droptargetcontext.java

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/*
 * @(#)DropTargetContext.java	1.35 03/01/23
 *
 * Copyright 2003 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package java.awt.dnd;

import java.awt.Component;

import java.awt.datatransfer.DataFlavor;
import java.awt.datatransfer.Transferable;
import java.awt.datatransfer.UnsupportedFlavorException;

import java.awt.dnd.peer.DropTargetContextPeer;

import java.io.IOException;
import java.io.Serializable;

import java.util.Arrays;
import java.util.List;


/**
 * A <code>DropTargetContext</code> is created 
 * whenever the logical cursor associated
 * with a Drag and Drop operation coincides with the visible geometry of
 * a <code>Component</code> associated with a <code>DropTarget</code>.
 * The <code>DropTargetContext</code> provides 
 * the mechanism for a potential receiver
 * of a drop operation to both provide the end user with the appropriate
 * drag under feedback, but also to effect the subsequent data transfer
 * if appropriate.
 *
 * @version 	1.35, 01/23/03
 * @since 1.2
 */

public class DropTargetContext implements Serializable {

    private static final long serialVersionUID = -634158968993743371L;

    /**
     * Construct a <code>DropTargetContext</code> 
     * given a specified <code>DropTarget</code>.
     * <P>
     * @param dt the DropTarget to associate with
     */

    DropTargetContext(DropTarget dt) {
	super();

	dropTarget = dt;
    }

    /**
     * This method returns the <code>DropTarget</code> associated with this
     * <code>DropTargetContext</code>.
     * <P>
     * @return the <code>DropTarget</code> associated with this <code>DropTargetContext</code>
     */

    public DropTarget getDropTarget() { return dropTarget; }

    /**
     * This method returns the <code>Component</code> associated with
     * this <code>DropTargetContext</code>.
     * <P>
     * @return the Component associated with this Context
     */

    public Component getComponent() { return dropTarget.getComponent(); }

    /**
     * Called when associated with the <code>DropTargetContextPeer</code>.
     * <P>
     * @param dtcp the <code>DropTargetContextPeer</code>
     */

    public void addNotify(DropTargetContextPeer dtcp) {
	dropTargetContextPeer = dtcp;
    }

    /**
     * Called when disassociated with the <code>DropTargetContextPeer</code>.
     */

    public void removeNotify() {
	dropTargetContextPeer = null;
	transferable          = null;
    }

    /**
     * This method sets the current actions acceptable to 
     * this <code>DropTarget</code>.
     * <P>
     * @param actions an <code>int</code> representing the supported action(s)
     */

    protected void setTargetActions(int actions) {
        DropTargetContextPeer peer = getDropTargetContextPeer();
        if (peer != null) {
            synchronized (peer) {
                peer.setTargetActions(actions);
                getDropTarget().doSetDefaultActions(actions);
            }
        } else {
            getDropTarget().doSetDefaultActions(actions);
        }
    }

    /**
     * This method returns an <code>int</code> representing the 
     * current actions this <code>DropTarget</code> will accept.
     * <P>
     * @return the current actions acceptable to this <code>DropTarget</code>
     */

    protected int getTargetActions() {
        DropTargetContextPeer peer = getDropTargetContextPeer();
        return ((peer != null)
			? peer.getTargetActions() 
			: dropTarget.getDefaultActions()
	);
    }

    /**
     * This method signals that the drop is completed and 
     * if it was successful or not.
     * <P>
     * @param success true for success, false if not
     * <P>
     * @throws InvalidDnDOperationException if a drop is not outstanding/extant
     */

    public void dropComplete(boolean success) throws InvalidDnDOperationException{
        DropTargetContextPeer peer = getDropTargetContextPeer();
        if (peer != null) {
	    peer.dropComplete(success);
        }
    }

    /**
     * accept the Drag.
     * <P>
     * @param dragOperation the supported action(s)
     */

    protected void acceptDrag(int dragOperation) {
        DropTargetContextPeer peer = getDropTargetContextPeer();
        if (peer != null) {
            peer.acceptDrag(dragOperation);
        }
    }

    /**
     * reject the Drag.
     */

    protected void rejectDrag() {
        DropTargetContextPeer peer = getDropTargetContextPeer();
        if (peer != null) {
            peer.rejectDrag();
        }
    }

    /**
     * called to signal that the drop is acceptable
     * using the specified operation.
     * must be called during DropTargetListener.drop method invocation.
     * <P>
     * @param dropOperation the supported action(s)
     */

    protected void acceptDrop(int dropOperation) {
        DropTargetContextPeer peer = getDropTargetContextPeer();
        if (peer != null) {
            peer.acceptDrop(dropOperation);
        }
    }

    /**
     * called to signal that the drop is unacceptable.
     * must be called during DropTargetListener.drop method invocation.
     */

    protected void rejectDrop() {
        DropTargetContextPeer peer = getDropTargetContextPeer();
        if (peer != null) {
            peer.rejectDrop();
        }
    }

    /**
     * get the available DataFlavors of the 
     * <code>Transferable</code> operand of this operation.
     * <P>
     * @return a <code>DataFlavor[]</code> containing the
     * supported <code>DataFlavor</code>s of the 
     * <code>Transferable</code> operand.
     */

    protected DataFlavor[] getCurrentDataFlavors() {
        DropTargetContextPeer peer = getDropTargetContextPeer();
        return peer != null ? peer.getTransferDataFlavors() : new DataFlavor[0];
    }

