java - 将图像从浏览器拖放到 JLabel 上

Question

我希望能够在 JLabel 从例如 JLabel 中删除时在其上设置图像。网络浏览器。我的实现基于 Drag-and-Drop Support for Images .

@Override
public boolean importData(JComponent comp, Transferable t) {
    if (comp instanceof JLabel) {
        JLabel label = (JLabel) comp;
        if (t.isDataFlavorSupported(DataFlavor.imageFlavor)) {
            try {
                image = (Image) t.getTransferData(DataFlavor.imageFlavor);
                ImageIcon icon = new ImageIcon(image);
                label.setIcon(icon);
                return true;
            } catch (Throwable th) {
                log.error("Failed to accept dropped image", th);
            }
        } else if (t.isDataFlavorSupported(DataFlavor.javaFileListFlavor)) {
            try {
                @SuppressWarnings("unchecked")
                List<File> files = (List<File>) t.getTransferData(DataFlavor.javaFileListFlavor);
                if (files.size() == 1) {
                        ImageIcon icon = new ImageIcon(files.get(0).getAbsolutePath());
                        label.setIcon(icon);
                }
                return true;
            } catch (Throwable th) {
                log.error("Failed to accept dropped image", th);
            }
        }
    }
    return false;
}

对于 DataFlavor.javaFileListFlavor 部分，一切正常，但使用 DataFlavor.imageFlavour 时，生成的图像始终为 null，并且在实例化 ImageIcon 时抛出 NullPointerException。

有人知道为什么会发生这种情况吗？

Answer 1

你的代码看起来没问题。我使用以下代码对其进行了测试，并将图像从我的网络浏览器 (Google Chrome) 拖放到 JPanel 上，将图像设置在 JLabel 中。

import javax.swing.ImageIcon;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.TransferHandler;
import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.awt.Image;
import java.awt.datatransfer.DataFlavor;
import java.awt.datatransfer.Transferable;
import java.awt.datatransfer.UnsupportedFlavorException;
import java.io.IOException;
import java.lang.reflect.InvocationTargetException;

public class DragAndDropTester {
  private static final JLabel TEST_LABEL = new JLabel( "TestLabel" );

  public static void main( String[] args ) {
    try {
      EventQueue.invokeAndWait( new Runnable() {
        public void run() {

          JFrame testFrame = new JFrame( "Test" );

          JPanel contents = new JPanel( new BorderLayout() );
          contents.add( TEST_LABEL, BorderLayout.CENTER );

          contents.setTransferHandler( createTransferHandler() );

          testFrame.getContentPane().add( contents );
          testFrame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
          testFrame.setSize( 200, 200 );
          testFrame.setVisible( true );
        }
      } );
    } catch ( InterruptedException e ) {
    } catch ( InvocationTargetException e ) {
    }
  }

  private static TransferHandler createTransferHandler(){
    return new TransferHandler(  ){
      @Override
      public boolean importData( JComponent comp, Transferable aTransferable ) {
        try {
          Object transferData = aTransferable.getTransferData( DataFlavor.imageFlavor );
          TEST_LABEL.setIcon( new ImageIcon( ( Image ) transferData ) );
        } catch ( UnsupportedFlavorException e ) {
        } catch ( IOException e ) {
        }
        return true;
      }

      @Override
      public boolean canImport( JComponent comp, DataFlavor[] transferFlavors ) {
        return true;
      }
    };
  }
}

这是在我的 Mac 上使用 JDK1.6 进行测试的

java version "1.6.0_29"
Java(TM) SE Runtime Environment (build 1.6.0_29-b11-402-10M3527)
Java HotSpot(TM) 64-Bit Server VM (build 20.4-b02-402, mixed mode)