Question

我有一个简单的任务要实现，它工作得很好，但我在Swing中遇到一个关于自定义拖动图像的棘手问题。任务背后的想法只是允许用户在列表组件和文本组件之间执行一些DND，但在拖动操作期间，在鼠标后面显示与列表中的渲染器完全相同的绘图。

为此，我将单元格渲染器用于列表中的选定元素，并将其绘制在临时图像上。然后将此图像发送到TransferHandler，一切都很好。当我修改整个组件的大小并使其更大时，问题就很明显了。在一定程度上，绘制的图片不再显示正确，而是应用了一些渐变，使内容难以阅读。以下是重现问题的代码片段：

import java.awt.Color;
import java.awt.Component;
import java.awt.GridLayout;

import javax.swing.DefaultListCellRenderer;
import javax.swing.DefaultListModel;
import javax.swing.DropMode;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.SwingUtilities;

public class BasicTextListDND {

    private JList<String> makeList() {
        DefaultListModel<String> m = new DefaultListModel<String>();
        for(int i = 0; i<10; i++) {
            m.addElement("Element "+i);            
        }
        JList<String> list = new JList<String>(m);

        list.setTransferHandler(new BasicListTransferHandler());
        list.setDropMode(DropMode.ON_OR_INSERT);
        list.setDragEnabled(true);
        list.setCellRenderer(new DefaultListCellRenderer() {

            /**
             * Comment for <code>serialVersionUID</code>
             */
            private static final long serialVersionUID = 1L;

            /** {@inheritDoc} */
            public Component getListCellRendererComponent(JList<?> list, Object value, int index,
                    boolean isSelected, boolean cellHasFocus) {
                Component listCellRendererComponent = super.getListCellRendererComponent(list, value, index, isSelected, cellHasFocus);
                if (cellHasFocus == false && isSelected == false) { 
                    if (index % 2 == 0) {
                        listCellRendererComponent.setBackground(Color.RED);
                    } else if (index % 3==0) {
                        listCellRendererComponent.setBackground(Color.GREEN);
                    } else {
                        listCellRendererComponent.setBackground(Color.BLUE);
                    }
                }
                return listCellRendererComponent;
            }

        });
        return list;
    }

    private JTextArea makeTextArea() {
        JTextArea textArea = new JTextArea("Drag here from JList!");
        return textArea;
    }

    public JComponent makeUI() {
        JPanel panel = new JPanel(new GridLayout(2,1));
        panel.add(new JScrollPane(makeTextArea()));
        panel.add(new JScrollPane(makeList()));
        return panel;
    }

    private static void createAndShowGUI() {
        JFrame f = new JFrame("BasicDnD");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        BasicTextListDND app = new BasicTextListDND();
        JComponent appContent = app.makeUI();
        f.setContentPane(appContent);
        f.setSize(600, 320);
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override 
            public void run() { 
                createAndShowGUI(); 
            }
        });
    }
}


/**
 * 
 */
public class BasicListTransferHandler extends TransferHandler {

    /**
     * Comment for <code>serialVersionUID</code>
     */
    private static final long serialVersionUID = 1L;

    @Override 
    public boolean canImport(TransferHandler.TransferSupport info) {
        if (!info.isDataFlavorSupported(DataFlavor.stringFlavor)) {
            return false;
        }
        JList.DropLocation dl = (JList.DropLocation)info.getDropLocation();
        if (dl.getIndex() == -1) {
            return false;
        }
        return true;
    }

    @Override 
    public int getSourceActions(JComponent c) {
        BufferedImage dragImage = makeImageFromString(c);
        if (dragImage != null) {
            setDragImage(dragImage);            
            Point mousePosition = c.getMousePosition();
            if (mousePosition != null) {
                setDragImageOffset(mousePosition);
            }
        }
        return COPY;
    }

    private final JPanel tempDrawPanel = new JPanel();

    private BufferedImage createDragImage(JList<String> list) {
        int width = 0;
        int height = 0;
        int[] selectedIndices = list.getSelectedIndices();
        for(int i =0; i<selectedIndices.length; i++){
            int idx = selectedIndices[i];
            Rectangle cellBounds = list.getCellBounds(idx, idx);
            height += cellBounds.height;
            width = Math.max(width, cellBounds.width); // we want to create a drag image as big as the largest cell
        }
        BufferedImage br = null;
        if (width > 0 && height > 0) {
            br = list.getGraphicsConfiguration().createCompatibleImage(width, height, Transparency.TRANSLUCENT);
        }
        return br;
    }

