Java GridBagLayout 不工作

Question

我正在尝试使用 GridBagLayout，但我没有得到我所期望的，而且我找不到这段代码中的错误:

public class GridBagEx1 extends JPanel {

    private static final long serialVersionUID = 1L;

    protected void makebutton(String name, GridBagLayout gridbag, GridBagConstraints c) {
        JButton button = new JButton(name);
        gridbag.setConstraints(button, c);
        add(button);
    }

    public void init() {
        GridBagLayout gridbag = new GridBagLayout();
        GridBagConstraints c = new GridBagConstraints();
        setLayout(gridbag);

        c.fill = BOTH;

        c.weightx = 1.0;
        c.weighty = 1.0;

        c.anchor = CENTER;

        c.insets.top = 5;
        c.insets.bottom = 5;
        c.insets.left = 5;
        c.insets.right = 5;

        c.gridx = 0;
        c.gridy = 0;
        c.gridheight = 1;
        c.gridwidth = 2;
        makebutton("Button1", gridbag, c);      

        c.gridx = 2;
        c.gridy = 0;
        c.gridheight = 1;
        c.gridwidth = 1;
        makebutton("Button2", gridbag, c);

        c.gridx = 3;
        c.gridy = 0;
        c.gridheight = 2;
        c.gridwidth = 2;
        makebutton("Button3", gridbag, c);

        c.gridx = 0;
        c.gridy = 1;
        c.gridheight = 1;
        c.gridwidth = 1;
        makebutton("Button4", gridbag, c);

        c.gridx = 1;
        c.gridy = 1;
        c.gridheight = 1;
        c.gridwidth = 2;
        makebutton("Button5", gridbag, c);

        c.gridx = 0;
        c.gridy = 2;
        c.gridheight = 1;
        c.gridwidth = 1;
        makebutton("Button6", gridbag, c);

        c.gridx = 1;
        c.gridy = 2;
        c.gridheight = 1;
        c.gridwidth = 2;
        makebutton("Button7", gridbag, c);

        c.gridx = 3;
        c.gridy = 2;
        c.gridheight = 1;
        c.gridwidth = 1;
        makebutton("Button8", gridbag, c);

        c.gridx = 4;
        c.gridy = 2;
        c.gridheight = 1;
        c.gridwidth = 1;
        makebutton("Button9", gridbag, c);
    }

    public static void main(String args[]) {
        JFrame frame = new JFrame();
        GridBagEx1 ex1 = new GridBagEx1();

        ex1.init();

        frame.add(ex1);
        frame.pack();
        frame.setVisible(true);
    }
}

这张图说明了我需要什么:

黄色是按钮名称，红色是行和列。

这是真正发生的事情:

谁能解释我的代码有什么问题？

Answer 1

问题是没有什么可以说服第二个网格列 (gridx=1) 具有任何宽度，因为第二列中没有仅需要适合的组件。因此，第二列的宽度为 0，因此尽管 Button1 确实跨越了前两列，但它看起来并不是那样，因为第一列满足了它的所有宽度需求；尽管 Button5 和 Button7 横跨第二和第三列，但它们的所有宽度需求都由第三列满足。

要修复它，您必须说服应该更宽的按钮(1、5、7)占用更多空间。在这里，我通过设置 c.ipadx = 35; 为这些按钮添加了填充。 (我还删除了 weightx = 1.0 约束。由于我不太明白的原因，它在保留时不起作用。):

来源:

public void init() {
    GridBagLayout gridbag = new GridBagLayout();
    GridBagConstraints c = new GridBagConstraints();
    setLayout(gridbag);

    c.fill = c.BOTH;

    //c.weightx = 1.0;
    //c.weighty = 1.0;

    c.anchor = c.CENTER;

    c.insets.top = 5;
    c.insets.bottom = 5;
    c.insets.left = 5;
    c.insets.right = 5;

    c.gridx = 0;
    c.gridy = 0;
    c.gridheight = 1;
    c.gridwidth = 2;
    c.ipadx = 35;
    makebutton("Button1", gridbag, c);

    c.gridx = 2;
    c.gridy = 0;
    c.gridheight = 1;
    c.gridwidth = 1;
    c.ipadx = 0;
    makebutton("Button2", gridbag, c);

    c.gridx = 3;
    c.gridy = 0;
    c.gridheight = 2;
    c.gridwidth = 2;
    c.ipadx = 0;
    makebutton("Button3", gridbag, c);

    c.gridx = 0;
    c.gridy = 1;
    c.gridheight = 1;
    c.gridwidth = 1;
    c.ipadx = 0;
    makebutton("Button4", gridbag, c);

    c.gridx = 1;
    c.gridy = 1;
    c.gridheight = 1;
    c.gridwidth = 2;
    c.ipadx = 35;
    makebutton("Button5", gridbag, c);

    c.gridx = 0;
    c.gridy = 2;
    c.gridheight = 1;
    c.gridwidth = 1;
    c.ipadx = 0;
    makebutton("Button6", gridbag, c);

    c.gridx = 1;
    c.gridy = 2;
    c.gridheight = 1;
    c.gridwidth = 2;
    c.ipadx = 35;
    makebutton("Button7", gridbag, c);

    c.gridx = 3;
    c.gridy = 2;
    c.gridheight = 1;
    c.gridwidth = 1;
    c.ipadx = 0;
    makebutton("Button8", gridbag, c);

    c.gridx = 4;
    c.gridy = 2;
    c.gridheight = 1;
    c.gridwidth = 1;
    c.ipadx = 0;
    makebutton("Button9", gridbag, c);
}

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编辑: 正如评论中指出的那样，上述方法不合适，因为它阻止了动态调整布局大小。要使布局扩展以填充其容器的大小，需要 weightx 和 weighty 约束，但第二列没有任何宽度。

这是对替代解决方案的尝试。这是一个肮脏的 hack，它在第二列的底部插入一个不可见的组件以强制该列具有宽度:

    c.gridx = 1;
    c.gridy = 3;
    c.gridheight = 1;
    c.gridwidth = 1;
    c.insets.set(0, 0, 0, 0);
    c.weighty = 0;
    add(Box.createRigidArea(new Dimension(50, 0)), c);

这在调整窗口大小时处理得相当好，因为虽然组件被赋予了固定的初始大小，但 GridBagLayout 会与其他组件成比例地放大它。不过，它仍然不完美。也许有更好的解决方案，但我找不到。