[英]How to draw a rectangle on a java applet using mouse drag event and make it stay
我的程序可以繪制矩形。 我有兩個問題我無法解決。 繪制矩形后,它不會停留。 我唯一的代碼清除畫布下的畫布,重繪僅在鼠標拖動時調用。 為什么當鼠標釋放或鼠標移動時我的畫布清晰。 第二件事不是問題,而是我無法弄清楚的事情,當我的矩形的高度或寬度為負時,矩形填充為黑色。
package pracpapp2;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class MouseTracker4July extends JFrame
implements MouseListener, MouseMotionListener {
private static final long serialVersionUID = 1L;
private JLabel mousePosition;
int x, y;
int x1, x2, y1, y2;
int w, h;
private JLabel recStart;
private JLabel recStop;
private JLabel cords;
// set up GUI and register mouse event handlers
public MouseTracker4July()
{
super( "Rectangle Drawer" );
mousePosition = new JLabel();
mousePosition.setHorizontalAlignment(SwingConstants.CENTER);
getContentPane().add( mousePosition, BorderLayout.CENTER );
JLabel text1 = new JLabel();
text1.setText( "At the center the mouse pointer's coordinates will be displayed." );
getContentPane().add( text1, BorderLayout.SOUTH );
recStart = new JLabel();
getContentPane().add(recStart, BorderLayout.WEST);
recStop = new JLabel();
getContentPane().add(recStop, BorderLayout.EAST);
cords = new JLabel();
getContentPane().add(cords, BorderLayout.NORTH);
addMouseListener( this ); // listens for own mouse and
addMouseMotionListener( this ); // mouse-motion events
setSize( 800, 600 );
setVisible( true );
}
// MouseListener event handlers
// handle event when mouse released immediately after press
public void mouseClicked( MouseEvent event )
{
mousePosition.setText( "Clicked at [" + event.getX() +
", " + event.getY() + "]" );
}
// handle event when mouse pressed
public void mousePressed( MouseEvent event )
{
mousePosition.setText( "Pressed at [" +(x1 = event.getX()) +
", " + (y1 = event.getY()) + "]" );
recStart.setText( "Start: [" + x1 +
", " + y1 + "]" );
}
// handle event when mouse released after dragging
public void mouseReleased( MouseEvent event )
{
mousePosition.setText( "Released at [" +(x2 = event.getX()) +
", " + (y2 = event.getY()) + "]" );
recStop.setText( "End: [" + x2 +
", " + y2 + "]" );
}
// handle event when mouse enters area
public void mouseEntered( MouseEvent event )
{
mousePosition.setText( "Mouse entered at [" + event.getX() +
", " + event.getY() + "]" );
}
// handle event when mouse exits area
public void mouseExited( MouseEvent event )
{
mousePosition.setText( "Mouse outside window" );
}
// MouseMotionListener event handlers
// handle event when user drags mouse with button pressed
public void mouseDragged( MouseEvent event )
{
mousePosition.setText( "Dragged at [" + (x = event.getX()) +
", " + (y = event.getY()) + "]" );
// call repaint which calls paint
repaint();
}
// handle event when user moves mouse
public void mouseMoved( MouseEvent event )
{
mousePosition.setText( "Moved at [" + event.getX() +
", " + event.getY() + "]" );
}
public void paint(Graphics g)
{
super.paint(g); // clear the frame surface
g.drawString("Start Rec Here", x1, y1);
g.drawString("End Rec Here", x, y);
w = x1 - x;
h = y1 - y;
w = w * -1;
h = h * -1;
g.drawRect(x1, y1, w, h);
cords.setText( "w = " + w + ", h = " + h);
}
public static void main( String args[] )
{
MouseTracker4July application = new MouseTracker4July();
application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
}
} // end class MouseTracker
好的,重新閱讀你的問題之后,似乎你可以少關心多個矩形:)
這是一個一次只有一個解決方案(接近你必須開始的):
import java.awt.BorderLayout;
import java.awt.Graphics;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.SwingConstants;
public class MouseTracker4July extends JFrame implements MouseListener, MouseMotionListener {
private static final long serialVersionUID = 1L;
private final JLabel mousePosition;
int x1, x2, y1, y2;
int x, y, w, h;
private final JLabel recStart;
private final JLabel recStop;
private final JLabel cords; // set up GUI and register mouse event handlers
boolean isNewRect = true;
public MouseTracker4July() {
super( "Rectangle Drawer" );
this.mousePosition = new JLabel();
this.mousePosition.setHorizontalAlignment( SwingConstants.CENTER );
getContentPane().add( this.mousePosition, BorderLayout.CENTER );
JLabel text1 = new JLabel();
text1.setText( "At the center the mouse pointer's coordinates will be displayed." );