    private BufferedImage makeImageFromString(JComponent src) {
        JList<String> sourceList = (JList<String>)src;
        BufferedImage  br = createDragImage(sourceList);
        if (br != null) {
            int[] selectedIndices = sourceList.getSelectedIndices();            
            int yD = 0;
            Graphics g = br.getGraphics();
            try{
                for(int idx: selectedIndices) {
                    ListCellRenderer<? super String> cellRenderer = sourceList.getCellRenderer();
                    String valueAt = sourceList.getModel().getElementAt(idx);
                    Component c = cellRenderer.getListCellRendererComponent(sourceList, valueAt, idx, false, false);
                    Rectangle itemCellBounds = sourceList.getCellBounds(idx, idx);                
                    SwingUtilities.paintComponent(g, c, tempDrawPanel, itemCellBounds.x, yD, itemCellBounds.width, itemCellBounds.height);
                    yD = itemCellBounds.y+itemCellBounds.height;
                }
            }finally {
                g.dispose();
            }
            br.coerceData(true);
        }
        return br;
    }

    @Override 
    protected Transferable createTransferable(JComponent c) {
        JList<String> list = (JList<String>)c;
        List<String> selectedValuesList = list.getSelectedValuesList();                
        StringBuffer buff = new StringBuffer();
        for (int i = 0; i < selectedValuesList.size(); i++) {
            String val = selectedValuesList.get(i);
            buff.append(val == null ? "" : val.toString());
            if (i != selectedValuesList.size()- 1) {
                buff.append("\n");
            }
        }
        return new StringSelection(buff.toString());
    }
}

问题在于，我认为，在makeImageFromString方法的某个地方，但是经过2天的Swing / AWT库挖掘并了解拖动图像是如何绘制的，我仍然无法解决这个问题。底线问题：如果拖动图像超过一定大小，AWT中是否存在应用此渐变的任何模糊逻辑？

任何帮助将不胜感激！马吕斯。

Answer 1

如何翻译图形上下文的来源：

//SwingUtilities.paintComponent(g, c, tempDrawPanel, itemCellBounds.x, yD, itemCellBounds.width, itemCellBounds.height);
//yD = itemCellBounds.y+itemCellBounds.height;
SwingUtilities.paintComponent(g, c, tempDrawPanel, 0, 0, itemCellBounds.width, itemCellBounds.height);
g.translate(0, itemCellBounds.height);

修改

@ user3619696：我误解了。

我猜想＆＃34;模糊的拖动图像＆＃34;不透明度取决于Windows桌面主题。因此，请尝试使用半透明JWindow代替TransferHandler#setDragImage(...)。

