java - 将自定义对象从嵌入式 FX (JFXPanel) 拖放到 Swing

Question

此问题是 Custom object drag-and-drop from FX to Swing 的后续问题 .

我正在为一个将 JavaFX 用于某些图形用户界面的 Swing 应用程序开发一个插件。我们添加了拖放功能以改善用户体验。首先，我们为我们的Scene 使用外部 JavaFX 窗口 (Stage)，现在我们想通过 JFXPanel 将它直接嵌入到 Swing 应用程序中>.

现在，奇怪的是，无论是在 Stage 中加载完全相同的 Scene 还是在一个 JFXPanel。

在尝试将具有自定义 MIME 类型的自定义 Java 对象(以序列化形式)从 JavaFX 应用程序拖到 Swing 应用程序时，我已经遇到了一些问题。但是，我的问题在我上面提到的问题中得到了解决。现在，使用嵌入式JavaFX应用程序，遇到了一些新问题，所以我想问问有没有人有类似的问题或知道这种情况的解决方案。

我写了一个 MVCE，它是一个简单的 Java 应用程序，一侧有一个支持拖动的 JFXPanel，另一侧有一个支持拖放的 JPanel:

public class MyApp {

    public static final DataFormat FORMAT = new DataFormat(
        // this works fine in a separate window
        //"JAVA_DATAFLAVOR:application/x-my-mime-type; class=java.lang.String",
        "application/x-my-mime-type; class=java.lang.String");

    public static final DataFlavor FLAVOR;

    static {
        try {
            FLAVOR = new DataFlavor("application/x-my-mime-type; class=java.lang.String");
        } catch (ClassNotFoundException ex) {
            throw new RuntimeException(ex);
        }
    }

    public static void main(String[] args) {
        new MyApp().run();
    }

    private void run() {
        JFrame frame = new JFrame();
        frame.setLayout(new GridLayout(1, 2));
        frame.add(buildFX());
        frame.add(buildSwing());
        frame.setSize(300, 300);
        frame.setVisible(true);
    }

    private JFXPanel buildFX() {
        BorderPane parent = new BorderPane();
        parent.setOnDragDetected(event -> {
            Dragboard dragboard = parent.startDragAndDrop(TransferMode.COPY);
            ClipboardContent content = new ClipboardContent();
            content.put(FORMAT, "Test");
            dragboard.setContent(content);
            event.consume();
        });
        JFXPanel panel = new JFXPanel();
        panel.setScene(new Scene(parent));
        return panel;
    }

    @SuppressWarnings("serial")
    private JPanel buildSwing() {
        JPanel panel = new JPanel();
        panel.setBackground(Color.ORANGE);
        panel.setTransferHandler(new TransferHandler() {

            @Override
            public boolean canImport(TransferSupport support) {
                return support.isDataFlavorSupported(FLAVOR);
            }

            @Override
            public boolean importData(TransferSupport support) {
                if (!canImport(support)) return false;
                try {
                    String data = (String) support.getTransferable().getTransferData(FLAVOR);
                    System.out.println(data);
                    return true;
                } catch (UnsupportedFlavorException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                }
                return false;
            }

        });
        return panel;
    }
}

根据另一个问题的回答，在DataFormat中使用前缀JAVA_DATAFLAVOR:是Swing正确处理MIME类型所必需的。但是，当在 JFXPanel(示例中禁用)中使用这样的 DataFormat 时，Java 似乎在从中拖动时试图构造一个 DataFlavor FX 应用程序无法解析带有前缀的 MIME 类型:

Exception in thread "AWT-EventQueue-0" java.lang.IllegalArgumentException: failed to parse:JAVA_DATAFLAVOR:application/x-my-mime-type; class=java.lang.String
    at java.awt.datatransfer.DataFlavor.<init>(Unknown Source)
    at javafx.embed.swing.SwingDnD$DnDTransferable.getTransferDataFlavors(SwingDnD.java:394)
    at sun.awt.datatransfer.DataTransferer.getFormatsForTransferable(Unknown Source)
    at sun.awt.dnd.SunDragSourceContextPeer.startDrag(Unknown Source)
    at java.awt.dnd.DragSource.startDrag(Unknown Source)
    at java.awt.dnd.DragSource.startDrag(Unknown Source)
    at java.awt.dnd.DragGestureEvent.startDrag(Unknown Source)
    at javafx.embed.swing.SwingDnD.startDrag(SwingDnD.java:280)
    at javafx.embed.swing.SwingDnD.lambda$null$66(SwingDnD.java:247)
    at java.awt.event.InvocationEvent.dispatch(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$500(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.run(Unknown Source)

