为什么 JavaFX TextArea 中的 selectRange() 有时不突出显示所选内容？

问题描述 投票：0回答：1

我在 JavaFX 主类中编写了以下代码：

package jfxTest;

import java.util.Random;

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.TextArea;
import javafx.scene.input.KeyCode;
import javafx.scene.input.KeyEvent;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;

public class Main extends Application {
    public static void main(String[] args) {
        Application.launch(args);
    }

    private static int selectionIndex = 0;
    private static TextArea textArea;

    @Override
    public void start(Stage primaryStage) {
        System.out.println("Starting JavaFX Window...");
        StackPane rootPane = new StackPane();
        textArea = new TextArea();

        textArea.setText("TEST");
        textArea.setEditable(false);
        createRandomOptions(8);

        textArea.addEventFilter(KeyEvent.KEY_PRESSED, event -> {
            if (event.getCode().equals(KeyCode.UP)) {
                select(selectionIndex <= 0 ? 0 : selectionIndex - 1);
            }
            if (event.getCode().equals(KeyCode.DOWN)) {
                String[] lines = textArea.getText().split("\n");
                select(selectionIndex >= lines.length - 1 ? lines.length - 1 : selectionIndex + 1);
            }
        });

        rootPane.getChildren().add(textArea);
        Scene scene = new Scene(rootPane, 900, 500);
        primaryStage.setScene(scene);
        primaryStage.show();
        System.out.println("Created window.");
        System.out.println("\nNow press up and down keys to navigate:\n"
                + "Notice, that although a new selection is displayed in the console, it is not\n"
                + "highlighted in the window itself. Even a call to getSelectedText() works fine.\n");
    }
    
    /**
     * Creates a bunch of random options in textArea.
     * @param newOptionCount
     */
    private static void createRandomOptions(int newOptionCount) {
        for (int i = 0; i < newOptionCount; i++) {
            textArea.appendText("\nSEL" + (new Random().nextInt(10000)));
        }
    }
    
    private static void select(int newSelectionIndex) {
        String[] lines = textArea.getText().split("\n");
        
        System.out.println("New selection index: " + newSelectionIndex);
        selectionIndex = newSelectionIndex;
        
        // Determine selection indexes
        int selectionStart = 0;
        int selectionEnd = 0;
        for (int i = 0; i < newSelectionIndex; i++) {
            selectionStart += lines[i].length() + 1;
        }
        selectionEnd = selectionStart + lines[newSelectionIndex].length();
        
        // Does not work. Selection does need to be applied twice by the user to be actually highlighted.
        textArea.selectRange(selectionStart, selectionEnd);
        
        System.out.println("Selected text: " + textArea.getSelectedText() + "\n");
    }
}

我知道它看起来很乱而且不太干净，但你应该明白我的意思。 现在问题如下： 当我使用箭头键（特别是向上和向下）在 

TextArea
中导航时，只有当用户应用两次（仅在最顶部和底部）时，选择才变得可见，尽管调用 
selectRange()
每次都会制作。

这是为什么呢？这是 JavaFX 库中的错误，还是我遗漏了什么？

这个问题我已经搜索过几次了，但还没有找到结果。 我还没有使用 AWT Swing 对此进行测试，但我非常有信心，使用它可以很好地工作。

我的 Java 是 OpenJDK 19，JavaFX 版本为 19。

java javafx textarea selection
1个回答
0
投票

向高级 UI 控件添加低级事件处理（例如鼠标和键盘事件处理程序）从来都不是一个特别好的主意。您始终面临着干扰控件内置功能的风险，或者内置功能干扰您的事件处理程序，从而导致无法提供您想要的功能的风险。

