Java GridBagLayout无法正常工作

Question

我尝试使用GridBagLayout，但我没有得到我期望的结果，而且我无法在此代码中找到错误：

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);
    }
}

这张照片说明了我的需求：

黄色是按钮名称，红色是行和列。

这才是真正发生的事情：

有人能解释我的代码中有什么问题吗？

Answer 1

问题在于没有任何东西说服第二个网格列（gridx = 1）具有任何宽度，因为没有组件需要在第二列中仅适合 。因此第二列的宽度为0，因此尽管Button1确实跨越前两列，但它看起来并不那样，因为第一列满足了它的所有宽度需求;虽然Button5和Button7跨在第二列和第三列，但第三列都满足了它们的所有宽度需求。

要修复它，你必须说服应该更宽的按钮（1,5,7）以占用更多空间。在这里，我通过设置c.ipadx = 35;为这些按钮添加了填充。 （我也删除了weightx = 1.0约束。由于我不太了解的原因，当它留在原因时它没有用。）：

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);
}

---

编辑：正如评论中所指出的，上述方法并不合适，因为它会阻止布局动态调整大小。要扩展布局以填充其容器的大小，需要weightx和weighty约束，但第二列不会获得任何宽度。

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

    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);

当调整窗口大小时，这很好地应对，因为尽管组件具有固定的初始大小，但GridBagLayout会按比例缩放它与其他组件。但它仍然不完美。也许有一个更好的解决方案，但我无法找到它。

Answer 2

我设法使用JGoodies FormLayout设计了所需的布局而没有任何黑客并支持动态调整大小：

import java.awt.Component;

import javax.swing.JButton;
import javax.swing.JPanel;

import com.jgoodies.forms.factories.FormFactory;
import com.jgoodies.forms.layout.ColumnSpec;
import com.jgoodies.forms.layout.FormLayout;
import com.jgoodies.forms.layout.RowSpec;

public class FormLayoutPanel extends JPanel
    {
    public FormLayoutPanel()
        {
        setAlignmentY( Component.BOTTOM_ALIGNMENT );
        setAlignmentX( Component.RIGHT_ALIGNMENT );
        setLayout( new FormLayout( new ColumnSpec[] {
            ColumnSpec.decode( "41px:grow" ),
            FormFactory.LABEL_COMPONENT_GAP_COLSPEC,
            ColumnSpec.decode( "25px:grow" ),
            FormFactory.LABEL_COMPONENT_GAP_COLSPEC,
            ColumnSpec.decode( "41px:grow" ),
            FormFactory.LABEL_COMPONENT_GAP_COLSPEC,
            ColumnSpec.decode( "41px:grow" ),
            FormFactory.LABEL_COMPONENT_GAP_COLSPEC,
            ColumnSpec.decode( "41px:grow" ), },
            new RowSpec[] {
                RowSpec.decode( "25px:grow" ),
                FormFactory.LINE_GAP_ROWSPEC,
                RowSpec.decode( "25px:grow" ),
                FormFactory.LINE_GAP_ROWSPEC,
                RowSpec.decode( "25px:grow" ), } ) );

        JButton button1 = new JButton( "1" );
        add( button1, "1, 1, 3, 1, fill, fill" );
        JButton button2 = new JButton( "2" );
        add( button2, "5, 1, fill, fill" );
        JButton button3 = new JButton( "3" );
        add( button3, "7, 1, 3, 3, fill, fill" );
        JButton button4 = new JButton( "4" );
        add( button4, "1, 3, fill, fill" );
        JButton button5 = new JButton( "5" );
        add( button5, "3, 3, 3, 1, fill, fill" );
        JButton button6 = new JButton( "6" );
        add( button6, "1, 5, fill, fill" );
        JButton button7 = new JButton( "7" );
        add( button7, "3, 5, 3, 1, fill, fill" );
        JButton button8 = new JButton( "8" );
        add( button8, "7, 5, fill, fill" );
        JButton button9 = new JButton( "9" );
        add( button9, "9, 5, fill, fill" );
        }
    }