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/*
* Copyright 2000-2018 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.navigator;
import java.io.Serializable;
import com.vaadin.navigator.ViewChangeListener.ViewChangeEvent;
import com.vaadin.ui.Component;
/**
* Interface for all views controlled by the navigator.
*
* Each view added to the navigator must implement this interface. Typically, a
* view is a {@link Component}, if it is not then you should override
* {@link #getViewComponent()} to define the component to show for the view.
*
* @author Vaadin Ltd
* @since 7.0
*/
public interface View extends Serializable {
/**
* Called before the view is shown on screen.
* <p>
* The event object contains information about parameters used when showing
* the view, in addition to references to the old view and the new view.
* <p>
* Override this method to perform initialization of your view.
* <p>
* By default does nothing.
*
* @param event
* an event object containing information about the parameters
* given by the user and references to the old view (if any)
*/
public default void enter(ViewChangeEvent event) {
}
/**
* Called when the user is requesting navigation away from the view.
* <p>
* This method allows the view to accept or prevent navigation away from the
* view or optionally delay navigation away until a later stage. For
* navigation to take place, the {@link ViewBeforeLeaveEvent#navigate()}
* method must be called either directly when handling this event or later
* to perform delayed navigation.
* <p>
* The default implementation calls {@link ViewBeforeLeaveEvent#navigate()}
* directly. If you override this and do nothing, the user will never be
* able to leave the view.
* <p>
* This method is triggered before any methods in any added
* {@link ViewChangeListener ViewChangeListeners}. Whenever you call
* {@link ViewBeforeLeaveEvent#navigate()}, any {@link ViewChangeListener}s
* will be triggered. They will be handled normally and might also prevent
* navigation.
*
* @since 8.1
* @param event
* an event object providing information about the event and
* containing the {@link ViewBeforeLeaveEvent#navigate()} method
* needed to perform navigation
*/
public default void beforeLeave(ViewBeforeLeaveEvent event) {
event.navigate();
}
/**
* Gets the component to show when navigating to the view.
*
* By default casts this View to a {@link Component} if possible, otherwise
* throws an IllegalStateException.
*
* @since 8.1
* @return the component to show, by default the view instance itself
*/
public default Component getViewComponent() {
if (!(this instanceof Component)) {
throw new IllegalStateException(
"View is not a Component. Override getViewComponent() to return the root view component");
}
return (Component) this;
}
}
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