仅使用没有前缀的纯 MIME 类型，拖放操作有效，我什至可以接收到正确的 DataFlavor (java.awt.datatransfer.DataFlavor[mimetype =application/x-my-mime-type;representationclass=java.lang.String])，但是丢弃的数据总是null。正如在另一个问题中看到的那样，在两个单独的窗口中使用第二种方法，我什至无法接收到 DataFlavor，但现在它以某种方式工作到这个有限的点。

Answer 1

可能对传输的工作方式存在一些误解。

尝试直接将传输数据作为字符串检索可能适用于“text/plain”或其他标准文本类型，并且正如您所注意到的，对于自定义未注册类型的特定情况有一些怪癖。但我认为自定义解决方法的努力是不合理的。

由于您完全控制自定义 MIME 类型的内容结构以及同一应用程序中数据生产者和消费者的两端，我建议不要处理内部工具包依赖于实现的前缀或类映射。可能更好的做法是只定义您的 MIME 类型，而没有不相关的元数据和格式错误的前缀(因为它应该是)。

定义“application/x-my-mime”类型并正确解码数据就足够了。

---

示例 1(序列化数据)

下面根据您的示例进行了更正，应该可以将数据很好地放入 Java 8 中的 Swing 框架。

package jfxtest;

import java.awt.Color;
import java.awt.GridLayout;
import java.awt.datatransfer.DataFlavor;
import java.io.InputStream;
import java.io.ObjectInputStream;
import java.util.Collections;
import javafx.embed.swing.JFXPanel;
import javafx.scene.Node;
import javafx.scene.Scene;
import javafx.scene.input.DataFormat;
import javafx.scene.input.TransferMode;
import javafx.scene.layout.BorderPane;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.TransferHandler;
import javax.swing.TransferHandler.TransferSupport;

public class MyApp {

  final static String MY_MIME_TYPE = "application/x-my-mime";
  public static final DataFormat FORMAT = new DataFormat(MY_MIME_TYPE);
  public static final DataFlavor FLAVOR = new DataFlavor(MY_MIME_TYPE, "My Mime Type");

  private void startDrag(Node node) {
    node.startDragAndDrop(TransferMode.COPY).setContent(
        Collections.singletonMap(FORMAT, "Test"));
  }

  private boolean processData(TransferSupport support) {
    try (InputStream in = (InputStream) support.getTransferable().getTransferData(FLAVOR)) {
      Object transferred = new ObjectInputStream(in).readObject();
      System.out.println("transferred: " + transferred + " (" + transferred.getClass() + ")");
      return true;
    } catch (Exception e) {
      e.printStackTrace();
    }
    return false;
  }  

  public static void main(String[] args) {
    new MyApp().run();
  }

  private void run() {
    JFrame frame = new JFrame();
    frame.setLayout(new GridLayout(1, 2));
    frame.add(buildSwing());
    SwingUtilities.invokeLater(() -> {
      frame.add(buildFX());
    });
    frame.setSize(300, 300);
    frame.setVisible(true);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  }

  private JFXPanel buildFX() {
    BorderPane parent = new BorderPane();
    parent.setOnDragDetected(event -> {
      startDrag(parent);
      event.consume();
    });
    JFXPanel panel = new JFXPanel();
    panel.setScene(new Scene(parent));
    return panel;
  }


  private JPanel buildSwing() {
    JPanel panel = new JPanel();
    panel.setBackground(Color.ORANGE);
    panel.setTransferHandler(new TransferHandler() {
      private static final long serialVersionUID = 1L;

      @Override
      public boolean canImport(TransferSupport support) {
        return support.isDataFlavorSupported(FLAVOR);
      }

      @Override
      public boolean importData(TransferSupport support) {
        if (canImport(support)) {
          return processData(support);
        }
        return false;
      }

    });
    return panel;
  }

}

输出:传输:测试(类java.lang.String)

这里的重要摘录是:

...

  final static String MY_MIME_TYPE = "application/x-my-mime";
  public static final DataFormat FORMAT = new DataFormat(MY_MIME_TYPE);
  public static final DataFlavor FLAVOR = new DataFlavor(MY_MIME_TYPE, "My Mime Type");

  private void startDrag(Node node) {
    node.startDragAndDrop(TransferMode.COPY).setContent(
        Collections.singletonMap(FORMAT, "Test"));    
  }

  private boolean processData(TransferSupport support) {
    try (InputStream in = (InputStream) support.getTransferable().getTransferData(FLAVOR)) {
      Object transferred = new ObjectInputStream(in).readObject();
      System.out.println("transferred: " + transferred + " (" + transferred.getClass() + ")");
      return true;
    } catch (Exception e) {
      e.printStackTrace();
    }
    return false;
  }

...  

