Question

我一直在努力了解JViewports并试图使用它。我一直在使用这个绅士的class，它只是扩展了JViewport类。

如果我想在实现JPanel类的6480 * 4860对象的中间设置视口，那么为什么这个代码给我一个空白视图，即使在调试时我确认实现JPanel的类我是使用已被添加到视图中？我是否完全混淆了对不同方法的调用，或者我对所用坐标及其含义的理解？还有一个：是否打电话

    v.setOpaque(true);

只设置视口不透明或者它也会设置所有子视图？如果我弄清楚如何正确使用视口，我想我会很快知道这个答案。

public myProgram(){ 
    ...

    myCustomJPanel = new MyCustonJPanel();
    myCustomJPanel.setBackground(Color.WHITE);
    GrabbableViewport v = new GrabbableViewport();
    v.setViewSize(new Dimension(720,540));
    v.setViewPosition(new Point(720,540));
    v.setView(myCustomJPanel);
    v.setViewPosition(new Point(720,540));
    v.setLocation(43, 5);
    appropriateParentPanel.add(v);
}

这是我尝试使用的课程。这个简短的问题需要更多的空间，但格式化的文本应该比纯文本更令你高兴！如果我没有弄错的话，问题不应该来自这里。

// Copyright (c) 2006 - 2008, Markus Strauch.
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package net.sf.sdedit.ui.components;

import java.awt.Component;
import java.awt.Cursor;
import java.awt.Image;
import java.awt.Point;
import java.awt.Rectangle;
import java.awt.Toolkit;
import java.awt.event.MouseEvent;

import javax.swing.ImageIcon;
import javax.swing.JComponent;
import javax.swing.JViewport;
import javax.swing.event.MouseInputListener;

/**
 * A <tt>GrabbableViewport</tt> is a <tt>JViewport</tt> that scrolls its
 * view when the mouse is dragged. While the mouse is being dragged, its cursor
 * is set to a &quot;grabbing hand&quot;, like in applications such as Acrobat
 * Reader.
 * 
 * @author Markus Strauch
 * 
 */
public class GrabbableViewport extends JViewport implements MouseInputListener {

    private static Cursor HAND = new Cursor(Cursor.MOVE_CURSOR);

    private static Cursor DFLT = new Cursor(Cursor.DEFAULT_CURSOR);

    public static void setHandCursorIcon(ImageIcon icon) {
        Image grabbingHand = icon.getImage();
        HAND = Toolkit.getDefaultToolkit().createCustomCursor(grabbingHand,
                new Point(0, 0), "hand cursor");
    }

    /**
     * Constructor.
     */
    public GrabbableViewport () {
        super ();
    }

    private Rectangle rect; 

    private Point point;    

    private JComponent view;    

    public void setView(Component view) {
        super.setView(view);
        if (this.view != view) {
            if (this.view != null) {
                this.view.removeMouseListener(this);
                this.view.removeMouseMotionListener(this);
            }
            if (view != null) {
                view.addMouseListener(this);
                view.addMouseMotionListener(this);
            }
            this.view = (JComponent) view;
        }
    }

    public void mouseClicked(MouseEvent e) {
    }

    public void mouseEntered(MouseEvent e) {
    }

    public void mouseExited(MouseEvent e) {
    }

    public void mousePressed(MouseEvent e) {
        view.setCursor(HAND);
        //((Component) e.getSource()).setCursor(HAND);
        rect = getViewRect();
        point = screenLocation(e);
    }

    private Point screenLocation(MouseEvent e) {
        Point root = view.getLocationOnScreen();
        Point mouse = e.getPoint();
        if (rect != null && !rect.contains(mouse)) {
            return null;
        }
        Point screenPoint = new Point(root.x + mouse.x, root.y + mouse.y);
        return screenPoint;
    }

    public void mouseReleased(MouseEvent e) {
        view.setCursor(DFLT);
        scrollTo(screenLocation(e));
        clear();
    }

    public void mouseDragged(MouseEvent e) {
        scrollTo(screenLocation(e));
    }

    public void mouseMoved(MouseEvent e) {
    }

    private void scrollTo(Point newPoint) {
        if (point != null && newPoint != null && rect != null) {
            int deltaX = point.x - newPoint.x;
            int deltaY = point.y - newPoint.y;
            rect.x = rect.x + deltaX;
            rect.y = rect.y + deltaY;
            ((JComponent) getView()).scrollRectToVisible(rect);
                point = newPoint;
        }
    }

            private void clear() {
                rect = null;
            point = null;
        }
    }

我可以给你一个sscce，但我觉得这应该很简单，虽然如果你问我可以快速拼凑一些例子。

Answer 1

由于GrabbableViewport extends JViewport，我猜测您应该在JScrollPane中使用它，如图here所示。如果没有，该示例可以帮助您使用ScrollPanePaint.MyPanel构建sscce。

myCustomJPanel = new MyCustonJPanel();
GrabbableViewport v = new GrabbableViewport();
v.setView(myCustomJPanel);
JScrollPane scrollPane = new JScrollPane();
scrollPane.setViewport(v);
enclosingContainer.add(scrollPane);

另请参阅此相关example利用现有JScrollPane操作。

如here所述，使用setOpaque(true)是绘制每个像素的承诺。

理解JViewPorts有些麻烦

1 个答案: