Select and drag Swing component

Question

I made an application that draws rectangles, dots, straights, etc. I wanted when the user clicked with the mouse on top of a drawn polygon, selected the polygon and dragged to where he wants on the screen, How to achieve this goal?

Answer 1

I don’t know exactly how you’re creating polygons.

But if it is a java.awt.Component, I think that solves it:

import java.awt.*;
import java.awt.event.*;
import javax.swing.SwingUtilities;

public class Mover extends MouseAdapter {

  private Dimension snapSize = new Dimension( 1, 1 );
  private Component source;
  private Point pressed;
  private boolean potentialDrag;
  private static Mover instance;
  private Point locationBeforeMove;

  private Mover() {
  }

  public void deregisterComponent( Component... components ) {
    for ( Component component : components ) {
      component.removeMouseListener( this );
    }
  }

  public void registerComponent( Component... components ) {
    for ( Component component : components ) {
      component.addMouseListener( this );
    }
  }

  public Dimension getSnapSize() {
    return snapSize;
  }

  public void setSnapSize( Dimension snapSize ) {
    if ( snapSize.width < 1
        || snapSize.height < 1 ) {
      throw new IllegalArgumentException( "snapSize deve ser maior que 0" );
    }

    this.snapSize = snapSize;
  }

  @Override
  public void mousePressed( MouseEvent e ) {
    if ( !SwingUtilities.isLeftMouseButton( e ) ) {
      return;
    }
    if ( e.isConsumed() ) {
      return;
    }

    setupForDragging( e );
  }

  private void setupForDragging( MouseEvent e ) {
    source = e.getComponent();
    source.addMouseMotionListener( this );
    potentialDrag = true;

    pressed = e.getLocationOnScreen();

    locationBeforeMove = source.getLocation();
  }

  /**
   * Move the component to its new location. The dragged Point must be in the destination coordinates.
   */
  @Override
  public void mouseDragged( MouseEvent e ) {
    if ( !SwingUtilities.isLeftMouseButton( e ) ) {
      return;
    }
    if ( e.isConsumed() ) {
      return;
    }
    Point dragged = e.getLocationOnScreen();
    int dragX = getDragDistance( dragged.x, pressed.x, snapSize.width );
    int dragY = getDragDistance( dragged.y, pressed.y, snapSize.height );

    Component source = e.getComponent();

    Point location = locationBeforeMove;
    if ( location == null ) {
      return;
    }

    int locationX = location.x + dragX;
    int locationY = location.y + dragY;

    while ( locationX < 0 ) {
      locationX += snapSize.width;
    }

    while ( locationY < 0 ) {
      locationY += snapSize.height;
    }

    Dimension d = getBoundingSize( source );

    while ( locationX + source.getSize().width > d.width ) {
      locationX -= snapSize.width;
    }

    while ( locationY + source.getSize().height > d.height ) {
      locationY -= snapSize.height;
    }

    source.setLocation( locationX, locationY );
  }


  private int getDragDistance( int larger, int smaller, int snapSize ) {
    int halfway = snapSize / 2;
    int drag = larger - smaller;
    drag += (drag < 0) ? -halfway : halfway;
    drag = (drag / snapSize) * snapSize;

    return drag;
  }

  private Dimension getBoundingSize( Component source ) {
    if ( source instanceof Window ) {
      GraphicsEnvironment env = GraphicsEnvironment.getLocalGraphicsEnvironment();
      Rectangle bounds = env.getMaximumWindowBounds();
      return new Dimension( bounds.width, bounds.height );
    }
    else {
      return source.getParent().getSize();
    }
  }

  @Override
  public void mouseReleased( MouseEvent e ) {
    if ( !SwingUtilities.isLeftMouseButton( e ) ) {
      return;
    }
    if ( !potentialDrag ) {
      return;
    }

    source.removeMouseMotionListener( this );
    potentialDrag = false;
  }

  public static Mover getInstance() {
    if ( instance == null ) {
      instance = new Mover();
    }
    return instance;
  }
}

To use the class:

Poligono poligono = new Poligono();
Mover.getInstance().registerComponent( poligono );

Answer 2

First I think you have to review the use of Swing because and will not be continued, I suggest the use of Java FX that is very cool, easy to use and has very cool components.

About the problem you would have to use some resource of drag & drop, that will work with the image positions. Something like this.

Answer 3

Depending on the purpose of this, you would have to do "on the arm": Detecting where the guy clicked, identifying which polygon is, and repainting the polygon on the screen by moving it and so on... That depends on how you’re drawing the polygon

Answer 4

If you want to do it by hand... it’s been a while since I work with Java, but I’ll try to give you some tips.

Whenever the user draws a polygon, keep in memory the coordinates of this polygon. It is good to keep also a kind of "Z-index" so you can have polygons on each other (if you want to allow this)

private Vector<Poligono> poligonos;
public Vector<Poligono> getPoligonos() { return this.poligonos; }
public void setPoligonos(Vector<Poligono> poligonos) { this.poligonos = poligonos; }

public void desenharPoligono(int startX, int startY, int endX, int endY) {
    this.getPoligonos().push(new Poligono(startX, startY, endX, endY));
}

When the user clicks fast (do not click and drag), scan your polygon list to see if it clicked on a coordinate that belongs to a polygon... If yes, bang, select your polygon!

public void verificarCoordenadas(int x, int y) {
    for (Poligono poligono : this.getPoligonos()) {
        if (poligono.contemCoordenada(x, y)) {
            poligono.selecionar();
            return;
        }
    }
}

If I give you more tips I take your learning challenge alone. Your next steps would be to create the class Poligono and implement their methods (contemCoordenada, selecionar, mover related)...

Gave me a little bit of Java now.