java - 在多个 JPanel 之间 Swing FocusTraversalPolicy

Question

我有两个包含多个组件的 JPanel 对象。每个面板都有自己的FocusTraversalPolicy。

我想在第一个面板的第一个组件处开始焦点循环。当焦点到达第一个面板的最后一个组件时，当我按 Tab 时，焦点应该跳转到第二个面板的第一个组件。

在两个面板上，FocusTraversalPolicyProvider 均已启用。

这是如何工作的？

public class Panel1 extends JPanel{

    private JTextField text1;
    private JTextField text2;

    public JPanel1(){
        init();
    }

    private void init(){
        text1 = new JTextField();
        text2 = new JTextField();

        this.setLayout(new FlowLayout());
        this.add(text1);
        this.add(text2);

        this.setFocusTraversalPolicyProvider(true);
        this.setFocusTraversalPolicy(new SimpleFocusTraversalPolicy(
            text1,
            text2
        ));
    }
}

public class Panel2 extends JPanel{

    private JTextField text1;
    private JTextField text2;

    public JPanel2(){
        init();
    }

    private void init(){
        text1 = new JTextField();
        text2 = new JTextField();

        this.setLayout(new FlowLayout());
        this.add(text1);
        this.add(text2);

        this.setFocusTraversalPolicyProvider(true);
        this.setFocusTraversalPolicy(new SimpleFocusTraversalPolicy(
            text1,
            text2
        ));
    }
}

public class ContainerPanel extends JPanel{

    private JPanel panel1, panel2;

    public ContainerPanel(){
        init();
    }

    private void init(){
        panel1 = new Panel1();
        panel2 = new Panel2();

        this.setLayout(new FlowLayout());
        this.add(panel1);
        this.add(panel2);

        /*
            what should I do here to jump from panel1 to panel2 after the last component of panel1?
        */
    }
}

Answer 1

您也许能够重写 FocusTraversalPolicy#getComponentAfter(...) 方法:

import java.awt.*;
import java.awt.event.*;
import java.util.*;
import java.util.List;
import javax.swing.*;

public class SimpleFocusTraversalPolicyTest {
  private JComponent makeUI() {
    JTextField t1 = new JTextField("3", 12);
    JTextField t2 = new JTextField("1", 12);
    JTextField t3 = new JTextField("4", 12);
    JTextField t4 = new JTextField("2", 12);
    JPanel p1 = new JPanel();
    p1.setBorder(BorderFactory.createTitledBorder("left"));
    p1.setFocusTraversalPolicy(new SimpleFocusTraversalPolicy(t2, t4, t1, t3));
    p1.add(t1); p1.add(t2); p1.add(t3); p1.add(t4);
    p1.setFocusTraversalPolicyProvider(true);
    p1.setFocusCycleRoot(false);

    JTextField t5 = new JTextField("4", 12);
    JTextField t6 = new JTextField("3", 12);
    JTextField t7 = new JTextField("2", 12);
    JTextField t8 = new JTextField("1", 12);
    JPanel p2 = new JPanel();
    p2.setBorder(BorderFactory.createTitledBorder("right"));
    p2.setFocusTraversalPolicy(new SimpleFocusTraversalPolicy(t8, t7, t6, t5));
    p2.add(t5); p2.add(t6); p2.add(t7); p2.add(t8);
    p2.setFocusTraversalPolicyProvider(true);
    p2.setFocusCycleRoot(false);

    JPanel p = new JPanel(new GridLayout(1, 2));
    p.add(p1);
    p.add(p2);
    return p;
  }
  public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {
      @Override public void run() {
        createAndShowGUI();
      }
    });
  }
  public static void createAndShowGUI() {
    JFrame f = new JFrame();
    f.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
    f.getContentPane().add(new SimpleFocusTraversalPolicyTest().makeUI());
    f.setSize(320, 240);
    f.setLocationRelativeTo(null);
    f.setVisible(true);
  }
}

//There is no SimpleFocusTraversalPolicy in your code, so this is just an example:
class SimpleFocusTraversalPolicy extends FocusTraversalPolicy {
  private final List<? extends Component> order;
  public SimpleFocusTraversalPolicy(Component... arrays) {
    super();
    this.order = Arrays.asList(arrays);
  }
  @Override public Component getFirstComponent(Container focusCycleRoot) {
    return order.get(0);
  }
  @Override public Component getLastComponent(Container focusCycleRoot) {
    return order.get(order.size() - 1);
  }
  @Override public Component getComponentAfter(Container focusCycleRoot, Component aComponent) {
    int idx = order.indexOf(aComponent) + 1;
    if (idx >= order.size() && !focusCycleRoot.isFocusCycleRoot()) {
      return null;
    } else {
      return order.get(idx % order.size());
    }
  }
  @Override public Component getComponentBefore(Container focusCycleRoot, Component aComponent) {
    int idx = order.indexOf(aComponent) - 1;
    if (idx < 0 && !focusCycleRoot.isFocusCycleRoot()) {
      return null;
    } else {
      return order.get((idx + order.size()) % order.size());
    }
  }
  @Override public Component getDefaultComponent(Container focusCycleRoot) {
    return order.get(0);
  }
}