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/*******************************************************************************
 * Copyright (c) 2000, 2008 IBM Corporation and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.swt.dnd;


import org.eclipse.swt.internal.*;
import org.eclipse.swt.internal.gtk.*;

/**
 * Transfer provides a mechanism for converting between a java
 * representation of data and a platform specific representation of data and
 * vice versa.  It is used in data transfer operations such as drag and drop and
 * clipboard copy/paste.
 *
 * You should only need to become familiar with this class if you are
 * implementing a Transfer subclass and you are unable to subclass the
 * ByteArrayTransfer class.
 *
 * @see ByteArrayTransfer
 * @see Drag and Drop snippets
 * @see SWT Example: DNDExample
 * @see Sample code and further information
 */
public abstract class Transfer {

/**
 * Returns a list of the platform specific data types that can be converted using
 * this transfer agent.
 *
 * Only the data type fields of the TransferData objects are filled
 * in.
 *
 * @return a list of the data types that can be converted using this transfer agent
 */
abstract public TransferData[] getSupportedTypes();

/**
 * Returns true if the TransferData data type can be converted
 * using this transfer agent, or false otherwise (including if transferData is
 * null).
 *
 * @param transferData a platform specific description of a data type; only the data
 *  type fields of the TransferData object need to be filled in
 *
 * @return true if the transferData data type can be converted using this transfer
 * agent
 */
abstract public boolean isSupportedType(TransferData transferData);

/**
 * Returns the platform specific names of the  data types that can be converted
 * using this transfer agent.
 *
 * @return the platform specific names of the data types that can be converted
 * using this transfer agent.
 */
abstract protected String[] getTypeNames();

/**
 * Returns the platform specific ids of the  data types that can be converted using
 * this transfer agent.
 *
 * @return the platform specific ids of the data types that can be converted using
 * this transfer agent
 */
abstract protected int[] getTypeIds();

/**
 * Converts a java representation of data to a platform specific representation of
 * the data.
 *
 * On a successful conversion, the transferData.result field will be set as follows:
 * 
 * Windows: COM.S_OK
 * 
GTK: 1
 * 
 *
 * If this transfer agent is unable to perform the conversion, the transferData.result
 * field will be set to a failure value as follows:
 * 
 * Windows: COM.DV_E_TYMED or COM.E_FAIL
 * 
GTK: 0
 * 
 *
 * @param object a java representation of the data to be converted; the type of
 * Object that is passed in is dependent on the Transfer subclass.
 *
 * @param transferData an empty TransferData object; this object will be
 * filled in on return with the platform specific representation of the data
 *
 * @exception org.eclipse.swt.SWTException 
 *    ERROR_INVALID_DATA - if object does not contain data in a valid format or is null
 * 
 */
abstract protected void javaToNative (Object object, TransferData transferData);

/**
 * Converts a platform specific representation of data to a java representation.
 *
 * @param transferData the platform specific representation of the data to be
 * converted
 *
 * @return a java representation of the converted data if the conversion was
 * successful; otherwise null.  If transferData is null then
 * null is returned.  The type of Object that is returned is
 * dependent on the Transfer subclass.
 */
abstract protected Object nativeToJava(TransferData transferData);

/**
 * Registers a name for a data type and returns the associated unique identifier.
 *
 * You may register the same type more than once, the same unique identifier
 * will be returned if the type has been previously registered.
 *
 * Note: On windows, do not call this method with pre-defined
 * Clipboard Format types such as CF_TEXT or CF_BITMAP because the
 * pre-defined identifier will not be returned
 *
 * @param formatName the name of a data type
 *
 * @return the unique identifier associated with this data type
 */
public static int registerType(String formatName){
	if (formatName == null) return GDK.GDK_NONE;
	byte[] buffer = Converter.wcsToMbcs(formatName, true);
	return (int)GDK.gdk_atom_intern(buffer, false);
}

/**
 * Test that the object is of the correct format for this Transfer class.
 *
 * @param object a java representation of the data to be converted
 *
 * @return true if object is of the correct form for this transfer type
 *
 * @since 3.1
 */
protected boolean validate(Object object) {
	return true;
}
}