package er.extensions.foundation;
import com.webobjects.foundation.NSArray;
import com.webobjects.foundation.NSMutableArray;
import com.webobjects.foundation._NSDelegate;
/**
* <p>By design, WebObjects' classes that accept a delegate only accept a single object. ERXMulticastingDelegate allows multiple
* delegate objects to be aggregated and presented as a single delegate object.</p>
*
* <p>Delegates are called in the order they are added. Methods are called until one of the delegates handles the message.
* Delegate methods that have a Object or boolean return type are called until one returns a non-null response that is not the default value.
* Delegate methods that have a void return type are always called.</p>
*
* <p>Here is an example if you have multiple delegates that you want to set up.</p>
* <pre>
* ERXDatabaseContextMulticastingDelegate multiDelegate = new ERXDatabaseContextMulticastingDelegate();
* multiDeletegate.addDelegate(new ERXDatabaseContextDelegate());
* multiDeletegate.addDelegate(new ERXEntityDependencyOrderingDelegate());
* EODatabaseContext.setDefaultDelegate(multiDelegate);
* </pre>
*
* <p>Here is a usage example to handle the case where a deletegate may already be set</p>
* <pre>
* Object newDelegate = new ERXEntityDependencyOrderingDelegate();
* ERXDatabaseContextMulticastingDelegate multiDelegate;
* if (EODatabaseContext.defaultDelegate() == null) {
* multiDelegate = new ERXDatabaseContextMulticastingDelegate();
* }
* else {
* if (EODatabaseContext.defaultDelegate() instanceof ERXDatabaseContextMulticastingDelegate) {
* multiDelegate = (ERXDatabaseContextMulticastingDelegate)EODatabaseContext.defaultDelegate();
* }
* else {
* multiDelegate = new ERXDatabaseContextMulticastingDelegate();
* multiDelegate.addDelegate(EODatabaseContext.defaultDelegate());
* }
* }
* multiDelegate.addDelegate(newDelegate);
* EODatabaseContext.setDefaultDelegate(multiDelegate);
* </pre>
*
* <p>This class needs to be implemented for each delegate interface. All methods on the interface should be implemented
* and should call one of the perform... or booleanPerform... methods on this class. See ERXDatabaseContextMulticastingDelegate
* for example usage. One result of this implementation is that delegates can be added and removed at any time.</p>
*
* @author chill
*/
public abstract class ERXMulticastingDelegate {
private NSMutableArray delegates = new NSMutableArray();
/**
* Adds <code>delegate</code> at the end of the chain. It becomes the last delegate called.
*
* @param delegate Object to add as one of the delegates called
*/
public void addDelegate(Object delegate) {
synchronized (delegates) {
if (hasDelegate(delegate)) {
throw new IllegalArgumentException("Delegate is already included");
}
_NSDelegate delegateObject = new _NSDelegate(getClass(), delegate);
delegates.addObject(delegateObject);
}
}
/**
* Adds <code>delegate</code> at the start of the chain. It becomes the first delegate called.
*
* @param delegate Object to add as one of the delegates called
*/
public void addDelegateAtStart(Object delegate) {
synchronized (delegates) {
if (hasDelegate(delegate)) {
throw new IllegalArgumentException("Delegate is already included");
}
_NSDelegate delegateObject = new _NSDelegate(getClass(), delegate);
delegates.insertObjectAtIndex(delegateObject, 0);
}
}
/**
* Removes <code>delegate</code> from the delegates called.
*
* @param delegate Object to remove as one of the delegates called
*/
public void removeDelegate(Object delegate) {
synchronized (delegates) {
if ( ! hasDelegate(delegate)) {
throw new IllegalArgumentException("Delegate is not present");
}
for (int i = 0; i < delegates.count(); i++) {
_NSDelegate delegateObject = (_NSDelegate)delegates.objectAtIndex(i);
if (delegateObject.delegate().equals(delegate))
{
delegates.removeObjectAtIndex(i);
break;
}
}
}
}
/**
* Returns <code>true</code> if delegate is represented in delegates().
