java - Swing 模糊拖动图像

Question

我有一个简单的任务要实现，它工作得很好，但我面临着一个关于 Swing 中自定义拖动图像的非常棘手的问题。该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，跟随鼠标显示与列表内渲染器完全相同的绘图。

为此，我对列表中的选定元素使用单元格渲染器，并将其绘制在临时图像上。然后将此图像发送到 TransferHandler，一切正常。当我修改整个组件的大小并使其变大时，问题就很明显了。到一定程度后，绘制的图片不再正确，而是应用了一些渐变，使内容难以阅读。以下是重现该问题的代码片段:

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());
    }
}

我认为问题出在 makeImageFromString 方法中的某处，但在 Swing/AWT 库中挖掘 2 天并了解拖动图像的绘制方式后，我仍然无法解决此问题。底线问题:如果拖动图像超过特定大小，AWT 中是否有任何模糊的逻辑应用此渐变？

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);

编辑:

@user3619696:我误会了。

我猜想“模糊拖动图像”的不透明度取决于 Windows 桌面主题。所以尝试使用半透明的 JWindow 而不是 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());
    }
}