import java.awt.*; import java.awt.datatransfer.*; import java.awt.dnd.*; import java.awt.image.*; import java.util.List; import javax.swing.*; public class BasicTextListDND2 { private JList<String> makeList() { DefaultListModel<String> m = new DefaultListModel<String>(); for(int i = 0; i<10; i++) { m.addElement("Element "+i); } JList<String> list = new JList<String>(m); list.setTransferHandler(new BasicListTransferHandler()); list.setDropMode(DropMode.ON_OR_INSERT); list.setDragEnabled(true); list.setCellRenderer(new DefaultListCellRenderer() { /** * Comment for <code>serialVersionUID</code> */ private static final long serialVersionUID = 1L; /** {@inheritDoc} */ public Component getListCellRendererComponent(JList<?> list, Object value, int index, boolean isSelected, boolean cellHasFocus) { Component listCellRendererComponent = super.getListCellRendererComponent(list, value, index, isSelected, cellHasFocus); if (cellHasFocus == false && isSelected == false) { if (index % 2 == 0) { listCellRendererComponent.setBackground(Color.RED); } else if (index % 3==0) { listCellRendererComponent.setBackground(Color.GREEN); } else { listCellRendererComponent.setBackground(Color.BLUE); } } return listCellRendererComponent; } }); return list; } private JTextArea makeTextArea() { JTextArea textArea = new JTextArea("Drag here from JList!"); return textArea; } public JComponent makeUI() { JPanel panel = new JPanel(new GridLayout(2,1)); panel.add(new JScrollPane(makeTextArea())); panel.add(new JScrollPane(makeList())); return panel; } private static void createAndShowGUI() { JFrame f = new JFrame("BasicDnD"); f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); BasicTextListDND2 app = new BasicTextListDND2(); JComponent appContent = app.makeUI(); f.setContentPane(appContent); f.setSize(600, 320); f.setLocationRelativeTo(null); f.setVisible(true); } public static void main(String[] args) { SwingUtilities.invokeLater(new Runnable() { @Override public void run() { createAndShowGUI(); } }); } } /** * */ class BasicListTransferHandler extends TransferHandler { /** * Comment for <code>serialVersionUID</code> */ private static final long serialVersionUID = 1L; private final JLabel label = new JLabel() { @Override public boolean contains(int x, int y) { return false; } }; private final JWindow window = new JWindow(); public BasicListTransferHandler() { super(); window.add(label); //window.setBackground(new Color(0, true)); window.setOpacity(.8f); DragSource.getDefaultDragSource().addDragSourceMotionListener(new DragSourceMotionListener() { @Override public void dragMouseMoved(DragSourceDragEvent dsde) { Point pt = dsde.getLocation(); pt.translate(10, 10); // offset if (!window.isVisible()) { window.setVisible(true); } window.setLocation(pt); } }); } @Override protected void exportDone(JComponent c, Transferable data, int action) { super.exportDone(c, data, action); window.setVisible(false); } @Override public boolean canImport(TransferHandler.TransferSupport info) { if (!info.isDataFlavorSupported(DataFlavor.stringFlavor)) { return false; } JList.DropLocation dl = (JList.DropLocation)info.getDropLocation(); if (dl.getIndex() == -1) { return false; } return true; } @Override public int getSourceActions(JComponent c) { BufferedImage dragImage = makeImageFromString(c); if (dragImage != null) { //setDragImage(dragImage); //Point mousePosition = c.getMousePosition(); //if (mousePosition != null) { // setDragImageOffset(mousePosition); //} label.setIcon(new ImageIcon(dragImage)); window.setLocation(-2000, -2000); window.pack(); } return COPY; } private final JPanel tempDrawPanel = new JPanel(); private BufferedImage createDragImage(JList<String> list) { int width = 0; int height = 0; int[] selectedIndices = list.getSelectedIndices(); for(int i =0; i<selectedIndices.length; i++){ int idx = selectedIndices[i]; Rectangle cellBounds = list.getCellBounds(idx, idx); height += cellBounds.height; width = Math.max(width, cellBounds.width); // we want to create a drag image as big as the largest cell } BufferedImage br = null; if (width > 0 && height > 0) { br = list.getGraphicsConfiguration().createCompatibleImage(width, height, Transparency.TRANSLUCENT); } return br; } private BufferedImage makeImageFromString(JComponent src) { JList<String> sourceList = (JList<String>)src; BufferedImage br = createDragImage(sourceList); if (br != null) { int[] selectedIndices = sourceList.getSelectedIndices(); int yD = 0; Graphics g = br.getGraphics(); try{ for(int idx: selectedIndices) { ListCellRenderer<? super String> cellRenderer = sourceList.getCellRenderer(); String valueAt = sourceList.getModel().getElementAt(idx); Component c = cellRenderer.getListCellRendererComponent(sourceList, valueAt, idx, false, false); Rectangle itemCellBounds = sourceList.getCellBounds(idx, idx); //SwingUtilities.paintComponent(g, c, tempDrawPanel, itemCellBounds.x, itemCellBounds.y + yD, itemCellBounds.width, itemCellBounds.height); //yD = itemCellBounds.y+itemCellBounds.height; SwingUtilities.paintComponent(g, c, tempDrawPanel, 0, 0, itemCellBounds.width, itemCellBounds.height); g.translate(0, itemCellBounds.height); } }finally { g.dispose(); } br.coerceData(true); } return br; } @Override protected Transferable createTransferable(JComponent c) { JList<String> list = (JList<String>)c; List<String> selectedValuesList = list.getSelectedValuesList(); StringBuffer buff = new StringBuffer(); for (int i = 0; i < selectedValuesList.size(); i++) { String val = selectedValuesList.get(i); buff.append(val == null ? "" : val.toString()); if (i != selectedValuesList.size()- 1) { buff.append("\n"); } } return new StringSelection(buff.toString()); } }

摆动模糊拖动图像

1 个答案: