Name: sgC58550 Date: 03/19/97


Image data placed in the system clipboard cannot be
retrieved by a Java application: getContents returns null. A
Java application cannot create a Transferable subclass to get
image data into the system clipboard which is a critical need
for what we are doing. The following test application illustrates
this issue. You can retrieve the GifEncoder class used along with
the needed ImageEncoder superclass and the IntHashtable class
from the following location:
http://www.acme.com/java/software/Package-Acme.JPM.Encoders.html
Compile these three dependencies before the following test
application. Also, replace the brightHouse.gif reference with a
small gif on your machine.
==================================================================
import java.awt.*;
import java.awt.event.*;
import java.awt.image.*;
import java.awt.datatransfer.*;
import java.io.*;
import Acme.JPM.Encoders.GifEncoder;


class Test
// ====
{
   public static void main (String args[])
   // ----
   {
      MyFrame frame = new MyFrame();

frame.setBackground(Color.white);
frame.setSize(500,500);
frame.setLayout(new BorderLayout());
      frame.show();

Panel toolbar = new Panel();
toolbar.setLayout(new FlowLayout());
frame.add("North",toolbar);
toolbar.show();
Button textToClip = new Button("Put Text in Clip");
toolbar.add(textToClip);
textToClip.addActionListener((ActionListener)frame);
Button textFromClip = new Button("Get and Display from Clip");
toolbar.add(textFromClip);
textFromClip.addActionListener((ActionListener)frame);
Button copyIt = new Button("Put Image in Clip");
toolbar.add(copyIt);
copyIt.addActionListener((ActionListener)frame);
frame.validate();
   }

} // end Test class



class MyFrame extends Frame implements ActionListener, ClipboardOwner
// =======
{
Image currImage;
boolean loadingImage;
String strContents;
Clipboard cToUse;

public MyFrame ()
   // -------
   {
      super("Clipboard test");
      enableEvents(AWTEvent.WINDOW_EVENT_MASK);
currImage = null;
strContents = null;
loadingImage = false;
cToUse = Toolkit.getDefaultToolkit().getSystemClipboard();
// cToUse = new Clipboard("Marks");
}

public void processWindowEvent (WindowEvent e)
   // ------------------
   {
      if (e.getID() == WindowEvent.WINDOW_CLOSING)
      {
         dispose();
         System.exit(0);
      }
   }

public void actionPerformed(ActionEvent e)
// ---------------
{
String command = e.getActionCommand();

if (command.equals("Put Text in Clip"))
{
System.out.println("Put Text in Clip received");
String textToClip = "Text from a Java Application.";
cToUse.setContents(new StringSelection(textToClip),this);
  }
else if (command.equals("Get and Display from Clip"))
{
System.out.println("Get and Display from Clip");
Transferable contents = cToUse.getContents(this);
if (contents == null)
{
System.out.println("Clipboard has no contents");
strContents = null;
  }
else
{
// Get and display the data flavors supported by the
// transferable object.
DataFlavor[] supportedFlavors = contents.getTransferDataFlavors();
if (supportedFlavors != null)
{
System.out.println("Data Flavors:");
for (int i = 0; i < supportedFlavors.length; i++)
{
DataFlavor tempFlav = supportedFlavors[i];
System.out.println("Next Data Flavor: " +
tempFlav.getHumanPresentableName() + " Mime Type: " +
tempFlav.getMimeType());
}
  }

if (contents.isDataFlavorSupported(DataFlavor.stringFlavor))
{
try
{
strContents =
(String)contents.getTransferData(DataFlavor.stringFlavor);
}
catch (UnsupportedFlavorException ufe)
{
System.out.println("Unsupported data flavor");
strContents = null;
}
catch (IOException ioe)
{
System.out.println("IO Exception");
strContents = null;
}
}
else
{
System.out.println("Requested flavor not supported");
strContents = null;
  }
}
repaint();
}
else if (command.equals("Put Image in Clip"))
{
System.out.println("Put Image in Clip received");
loadingImage = true;
currImage = Toolkit.getDefaultToolkit().getImage("brightHouse.gif");
prepareImage(currImage,this);
  }
  }

public void lostOwnership(Clipboard clipboard, Transferable contents)
// -------------
{
System.out.println("Lost ownership");
}