getContentPane().add( text1, BorderLayout.SOUTH );
this.recStart = new JLabel();
getContentPane().add( this.recStart, BorderLayout.WEST );
this.recStop = new JLabel();
getContentPane().add( this.recStop, BorderLayout.EAST );
this.cords = new JLabel();
getContentPane().add( this.cords, BorderLayout.NORTH );
addMouseListener( this ); // listens for own mouse and
addMouseMotionListener( this ); // mouse-motion events
setSize( 800, 600 );
setVisible( true );
}
// MouseListener event handlers // handle event when mouse released immediately after press
public void mouseClicked( final MouseEvent event ) {
this.mousePosition.setText( "Clicked at [" + event.getX() + ", " + event.getY() + "]" );
repaint();
}
// handle event when mouse pressed
public void mousePressed( final MouseEvent event ) {
this.mousePosition.setText( "Pressed at [" + ( this.x1 = event.getX() ) + ", " + ( this.y1 = event.getY() ) + "]" );
this.recStart.setText( "Start: [" + this.x1 + ", " + this.y1 + "]" );
this.isNewRect = true;
repaint();
}
// handle event when mouse released after dragging
public void mouseReleased( final MouseEvent event ) {
this.mousePosition.setText( "Released at [" + ( this.x2 = event.getX() ) + ", " + ( this.y2 = event.getY() ) + "]" );
this.recStop.setText( "End: [" + this.x2 + ", " + this.y2 + "]" );
repaint();
}
// handle event when mouse enters area
public void mouseEntered( final MouseEvent event ) {
this.mousePosition.setText( "Mouse entered at [" + event.getX() + ", " + event.getY() + "]" );
repaint();
}
// handle event when mouse exits area
public void mouseExited( final MouseEvent event ) {
this.mousePosition.setText( "Mouse outside window" );
repaint();
}
// MouseMotionListener event handlers // handle event when user drags mouse with button pressed
public void mouseDragged( final MouseEvent event ) {
this.mousePosition.setText( "Dragged at [" + ( this.x2 = event.getX() ) + ", " + ( this.y2 = event.getY() ) + "]" ); // call repaint which calls paint repaint();
this.isNewRect = false;
repaint();
}
// handle event when user moves mouse
public void mouseMoved( final MouseEvent event ) {
this.mousePosition.setText( "Moved at [" + event.getX() + ", " + event.getY() + "]" );
repaint();
}
@Override
public void paint( final Graphics g ) {
super.paint( g ); // clear the frame surface
g.drawString( "Start Rec Here", this.x1, this.y1 );
g.drawString( "End Rec Here", this.x2, this.y2 );
int width = this.x1 - this.x2;
int height = this.y1 - this.y2;
this.w = Math.abs( width );
this.h = Math.abs( height );
this.x = width < 0 ? this.x1
: this.x2;
this.y = height < 0 ? this.y1
: this.y2;
if ( !this.isNewRect ) {
g.drawRect( this.x, this.y, this.w, this.h );
}
this.cords.setText( "w = " + this.w + ", h = " + this.h );
}
public static void main( final String args[] ) {
MouseTracker4July application = new MouseTracker4July();
application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
}
} // end class MouseTracker
您需要將繪制的項目存儲在某些數據結構中,並確保在重新繪制時將結構中的每個項目繪制到畫布上。
此外,您需要為每個鼠標事件添加重繪。
像這樣:(這假設你想保留所有矩形) - 你可以通過消除arraylist並用一個rect實例替換單個rect。
import java.awt.BorderLayout;
import java.awt.Graphics;
import java.awt.Rectangle;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import java.util.ArrayList;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.SwingConstants;
public class MouseTracker4July extends JFrame implements MouseListener, MouseMotionListener {
private static final long serialVersionUID = 1L;
private final JLabel mousePosition;
int x1, x2, y1, y2;
int w, h;
private final JLabel recStart;
private final JLabel recStop;
private final JLabel cords; // set up GUI and register mouse event handlers
private final ArrayList< Rectangle > rectangles = new ArrayList< Rectangle >();
private boolean isNewRect = true;
public MouseTracker4July() {
super( "Rectangle Drawer" );
this.mousePosition = new JLabel();
this.mousePosition.setHorizontalAlignment( SwingConstants.CENTER );
getContentPane().add( this.mousePosition, BorderLayout.CENTER );
JLabel text1 = new JLabel();
text1.setText( "At the center the mouse pointer's coordinates will be displayed." );
getContentPane().add( text1, BorderLayout.SOUTH );
