">
    <children>
        <SplitPane dividerPositions="0.29797979797979796" layoutX="200.0" layoutY="120.0" prefHeight="400.0" prefWidth="600.0" AnchorPane.bottomAnchor="0.0" AnchorPane.leftAnchor="0.0" AnchorPane.rightAnchor="0.0" AnchorPane.topAnchor="0.0">
            <items>
                <AnchorPane minHeight="0.0" minWidth="0.0" prefHeight="160.0" prefWidth="100.0">
                    <children>
                  <JFXListView fx:id="contactList" AnchorPane.bottomAnchor="0.0" AnchorPane.leftAnchor="0.0" AnchorPane.rightAnchor="0.0" AnchorPane.topAnchor="0.0" />
                        <JFXButton fx:id="addContactButton" buttonType="RAISED" layoutX="133.0" layoutY="357.0" onAction="#clickAddContact" ripplerFill="#10ae07" text="+" textAlignment="CENTER" AnchorPane.bottomAnchor="14.0" AnchorPane.rightAnchor="14.0" />
                    </children>
                </AnchorPane>
                <AnchorPane minHeight="0.0" minWidth="0.0" prefHeight="160.0" prefWidth="100.0">
                    <children>
                        <JFXTextArea fx:id="messageTextArea" focusColor="#40a85c" layoutX="15.0" layoutY="237.0" maxHeight="50.0" minHeight="10.0" prefHeight="50.0" prefWidth="339.0" AnchorPane.bottomAnchor="10.0" AnchorPane.leftAnchor="5.0" AnchorPane.rightAnchor="72.0" />
                        <ScrollPane layoutX="12.0" layoutY="12.0" prefHeight="276.0" prefWidth="394.0" AnchorPane.bottomAnchor="65.0" AnchorPane.leftAnchor="5.0" AnchorPane.rightAnchor="5.0" AnchorPane.topAnchor="5.0">
                     <content>
                        <GridPane fx:id="chatGridPane" maxHeight="1.7976931348623157E308" maxWidth="1.7976931348623157E308">
                          <columnConstraints>
                            <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
                            <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
                          </columnConstraints>
                          <rowConstraints>
                            <RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
                            <RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
                            <RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
                          </rowConstraints>
                        </GridPane>
                     </content></ScrollPane>
                  <JFXButton fx:id="sendButton" layoutX="350.0" layoutY="338.0" onAction="#clickSendMessage" prefHeight="50.0" prefWidth="64.0" ripplerFill="#18cd00" text="SEND" textAlignment="CENTER" textFill="#0dae04" AnchorPane.bottomAnchor="5.0" AnchorPane.leftAnchor="344.0" AnchorPane.rightAnchor="5.0" />
                    </children>
                </AnchorPane>
            </items>
        </SplitPane>
    </children>
</AnchorPane>

Answer 1

在我看来，将负责启动应用程序并加载 .fxml 文件的类与您的 Controller 类混合在一起是不好的做法>，它关心控制你的 UI，例如，在你的情况下，你有 clickSendMessage() 方法，该方法必须位于 Controller 类中。

所以我建议您编写一个单独的类，即您的 Controller ，将 Controller 附加到 .fxml 文件，然后您可以更轻松地处理 UI 和逻辑部分之间的所有交互。我可以向您展示一个简单的例子:

package stackoverflow;

import javafx.fxml.Initializable;

import java.net.URL;
import java.util.ResourceBundle;

public class TestController implements Initializable {

    @Override
    public void initialize(URL location, ResourceBundle resources) {
        // here are  all stuffs initialized
    }
}

然后 .fxml 文件如下所示:

<?xml version="1.0" encoding="UTF-8"?>

<?import javafx.scene.layout.AnchorPane?>
<AnchorPane prefHeight="500.0" prefWidth="700.0" xmlns="http://javafx.com/javafx/8.0.91" xmlns:fx="http://javafx.com/fxml/1" 
fx:controller="stackoverflow.TestController">
// here you can fill it with content
</AnchorPane>

现在你有了单独的 Controller 和 .fxml，这样你就可以像在主类中一样加载这个 .fxml 然后你可以在你的类中添加所有内容您想要控制您的应用程序(包括该方法)的 Controller 。这是构建 javafx 应用程序的一种非常简单明了的方法。我认为这是可以理解的，但如果我错过了什么，请随时问我。