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/*
* Copyright 2000-2022 Vaadin Ltd.
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not
* use this file except in compliance with the License. You may obtain a copy of
* the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations under
* the License.
*/
package com.vaadin.event.dd.acceptcriteria;
import java.io.Serializable;
import com.vaadin.event.Transferable;
import com.vaadin.event.dd.DragAndDropEvent;
import com.vaadin.event.dd.DropHandler;
import com.vaadin.server.PaintException;
import com.vaadin.server.PaintTarget;
/**
* Criterion that can be used create policy to accept/discard dragged content
* (presented by {@link Transferable}).
*
* The drag and drop mechanism will verify the criteria returned by
* {@link DropHandler#getAcceptCriterion()} before calling
* {@link DropHandler#drop(DragAndDropEvent)}.
*
* The criteria can be evaluated either on the client (browser - see
* {@link ClientSideCriterion}) or on the server (see
* {@link ServerSideCriterion}). If no constraints are needed, an
* {@link AcceptAll} can be used.
*
* In addition to accepting or rejecting a possible drop, criteria can provide
* additional hints for client side painting.
*
* @see DropHandler
* @see ClientSideCriterion
* @see ServerSideCriterion
*
* @since 6.3
*/
public interface AcceptCriterion extends Serializable {
/**
* Returns whether the criteria can be checked on the client or whether a
* server request is needed to check the criteria.
*
* This requirement may depend on the state of the criterion (e.g. logical
* operations between criteria), so this cannot be based on a marker
* interface.
*/
public boolean isClientSideVerifiable();
public void paint(PaintTarget target) throws PaintException;
/**
* This needs to be implemented if and only if a criterion does some lazy
* server side initialization. The UIDL painted in this method will be
* passed to client side drop handler implementation. Implementation can
* assume that {@link #accept(DragAndDropEvent)} is called before this
* method.
*
* @param target
* @throws PaintException
*/
public void paintResponse(PaintTarget target) throws PaintException;
/**
* Validates the data in event to be appropriate for the
* {@link DropHandler#drop(DragAndDropEvent)} method.
* <p>
* Note that even if your criterion is validated on client side, you should
* always validate the data on server side too.
*
* @param dragEvent
* @return
*/
public boolean accept(DragAndDropEvent dragEvent);
}
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