GridBagLayout錨點精確度-有解無憂

我可以消除容器周圍的隨機紅線還是這是 JDK 中的錯誤？3x3 網格使用未按預期作業的約束
添加了 9 個尺寸更小的組件。enchor

GridBagLayout 錨點精確度

重現問題的完整源代碼

import static java.awt.Color.red;
import static java.awt.Color.white;
import static java.awt.GridBagConstraints.CENTER;
import static java.awt.GridBagConstraints.FIRST_LINE_END;
import static java.awt.GridBagConstraints.FIRST_LINE_START;
import static java.awt.GridBagConstraints.LAST_LINE_END;
import static java.awt.GridBagConstraints.LAST_LINE_START;
import static java.awt.GridBagConstraints.LINE_END;
import static java.awt.GridBagConstraints.LINE_START;
import static java.awt.GridBagConstraints.PAGE_END;
import static java.awt.GridBagConstraints.PAGE_START;
import static javax.swing.BorderFactory.createLineBorder;
import static javax.swing.JFrame.EXIT_ON_CLOSE;

import java.awt.Dimension;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;

import javax.swing.JFrame;
import javax.swing.JPanel;

public class GridBagLayoutTest {
    
    public static void main(String[] args) {
        JPanel pane = new JPanel(new GridBagLayout());
        pane.setBackground(red);
        pane.setPreferredSize(new Dimension(500, 500));
        // pane.setBorder(createEmptyBorder());
        // pane.setBorder(createLineBorder(white, 1));
        pane.setBorder(createLineBorder(white, 2));
        // pane.setBorder(createLineBorder(white, 3));
        
        GridBagConstraints c = new GridBagConstraints();
        c.weightx = 1;
        c.weighty = 1;
        c.gridx = 0;
        c.gridy = 0;
        c.anchor = FIRST_LINE_START;
        pane.add(rectangle(), c);
        c.gridx = 1;
        c.gridy = 0;
        c.anchor = PAGE_START;
        pane.add(rectangle(), c);
        c.gridx = 2;
        c.gridy = 0;
        c.anchor = FIRST_LINE_END;
        pane.add(rectangle(), c);
        c.gridx = 0;
        c.gridy = 1;
        c.anchor = LINE_START;
        pane.add(rectangle(), c);
        c.gridx = 1;
        c.gridy = 1;
        c.anchor = CENTER;
        pane.add(rectangle(), c);
        c.gridx = 2;
        c.gridy = 1;
        c.anchor = LINE_END;
        pane.add(rectangle(), c);
        c.gridx = 0;
        c.gridy = 2;
        c.anchor = LAST_LINE_START;
        pane.add(rectangle(), c);
        c.gridx = 1;
        c.gridy = 2;
        c.anchor = PAGE_END;
        pane.add(rectangle(), c);
        c.gridx = 2;
        c.gridy = 2;
        c.anchor = LAST_LINE_END;
        pane.add(rectangle(), c);
        
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(EXIT_ON_CLOSE);
        frame.setPreferredSize(new Dimension(600, 600));
        frame.getContentPane().setLayout(new GridBagLayout());
        frame.getContentPane().setBackground(white);
        frame.getContentPane().add(pane);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }
    
    public static JPanel rectangle() {
        JPanel rect = new JPanel();
        rect.setBackground(white);
        rect.setPreferredSize(new Dimension(100, 100));
        return rect;
    }
}

uj5u.com熱心網友回復：

這是JDK中的錯誤嗎？

好吧，您正在嘗試以一種并非旨在使用的方式使用 GridBagLayout。您正在嘗試使用每行/列中的 3 個組件創建一個 5 個組件網格。

每個單元格的大小為 500 / 3 = 166.666。

當您嘗試設定每個組件的位置時，您會遇到一些舍入問題。有時它向上取整，有時向下取整。

要檢查這一點，您可以去掉 setBorder(...) 陳述句，然后在 setVisible() 陳述句之后添加：

for (Component panel: pane.getComponents())
    System.out.println(panel.getBounds());

你會看到如下輸出：

java.awt.Rectangle[x=1,y=1,width=100,height=100]
java.awt.Rectangle[x=200,y=1,width=100,height=100]
java.awt.Rectangle[x=399,y=1,width=100,height=100]
java.awt.Rectangle[x=1,y=200,width=100,height=100]
java.awt.Rectangle[x=200,y=200,width=100,height=100]
java.awt.Rectangle[x=399,y=200,width=100,height=100]
java.awt.Rectangle[x=1,y=399,width=100,height=100]
java.awt.Rectangle[x=200,y=399,width=100,height=100]
java.awt.Rectangle[x=399,y=399,width=100,height=100]

