Java:MigLayout Center 中心不工作 |绝对定位的替代方案

Question

该元素不会垂直居中，我不知道为什么。我尝试过“中心中心”，但它不起作用。

Mig布局

private JPanel panel = new JPanel(new MigLayout("center center, filly"));

组件

panel.add(header, "span");
panel.add(input, "split 4");
panel.add(unit1);
panel.add(to);
panel.add(unit2, "wrap");
panel.add(convert, "span");
panel.add(output, "span");

我想将组件居中，但不使用绝对定位(因为我知道如何使用此方法居中)

Answer 1

TL;DR

真为你感到羞耻

• 中心中心不是中心，中心
• center, center, filly - filly 减轻垂直中心
• 要对齐各个组件，您需要对齐中心 - 例如，panel.add(new JLabel("Header"), "span,align center");

<小时/>

假设您询问如何水平对齐组件，则需要为每个组件指定这一点。然而，首先最好看看下面这行代码实际上做了什么。

private JPanel panel = new JPanel(new MigLayout("center center, filly"));

或者更具体地说，以下摘录的含义。

new MigLayout("center center, filly")

center center - 这会水平对齐 JPanel 上的打包组件。

假设您试图使组件垂直和水平居中，您实际上需要center, center。请注意两个 center 关键字之间的 ,。

filly - 引用白皮书，“为列和/或行声明容器中的所有可用空间”。

这很大程度上减轻了“center，center”的影响，而您真正需要的是center，filly。

<小时/>

现在，要跨多列水平对齐组件，您需要将关键字 align center 添加到要执行此操作的每个组件。例如

panel.add(new JLabel("Header"), "span, align center");

您的组件的一个示例是

String[] dummyList  = new String[] {
    "Val 1",
    "Val 2"
};
JPanel migPanel = new JPanel(new MigLayout("center, filly")); //Maybe you wanted center, center. I'm not sure
migPanel.add(new JLabel("Header"), "span, align center");
migPanel.add(new JTextField("Input"), "split 4");
migPanel.add(new JComboBox<String>(dummyList));
migPanel.add(new JLabel("To"), "span");
migPanel.add(new JComboBox<String>(dummyList), "wrap");
migPanel.add(new JButton("Convert"), "span, align center");
migPanel.add(new JTextField("Output"), "span, align center");

<小时/>

如MadProgrammer提到还有其他布局可用于实现与您所拥有的外观非常相似的外观； GridBagLayout是最简单的。

混合使用 GridBagConstraints 您可以实现非常相似的布局。

例如，

String[] dummyList  = new String[] {
    "Val 1",
    "Val 2"
};
JPanel gridBagPanel = new JPanel(new GridBagLayout());
GridBagConstraints gc = new GridBagConstraints();

gc.weighty = 1; //Delete this line if you are after an equivalent of `center, center` from the MigLayout
gc.gridwidth = 4;
gridBagPanel.add(new JLabel("Header"), gc);

gc.gridy = 1;
gc.gridwidth = 1;
gridBagPanel.add(new JTextField("Input"), gc);

gc.gridx = 1;
gridBagPanel.add(new JComboBox<String>(dummyList), gc);

gc.gridx = 2;
gridBagPanel.add(new JLabel("To"), gc);

gc.gridx = 3;
gridBagPanel.add(new JComboBox<String>(dummyList), gc);

gc.gridy = 2;
gc.gridx = 0;
gc.gridwidth = 4;
gridBagPanel.add(new JButton("Convert"), gc);

gc.gridy = 3;
gridBagPanel.add(new JTextField("Output"), gc);

<小时/>

可运行示例 - LayoutExample.java

import java.awt.EventQueue;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;

import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTabbedPane;
import javax.swing.JTextField;

import net.miginfocom.swing.MigLayout;

@SuppressWarnings("serial")
public class LayoutExample extends JFrame {
    private JTabbedPane tabs;
    private JPanel migPanel;
    private JPanel gridBagPanel;
    private JPanel migPanelCC;
    private JPanel gridBagPanelCC;
    private String[] dummyList  = new String[] {
        "Val 1",
        "Val 2"
    };

    private LayoutExample() {
        super("Layout Example");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        setUpTabs();
        add(tabs);

        setSize(800, 500);
        setVisible(true);
    }

    private void setUpTabs() {
        tabs = new JTabbedPane();

        setUpMig();
        tabs.add(migPanel, "Mig Panel");

        setUpMigCC();
        tabs.add(migPanelCC, "Mig Panel Center Center");

        setUpGridBag();
        tabs.add(gridBagPanel, "Grid Bag Panel");

        setUpGridBagCC();
        tabs.add(gridBagPanelCC, "Grid Bag Panel Center Center");
    }

    private void setUpMig() {
        migPanel = new JPanel(new MigLayout("center, filly"));
        addToMigPanel(migPanel);
    }

    private void setUpMigCC() {
        migPanelCC = new JPanel(new MigLayout("center, center"));
        addToMigPanel(migPanelCC);
    }

    private void addToMigPanel(JPanel mPanel) {
        mPanel.add(new JLabel("Header"), "span, align center");
        mPanel.add(new JTextField("Input"), "split 4");
        mPanel.add(new JComboBox<String>(dummyList));
        mPanel.add(new JLabel("To"), "span");
        mPanel.add(new JComboBox<String>(dummyList), "wrap");
        mPanel.add(new JButton("Convert"), "span, align center");
        mPanel.add(new JTextField("Output"), "span, align center");
    }

    private void setUpGridBag() {
        gridBagPanel = new JPanel(new GridBagLayout());
        GridBagConstraints gc = new GridBagConstraints();

        gc.weighty = 1;
        addToGridBagPanel(gridBagPanel, gc);
    }

    private void setUpGridBagCC() {
        gridBagPanelCC = new JPanel(new GridBagLayout());
        GridBagConstraints gc = new GridBagConstraints();

        addToGridBagPanel(gridBagPanelCC, gc);
    }

    private void addToGridBagPanel(JPanel gblPanel, GridBagConstraints gc) {
        gc.gridwidth = 4;
        gblPanel.add(new JLabel("Header"), gc);

        gc.gridy = 1;
        gc.gridwidth = 1;
        gblPanel.add(new JTextField("Input"), gc);

        gc.gridx = 1;
        gblPanel.add(new JComboBox<String>(dummyList), gc);

        gc.gridx = 2;
        gblPanel.add(new JLabel("To"), gc);

        gc.gridx = 3;
        gblPanel.add(new JComboBox<String>(dummyList), gc);

        gc.gridy = 2;
        gc.gridx = 0;
        gc.gridwidth = 4;
        gblPanel.add(new JButton("Convert"), gc);

        gc.gridy = 3;
        gblPanel.add(new JTextField("Output"), gc);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(() -> new LayoutExample());
    }
}

<小时/>

最后，使用绝对定位不是一个好主意。这是因为当容器改变大小时，容器内的组件不会自动调整。这对于大多数情况来说效果不佳，因为您可能会很快丢失重要的 UI 组件，或者可能有大量额外的空白。