    /** 
     * This method returns a the currently available DataFlavors 
     * of the <code>Transferable</code> operand
     * as a <code>java.util.List</code>.
     * <P>
     * @return the currently available 
     * DataFlavors as a <code>java.util.List</code>
     */

    protected List getCurrentDataFlavorsAsList() {
	return Arrays.asList(getCurrentDataFlavors());
    }

    /**
     * This method returns a <code>boolean</code> 
     * indicating if the given <code>DataFlavor</code> is
     * supported by this <code>DropTargetContext</code>.
     * <P>
     * @param df the <code>DataFlavor</code>
     * <P>
     * @return if the <code>DataFlavor</code> specified is supported
     */

    protected boolean isDataFlavorSupported(DataFlavor df) {
	return getCurrentDataFlavorsAsList().contains(df);
    }

    /**
     * get the Transferable (proxy) operand of this operation
     * <P>
     * @throws InvalidDnDOperationException if a drag is not outstanding/extant
     * <P>
     * @return the <code>Transferable</code>
     */

    protected Transferable getTransferable() throws InvalidDnDOperationException {
        DropTargetContextPeer peer = getDropTargetContextPeer();
        if (peer == null) {
	    throw new InvalidDnDOperationException();
	} else {
            if (transferable == null) {
                Transferable t = peer.getTransferable();
                boolean isLocal = peer.isTransferableJVMLocal();
                synchronized (this) {
                    if (transferable == null) {
                        transferable = createTransferableProxy(t, isLocal);
                    }
                }
	    }

	    return transferable;
	}
    }

    /**
     * Get the <code>DropTargetContextPeer</code>
     * <P>
     * @return the platform peer
     */

    DropTargetContextPeer getDropTargetContextPeer() { 
	return dropTargetContextPeer;
    }

    /**
     * Creates a TransferableProxy to proxy for the specified
     * Transferable.
     * 
     * @param t the <tt>Transferable</tt> to be proxied
     * @param local <tt>true</tt> if <tt>t</tt> represents
     *        the result of a local drag-n-drop operation.
     * @return the new <tt>TransferableProxy</tt> instance.   
     */
    protected Transferable createTransferableProxy(Transferable t, boolean local) {
	return new TransferableProxy(t, local);
    }

/****************************************************************************/

  
    /**
     * <code>TransferableProxy</code> is a helper inner class that implements
     * <code>Transferable</code> interface and serves as a proxy for another 
     * <code>Transferable</code> object which represents data transfer for
     * a particular drag-n-drop operation.
     * <p>
     * The proxy forwards all requests to the encapsulated transferable 
     * and automatically performs additional conversion on the data 
     * returned by the encapsulated transferable in case of local transfer.
     */

    protected class TransferableProxy implements Transferable {

	/**
         * Constructs a <code>TransferableProxy</code> given 
         * a specified <code>Transferable</code> object representing
         * data transfer for a particular drag-n-drop operation and 
         * a <code>boolean</code> which indicates whether the 
         * drag-n-drop operation is local (within the same JVM).
         * <p>
         * @param t the <code>Transferable</code> object
         * @param local <code>true</code>, if <code>t</code> represents
         *        the result of local drag-n-drop operation
         */
 	TransferableProxy(Transferable t, boolean local) {
	    proxy = new sun.awt.datatransfer.TransferableProxy(t, local);
	    transferable = t;
	    isLocal	 = local;
	}

	/** 
         * Returns an array of DataFlavor objects indicating the flavors 
         * the data can be provided in by the encapsulated transferable.
         * <p>
         * @return an array of data flavors in which the data can be 
         *         provided by the encapsulated transferable
         */
        public DataFlavor[] getTransferDataFlavors() {
	    return proxy.getTransferDataFlavors();
	}

	/**
         * Returns whether or not the specified data flavor is supported by
         * the encapsulated transferable.
         * @param flavor the requested flavor for the data
         * @return <code>true</code> if the data flavor is supported,
         *         <code>false</code> otherwise
         */
        public boolean isDataFlavorSupported(DataFlavor flavor) {
	    return proxy.isDataFlavorSupported(flavor);
	}

        /**
         * Returns an object which represents the data provided by 
         * the encapsulated transferable for the requested data flavor.
         * <p>
         * In case of local transfer a serialized copy of the object
         * returned by the encapsulated transferable is provided when 
         * the data is requested in application/x-java-serialized-object 
         * data flavor.
         *
         * @param df the requested flavor for the data
         * @throws IOException if the data is no longer available
         *              in the requested flavor.
         * @throws UnsupportedFlavorException if the requested data flavor is
         *              not supported.
         */
        public Object getTransferData(DataFlavor df)
	    throws UnsupportedFlavorException, IOException
	{
	    return proxy.getTransferData(df);
	}

	/*
	 * fields
	 */

	// We don't need to worry about client code changing the values of
	// these variables. Since TransferableProxy is a protected class, only
	// subclasses of DropTargetContext can access it. And DropTargetContext
	// cannot be subclassed by client code because it does not have a
	// public constructor.

        /**
         * The encapsulated <code>Transferable</code> object.
         */
	protected Transferable	transferable;

        /**
         * A <code>boolean</code> indicating if the encapsulated 
         * <code>Transferable</code> object represents the result
         * of local drag-n-drop operation (within the same JVM).
         */
	protected boolean	isLocal;

	private sun.awt.datatransfer.TransferableProxy proxy;
    }

/****************************************************************************/

    /*
     * fields
     */

    /**
     * The DropTarget associated with this DropTargetContext.
     *
     * @serial
     */
    private DropTarget dropTarget;

    private transient DropTargetContextPeer dropTargetContextPeer;

    private transient Transferable transferable;
}