关于 Java Swing：Java Swing – 将矩形拖到 JPanel 上的有效方法？

Java Swing - Valid approach for dragging rectangles onto a JPanel?

我有一些绘制矩形的代码。它用于在 JPanel 上绘制矩形，以标记小部件的边界。这里首先是代码，然后我将解释我的问题cq。问题。

首先，我有一个扩展 JPanel.

的类 (WidgetDrawingPanel)

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public WidgetDrawingPanel(int width, int height) {
/*To make things visible at least*/
widgets.add(new Widget(10,10,100,100, WidgetType.TextField));
widgets.add(new Widget(50,50,100,200, WidgetType.TextField));
this.width = width;
this.height = height;
this.setBackground(Color.BLUE);
addListener(); //adds both MouseMotionListener and MouseListener
}

下面你会看到我引用了很多 ch。这是一个 CoordinateHolder，它保存了我的鼠标移动的起始坐标和当前坐标。

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private void addListener() {
this.addMouseMotionListener(new MouseMotionListener() {
@Override
public void mouseDragged(MouseEvent arg0) {
ch.currentX = arg0.getX();
ch.currentY = arg0.getY();
System.out.println("dragging" + ch.currentX +","+ch.currentY);
WidgetDrawingPanel.this.repaint();
}
});
this.addMouseListener(new MouseListener() {
@Override
public void mouseReleased(MouseEvent event) {
ch.endX = event.getX();
ch.endY = event.getY();
try {
checkCoords();
} catch (OutsidePanelException e) {
e.printStackTrace();
JOptionPane.showMessageDialog(null,"drawn Outside Panel");
}
}

@Override
public void mousePressed(MouseEvent event) {
ch = new CoordinateHolder(event.getX(), event.getY());
}
});
}

，最后是 paintComponent(Grapics) 方法。有循环通过Widgets，实际上只是已经绘制了Rects(x，y，w，h 属性)，但是其中的信息多一点，这在应用程序的绘图部分没有用。每次释放鼠标时，CoordinateHolder 都会转换为 Widget，并添加到 Widgets.

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@Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
System.out.println("Paint");
g.setColor(Color.BLUE);
g.fillRect(0, 0, width, height); //making the whole panel blue
g.setColor(Color.RED);
Graphics2D g2 = (Graphics2D)g;
g2.setStroke(new BasicStroke(3));
for (Widget w : widgets) {
g.drawRect(w.getX(), w.getY(), w.getW(), w.getH());
}
if (ch != null)
g.drawRect(ch.startX, ch.startY, ch.currentX - ch.startX, ch.currentY - ch.startY);
}

这段代码可以工作，但我怀疑这是非常低效和低效的，因为上面的代码会在鼠标拖动时不断刷新 JPanel，也就是说，每 10 毫秒一次？我想它很快就会变慢，尤其是当用户创建大量矩形时(它们也不断重绘，如 painComponent(Graphics) 所示)。

问题cq。问题

有没有更好、更省资源的方法，用户可以流畅地拖动矩形？

我在 Java 的 JFrame 上阅读了这个 Drag rectangle 的答案，但该答案的作者似乎和我一样。但是再一次，这太低效了，对吧？或者计算机是否应该能够轻松地不断重绘组件，这实际上是一种有效的方法吗？

要显示大量不变的背景形状，请将它们绘制到 BufferedImage 中，然后在 paintComponent(...) 方法中显示该 BufferedImage。因此，在绘制形状时，将其绘制在 paintComponent(...) 中，但一旦绘制完成，可能在 mouseRelease 上，然后在后台 BufferedImage.

中绘制它

请注意，最会减慢您当前绘图代码的可能是您的调试 SOP 语句，但我假设这些将从完成的代码中删除。

例如：

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import java.awt.*;
import java.awt.event.*;
import java.awt.image.BufferedImage;

import javax.swing.*;

@SuppressWarnings("serial")
public class DrawingPanel extends JPanel {
private static final int PREF_W = 600;
private static final int PREF_H = 400;
private static final Color DRAWING_COLOR = new Color(255, 100, 200);
private static final Color FINAL_DRAWING_COLOR = Color.red;

private BufferedImage backgroundImg;
private Point startPt = null;
private Point endPt = null;
private Point currentPt = null;

public DrawingPanel() {
backgroundImg = new BufferedImage(PREF_W, PREF_H,
BufferedImage.TYPE_INT_ARGB);
Graphics g = backgroundImg.getGraphics();
g.setColor(Color.blue);
g.fillRect(0, 0, PREF_W, PREF_H);
g.dispose();

MyMouseAdapter myMouseAdapter = new MyMouseAdapter();
addMouseMotionListener(myMouseAdapter);
addMouseListener(myMouseAdapter);
}

@Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
if (backgroundImg != null) {
g.drawImage(backgroundImg, 0, 0, this);
}

if (startPt != null && currentPt != null) {
g.setColor(DRAWING_COLOR);
int x = Math.min(startPt.x, currentPt.x);
int y = Math.min(startPt.y, currentPt.y);
int width = Math.abs(startPt.x - currentPt.x);
int height = Math.abs(startPt.y - currentPt.y);
g.drawRect(x, y, width, height);
}
}

@Override
public Dimension getPreferredSize() {
return new Dimension(PREF_W, PREF_H);
}

public void drawToBackground() {
Graphics g = backgroundImg.getGraphics();
g.setColor(FINAL_DRAWING_COLOR);
int x = Math.min(startPt.x, endPt.x);
int y = Math.min(startPt.y, endPt.y);
int width = Math.abs(startPt.x - endPt.x);
int height = Math.abs(startPt.y - endPt.y);
g.drawRect(x, y, width, height);
g.dispose();

startPt = null;
repaint();
}

private class MyMouseAdapter extends MouseAdapter {
@Override
public void mouseDragged(MouseEvent mEvt) {
currentPt = mEvt.getPoint();
DrawingPanel.this.repaint();
}

@Override
public void mouseReleased(MouseEvent mEvt) {
endPt = mEvt.getPoint();
currentPt = null;
drawToBackground();
}

@Override
public void mousePressed(MouseEvent mEvt) {
startPt = mEvt.getPoint();
}
}

private static void createAndShowGui() {
DrawingPanel mainPanel = new DrawingPanel();

JFrame frame = new JFrame("Drawing Panel");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(mainPanel);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}

public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}