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/*
* Copyright 2011 ArcBees Inc.
*
* 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.gwtplatform.mvp.client.proxy;
import com.google.gwt.user.client.rpc.AsyncCallback;
import com.google.web.bindery.event.shared.EventBus;
/**
* An implementation of {@link AsyncCallback} that sends events on the {@link EventBus} whenever
* an async call starts, succeeds, or fails. The events fired are {@link AsyncCallStartEvent},
* {@link AsyncCallSucceedEvent}, {@link AsyncCallFailEvent}.
*
* So the way to use {@link NotifyingAsyncCallback} is the following:
*
* NotifyingAsyncCallback callback = new NotifyingAsyncCallback(eventBus) { ... };
* callback.prepare();
* someRpcMethod(callback);
* callback.checkLoading();
*
*
* @param The type of the return value. See {@link AsyncCallback}.
*/
public abstract class NotifyingAsyncCallback implements AsyncCallback {
/**
* This enum indicates the state of the notifying async callback. It starts in
* the {@code UNKNOWN} state and moves to {@code INITIALIZED} when {@link #prepare}
* is called. If {@link #checkLoading} is called before the async call has succeeded
* or failed, then it moves to {@code LOADING}. When the call terminates it moves to
* {@code SUCCEEDED} or {@code FAILED}.
*/
public enum State {
UNKNOWN,
INITIALIZED,
LOADING,
SUCCEEDED,
FAILED
}
// Using a static counter to ensure we only fire once, otherwise we risk running into an
// infinite loop if the handler requires an async call to fetch the presenter (which is the
// case when using @ProxyEvent).
// Using an external injected resource would be better, but it's really cumbersome here because
// this class is created inside generators
static int counter;
private final EventBus eventBus;
private State state;
public NotifyingAsyncCallback(EventBus eventBus) {
this.eventBus = eventBus;
state = State.UNKNOWN;
}
@Override
public final void onFailure(final Throwable caught) {
assert state == State.INITIALIZED || state == State.LOADING;
if (state == State.LOADING) {
counter--;
if (counter == 0) {
AsyncCallFailEvent.fire(eventBus, caught);
}
}
state = State.FAILED;
failure(caught);
}
@Override
public final void onSuccess(T result) {
assert state == State.INITIALIZED || state == State.LOADING;
if (state == State.LOADING) {
counter--;
if (counter == 0) {
AsyncCallSucceedEvent.fire(eventBus);
}
}
state = State.SUCCEEDED;
success(result);
}
/**
* This method is used to place that the async callback in its {@code INITIALIZED} stated. It
* should be call prior to invoking any RPC that takes this callback as a parameter. See
* {@link NotifyingAsyncCallback} for usage.
*/
public void prepare() {
assert state != State.LOADING;
state = State.INITIALIZED;
}
/**
* This method is used to indicate that the async callback is currently loading. It will not
* do anything if the call is already finished (i.e. in the case of an immediate failure or
* success). See {@link NotifyingAsyncCallback} for usage.
*/
public void checkLoading() {
assert state != State.UNKNOWN;
if (state == State.INITIALIZED) {
counter++;
if (counter == 1) {
AsyncCallStartEvent.fire(eventBus);
}
state = State.LOADING;
}
}
/**
* This method is called whenever the asynchronous call returns successfully.
*
* @param result the return value of the remote produced call.
*/
protected abstract void success(T result);
/**
* This method is called whenever the asynchronous call returns with a failure. Override this
* method if you want to perform clean-up operation when an async call fails. The default
* implementation is empty.
*
* @param caught failure encountered while executing a remote procedure call.
*/
protected void failure(Throwable caught) {
}
}