*
* @param delegate Object to test for membership in delegates()
* @return <code>true</code> if delegate is represented in delegates()
*/
public boolean hasDelegate(Object delegate) {
synchronized (delegates) {
for (int i = 0; i < delegates.count(); i++) {
_NSDelegate delegateObject = (_NSDelegate)delegates.objectAtIndex(i);
if (delegateObject.delegate().equals(delegate))
{
return true;
}
}
return false;
}
}
/**
* This method returns an array of <code>com.webobjects.foundation._NSDelegate</code>, <b>not</b>
* the delegate objects originally added by calling addDelegate... Call <code>delegate()</code>
* on the elements in this list to examine the delegate objects originally added by calling addDelegate...
*
* @return the delegates in the order they will be called
*/
public NSArray delegates() {
synchronized (delegates) {
return delegates.immutableClone();
}
}
/**
* Use this to set the delegate order if the addDelegate... methods are not sufficient.
* <code>orderedDelegates</code> should be a re-arrangement of the list returned by <code>delegates()</code>.
*
* @param orderedDelegates array of <code>com.webobjects.foundation._NSDelegate</code> in the order in which delegates should be called
*/
public void setDelegateOrder(NSArray orderedDelegates) {
synchronized (delegates) {
for (int i = 0; i < orderedDelegates.count(); i++) {
if ( ! (orderedDelegates.objectAtIndex(i) instanceof _NSDelegate)) {
throw new IllegalArgumentException("Object of class " + orderedDelegates.objectAtIndex(i).getClass().getName() +
" must be instanceof _NSDelegate");
}
}
delegates = orderedDelegates.mutableClone();
}
}
/**
* This is the central method for dispatching messages to the delegates aggregated by this object.
* The other perform... and booleanPerform... methods simply call this method.
*
* @param methodName the name of the delegate method to call
* @param args 0 or more arguments to pass to the delegate method
* @param defaultResult the value to return if none of the delegates implement this method
* @return value returned by the last delegate called
*/
protected Object perform(String methodName, Object args[], Object defaultResult) {
Object result = null;
synchronized (delegates) {
for (int i = 0; (result == null || result.equals(defaultResult)) && i < delegates.count(); i++) {
_NSDelegate delegate = (_NSDelegate) delegates.objectAtIndex(i);
if (delegate.respondsTo(methodName)) {
result = delegate.perform(methodName, args);
}
}
}
return result == null ? defaultResult : result;
}
protected Object perform(String methodName, Object defaultResult)
{
return perform(methodName, new Object[0], defaultResult);
}
protected Object perform(String methodName, Object arg, Object defaultResult)
{
return perform(methodName, new Object[] {arg}, defaultResult);
}
protected Object perform(String methodName, Object arg1, Object arg2, Object defaultResult)
{
return perform(methodName, new Object[] {arg1, arg2}, defaultResult);
}
protected Object perform(String methodName, Object arg1, Object arg2, Object arg3, Object defaultResult)
{
return perform(methodName, new Object[] {arg1, arg2, arg3}, defaultResult);
}
protected Object perform(String methodName, Object arg1, Object arg2, Object arg3, Object arg4, Object arg5, Object defaultResult)
{
return perform(methodName, new Object[] {arg1, arg2, arg3, arg4, arg5}, defaultResult);
}
protected boolean booleanPerform(String methodName, boolean defaultResult)
{
return booleanPerform(methodName, new Object[0], defaultResult);
}
protected boolean booleanPerform(String methodName, Object arg, boolean defaultResult)
{
return booleanPerform(methodName, new Object[] {arg}, defaultResult);
}
protected boolean booleanPerform(String methodName, Object arg1, Object arg2, boolean defaultResult)
{
return booleanPerform(methodName, new Object[] {arg1, arg2}, defaultResult);
}
protected boolean booleanPerform(String methodName, Object arg1, Object arg2, Object arg3, boolean defaultResult)
{
return booleanPerform(methodName, new Object[] {arg1, arg2, arg3}, defaultResult);
}
protected boolean booleanPerform(String methodName, Object args[], boolean defaultResult)
{
Boolean result = (Boolean) perform(methodName, args, Boolean.valueOf(defaultResult));
return result != null ? result.booleanValue() : false;
}
}