JToolBar IllegalArgumentException，当放回到GridBagLayout中时 [英] JToolBar IllegalArgumentException when dropped back into GridBagLayout

问题描述

当工具栏从GUI上拖动然后关闭(以将其返回到GUI)时，为什么此代码会引发IllegalArgumentException?

Why does this code throw an IllegalArgumentException when the tool bar is dragged off the GUI, then closed (to return it to the GUI)?

我可以理解为什么添加没有约束的组件可能会不合适，但是在这种情况下，最初将工具栏添加到没有约束的面板(使用GridBagLayout)不会导致此类问题.为什么它会在第二次及以后被添加?

I could understand why it might be improper to add a component with no constraint, but in this case, the initial addition of the toolbar to the panel (which uses GridBagLayout) without a constraint causes no such problem. Why should it occur the 2nd and subsequent times it is added?

该代码改编自此答案，但是两个代码都显示相同的问题.

The code is adapted from this answer, but both codes show the same problem.

import java.awt.*;
import javax.swing.*;

public class GridBagToolBarOddity {

    public static void main(String[] args) {
        Runnable r = new Runnable() {

            @Override
            public void run() {
                JPanel gui = new JPanel(new GridBagLayout());
                JToolBar tb = new JToolBar();
                tb.add(new JLabel("Drag me off, then drop me back!"));
                gui.add(tb);

                gui.setPreferredSize(new Dimension(300, 100));
                gui.setBackground(Color.RED);

                JFrame f = new JFrame("Demo");
                f.add(gui);
                f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
                f.setLocationByPlatform(true);

                f.pack();
                f.setVisible(true);
            }
        };
        SwingUtilities.invokeLater(r);
    }
}

异常

Exception in thread "AWT-EventQueue-0" java.lang.IllegalArgumentException: 
    cannot add to layout: constraints must be a GridBagConstraint
        at java.awt.GridBagLayout.addLayoutComponent(GridBagLayout.java:702)
        at java.awt.Container.addImpl(Container.java:1120)
        at java.awt.Container.add(Container.java:966)
        at javax.swing.plaf.basic.BasicToolBarUI$FrameListener.windowClosing(BasicToolBarUI.java:1265)
        at java.awt.Window.processWindowEvent(Window.java:2051)
        at javax.swing.JDialog.processWindowEvent(JDialog.java:681)
        at java.awt.Window.processEvent(Window.java:2009)
        at java.awt.Component.dispatchEventImpl(Component.java:4861)
        at java.awt.Container.dispatchEventImpl(Container.java:2287)
        at java.awt.Window.dispatchEventImpl(Window.java:2719)
        at java.awt.Component.dispatchEvent(Component.java:4687)
        at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:735)
        at java.awt.EventQueue.access$200(EventQueue.java:103)
        at java.awt.EventQueue$3.run(EventQueue.java:694)
        at java.awt.EventQueue$3.run(EventQueue.java:692)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
        at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
        at java.awt.EventQueue$4.run(EventQueue.java:708)
        at java.awt.EventQueue$4.run(EventQueue.java:706)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:705)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)

推荐答案

这是BasicToolBarUI源代码的片段

That's snippet from BasicToolBarUI source

    public void windowClosing(WindowEvent w) {
        if (toolBar.isFloatable()) {
            if (dragWindow != null)
                dragWindow.setVisible(false);
            floating = false;
            if (floatingToolBar == null)
                floatingToolBar = createFloatingWindow(toolBar);
            if (floatingToolBar instanceof Window) ((Window)floatingToolBar).setVisible(false);
            floatingToolBar.getContentPane().remove(toolBar);
            String constraint = constraintBeforeFloating;
            if (toolBar.getOrientation() == JToolBar.HORIZONTAL) {
                if (constraint == "West" || constraint == "East") {
                    constraint = "North";
                }
            } else {
                if (constraint == "North" || constraint == "South") {
                    constraint = "West";
                }
            }
            if (dockingSource == null)
                dockingSource = toolBar.getParent();
            if (propertyListener != null)
                UIManager.removePropertyChangeListener(propertyListener);
            dockingSource.add(toolBar, constraint);

如您所见，它尝试将constraintBeforeFloating字符串作为约束传递，但是GridBagLayout需要GridBagConstraints.

As you can see it tries to pass constraintBeforeFloating String as constraint but GridBagLayout expects GridBagConstraints.

constraintBeforeFloating = calculateConstraint();

和

private String calculateConstraint() {
    String constraint = null;
    LayoutManager lm = dockingSource.getLayout();
    if (lm instanceof BorderLayout) {
        constraint = (String)((BorderLayout)lm).getConstraints(toolBar);
    }
    return (constraint != null) ? constraint : constraintBeforeFloating;
}

因此，当浮动功能关闭时，UI会尝试将curretn约束(字符串)传递给GridBagLayout并失败.

So when floating is closed UI tries to pass curretn constraint (String) to GridBagLayout and fails.

这篇关于JToolBar IllegalArgumentException，当放回到GridBagLayout中时的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！