我有一些代码来绘制矩形.它用于在JPanel上绘制矩形,以标记小部件的边界.这里代码首先,之后我将解释我的问题cq.题.
首先,我有一个扩展JPanel的类(WidgetDrawingPanel).
public WidgetDrawingPanel(int width,int height) {
/*To make things visible at least*/
widgets.add(new Widget(10,10,100,WidgetType.TextField));
widgets.add(new Widget(50,50,200,WidgetType.TextField));
this.width = width;
this.height = height;
this.setBackground(Color.BLUE);
addListener(); //adds both MouseMotionListener and MouseListener
}
下面你会看到我参考很多.这是一个CoordinateHolder,它保存鼠标移动的开始和当前坐标.
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,paintComponent(Grapics)方法.有循环遍历Widgets,它实际上只是已经绘制的Rects(x,y,w,h属性),但是更多的信息,这在应用程序的绘图部分中没用.每次释放鼠标时,CoordinateHolder都会转换为Widget,并添加到小部件中.
@Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
System.out.println("Paint");
g.setColor(Color.BLUE);
g.fillRect(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);
}
这段代码工作正常,但我怀疑这是非常低效和无法实现的,因为上面的代码不断刷新JPanel鼠标拖动,也就是说,每10分钟一次？我想它很快就会变慢,特别是当用户创建了很多矩形时(它们也在不断重绘,如painComponent(Graphics)中所示).
问题cq.问题
是否有更好的,资源消耗更少的方法,用户可以平滑地拖动矩形？
我读了这个Drag rectangle on JFrame in Java的答案,但那个答案的作者似乎和我一样.但是,再一次,那是不太合适的,对吧？或者计算机是否应该能够轻松地连续重绘组件,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,然后在paintComponent(…)方法中显示BufferedImage.因此,在绘制一个形状时,在paintComponent(…)中绘制它,但是一旦绘制完形状,可能在mouseRelease上绘制,然后在后台BufferedImage中绘制它.
请注意,最能减慢当前绘图代码的是调试SOP语句,但我认为这些将从完成的代码中删除.
例如：
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(255,200);
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,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,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,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,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();
}
});
}
}
