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/*
@VaadinApache2LicenseForJavaFiles@
*/
package com.vaadin.terminal;
import com.vaadin.terminal.gwt.server.ClientConnector;
/**
* An extension is an entity that is attached to a Component or another
* Extension and independently communicates between client and server.
* <p>
* Extensions can use shared state and RPC in the same way as components.
* <p>
* AbstractExtension adds a mechanism for adding the extension to any Connector
* (extend). To let the Extension determine what kind target it can be added to,
* the extend method is declared as protected.
*
* @author Vaadin Ltd
* @since 7.0.0
*/
public abstract class AbstractExtension extends AbstractClientConnector
implements Extension {
private boolean previouslyAttached = false;
/**
* Gets a type that the parent must be an instance of. Override this if the
* extension only support certain targets, e.g. if only TextFields can be
* extended.
*
* @return a type that the parent must be an instance of
*/
protected Class<? extends ClientConnector> getSupportedParentType() {
return ClientConnector.class;
}
/**
* Add this extension to the target connector. This method is protected to
* allow subclasses to require a more specific type of target.
*
* @param target
* the connector to attach this extension to
*/
protected void extend(AbstractClientConnector target) {
target.addExtension(this);
}
/**
* Remove this extension from its target. After an extension has been
* removed, it can not be attached again.
*/
public void removeFromTarget() {
getParent().removeExtension(this);
}
@Override
public void setParent(ClientConnector parent) {
if (previouslyAttached && parent != null) {
throw new IllegalStateException(
"An extension can not be set to extend a new target after getting detached from the previous.");
}
Class<? extends ClientConnector> supportedParentType = getSupportedParentType();
if (parent == null || supportedParentType.isInstance(parent)) {
super.setParent(parent);
previouslyAttached = true;
} else {
throw new IllegalArgumentException(getClass().getName()
+ " can only be attached to targets of type "
+ supportedParentType.getName() + " but attach to "
+ parent.getClass().getName() + " was attempted.");
}
}
}
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