请注意，出于说明目的，数据检索非常简单，对于实际应用程序，可能希望添加更严格的流读取、处理错误等。

---

示例 2(带有文本的自定义 mime)

第一个示例传输一个序列化对象(这通常是一件好事和简单的事情，因为您可以传输任何可序列化的东西，但很难传输/接受，比如第 3 方 JSON)。在不太可能的情况下，当您希望为自定义 MIME 而不是序列化对象生成真实文本或其他任意内容时，以下内容应该可以完成工作:

package jfxtest;

import java.awt.Color;
import java.awt.GridLayout;
import java.awt.datatransfer.DataFlavor;
import java.io.InputStream;
import java.io.ObjectInputStream;
import java.nio.charset.StandardCharsets;
import java.util.Collections;
import javafx.embed.swing.JFXPanel;
import javafx.scene.Node;
import javafx.scene.Scene;
import javafx.scene.input.DataFormat;
import javafx.scene.input.TransferMode;
import javafx.scene.layout.BorderPane;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.TransferHandler;
import javax.swing.TransferHandler.TransferSupport;

public class MyApp {

  final static String MY_MIME_TYPE = "application/x-my-mime";
  public static final DataFormat FORMAT = new DataFormat(MY_MIME_TYPE);
  public static final DataFlavor FLAVOR = new DataFlavor(MY_MIME_TYPE, "My Mime Type");

  private void startDrag(Node node) {
    node.startDragAndDrop(TransferMode.COPY).setContent(
        // put a ByteBuffer to transfer the content unaffected
        Collections.singletonMap(FORMAT, StandardCharsets.UTF_8.encode("Test")));
  }

  private boolean processData(TransferSupport support) {
    try (InputStream in = (InputStream) support.getTransferable().getTransferData(FLAVOR)) {
      byte[] textBytes = new byte[in.available()];
      in.read(textBytes);
      String transferred = new String(textBytes, StandardCharsets.UTF_8); 
      System.out.println("transferred text: " + transferred);
      return true;
    } catch (Exception e) {
      e.printStackTrace();
    }
    return false;
  }  

  public static void main(String[] args) {
    new MyApp().run();
  }

  private void run() {
    JFrame frame = new JFrame();
    frame.setLayout(new GridLayout(1, 2));
    frame.add(buildSwing());
    SwingUtilities.invokeLater(() -> {
      frame.add(buildFX());
    });
    frame.setSize(300, 300);
    frame.setVisible(true);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  }

  private JFXPanel buildFX() {
    BorderPane parent = new BorderPane();
    parent.setOnDragDetected(event -> {
      startDrag(parent);
      event.consume();
    });
    JFXPanel panel = new JFXPanel();
    panel.setScene(new Scene(parent));
    return panel;
  }


  private JPanel buildSwing() {
    JPanel panel = new JPanel();
    panel.setBackground(Color.ORANGE);
    panel.setTransferHandler(new TransferHandler() {
      private static final long serialVersionUID = 1L;

      @Override
      public boolean canImport(TransferSupport support) {
        return support.isDataFlavorSupported(FLAVOR);
      }

      @Override
      public boolean importData(TransferSupport support) {
        if (canImport(support)) {
          return processData(support);
        }
        return false;
      }

    });
    return panel;
  }

}

输出:传输的文本:测试

这里最重要的部分是:

...

  private void startDrag(Node node) {
    node.startDragAndDrop(TransferMode.COPY).setContent(
        // put a ByteBuffer to transfer the content unaffected
        Collections.singletonMap(FORMAT, StandardCharsets.UTF_8.encode("Test")));
  }

  private boolean processData(TransferSupport support) {
    try (InputStream in = (InputStream) support.getTransferable().getTransferData(FLAVOR)) {
      byte[] textBytes = new byte[in.available()];
      in.read(textBytes);
      String transferred = new String(textBytes, StandardCharsets.UTF_8); 
      System.out.println("transferred text: " + transferred);
      return true;
    } catch (Exception e) {
      e.printStackTrace();
    }
    return false;
  }  

...

再次说明，流、错误等在这里的处理很简单。

---

需要注意的一件事是，还有一个预定义的“application/x-java-serialized-object”(DataFlavor.javaSerializedObjectMimeType)用于更通用和更容易的反序列化。但长期自定义 MIME 似乎更灵活，整体处理起来更直接。