Question

我在GroupLayout中有一个JFrame。当用户单击按钮时，我想在此JFrame中交换两个组件的位置。我使用GroupLayout中的方法replace()来替换另一个。以下是我想要交换两个按钮位置的代码：buttons[0]和buttons[1]：

groupLayout.replace(buttons[1], buttons[2]);
groupLayout.replace(buttons[2], buttons[1]);

但是，当我运行此程序时，程序会NullPointerException。该例外不提供任何有用的信息：

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at javax.swing.GroupLayout$ComponentInfo.setBounds(Unknown Source)
    at javax.swing.GroupLayout.layoutContainer(Unknown Source)
    at java.awt.Container.layout(Unknown Source)
    at java.awt.Container.doLayout(Unknown Source)
    at java.awt.Container.validateTree(Unknown Source)
    at java.awt.Container.validateTree(Unknown Source)
    at java.awt.Container.validateTree(Unknown Source)
    at java.awt.Container.validate(Unknown Source)
    at javax.swing.RepaintManager$2.run(Unknown Source)
    at javax.swing.RepaintManager$2.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at javax.swing.RepaintManager.validateInvalidComponents(Unknown Source)
    at javax.swing.RepaintManager$ProcessingRunnable.run(Unknown Source)
    at java.awt.event.InvocationEvent.dispatch(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$200(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.run(Unknown Source)

（起初，我认为这是因为按钮[2]已被删除。但是当我尝试replace(buttons[1],buttons[3])之前没有将按钮[3]添加到groupLayout时，没有出错。所以我仍然可以不知道发生了什么问题。）

然后，我提出了一个维护对该组的引用的想法，该组仅包含我想要更改的组件，以便稍后对其进行操作。这是我的代码：

if(count % 2 == 1) {
    groupLayout.replace(buttons[1], buttons[2]);
    button2HorizontalGroup.addComponent(buttons[1]);
    button2VerticalGroup.addComponent(buttons[1]);
}else {
    groupLayout.replace(buttons[2], buttons[1]);
    button2HorizontalGroup.addComponent(buttons[2]);
    button2VerticalGroup.addComponent(buttons[2]);
}

但这可能更像是一种破解而非解决方案。另外，如果要交换大量组件，可能会很麻烦。在GroupLayout中交换组件有没有更好的解决方案？（也欢迎其他布局的解决方案:)）

感谢。

更新

@ user1803551：这是我的代码（GroupLayoutTest是一个扩展JFrame的类）：

public GroupLayoutTest() {
    // Allow group layout to automatically creat the gap between components and containers.
    groupLayout.setAutoCreateGaps(true);
    groupLayout.setAutoCreateContainerGaps(true);
    setLayout(groupLayout);


    buttons = new JButton[4];
    buttons[0] = new JButton("small 1");
    buttons[1] = new JButton("medium 2");
    buttons[2] = new JButton("big 3");

    buttons[1].addActionListener(replaceHandler);
    buttons[2].addActionListener(replaceHandler);

    button1HorizontalGroup.addComponent(buttons[1]);
    button1VerticalGroup.addComponent(buttons[1]);
    button2HorizontalGroup.addComponent(buttons[2]);
    button2VerticalGroup.addComponent(buttons[2]);

    groupLayout.setHorizontalGroup(
            groupLayout.createParallelGroup()
            .addGroup(groupLayout.createSequentialGroup()
                    .addGap(39)
                    .addComponent(buttons[0])
                    // Make it like a Spring
                    .addPreferredGap(LayoutStyle.ComponentPlacement.RELATED, GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                    .addGap(10)
                    .addGroup(button1HorizontalGroup)
                    .addGap(52))
            .addGroup(groupLayout.createSequentialGroup()
                    .addPreferredGap(LayoutStyle.ComponentPlacement.RELATED, GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                    .addGap(0)
                    .addGroup(button2HorizontalGroup)
                    .addContainerGap(GroupLayout.DEFAULT_SIZE, 160))
    );
    groupLayout.setVerticalGroup(
            groupLayout.createSequentialGroup()
            .addContainerGap(50, 50)
            .addGroup(groupLayout.createParallelGroup()
                    .addComponent(buttons[0])
                    .addGroup(button1VerticalGroup) )
            .addGap(10)
            .addPreferredGap(LayoutStyle.ComponentPlacement.RELATED, GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
            .addGroup(button2VerticalGroup)
            .addContainerGap(168, 168));

    groupLayout.linkSize(SwingConstants.HORIZONTAL, buttons[1],buttons[2]);
    pack();
    setLocationRelativeTo(null);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}

private class ReplaceHandler implements ActionListener {

    private int count = 0;
    @Override
    public void actionPerformed(ActionEvent e) {
        count += 1;
        if(count % 2 == 1) {
            groupLayout.replace(buttons[1], buttons[2]);
            button2HorizontalGroup.addComponent(buttons[1]);
            button2VerticalGroup.addComponent(buttons[1]);
        }else {
            groupLayout.replace(buttons[2], buttons[1]);
            button2HorizontalGroup.addComponent(buttons[2]);
            button2VerticalGroup.addComponent(buttons[2]);
        }
        groupLayout.linkSize(SwingConstants.HORIZONTAL, buttons[1],buttons[2]);
    }

}

@camickr：正如您从上面的代码中看到的那样，我对第一次体验GroupLayout感到非常开心。我点击它时，我想要一个按钮（＆＃34;媒体＆＃34;和＃34;小＆＃34;）互相交换。毕竟，谢谢你的建议。：）

Answer 1

我正在玩我的第一次GroupLayout体验。

嗯，你应该先学习其他布局管理员

当我点击它时，我想让一个按钮（“中”和“小”）相互交换。

创建一个JPanel以包含两个按钮，并将面板添加到布局中。

使一个按钮可见，另一个按钮不可见。当您单击该按钮时，您可以切换两个按钮的可见性状态。

java swing GroupLayout - 如何交换组件的位置

1 个答案: