GridBagLayout问题

Question

我正在尝试使用GridBagLayout。我需要一个垂直和水平居中的JLabel -这很简单，我甚至不需要创建任何GridBagConstraints。我还想在右下角放置一个JButton，当我尝试这样做时，我的居中面板正在向左移动，或者按钮正在向上移动。

EXPECTING     GETTING THIS  OR THIS
+-----------+ +-----------+ +-----------+
|           | |           | |           |
|           | |           | |           |
|           | |           | |           |
|   +---+   | | +---+     | | +---+     |
|   |   |   | | |   |     | | |   |     |
|   +---+   | | +---+     | | +---++---+|
|           | |           | |      |   ||
|           | |           | |      +---+|
|       +---+ |       +---+ |           |
|       |   | |       |   | |           |
+-------+---+ +-------+---+ +-----------+

bigPanel = new JPanel();
bigPanel.setPreferredSize(new Dimension(320, 640));
bigPanel.setLayout(new GridBagLayout());

label = new JLabel();
label.setPreferredSize(new Dimension(100,95));

button = new JButton();
button.setPreferredSize(new Dimension(100,25));

GridBagConstraints c = new GridBagConstraints();

c.anchor = GridBagConstraints.CENTER;
bigPanel.add(label, c);

c.anchor = GridBagConstraints.LAST_LINE_END;
bigPanel.add(button, c);

我也在尝试使用这里描述的其他约束，http://docs.oracle.com/javase/tutorial/uiswing/layout/gridbag.html，但每次都会出现错误。

Answer 1

如果组件不填充单元格，则anchor设置组件在单元格中的位置。

您尚未定义布局的网格。默认行为是从左到右添加组件。

下面是一个使用GridBagLayout实现所需功能的示例。标签和按钮放在同一个单元格中，该单元格填充了面板。

public class Test extends JPanel {
    public Test() {
        super();
        GridBagLayout gridBagLayout = new GridBagLayout();
        gridBagLayout.columnWeights = new double[] { 1.0 }; // expands the  1rst cell of the layout on the vertical axis
        gridBagLayout.rowWeights = new double[] { 1.0 }; // expands the 1rst cell of the layout on the horizontal axis
        setLayout(gridBagLayout);

        JLabel label = new JLabel("test");          
        label.setOpaque(true);
        label.setBackground(Color.RED);
        label.setPreferredSize(new Dimension(100, 95));
        GridBagConstraints gbc_label = new GridBagConstraints();
        gbc_label.gridx = 0; // set label cell (0,0)
        gbc_label.gridy = 0;
        gbc_label.insets = new Insets(0, 0, 5, 5);

        add(label, gbc_label);

        JButton button = new JButton("button");
        GridBagConstraints gbc_button = new GridBagConstraints();
        gbc_button.gridx = 0; // set buttoncell (0,0)
        gbc_button.gridy = 0;
        gbc_button.anchor = GridBagConstraints.SOUTHEAST;

        add(button, gbc_button);
        button.setPreferredSize(new Dimension(100, 25));
    }
}