// This method is called as an image is loaded.
//
public boolean imageUpdate (Image img,
// -----------
int infoflags,
int x, int y,
                                    int width, int height)
{
if ((infoflags & ImageObserver.ALLBITS) == ImageObserver.ALLBITS)
{
loadingImage = false;
repaint();
}
return true;
   }


// Override of the paint method to draw the image.
//
public void paint(Graphics g)
// -----
{
if (strContents == null)
g.drawString("No string present",200,200);
  else
g.drawString(strContents,200,200);

if ((currImage != null) && (!loadingImage))
{
loadingImage = true;

// Get image in byte arrary form.
         ByteArrayOutputStream baos = null;
try
{
baos = new ByteArrayOutputStream(5000);
GifEncoder myEncoder = new GifEncoder(currImage,baos);
System.out.println("Beginning encoding");
myEncoder.encode();
  } catch (IOException ioe)
{
System.out.println("encode ioe");
return;
}

System.out.println("Setting clipboard contents: " +
cToUse.getName());
cToUse.setContents(new ImageSelection(currImage),this);

}
}
} // end myFrame


class ImageSelection implements Transferable
// --------------
{
DataFlavor[] flavors;
private Image data;

public ImageSelection(Image data)
// --------------
{
this.data = data;

DataFlavor sFlav = new DataFlavor("image/gif","Image");
flavors = new DataFlavor[1];
flavors[0] = sFlav;
}

public synchronized DataFlavor[] getTransferDataFlavors()
{
return flavors;
}

public boolean isDataFlavorSupported(DataFlavor flavor)
{
return (flavor.equals(flavors[0]));
}

public synchronized Object getTransferData(DataFlavor flavor) throws
UnsupportedFlavorException, IOException
{
if (flavor.equals(flavors[0]))
{
return (Object)data;
}
else
{
throw new UnsupportedFlavorException(flavor);
}
}

}
==================================================================
The above application creates a frame. Follow the steps below
after compiling the above:
1. java Test
2. Press the Put Text in Clip button.
3. Press the Get and Display in Clip button to ensure at least text
   is working.
4. Press the Put Image in Clip button and wait for the "Setting ..."
   message to appear.
5. Press the Get and Display in Clip button again and you will see
   that the contents of the clipboard is still text ignoring the
   image input.

If you use another application to place image data in the clipboard,
the getContents, Get and Display in Clip button, returns null.
======================================================================

Here is a simpler test case:


import java.awt.*;
import java.io.*;
import java.awt.datatransfer.*;

class Mainx implements ClipboardOwner {
    //ClipboardOwner Example
    Mainx() {
        // Retrieve handle to clipboard and contents
        Clipboard clipboard =
            Toolkit.getDefaultToolkit().getSystemClipboard();
    
        clipboard.setContents(new StringSelection("Hello"), this);
        Transferable t = clipboard.getContents(this);
        try
        { if (t == null) System.out.println("Null");
           else if(!t.isDataFlavorSupported(DataFlavor.stringFlavor))
             System.out.println("Not a string");
           else
             System.out.println(
               (String)t.getTransferData(DataFlavor.stringFlavor));
        }
        catch (UnsupportedFlavorException e) {}
        catch (IOException e) {}
        System.exit(0);
    }

    public void lostOwnership(Clipboard clipboard, Transferable contents) {
        System.out.println("lost ownership");
        System.exit(0);
    }
    
    public static void main(String[] args) {
        new Mainx();
    }
}

dale.mcduffie@Eng 1998-10-21

Name: skT45625 Date: 05/19/2000


java version "1.3.0"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.3.0-C)
Java HotSpot(TM) Client VM (build 1.3.0-C, mixed mode)


The code below:

    Clipboard clipboard = Toolkit.getDefaultToolkit().getSystemClipboard();
    Transferable transferable = clipboard.getContents(this);
    if ( transferable == null )
         System.out.println("Didn't expect this!");

returns a null Transferable object when I have copied graphics into the
Clipboard from an Application, e.g. Paint or a JPeg from IE5.

It works fine if I paste text into the Clipboard, but Iwant to paste graphics
into the Clipboard and then produce an ImageIcon object from the data in the
Clipboard to display in my Applet.

Please help.
(Review ID: 105104)
======================================================================