So zeichnen Sie mit dem Mausziehereignis ein Rechteck in einem Java-Applet und sorgen dafür, dass es bleibt

Question

Ich habe mein Programm, das Rechtecke zeichnen kann.Ich habe zwei Probleme, die ich nicht lösen kann.Nachdem ich das Rechteck gezeichnet habe, bleibt es nicht bestehen.Der einzige Code, den ich habe, der die Leinwand unter Farbe löscht, Repaint wird nur beim Ziehen mit der Maus aufgerufen.Warum wird meine Leinwand gelöscht, wenn ich die Maus loslasse oder bewege?Das zweite Problem stellt kein so großes Problem dar, aber ich kann es nicht herausfinden: Wenn entweder die Höhe oder die Breite meines Rechtecks ​​negativ ist, wird das Rechteck schwarz ausgefüllt.

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

Answer 1

Ok, nachdem ich Ihre Frage noch einmal gelesen habe, scheint es Ihnen egal zu sein, mehrere Rechtecke zu haben :)

Hier ist eine Lösung mit jeweils nur einem (was dem nahekommt, was Sie zu Beginn hatten):

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

Answer 2

Sie müssen Ihre gezeichneten Elemente in einer Datenstruktur speichern und sicherstellen, dass jedes Element in der Struktur beim Neulackieren auf die Leinwand gemalt wird.

Außerdem müssen Sie jedem Ihrer Mausereignisse Repaint hinzufügen.

So was:(Dies setzt voraus, dass Sie ALLE Rects behalten möchten) – Sie können ein einzelnes Rect verwenden, indem Sie die Array-Liste entfernen und durch eine einzelne Rect-Instanz ersetzen.

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

Answer 3

Informieren Sie sich über diese beiden Individuelle Malansätze.Ein Ansatz ist oben beschrieben und der zweite Ansatz zeigt, wie ein BufferedImage verwendet wird.Das für beide Ansätze verwendete Beispiel ermöglicht es Ihnen, dem Rahmen mehrere Rechtecke hinzuzufügen.

Answer 4

Wenn Ihnen einige Anzeigeinformationen egal sind, löschen Sie einfach alle „mousePosition.setText(...)“ in den Maus-Listenern, da diese zu unnötigen repaint()-Aufrufen führen.

Fügen Sie dann zwei Felder hinzu:„int rx, ry;“, fügen Sie mehrere Methoden hinzu/ändern Sie sie wie folgt:

        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);
    }

Das einzige Problem, das ich festgestellt habe, ist, dass das Rechteck beim ersten Zeichnen nicht angezeigt wird.