要解決此問題，您可以創建一個 5x5 網格并將每個組件添加到網格中的相應單元格：

import static java.awt.Color.red;
import static java.awt.Color.white;
import static java.awt.GridBagConstraints.CENTER;
import static java.awt.GridBagConstraints.FIRST_LINE_END;
import static java.awt.GridBagConstraints.FIRST_LINE_START;
import static java.awt.GridBagConstraints.LAST_LINE_END;
import static java.awt.GridBagConstraints.LAST_LINE_START;
import static java.awt.GridBagConstraints.LINE_END;
import static java.awt.GridBagConstraints.LINE_START;
import static java.awt.GridBagConstraints.PAGE_END;
import static java.awt.GridBagConstraints.PAGE_START;
import static javax.swing.BorderFactory.createLineBorder;
import static javax.swing.JFrame.EXIT_ON_CLOSE;

import java.awt.Dimension;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;

import javax.swing.JFrame;
import javax.swing.JPanel;

import java.util.Arrays;

public class GridBagLayoutTest2 {

    public static void main(String[] args) {
        GridBagLayout gbl = new GridBagLayout();
        JPanel pane = new JPanel(gbl);
        pane.setBackground(red);
//        pane.setPreferredSize(new Dimension(500, 500));
        // pane.setBorder(createEmptyBorder());
        // pane.setBorder(createLineBorder(white, 1));
        pane.setBorder(createLineBorder(white, 2));
        // pane.setBorder(createLineBorder(white, 3));


        //  The minimimum width of a column is 100 pixels
        //  and the minimum height of a row is 100 pixels.

        int[] columns = new int[5];
        Arrays.fill(columns, 100);
        gbl.columnWidths = columns;

        int[] rows = new int[5];
        Arrays.fill(rows, 100);
        gbl.rowHeights = rows;

        GridBagConstraints c = new GridBagConstraints();
        c.weightx = 1;
        c.weighty = 1;
        c.gridx = 0;
        c.gridy = 0;
//        c.anchor = FIRST_LINE_START;
        pane.add(rectangle(), c);
        c.gridx = 2;
        c.gridy = 0;
//        c.anchor = PAGE_START;
        pane.add(rectangle(), c);
        c.gridx = 4;
        c.gridy = 0;
//        c.anchor = FIRST_LINE_END;
        pane.add(rectangle(), c);
        c.gridx = 0;
        c.gridy = 2;
//        c.anchor = LINE_START;
        pane.add(rectangle(), c);
        c.gridx = 2;
        c.gridy = 2;
//        c.anchor = CENTER;
        pane.add(rectangle(), c);
        c.gridx = 4;
        c.gridy = 2;
//        c.anchor = LINE_END;
        pane.add(rectangle(), c);
        c.gridx = 0;
        c.gridy = 4;
//        c.anchor = LAST_LINE_START;
        pane.add(rectangle(), c);
        c.gridx = 2;
        c.gridy = 4;
//        c.anchor = PAGE_END;
        pane.add(rectangle(), c);
        c.gridx = 4;
        c.gridy = 4;
//        c.anchor = LAST_LINE_END;
        pane.add(rectangle(), c);

        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(EXIT_ON_CLOSE);
        frame.setPreferredSize(new Dimension(600, 600));
        frame.getContentPane().setLayout(new GridBagLayout());
        frame.getContentPane().setBackground(white);
        frame.getContentPane().add(pane);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    public static JPanel rectangle() {
        JPanel rect = new JPanel();
        rect.setBackground(white);
        rect.setPreferredSize(new Dimension(100, 100));
        return rect;
    }
}

之所以可行，請參閱：使用 JLayeredPane 創建棋盤游戲布局

編輯：

GridLayout 有同樣的問題。如果父面板的寬度/高度不能被 GridLayout 中的組件數整除，那么組件將不會填滿整個空間，并且父面板的背景會透出來。

作為您提供的代碼的破解，您可以使用：

Border line = new LineBorder(Color.WHITE);
Border empty = new EmptyBorder(-1, -1, -1, -1);
Border compound = new CompoundBorder(line, empty);
pane.setBorder(compound);

這將允許繪制 LineBorder 而不會影響面板中組件的位置，因為邊框插入將保持 (0, 0, 0, 0)。

您還應該能夠使用 MatteBorder 并且只繪制底線并相應地調整 EmptyBorder。

轉載請註明出處，本文鏈接：https://www.uj5u.com/caozuo/416542.html

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