com.google.gwt.user.client.Timer Maven / Gradle / Ivy
/*
* Copyright 2007 Google 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.google.gwt.user.client;
import com.google.gwt.core.client.JavaScriptObject;
import com.google.gwt.core.client.impl.Impl;
/**
* A simplified, browser-safe timer class. This class serves the same purpose as
* java.util.Timer, but is simplified because of the single-threaded
* environment.
*
*
* To schedule a timer, simply create a subclass of it (overriding {@link #run})
* and call {@link #schedule} or {@link #scheduleRepeating}.
*
*
*
* NOTE: If you are using a timer to schedule a UI animation, use
* {@link com.google.gwt.animation.client.AnimationScheduler} instead. The
* browser can optimize your animation for maximum performance.
*
*
*
*
Example
* {@example com.google.gwt.examples.TimerExample}
*
*/
public abstract class Timer {
private static native JavaScriptObject createCallback(Timer timer, int cancelCounter) /*-{
return $entry(function() { [email protected]::fire(I)(cancelCounter); });
}-*/;
private boolean isRepeating;
private Integer timerId = null;
/**
* Workaround for broken clearTimeout in IE. Keeps track of whether cancel has been called since
* schedule was called. See https://code.google.com/p/google-web-toolkit/issues/detail?id=8101
*/
private int cancelCounter = 0;
/**
* Returns {@code true} if the timer is running. Timer is running if and only if it is scheduled
* but it is not expired or cancelled.
*/
public final boolean isRunning() {
return timerId != null;
}
/**
* Cancels this timer. If the timer is not running, this is a no-op.
*/
public void cancel() {
if (!isRunning()) {
return;
}
cancelCounter++;
if (isRepeating) {
Impl.clearInterval(timerId);
} else {
Impl.clearTimeout(timerId);
}
timerId = null;
}
/**
* This method will be called when a timer fires. Override it to implement the
* timer's logic.
*/
public abstract void run();
/**
* Schedules a timer to elapse in the future. If the timer is already running then it will be
* first canceled before re-scheduling.
*
* @param delayMillis how long to wait before the timer elapses, in milliseconds
*/
public void schedule(int delayMillis) {
if (delayMillis < 0) {
throw new IllegalArgumentException("must be non-negative");
}
if (isRunning()) {
cancel();
}
isRepeating = false;
timerId = Impl.setTimeout(createCallback(this, cancelCounter), delayMillis);
}
/**
* Schedules a timer that elapses repeatedly. If the timer is already running then it will be
* first canceled before re-scheduling.
*
* @param periodMillis how long to wait before the timer elapses, in milliseconds, between each
* repetition
*/
public void scheduleRepeating(int periodMillis) {
if (periodMillis <= 0) {
throw new IllegalArgumentException("must be positive");
}
if (isRunning()) {
cancel();
}
isRepeating = true;
timerId = Impl.setInterval(createCallback(this, cancelCounter), periodMillis);
}
/*
* Called by native code when this timer fires.
*
* Only call run() if cancelCounter has not changed since the timer was scheduled.
*/
final void fire(int scheduleCancelCounter) {
// Workaround for broken clearTimeout in IE.
if (scheduleCancelCounter != cancelCounter) {
return;
}
if (!isRepeating) {
timerId = null;
}
// Run the timer's code.
run();
}
}