java - 重点组件参考

Question

我正在开发一个简单的基于 java swing 的应用程序。如何获取和设置表单当前聚焦的文本字段/文本区域的文本？

我知道如何确定哪个组件具有焦点，但我不知道如何获取组件的选定文本。我使用 getFocusOwner()，但它返回一个组件，因此没有实现方法 getSelectedText()。我是否需要以某种方式进行类型转换？

Answer 1

是的：

Component focusOwner = ...
if(focusOwner instanceof JTextComponent) { // a textfield or textarea is focused
    JTextComponent textComp = (JTextComponent) focusOwner;
    String s = textComp.getText();
}

Answer 2

根据您的确切上下文，您可能会考虑使用自定义 TextAction：它的方法getTextComponent(ActionEvent)返回最新的焦点文本组件。一段代码：

    Action logSelected = new TextAction("log selected") {

        @Override
        public void actionPerformed(ActionEvent e) {
            JTextComponent text = getTextComponent(e);
            System.out.println("selected: " + text.getSelectedText());
        }

    };

    JComponent content = new JPanel();
    content.add(new JTextField("sometext", 20));
    content.add(new JTextField("other content", 20));
    content.add(new JCheckBox("just some focusable comp"));
    content.add(new JButton(logSelected));

Answer 3

我使用 getFocusOwner()，但它返回一个组件，因此没有实现方法 getSelectedText()。我是否需要以某种方式进行类型转换？

一种方法是测试instanceof@user1235867 +1

另一个也是最有效的方法是帮助数组J/Components和简单地确定哪些J/Component有电流KeyboardFocusManager#getFocusOwner()在Window

FocusOwner注意在两个顶级容器之间切换是非常异步的，并且需要将事件包装到invokeLater

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
//http://www.coderanch.com/t/342205/GUI/java/Tab-order-swing-components
public class Testing {

    private static final long serialVersionUID = 1L;
    private Component[] focusList;
    private int focusNumber = 0;
    private JFrame frame;

    public Testing() {
        JTextField tf1 = new JTextField(5);
        JTextField tf2 = new JTextField(5);
        JTextField tf3 = new JTextField(5);
        JButton b1 = new JButton("B1");
        JButton b2 = new JButton("B2");
        tf2.setEnabled(false);
        focusList = new Component[]{tf1, b1, tf2, b2, tf3};
        JPanel panel = new JPanel(new GridLayout(5, 1));
        panel.add(tf1);
        panel.add(b1);
        panel.add(tf2);
        panel.add(b2);
        panel.add(tf3);
        frame = new JFrame();
        frame.setFocusTraversalPolicy(new MyFocusTraversalPolicy());
        frame.add(panel);
        frame.pack();
        frame.setLocation(150, 100);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
        KeyboardFocusManager.getCurrentKeyboardFocusManager().addKeyEventDispatcher(new KeyEventDispatcher() {

            public boolean dispatchKeyEvent(KeyEvent ke) {
                if (ke.getID() == KeyEvent.KEY_PRESSED) {
                    if (ke.getKeyCode() == KeyEvent.VK_TAB) {
                        Component comp = KeyboardFocusManager.getCurrentKeyboardFocusManager().getFocusOwner();
                        if (comp.isEnabled() == false) {
                            if (ke.isShiftDown()) {
                                KeyboardFocusManager.getCurrentKeyboardFocusManager().focusPreviousComponent();
                            } else {
                                KeyboardFocusManager.getCurrentKeyboardFocusManager().focusNextComponent();
                            }
                        }
                    }
                }
                return false;
            }
        });
    }

    private class MyFocusTraversalPolicy extends FocusTraversalPolicy {

        public Component getComponentAfter(Container focusCycleRoot, Component aComponent) {
            focusNumber = (focusNumber + 1) % focusList.length;
            return focusList[focusNumber];
        }

        public Component getComponentBefore(Container focusCycleRoot, Component aComponent) {
            focusNumber = (focusList.length + focusNumber - 1) % focusList.length;
            return focusList[focusNumber];
        }

        public Component getDefaultComponent(Container focusCycleRoot) {
            return focusList[0];
        }

        public Component getLastComponent(Container focusCycleRoot) {
            return focusList[focusList.length - 1];
        }

        public Component getFirstComponent(Container focusCycleRoot) {
            return focusList[0];
        }
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                Testing testing = new Testing();
            }
        });
    }
}