[英]Java Swing GUI BorderLayout: Location of components
I'm new to Java and I'm playing around with a simple GUI example:我是 Java 的新手,我正在玩一个简单的 GUI 示例:
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.geom.Rectangle2D;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.WindowConstants;
public class DrawTest {
class DrawingPanel extends JPanel {
private Rectangle2D shape;
public DrawingPanel(Rectangle2D shape) {
this.shape = shape;
}
public void paintComponent(Graphics g) {
Graphics2D g2D = (Graphics2D) g;
super.paintComponent(g2D);
g2D.setColor(new Color(31, 21, 1));
g2D.fill(shape);
}
}
public void draw() {
JFrame frame = new JFrame();
Rectangle2D shape = new Rectangle2D.Float();
final DrawingPanel drawing = new DrawingPanel(shape);
shape.setRect(0, 0, 400, 400);
frame.getContentPane().add(BorderLayout.NORTH, new JButton("TestN"));
frame.getContentPane().add(BorderLayout.SOUTH, new JButton("TestS"));
frame.getContentPane().add(BorderLayout.EAST, new JButton("TestE"));
frame.getContentPane().add(BorderLayout.WEST, new JButton("TestW"));
frame.getContentPane().add(BorderLayout.CENTER, drawing);
frame.pack();
frame.setSize(500,500);
frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
frame.setVisible(true);
}
}
public class DrawMain {
public static void main(String[] args) {
DrawTest test = new DrawTest();
test.draw();
}
}
As expected, this code produces a frame with the rectangle at the centre and buttons around it.正如预期的那样,这段代码生成了一个框架,矩形在中心,按钮在它周围。 However, if I change the code like this:
但是,如果我像这样更改代码:
frame.getContentPane().add(BorderLayout.NORTH, drawing);
frame.getContentPane().add(BorderLayout.SOUTH, new JButton("TestS"));
frame.getContentPane().add(BorderLayout.EAST, new JButton("TestE"));
frame.getContentPane().add(BorderLayout.WEST, new JButton("TestW"));
frame.getContentPane().add(BorderLayout.CENTER, new JButton("TestC"));
the "TestC" button gets a huge area in the middle while the rectangle doesn't get enough space. “TestC”按钮在中间有一个很大的区域,而矩形没有足够的空间。 This is even true if I remove the other buttons (TestS, TestE, TestW): I get a huge TestC button and a tiny part of the rectangle (even not the scaled rectangle) at the top.
如果我移除其他按钮(TestS、TestE、TestW),情况也是如此:我在顶部得到一个巨大的 TestC 按钮和矩形的一小部分(甚至不是缩放的矩形)。
Why doesn't the rectangle get enough space when it's drawn at the top (NORTH) but does get it when it's drawn at the CENTER?为什么矩形在顶部(北)绘制时没有足够的空间,但在中心绘制时却得到了?
The DrawingPanel
should @Override getPreferredSize()
to return an appropriate size. DrawingPanel
应该@Override getPreferredSize()
以返回适当的大小。
The layout manager will then take that preferred size as a hint .然后,布局管理器将采用该首选尺寸作为提示。 Some layout managers will expand a component's height or width according to the logic of the layout and constraint.
一些布局管理器会根据布局和约束的逻辑扩展组件的高度或宽度。 EG a
BorderLayout
will stretch components in the PAGE_START
/ PAGE_END
to the width of the content pane, and LINE_START
/ LINE_END
to the height of the tallest of either of those, or the CENTER
.例如,
BorderLayout
会将PAGE_START
/ PAGE_END
中的组件拉伸到内容窗格的宽度,并将LINE_START
/ LINE_END
到其中最高者或CENTER
的高度。 A GridBagLayout
OTOH will completely hide / remove a component for which there is not enough space to display it at the preferred size, and that's where 'pack' comes in. GridBagLayout
OTOH 将完全隐藏/删除没有足够空间以首选大小显示它的组件,这就是“pack”的用武之地。
So change frame.setSize(500,500);
所以改变
frame.setSize(500,500);
(which is no better than a guess) to frame.pack();
(这并不比猜测更好)到
frame.pack();
, which will make frame the minimum size it needs to be, in order to display the components it contains. ,这将使框架成为它需要的最小尺寸,以便显示它包含的组件。
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