在您的情况下，后者正在发生：

TextArea
已经实现了按下按键时更改选择。如果按下箭头键而没有修饰键，则选择将被清除。此默认行为是在调用按键后发生的，因此默认行为就是您看到的行为。

您可以通过添加来查看发生了什么

textArea.selectionProperty().addListener((obs, oldSel, newSel) -> System.out.printf("Selection change: %s -> %s%n", oldSel, newSel) ); 
看起来您只是在这里使用了错误的控件。如果您有一个不可编辑的 
TextArea
，其中您将每一行视为不同的项目，那么听起来您正在尝试重新实现 
ListView
，它已经实现了诸如选择单个项目之类的功能。您可以简单地重新实现您的示例：


import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.ListView;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;

import java.util.Random;

public class Main extends Application {
    public static void main(String[] args) {
        Application.launch(args);
    }

    private ListView<String> listView;

    @Override
    public void start(Stage primaryStage) {
        System.out.println("Starting JavaFX Window...");
        StackPane rootPane = new StackPane();
        listView = new ListView<>();


        listView.getItems().add("TEST");
        createRandomOptions(8);


        rootPane.getChildren().add(listView);
        Scene scene = new Scene(rootPane, 900, 500);
        primaryStage.setScene(scene);
        primaryStage.show();
        System.out.println("Created window.");
        System.out.println("\nNow press up and down keys to navigate:\n"
                + "Notice, that although a new selection is displayed in the console, it is not\n"
                + "highlighted in the window itself. Even a call to getSelectedText() works fine.\n");
    }


    /**
     * Creates a bunch of random options in textArea.
     * @param newOptionCount
     */
    private void createRandomOptions(int newOptionCount) {
        for (int i = 0; i < newOptionCount; i++) {
            listView.getItems().add("SEL" + (new Random().nextInt(10000)));
        }
    }

}

如果您确实想修改文本区域中的选定内容，请使用 
TextFormatter
 和可修改选择的过滤器。这看起来像这样（不过，我再次认为这只是重新发明轮子）。请注意，这也符合您（大概）想要的鼠标点击方式：


import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.IndexRange;
import javafx.scene.control.TextArea;
import javafx.scene.control.TextFormatter;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;

import java.util.Random;

public class Main extends Application {
    public static void main(String[] args) {
        Application.launch(args);
    }

    private TextArea textArea;

    @Override
    public void start(Stage primaryStage) {
        System.out.println("Starting JavaFX Window...");
        StackPane rootPane = new StackPane();
        textArea = new TextArea();

        textArea.selectionProperty().addListener((obs, oldSel, newSel) -> System.out.printf("Selection change: %s -> %s%n", oldSel, newSel));

        textArea.setText("TEST");
        textArea.setEditable(false);
        createRandomOptions(8);

        textArea.setTextFormatter(new TextFormatter<String>(this::modifySelection));

        rootPane.getChildren().add(textArea);
        Scene scene = new Scene(rootPane, 900, 500);
        primaryStage.setScene(scene);
        primaryStage.show();
        System.out.println("Created window.");
        System.out.println("\nNow press up and down keys to navigate:\n"
                + "Notice, that although a new selection is displayed in the console, it is not\n"
                + "highlighted in the window itself. Even a call to getSelectedText() works fine.\n");
    }
    
    private TextFormatter.Change modifySelection(TextFormatter.Change change) {
        IndexRange selection = change.getSelection();
        String[] lines = change.getControlNewText().split("\n");
        int lineStart = 0 ;
        for (String line : lines) {
            int lineEnd = lineStart + line.length();
            System.out.printf("Line: %d %d %s%n", lineStart, lineEnd, line);
            if (lineStart <= selection.getStart() && lineEnd >= selection.getStart()) {
                change.setAnchor(lineStart);
            }
            if (lineStart <= selection.getEnd() && lineEnd >= selection.getEnd()) {
                change.setCaretPosition(lineEnd);
            }
            lineStart += line.length() + 1; // +1 to account for line terminator itself
        }
        return change;
    }

    /**
     * Creates a bunch of random options in textArea.
     * @param newOptionCount
     */
    private void createRandomOptions(int newOptionCount) {
        for (int i = 0; i < newOptionCount; i++) {
            textArea.appendText("\nSEL" + (new Random().nextInt(10000)));
        }
    }

}

    



      

      
    

  

  

    
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