java - GridLayout 行为异常

Question

我正在尝试手动编写 Swing(是的，我知道这很疯狂)，出于某种原因，我在这里创建了这个部分面板:

private JPanel createColorSliderPanel() {
    JPanel colorSliderPanel = new JPanel(new GridLayout(3, 1, 0, 5));

    JPanel redSliderPanel = new JPanel(new BorderLayout());
    JPanel greenSliderPanel = new JPanel(new BorderLayout());
    JPanel blueSliderPanel = new JPanel(new BorderLayout());

    GridLayout grid = (GridLayout) colorSliderPanel.getLayout();


    redSlider = new JSlider();
    greenSlider = new JSlider();
    blueSlider = new JSlider();

    redField = new JTextField();
    greenField = new JTextField();
    blueField = new JTextField();

    redField.setEditable(false);
    greenField.setEditable(false);
    blueField.setEditable(false);

    JLabel redLabel = new JLabel("Red");
    JLabel greenLabel = new JLabel("Green");
    JLabel blueLabel = new JLabel("Blue");

    redLabel.setPreferredSize(new Dimension(64, 16));
    redField.setPreferredSize(new Dimension(32, 16));
    redSliderPanel.add(redLabel, BorderLayout.WEST);
    redSliderPanel.add(redSlider, BorderLayout.CENTER);
    redSliderPanel.add(redField, BorderLayout.EAST);

    greenLabel.setPreferredSize(new Dimension(64, 16));
    greenField.setPreferredSize(new Dimension(32, 16));
    greenSliderPanel.add(redLabel, BorderLayout.WEST);
    greenSliderPanel.add(redSlider, BorderLayout.CENTER);
    greenSliderPanel.add(redField, BorderLayout.EAST);

    blueLabel.setPreferredSize(new Dimension(64, 16));
    blueField.setPreferredSize(new Dimension(32, 16));
    blueSliderPanel.add(redLabel, BorderLayout.WEST);
    blueSliderPanel.add(redSlider, BorderLayout.CENTER);
    blueSliderPanel.add(redField, BorderLayout.EAST);


    colorSliderPanel.add(redSliderPanel);
    colorSliderPanel.add(greenSliderPanel);
    colorSliderPanel.add(blueSliderPanel);

    return colorSliderPanel;
}

未按预期工作:

它应该将我制作的三个面板堆叠在一起。我将它添加到我的 JFrame 中，如下所示:

JPanel sliderPanel = createColorSliderPanel();
...
contentPane.add(sliderPanel, BorderLayout.SOUTH);

知道为什么它无法正常显示吗？

Answer 1

问题是，您只将 redSlider/Field/Label 添加到所有其他面板

redSliderPanel.add(redLabel, BorderLayout.WEST);
redSliderPanel.add(redSlider, BorderLayout.CENTER);
redSliderPanel.add(redField, BorderLayout.EAST);

greenSliderPanel.add(redLabel, BorderLayout.WEST);
greenSliderPanel.add(redSlider, BorderLayout.CENTER);
greenSliderPanel.add(redField, BorderLayout.EAST);

blueSliderPanel.add(redLabel, BorderLayout.WEST);
blueSliderPanel.add(redSlider, BorderLayout.CENTER);
blueSliderPanel.add(redField, BorderLayout.EAST);

执行此操作将从之前添加的容器中删除 redSlider、redField 和 redLabel，这意味着它只会出现在blueSliderPanel。

不要使用setPreferred/Minimum/MaximumSize，您无法控制组件衡量其所需大小的指标。向组件提供大小调整提示，以便它们能够做出更好的决策。

redField = new JTextField(4);
greenField = new JTextField(4);
blueField = new JTextField(4);

Then don't add the fields to sub panels first

然后，不要先将字段添加到单独的面板中，但是，您可能会发现像 GridBagLayout 这样的东西是更好的选择...

JPanel colorSliderPanel = new JPanel(new GridBagLayout());

redSlider = new JSlider();
greenSlider = new JSlider();
blueSlider = new JSlider();

redField = new JTextField(4);
greenField = new JTextField(4);
blueField = new JTextField(4);

redField.setEditable(false);
greenField.setEditable(false);
blueField.setEditable(false);

JLabel redLabel = new JLabel("Red");
JLabel greenLabel = new JLabel("Green");
JLabel blueLabel = new JLabel("Blue");

addTo(colorSliderPanel, redLabel, redSlider, redField, 0);
addTo(colorSliderPanel, greenLabel, greenSlider, greenField, 1);
addTo(colorSliderPanel, blueLabel, blueSlider, blueField, 2);

还有 addTo 方法...

protected void addTo(JPanel parent, JLabel label, JSlider slider, JTextField field, int gridY) {

    GridBagConstraints gbc = new GridBagConstraints();
    gbc.anchor = GridBagConstraints.WEST;
    gbc.gridx = 0;
    gbc.gridy = gridY;
    parent.add(label, gbc);

    gbc.fill = GridBagConstraints.HORIZONTAL;
    gbc.gridx++;
    gbc.weightx = 1;
    parent.add(slider, gbc);

    gbc.gridx++;
    gbc.weightx = 0;
    parent.add(field, gbc);

}