this.recStart = new JLabel();
getContentPane().add( this.recStart, BorderLayout.WEST );
this.recStop = new JLabel();
getContentPane().add( this.recStop, BorderLayout.EAST );
this.cords = new JLabel();
getContentPane().add( this.cords, BorderLayout.NORTH );
addMouseListener( this ); // listens for own mouse and
addMouseMotionListener( this ); // mouse-motion events
setSize( 800, 600 );
setVisible( true );
}
// MouseListener event handlers // handle event when mouse released immediately after press
public void mouseClicked( final MouseEvent event ) {
this.mousePosition.setText( "Clicked at [" + event.getX() + ", " + event.getY() + "]" );
repaint();
}
// handle event when mouse pressed
public void mousePressed( final MouseEvent event ) {
this.mousePosition.setText( "Pressed at [" + ( this.x1 = event.getX() ) + ", " + ( this.y1 = event.getY() ) + "]" );
this.recStart.setText( "Start: [" + this.x1 + ", " + this.y1 + "]" );
repaint();
}
// handle event when mouse released after dragging
public void mouseReleased( final MouseEvent event ) {
this.mousePosition.setText( "Released at [" + ( this.x2 = event.getX() ) + ", " + ( this.y2 = event.getY() ) + "]" );
this.recStop.setText( "End: [" + this.x2 + ", " + this.y2 + "]" );
Rectangle rectangle = getRectangleFromPoints();
this.rectangles.add( rectangle );
this.w = this.h = this.x1 = this.y1 = this.x2 = this.y2 = 0;
this.isNewRect = true;
repaint();
}
private Rectangle getRectangleFromPoints() {
int width = this.x1 - this.x2;
int height = this.y1 - this.y2;
Rectangle rectangle = new Rectangle( width < 0 ? this.x1
: this.x2, height < 0 ? this.y1
: this.y2, Math.abs( width ), Math.abs( height ) );
return rectangle;
}
// handle event when mouse enters area
public void mouseEntered( final MouseEvent event ) {
this.mousePosition.setText( "Mouse entered at [" + event.getX() + ", " + event.getY() + "]" );
repaint();
}
// handle event when mouse exits area
public void mouseExited( final MouseEvent event ) {
this.mousePosition.setText( "Mouse outside window" );
repaint();
}
// MouseMotionListener event handlers // handle event when user drags mouse with button pressed
public void mouseDragged( final MouseEvent event ) {
this.mousePosition.setText( "Dragged at [" + ( this.x2 = event.getX() ) + ", " + ( this.y2 = event.getY() ) + "]" ); // call repaint which calls paint repaint();
this.isNewRect = false;
repaint();
}
// handle event when user moves mouse
public void mouseMoved( final MouseEvent event ) {
this.mousePosition.setText( "Moved at [" + event.getX() + ", " + event.getY() + "]" );
repaint();
}
@Override
public void paint( final Graphics g ) {
super.paint( g ); // clear the frame surface
g.drawString( "Start Rec Here", this.x1, this.y1 );
g.drawString( "End Rec Here", this.x2, this.y2 );
Rectangle newRectangle = getRectangleFromPoints();
if ( !this.isNewRect ) {
g.drawRect( newRectangle.x, newRectangle.y, newRectangle.width, newRectangle.height );
}
for( Rectangle rectangle : this.rectangles ) {
g.drawRect( rectangle.x, rectangle.y, rectangle.width, rectangle.height );
}
this.cords.setText( "w = " + this.w + ", h = " + this.h );
}
public static void main( final String args[] ) {
MouseTracker4July application = new MouseTracker4July();
application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
}
} // end class MouseTracker
閱讀這兩種自定義繪畫方法 。 上面描述了一種方法,第二種方法顯示了如何使用BufferedImage。 兩種方法使用的示例允許您向框架添加多個矩形。
如果您不關心某些顯示信息,只需刪除鼠標偵聽器中的每個“mousePosition.setText(...)”,就會產生不必要的repaint()調用。
然后,添加兩個字段:“int rx,ry;”,添加/修改以下幾種方法:
public void mouseDragged(MouseEvent event) {
// mousePosition.setText("Dragged at [" + (x = event.getX()) + ", "
// + (y = event.getY()) + "]");
// call repaint which calls paint
x = event.getX();
y = event.getY();
compRectPos();
repaint();
}
private void compRectPos()
{
rx = x1;
ry = y1;
w = x - x1;
h = y - y1;
if ( w < 0)
rx += w;
if (h < 0)
ry += h;
w = Math.abs(w);
h = Math.abs(h);
}
public void paint(Graphics g) {
super.paint(g); // clear the frame surface
g.drawString("Start Rec Here", x1, y1);
g.drawString("End Rec Here", x, y);
g.drawRect(rx, ry, w, h);
cords.setText("w = " + w + ", h = " + h);
}
我發現的唯一問題是,首次繪制時矩形不會出現。
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